AVMA Guidelines
for the Euthanasia
of Animals: 2013 Edition
Members of the Panel on Euthanasia
Steven Leary, DVM, DACLAM (Chair); Washington University, St. Louis, Missouri
Wendy Underwood, DVM (Vice Chair); Eli Lilly and Company, Indianapolis, Indiana
Raymond Anthony, PhD (Ethicist); University of Alaska Anchorage, Anchorage, Alaska
Samuel Cartner, DVM, MPH, PhD, DACLAM (Lead, Laboratory Animals Working Group);
University of Alabama at Birmingham, Birmingham, Alabama
Douglas Corey, DVM (Lead, Equine Working Group); Associated Veterinary Clinic, Walla Walla, Washington
Temple Grandin, PhD (Lead, Physical Methods Working Group); Colorado State University, Fort Collins, Colorado
Cheryl Greenacre, DVM, DABVP (Lead, Avian Working Group); University of Tennessee, Knoxville, Tennessee
Sharon Gwaltney-Brant, DVM, PhD, DABVT, DABT (Lead, Noninhaled Agents Working Group); ASPCA Poison
Control Center, Urbana, Illinois
Mary Ann McCrackin, DVM, PhD, DACVS (Lead, Companion Animals Working Group); Virginia Polytechnic
Institute and State University, Blacksburg, Virginia
Robert Meyer, DVM, DACVA (Lead, Inhaled Agents Working Group);
Mississippi State University, Mississippi State, Mississippi
David Miller, DVM, PhD, DACZM (Lead, Reptiles, Zoo and Wildlife Working Group); Loveland, Colorado
Jan Shearer, DVM, MS, DACAW (Lead, Animals Farmed for Food and Fiber Working Group);
Iowa State University, Ames, Iowa
Roy Yanong, VMD (Lead, Aquatics Working Group); University of Florida, Ruskin, Florida
AVMA Staff Consultants
Gail C. Golab, PhD, DVM, MANZCVS, DACAW; Director, Animal Welfare Division
Emily Patterson-Kane, PhD; Animal Welfare Scientist, Animal Welfare Division
The following individuals contributed substantively through their participation in the Panel’s Working Groups and their assistance is sincerely
appreciated.
Inhaled Agents—Scott Helms, DVM, DABVP; Lee Niel, PhD; Daniel Weary, PhD
Noninhaled Agents—Virginia Fajt, DVM, PhD, DACVCP; Don Sawyer, DVM, PhD, DACVA, DABVP
Physical Methods—Rose Gillesby, DVM; Jeff Hill, PhD; Jennifer Woods, BSc
Aquatics—Craig Harms, DVM, PhD, DACZM; Helen Roberts, DVM; Nick Saint-Erne, DVM; Michael Stoskopf, DVM, PhD, DACZM
Avian—Laurel Degernes, DVM, MPH, DABVP; Laurie Hess, DVM, DABVP; Kemba Marshall, DVM, DABVP; James Morrisey, DVM, DABVP;
Joanne Paul-Murphy, DVM, DACZM, DACAW
Companion Animals—Kathleen Cooney, MS, DVM; Stacey Frick, DVM; John Mays; Rebecca Rhoades, DVM
Equids—Fairfield Bain, DVM, MBA, DACVIM, DACVP, DACVECC; Midge Leitch, VMD, DACVS; Thomas R. Lenz, DVM, MS, DACT;
Nathaniel Messer, DVM, DABVP; Hayden Sears, DVM; Stuart Shoemaker, DVM, ACVS
Food and Fiber Animals—Eric Benson, PhD; C. Scanlon Daniels, DVM, MBA; John Deen, DVM, PhD, DABVP, DACAW;
Robert Evans, PhD, DVM, DACPV; Jerome Geiger, DVM, MS; Dee Griffin, DVM, MS; Christa Goodell, DVM; Glen Johnson, DVM;
Richard Reynnells, PhD; James Reynolds, DVM, MVPM, DACAW; Bruce Webster, PhD
Laboratory Animals—James Artwhol, MS, DVM, DACLAM; Larry Carbone, DVM, PhD, DACLAM;
Paul Flecknell, VetMB, MRCVS, PhD, DECVA, DECLAM, DACLAM, FRCVS; David P. Friedman, PhD;
Kathleen Pritchett-Corning, DVM, DACLAM, MRCVS
Reptiles, Zoo and Wild Animals—Scott Citino, DVM, DACZM; Mark Drew, DVM, MS, DACZM; Julie Goldstein, DVM; Barry Hartup, DVM, PhD;
Gregory Lewbart, MS, VMD, DACZM; Douglas Mader, MS, DVM, DABVP, FRSM; Patrick Morris, DVM, DACZM
Copyright © 2013 by the
American Veterinary Medical Association
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ISBN 978-1-882691-21-0
Version 2013.0.1
CONTENTS
Part I—Introduction and General Comments
I1. Preface .................................................................... 5
I2. Historical Context and Current Edition ................... 5
I2.1 History of the Panel on Euthanasia ................... 5
I2.2 Substantive Changes Since the Last Edition ...... 5
I2.3 Statement of Use............................................... 6
I3. What Is Euthanasia? ................................................ 6
I3.1 A Good Death as a Matter of Humane Disposition.. 7
I3.2 A Good Death as a Matter of Humane
Technique....................................................... 7
I4. Euthanasia and Veterinary Medical Ethics ............... 7
I5. Evaluating Euthanasia Methods ............................. 10
I5.1 Consciousness and Unconsciousness .............. 11
I5.2 Pain and Its Perception ................................... 12
I5.3 Stress and Distress .......................................... 13
I5.4 Animal Behavior ............................................. 13
I5.5 Human Behavior............................................. 14
I6. Mechanisms of Euthanasia .................................... 15
I7. Confirmation of Death .......................................... 16
I8. Disposal of Animal Remains .................................. 16
Part II—Methods of Euthanasia
M1. Inhaled Agents .................................................... 18
M1.1 Common Considerations .............................. 18
M1.2 Principles Governing Administration ............ 19
M1.3 Inhaled Anesthetics ...................................... 20
M1.4 Carbon Monoxide......................................... 22
M1.5 Nitrogen, Argon ............................................ 23
M1.6 Carbon Dioxide ............................................ 24
M2. Noninhaled Agents.............................................. 26
M2.1 Common Considerations .............................. 26
M2.1.1 Compounding....................................... 27
M2.1.2 Residue/Disposal Issues......................... 27
M2.2 Routes of Administration .............................. 27
M2.2.1 Parenteral Injection ............................... 27
M2.2.2 Immersion ............................................ 28
M2.2.3 Topical Application ............................... 28
M2.2.4 Oral Administration .............................. 28
M2.3 Barbituric Acid Derivatives ........................... 28
M2.4 Pentobarbital Combinations ......................... 29
M2.5 Tributame ..................................................... 29
M2.6 T-61 .............................................................. 29
M2.7 Ultrapotent Opiods....................................... 30
M2.8 Dissociative Agents and α2-Adrenergic
Receptor Agonists .................................... 30
M2.9 Potassium Chloride and Magnesium Salts ..... 30
M2.10 Chloral Hydrate and α Chloralose .............. 31
M2.11 Alcohols ..................................................... 31
M2.12 Tricaine Methanesulfonate (MS 222, TMS) . 32
M2.13 Benzocaine Hydrochloride .......................... 32
M2.14 Clove Oil, Isoeugenol, and Eugenol ............ 33
M2.15 2-Phenoxyethanol....................................... 33
M2.16 Quinaldine (2-Methylquinoline,
Quinalidine Sulfate) ................................. 34
M2.17 Metomidate ................................................ 34
M2.18 Sodium Hypochlorite ................................. 34
M2.19 Formaldehyde ............................................ 34
M2.20 Unacceptable Agents................................... 34
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
M3. Physical Methods ................................................ 34
M3.1 Common Considerations .............................. 34
M3.2 Penetrating Captive Bolt ............................... 35
M3.3 Nonpenetrating Captive Bolt ........................ 35
M3.4 Manually Applied Blunt Force Trauma
to the Head .............................................. 36
M3.5 Gunshot ....................................................... 36
M3.5.1 Basic Principles of Firearms................... 36
M3.5.2 Muzzle Energy Requirements ................ 37
M3.5.3 Bullet Selection ..................................... 37
M3.5.4 Firearm Safety ....................................... 37
M3.6 Cervical Dislocation ...................................... 38
M3.7 Decapitation ................................................. 38
M3.8 Electrocution ................................................ 39
M3.9 Kill Traps ...................................................... 40
M3.10 Maceration.................................................. 41
M3.11 Focused Beam Microwave Irradiation ......... 41
M3.12 Thoracic (Cardiopulmonary, Cardiac)
Compression............................................ 41
M3.13 Adjunctive Methods.................................... 41
M3.13.1 Exsanguination ................................... 41
M3.13.2 Pithing ................................................ 41
Part III—Methods of Euthanasia
by Species and Environment
S1. Companion Animals ............................................. 43
S1.1 General Considerations .................................. 43
S1.2 Acceptable Methods ....................................... 43
S1.2.1 Noninhaled Agents ................................. 43
S1.3 Acceptable With Conditions Methods ............ 44
S1.3.1 Noninhaled Agents ................................. 44
S1.3.2 Inhaled Agents ....................................... 45
S1.3.3 Physical Methods ................................... 45
S1.4 Adjunctive Methods ....................................... 46
S1.5 Unacceptable Methods ................................... 46
S1.6 Special Considerations ................................... 46
S1.6.1 Dangerous or Fractious Animals ............. 46
S1.6.2 Disposal of Animal Remains ................... 46
S1.7 Fetuses and Neonates..................................... 46
S1.8 Euthanasia in Specific Environments ............. 47
S1.8.1 Individual Animals in Presence of Owners ... 47
S1.8.2 Breeding Facilities .................................. 47
S1.8.3 Animal Control, Sheltering, and Rescue
Facilities ............................................. 47
S1.8.4 Laboratory Animal Facilities ................... 47
S2. Laboratory Animals .............................................. 48
S2.1 General Considerations .................................. 48
S2.2 Small Laboratory and Wild-Caught Rodents
(Mice, Rats, Hamsters, Guinea Pigs, Gerbils,
Degus, Cotton Rats).................................... 48
S2.2.1 Acceptable Methods ............................... 48
S2.2.2 Acceptable With Conditions Methods .... 48
S2.2.3 Unacceptable Methods ........................... 49
S2.2.4 Fetuses and Neonates ............................. 50
S2.3 Laboratory Farm Animals, Dogs, Cats,
Ferrets, and Nonhuman Primates .............. 50
S2.3.1 General Considerations .......................... 50
S2.3.2 Special Cases .......................................... 50
3
CONTENTS
S2.4 Laboratory Rabbits ......................................... 50
S2.4.1 General Considerations .......................... 50
S2.4.2 Acceptable Methods ............................... 50
S2.4.3 Acceptable With Conditions Methods .... 50
S2.4.4 Special Cases .......................................... 51
S2.5 Laboratory Finfish, Aquatic Invertebrates,
Amphibians, and Reptiles............................. 51
S3. Animals Farmed for Food and Fiber ..................... 51
S3.1 General Considerations .................................. 51
S3.2 Bovids and Small Ruminants.......................... 51
S3.2.1 Cattle ..................................................... 51
S3.2.2 Sheep and Goats..................................... 55
S3.3 Swine ............................................................. 58
S3.3.1 Mature Sows, Boars, and
Grower-Finisher Pigs .............................58
S3.3.2 Nursery Pigs (70 lb or Lighter) ............... 60
S3.3.3 Suckling Pigs .......................................... 61
S3.4 Poultry ........................................................... 62
S3.4.1 Acceptable Methods ............................... 62
S3.4.2 Acceptable With Conditions Methods .... 62
S3.4.3 Adjunctive Methods ............................... 63
S3.4.4 Embryos and Neonates........................... 63
S4. Equids .................................................................. 63
S4.1 General Considerations .................................. 63
S4.1.1 Human Safety......................................... 63
S4.1.2 Disposal of Remains ............................... 64
S4.2 Methods......................................................... 64
S4.2.1 Acceptable Methods ............................... 64
S4.2.2 Acceptable With Conditions Methods .... 64
S4.2.3 Adjunctive Methods ............................... 64
S4.2.4 Unacceptable Methods ........................... 64
S4.3 Special Cases and Exceptions ......................... 65
S5. Avians................................................................... 65
S5.1 General Considerations ............................. 65
S5.1.1 Anatomy and Physiology ........................ 65
S5.1.2 Restraint ................................................. 65
S5.2 Methods......................................................... 65
S5.2.1 Acceptable Methods ............................... 65
S5.2.2 Acceptable With Conditions Methods .... 66
S5.2.3 Adjunctive Methods ............................... 67
S5.2.4 Unacceptable Methods ........................... 67
S5.3 Eggs, Embryos, and Neonates ........................ 67
S6. Finfish and Aquatic Invertebrates ........................ 67
S6.1 General Considerations .................................. 67
S6.1.1 Terms Applicable to Ending Life............. 68
S6.1.2 Human and Animal Considerations........ 68
S6.1.3 Preparation and Environment................. 68
S6.1.4 Indicators of Death in Finfish and
Aquatic Invertebrates ........................... 69
S6.1.5 Disposition of Euthanized Animals......... 69
S6.1.6 Finfish and Aquatic Invertebrates
Intended for Human Consumption ...... 69
4
S6.2 Finfish ................................................................ 69
S6.2.1 Noninhaled Agents ................................. 69
S6.2.2 Physical Methods ................................... 70
S6.2.3 Adjunctive Methods ............................... 71
S6.2.4 Unacceptable Methods ........................... 71
S6.2.5 Life Stage Considerations ....................... 71
S6.2.6 Finfish in Particular Environments ......... 72
S6.3 Aquatic Invertebrates ..................................... 74
S6.3.1 Acceptable First Steps of 2-Step
Methods .............................................. 74
S6.3.2 Acceptable Second Steps of 2-Step
Methods.............................................. 74
S6.3.3 Life Stage Considerations ....................... 74
S6.3.4 Unacceptable Methods ........................... 74
S7. Captive and Free-Ranging Nondomestic
Animals ............................................................. 74
S7.1 General Considerations .................................. 75
S7.2 Captive Invertebrates ..................................... 75
S7.2.1 Acceptable Methods ............................... 76
S7.2.2 Acceptable With Conditions Methods .... 76
S7.2.3 Unacceptable Methods ........................... 76
S7.2.4 Developmental Stages of Invertebrates ... 76
S7.3 Captive Amphibians and Reptiles................... 76
S7.3.1 Anatomy and Physiology ........................ 76
S7.3.2 Restraint ................................................. 76
S7.3.3 Verification of Death ............................... 76
S7.3.4 Acceptable Methods ............................... 76
S7.3.5 Acceptable With Conditions Methods .... 77
S7.3.6 Adjunctive Methods ............................... 78
S7.3.7 Unacceptable Methods ........................... 78
S7.3.8 Special Cases and Exceptions ................. 78
S7.3.9 Destruction of Viable Eggs...................... 78
S7.4 Captive Nonmarine Mammals........................ 78
S7.4.1 General Considerations .......................... 78
S7.4.2 Restraint ................................................. 79
S7.4.3 Acceptable Methods ............................... 79
S7.4.4 Acceptable With Conditions Methods .... 79
S7.4.5 Adjunctive Methods ............................... 80
S7.4.6 Unacceptable Methods ........................... 80
S7.4.7 Embryos, Fetuses, and Neonates ............ 80
S7.5 Captive Marine Mammals ............................. 80
S7.5.1 Acceptable Methods ............................... 80
S7.5.2 Acceptable With Conditions Methods .... 80
S7.6 Free-Ranging Wildlife ................................... 81
S7.6.1 General Considerations .......................... 81
S7.6.2 Special Considerations ........................... 81
S7.6.3 Methods ................................................. 82
S7.6.4 Embryos, Fetuses, and Neonates ............ 83
S7.7 Free-Ranging Marine Mammals..................... 83
S7.7.1 Acceptable Methods ............................... 83
S7.7.2 Acceptable With Conditions Methods .... 83
S7.7.3 Adjunctive Methods ............................... 84
S7.7.4 Unacceptable Methods ........................... 84
References ................................................................ 84
Glossary .................................................................... 98
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Part I—Introduction and General Comments
I1. PREFACE
Animal issues are no longer socially invisible. During the past half-century, efforts to ensure the respectful and humane treatment of animals have garnered
global attention.1,2 Concern for the welfare of animals
is reflected in the growth of animal welfare science
and ethics. The former is evident in the emergence of
academic programs, scientific journals, and funding
streams committed either partially or exclusively to the
study of how animals are impacted by various environments and human interventions. The latter has seen
the application of numerous ethical approaches (eg,
rights-based theories, utilitarianism, virtue ethics, contractarianism, pragmatic ethics) to assessing the moral
value of animals and the nature of the human-animal
relationship.1,3–9 The proliferation of interest in animal
use and care, at the national and international levels, is
also apparent in recent protections accorded to animals
in new and amended laws and regulations, institutional
and corporate policies, and purchasing and trade agreements. Changing societal attitudes toward animal care
and use have inspired scrutiny of some traditional and
contemporary practices applied in the management of
animals used for agriculture, research and teaching,
companionship, and recreation or entertainment and
of animals encountered in the wild. Attention has also
been focused on conservation and the impact of human
interventions on terrestrial and aquatic wildlife and the
environment. Within these contexts, stakeholders look
to veterinarians to provide leadership on how to care
well for animals, including how to relieve unnecessary
pain and suffering.
In creating the 2013 edition of the AVMA Guidelines for the Euthanasia of Animals (Guidelines), the
Panel on Euthanasia (POE) made every effort to identify and apply the best research and empirical information available. As new research is conducted and more
practical experience gained, recommended methods
of euthanasia may change. As such, the AVMA and its
POE have made a commitment to ensure the Guidelines reflect an expectation and paradigm of continuous
improvement that is consistent with the obligations of
the Veterinarian’s Oath.10 As for other editions of the
document, modifications of previous recommendations
are also informed by continued professional and public
sensitivity to the ethical care of animals.
While some euthanasia methods may be utilized in
slaughter and depopulation, recommendations related
to humane slaughter and depopulation fall outside the
purview of the Guidelines and will be addressed by separate documents that are under development.
The Guidelines set criteria for euthanasia, specify
appropriate euthanasia methods and agents, and are
intended to assist veterinarians in their exercise of professional judgment. The Guidelines acknowledge that
euthanasia is a process involving more than just what
happens to an animal at the time of its death. Apart
from delineating appropriate methods and agents, these
Guidelines also recognize the importance of considerAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
ing and applying appropriate pre-euthanasia (eg, sedation) and animal handling practices, as well as attention to disposal of animals’ remains.
I2. HISTORICAL CONTEXT
AND CURRENT EDITION
I2.1 HISTORY OF THE PANEL ON EUTHANASIA
Since 1963 the AVMA has convened a POE to
evaluate methods and potential methods of euthanasia
for the purpose of creating guidelines for veterinarians
who carry out or oversee the euthanasia of animals.
The scope of the 1963 edition was limited to methods
and recommendations applicable to dogs, cats, and
other small mammals. Subsequent editions published
in 1972 and 1978 encompassed more methods and species (laboratory animals and food animals, respectively), and included additional information about animals’
physiologic and behavioral responses to euthanasia
(specifically, pain, stress, and distress), euthanasia’s effects on observers, and the economic feasibility and environmental impacts of various approaches. In 1986 information on poikilothermic, aquatic, and fur-bearing
wildlife was introduced; in 1993 recommendations for
horses and wildlife were added; and in 2000 an update
acknowledged a need for more research on approaches
suitable for depopulation. An interim revision by the
AVMA Animal Welfare Committee in 2007 incorporated information derived from an existing, but separate,
AVMA policy on the use of maceration to euthanize
day-old chicks, poults, and pipped eggs, and the name
of the report was changed to the AVMA Guidelines on
Euthanasia.
The 2013 iteration of the Guidelines constitutes
the eighth edition of the POE’s report. The process for
compiling this edition was substantially changed to include more breadth and depth of expertise in the affected species and environments in which euthanasia
is performed. More than three years of deliberation
by more than 60 individuals, including veterinarians,
animal scientists, behaviorists, psychologists, and an
animal ethicist, resulted in the commentary and recommendations that follow. A comment period allowed
AVMA members an opportunity to provide input and
share their experiences directly with POE members.
Their input helps ensure the resulting document is not
only scientifically robust, but practically sound.
I2.2 SUBSTANTIVE CHANGES
SINCE THE LAST EDITION
In the 2013 Guidelines, methods, techniques, and
agents of euthanasia have been updated and detailed
descriptions have been included to assist veterinarians
in applying their professional judgment. Species-specific sections have been expanded or added to include
more guidance for terrestrial and aquatic species kept
for a variety of purposes and under different conditions.
Information has been incorporated about the handling
of animals before and during euthanasia, including un5
der free-ranging conditions, where the needs of animals
and the challenges faced by veterinarians and other
personnel may be quite different from those in domestic environments. And, where possible, appropriate
flowcharts, illustrations, tables, and appendices have
been used to clarify recommendations. Appendices 1
through 3 also may be useful as a quick reference guide,
but those performing euthanasia are strongly advised to
refer to the full text of the document for important additional information. Section labels have been included
in Appendix 1 to assist readers in locating related text
for particular species.
Collection of animals for scientific investigations,
euthanasia of injured or diseased wildlife, and removal
of animals causing damage to property or threatening
human safety are addressed. Recognizing that veterinary responsibilities associated with euthanasia are not
restricted to the process itself, additional information
about confirmation of death and disposal of animal remains has been included.
One area identified as needing additional guidance
in the last iteration of the Guidelines was depopulation
(ie, the rapid destruction of large numbers of animals
in response to emergencies, such as the control of catastrophic infectious diseases or exigent situations caused
by natural disasters). Depopulation may employ euthanasia techniques, but not all depopulation methods
meet the criteria for euthanasia. Because they do not always meet the criteria for euthanasia, these techniques
will be addressed in a separate document, the AVMA
Guidelines for the Depopulation of Animals. Similarly,
because methods used for slaughter or harvest may also
not meet all the conditions necessary to be deemed
euthanasia, these techniques will be addressed by a
third document, the AVMA Guidelines for the Humane
Slaughter of Animals.
I2.3 STATEMENT OF USE
The Guidelines are designed for use by members
of the veterinary profession who carry out or oversee
the euthanasia of animals. As such, they are intended to
apply only to nonhuman species.
The species addressed by the practice of veterinary
medicine are diverse. A veterinarian experienced with the
species of interest should be consulted when choosing a
method of euthanasia, particularly when little species-specific research on euthanasia has been conducted. Methods
and agents selected will often be situation specific, as a
means of minimizing potential risks to the animal’s welfare and personnel safety. Given the complexity of issues
that euthanasia presents, references on anatomy, physiology, natural history, husbandry, and other disciplines may
assist in understanding how various methods may impact
an animal during the euthanasia process.
Veterinarians performing or overseeing euthanasia must assess the potential for animal distress due to
physical discomfort, abnormal social settings, novel
physical surroundings, pheromones or odors from
nearby or previously euthanized animals, the presence of humans, or other factors. In addition, human
safety and perceptions, availability of trained personnel, potential infectious disease concerns, conservation
or other animal population objectives, regulatory over6
sight that may be species specific, available equipment
and facilities, options for disposal, potential secondary
toxicity, and other factors must be considered. Human
safety is of utmost importance, and appropriate safety
equipment, protocols, and knowledge must be available
before animals are handled. Advance preparation includes protocols and supplies for addressing personnel
injury due to animal handling or exposure to drugs and
equipment used during the process. Once euthanasia
has been carried out, death must be carefully verified.
All laws and regulations pertaining to the species being
euthanized, the methods employed, and disposal of the
animal’s remains and/or water containing any pharmaceuticals used for euthanasia must be followed.
The POE’s objective in creating the Guidelines is
to provide guidance for veterinarians about how to prevent and/or relieve the pain and suffering of animals
that are to be euthanized. While every effort has been
made to identify and recommend appropriate approaches for common species encountered under common
conditions, the POE recognized there will be less than
perfect situations in which a recommended method of
euthanasia may not be possible and a method or agent
that is best under the circumstances will need to be applied. For this reason, although the Guidelines may be
interpreted and understood by a broad segment of the
general population, a veterinarian should be consulted
in their application.
I3. WHAT IS EUTHANASIA?
Euthanasia is derived from the Greek terms eu
meaning good and thanatos meaning death. The term is
usually used to describe ending the life of an individual
animal in a way that minimizes or eliminates pain and
distress. A good death is tantamount to the humane termination of an animal’s life.
In the context of these Guidelines, the veterinarian’s prima facie duty in carrying out euthanasia includes, but is not limited to, (1) his or her humane disposition to induce death in a manner that is in accord
with an animal’s interest and/or because it is a matter
of welfare, and (2) the use of humane techniques to
induce the most rapid and painless and distress-free
death possible. These conditions, while separate, are
not mutually exclusive and are codependent.
Debate exists about whether euthanasia appropriately describes the killing of some animals at the end
of biological experiments11 and of unwanted shelter
animals. The Panel believes that evaluating the social
acceptability of various uses of animals and/or the rationale for inducing death in these cases is beyond its
purview; however, current AVMA policy supports the
use of animals for various human purposes,12 and also
recognizes the need to euthanize animals that are unwanted or unfit for adoption.13 Whenever animals are
used by humans, good animal care practices should be
implemented and adherence to those good practices
should be enforced. When evaluating our responsibilities toward animals, it is important to be sensitive to the
context and the practical realities of the various types of
human-animal relationships. Impacts on animals may
not always be the center of the valuation process, and
there is disagreement on how to account for conflicting
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
interspecific interests. The Panel recognizes these are
complex issues raising concerns across a large number
of domains, including scientific, ethical, economic, environmental, political, and social.
I3.1 A GOOD DEATH AS A MATTER
OF HUMANE DISPOSITION
Humane disposition reflects the veterinarian’s desire to do what is best for the animal and serves to bring
about the best possible outcome for the animal. Thus,
euthanasia as a matter of humane disposition can be
either intent or outcome based.
Euthanasia as a matter of humane disposition occurs when death is a welcome event and continued
existence is not an attractive option for the animal as
perceived by the owner and veterinarian. When animals are plagued by disease that produces insurmountable suffering, it can be argued that continuing to live
is worse for the animal than death or that the animal no
longer has an interest in living. The humane disposition is to act for the sake of the animal or its interests,
because the animal will not be harmed by the loss of
life. Instead, there is consensus that the animal will be
relieved of an unbearable burden. As an example, when
treating a companion animal that is suffering severely
at the end of life due to a debilitating terminal illness,
a veterinarian may recommend euthanasia, because the
loss of life (and attendant natural decline in physical
and psychological faculties) to the animal is not relatively worse compared with a continued existence that
is filled with prolonged illness, suffering, and duress.
In this case, euthanasia does not deprive the animal of
the opportunity to enjoy more goods of life (ie, to have
more satisfactions fulfilled or enjoy more pleasurable
experiences). And, these opportunities or experiences
are much fewer or lesser in intensity than the presence
or intensity of negative states or affect. Death, in this
case, may be a welcome event and euthanasia helps to
bring this about, because the animal’s life is not worth
living but, rather, is worth avoiding.
Veterinarians may also be motivated to bring about
the best outcome for the animal. Often, veterinarians
face the difficult question of trying to decide (or helping
the animal’s owner to decide) when euthanasia would
be a good outcome. In making this decision many veterinarians appeal to indices of welfare or quality of life.
Scientists have described welfare as having three components: that the animal functions well, feels well, and
has the capacity to perform behaviors that are innate or
species-specific adaptations14–16 (an alternative view is
also available17). An animal has good welfare if, overall, its life has positive value for it. When an animal
no longer continues to enjoy good welfare (when it no
longer has a life worth living because, on balance, its
life no longer has positive value for it, or will shortly be
overcome by negative states), the humane thing to do is
to give it a good death. Euthanasia relieves the animal’s
suffering, which is the desired outcome.
I3.2 A GOOD DEATH AS A MATTER
OF HUMANE TECHNIQUE
When the decision has been made to euthanize and
the goal is to minimize pain, distress, and negative efAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
fect to the animal, the humaneness of the technique (ie,
how we bring about the death of animals) is also an important ethical issue. As veterinarians and human beings it is our responsibility to ensure that if an animal’s
life is to be taken, it is done with the highest degree of
respect, and with an emphasis on making the death as
painless and distress free as possible. When euthanasia
is the preferred option, the technique employed should
result in rapid loss of consciousness followed by cardiac or respiratory arrest and, ultimately, a loss of brain
function. In addition, animal handling and the euthanasia technique should minimize distress experienced
by the animal prior to loss of consciousness. The POE
recognized that complete absence of pain and distress
cannot always be achieved. The Guidelines attempt to
balance the ideal of minimal pain and distress with the
reality of the many environments in which euthanasia
is performed.
While recommendations are made, it is important
for those utilizing these recommendations to understand that, in some instances, agents and methods of
euthanasia identified as appropriate for a particular species may not be available or may become less than an
ideal choice due to differences in circumstances. Conversely, when settings are atypical, methods normally
not considered appropriate may become the method
of choice. Under such conditions, the humaneness (or
perceived lack thereof) of the method used to bring
about the death of an animal may be distinguished
from the intent or outcome associated with an act of
killing. Following this reasoning, it may still be an act
of euthanasia to kill an animal in a manner that is not
perfectly humane or that would not be considered appropriate in other contexts. For example, due to lack of
control over free-ranging wildlife and the stress associated with close human contact, use of a firearm may
be the most appropriate means of euthanasia. Also,
shooting a suffering animal that is in extremis, instead
of catching and transporting it to a clinic to euthanize it
using a method normally considered to be appropriate
(eg, barbiturates), is consistent with one interpretation
of a good death. The former method promotes the animal’s overall interests by ending its misery quickly, even
though the latter technique may be considered to be
more acceptable under normal conditions.18 Neither of
these examples, however, absolves the individual from
her or his responsibility to ensure that recommended
methods and agents of euthanasia are preferentially
used.
I4. EUTHANASIA AND
VETERINARY MEDICAL ETHICS
The AVMA has worked to ensure that veterinarians
remain educated about public discourse around animal
ethics and animal welfare issues and that they are able
to participate in meaningful ways. While an essential
ingredient in public discourses about animals, sound
science is by itself inadequate to address questions of
ethics and values that surround the appropriate treatment of animals, especially as they relate to end-of-life
issues. To this end, and consistent with its charge, the
POE hopes to provide veterinarians, those under their
supervision, and the public with well-informed and
7
credible arguments on how to approach the ethically
important issue of the death of an animal. In so doing,
it hopes to promote greater understanding regarding
the contexts or settings involving euthanasia and the
complexity of end-of-life issues involving animals.
While not a regulatory body, the AVMA also hopes
to offer guidance to those who may apply these Guidelines as part of regulatory structures designed to protect the welfare of animals used for human purposes. By
creating and maintaining these Guidelines, the AVMA
hopes to ensure that when a veterinarian or other professional intentionally kills an animal under his or her
charge, it is done with respect for the interests of the
animal and that the process is as humane as possible
(ie, that it minimizes pain and distress to the animal
and that death occurs as rapidly as possible).
The AVMA does not take the death of nonhuman
animals lightly and attempts to provide guidance for its
members on both the morality and practical necessity
of the intentional killing of animals. Veterinarians, in
carrying out the tenets of their Oath, may be compelled
to bring about the intentional death of animals for a
variety of reasons. The finality of death is, in part, what
makes it an ethically important issue; death forever cuts
off future positive states, benefits, or opportunities.19 In
cases where an animal no longer has a good life, however, its death also extinguishes permanently any and
all future harms associated with poor welfare or quality
of life.18 What constitutes a good life and what counts
as an impoverished life, or one that has limited quality
such that the death of the animal is the most humane
option, are research areas in need of further study by
the veterinary and ethics communities.20,21 Animal scientists and veterinarians are also investigating the processes by which an animal dies during the antemortem
period and euthanasia methods and techniques that
mitigate harmful effects.22–25 Further research is also
needed regarding the different contexts within which
euthanasia occurs, so that improvements in the performance and outcomes of euthanasia can be made.
The intentional killing of healthy animals, as well
as those that are impaired, is a serious concern for the
public. When animals must be killed and veterinarians
are called upon to assist, the AVMA encourages careful consideration of the decision to euthanize and the
method(s) used. This is also true for euthanasia carried
out during the course of disease control or protection
of public health, as a means of domestic or wild animal
population control, in conjunction with animal use in
biomedical research, and in the process of food and fiber production. Killing of healthy animals under such
circumstances, while unpleasant and morally challenging, is a practical necessity. The AVMA recognizes such
actions as acceptable if those carrying out euthanasia
adhere to strict policies, guidelines, and applicable regulations.
In thinking seriously about veterinary medical ethics, veterinarians should familiarize themselves with
the plurality of public moral views surrounding animal issues and also be cognizant of personal views and
complicating factors that may impact their own ethical
decision making. While the Veterinarian’s Oath,10 Principles of Veterinary Medical Ethics of the AVMA,26 state
8
veterinary practice acts, and other guidance emanating
from veterinary professional organizations and regulatory bodies provide direction for how veterinarians
should interact with clients and their animals, different
veterinarians may have different personal ethical values1,27 and this may impact their recommendations.
In their capacity as animal advocate and client advisor, the precision and credibility of advice provided
by veterinarians will help to advance client compliance. In many instances when veterinarians are called
upon to benefit society through their scientific knowledge, practical experience, and understanding of how
animals are benefited and harmed, straightforward answers may not be forthcoming. In such cases, veterinarians and animal welfare scientists may have to facilitate
conscientious decision making by promoting ethical
dialogue.28–31 As advisor and conduit for information
(and while respecting the autonomy of their clients to
make decisions on behalf of their animals), veterinarians should advance pertinent scientific knowledge and
ethical concerns related to practices and procedures so
that their clients and/or society can make informed decisions.1
Veterinarians who are committed to a broad understanding of the “do no harm” principle may have
to determine whether an animal’s life is worth living,
especially when there is no consensus on when it is appropriate to let that life go. While welfare or quality of
life is typically adopted as part of the assessment of an
animal’s interests, what is in an animal’s interest need
not be singularly identified with its welfare, especially if
welfare is defined narrowly and if the animal is harmed
more by its continued life than its death. For example,
if welfare is defined solely in terms of an animal’s subjective experience, euthanasia may be warranted even
if the animal is not showing signs of suffering at the
present time and if there is some commitment to avoid
harm. Euthanasia may be considered to be the right
course to spare the animal from what is to come (in
conjunction with a more holistic or objective account
of what is in an animal’s interest), if medical intervention would only prolong a terminal condition, or if current health conditions cannot be successfully mitigated.
In these instances, intentional killing need not be motivated by narrow welfare-based interests32 but may be
connected to the overall value of death to the animal.
That some animals are subjects-of-a-life,33–36 and that
human caretakers have moral responsibilities to their
animals and do not want to see them endure continued
harm,37,38 may be factors in deciding whether death is in
an animal’s interest. (A subject-of-a-life is a being that
is regarded as having inherent value and should not be
treated as a mere means to an end. It is a being that
possesses an internal existence and has needs, desires,
preferences, and a psychosocial identity that extends
through time.3,6)
In some cases (eg, animals used for research), intentional killing of the animal to minimize harm to
it may be trumped by more pressing ends. Here, the
decision to kill an animal and how to do so will be
complicated by external factors, such as productivity,
the greater public and general good, economics, and
concern for other animals. In human-animal relationAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
ships there usually are other mitigating factors that
are relevant besides ones pertaining only to animal
welfare or the animal’s interest(s). In laboratory situations, for example, where animals are employed as
research subjects and death may be a terminal point,
animal welfare considerations are balanced against the
merits of the experimental design and merits of the research. In such cases, ensuring the respectful and humane treatment of research animals will be largely up
to institutional animal care and use committees (IACUC). These committees must apply the principles of
refinement, replacement, and reduction, and ensure a
respectful death for research animals. The decision to
induce death may also involve whether replacements
can be created for the animals that are killed.39,40 These
other factors might justify killing an animal, despite
the fact that the animal might otherwise have had a
life worth living. For example, killing may be justified
for disease control or public health purposes, population control, biomedical research, or slaughter for
food and/or fiber. In other instances, keeping an animal alive that does not have a life worth living can be
justified (eg, research circumstances where it would
be impractical to kill the animal or when ensuring its
survival would promote a greater good18).
There may be instances in which the decision to
kill an animal is questionable, especially if the animal is predicted to have a life worth living if it is not
killed. One example is the healthy companion animal
whose owner wants to euthanize it because keeping
it in the home is no longer possible or convenient.
In this case, the veterinarian, as advisor and animal
advocate, should be able to speak frankly about the
animal’s condition and suggest alternatives to euthanasia.
Prima facie, it is the ethical responsibility of veterinarians to direct animal owners toward euthanasia as a compassionate treatment option when the
alternative is prolonged and unrelenting suffering.41
However, accommodating a pluralism of values, interests, and duties in animal ethics is challenging.
This underscores the need for veterinarians to consider the broader context in thinking about what animal care she or he will prescribe. There are no easy
reductionist formulas to which to appeal. In many
cases, advice will need to be responsive to the needs
at hand. Attention must be given to how the welfare
and suffering of the animal are understood within
the context of its whole life and in light of socially
acceptable ways in which humans and animals interact in different environments.
Because veterinarians are committed to improving
animal and human health and welfare, and because
they work tirelessly to discover causes and cures for
animal diseases and promote good animal management, some may feel a sense of disquiet or defeat when
euthanasia becomes the better course of action. The
POE hopes that these Guidelines and other AVMA
policies will assist veterinarians who may be struggling with what may seem to be gratuitous euthanasia, the acceptability of certain procedures, and the
sometimes routine nature of performing euthanasia.
Toward that end, the decision aids in Figures 1 and 2a
are offered as a resource.
Figure 1—Veterinarians may appeal to this decision tree as a way to decide whether euthanasia is warranted when the proper course of action is not clear.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
9
Figure 2—When attempting to make the best decision possible in a thorough and balanced way, veterinarians may find this decision matrix helpful. It can assist in assessing the morality of euthanasia in
particular cases, especially if they are less straightforward.
I5. EVALUATING EUTHANASIA METHODS
In evaluating methods of euthanasia, the POE considered the following criteria: (1) ability to induce loss
of consciousness and death with a minimum of pain
and distress; (2) time required to induce loss of consciousness; (3) reliability; (4) safety of personnel; (5)
irreversibility; (6) compatibility with intended animal use and purpose; (7) documented emotional effect on observers or operators; (8) compatibility with
subsequent evaluation, examination, or use of tissue;
(9) drug availability and human abuse potential; (10)
compatibility with species, age, and health status; (11)
ability to maintain equipment in proper working order;
(12) safety for predators or scavengers should the animal’s remains be consumed; (13) legal requirements;
and (14) environmental impacts of the method or disposition of the animal’s remains.
Euthanasia methods are classified in the Guidelines as acceptable, acceptable with conditions, and
unacceptable. Acceptable methods are those that consistently produce a humane death when used as the sole
means of euthanasia. Methods acceptable with conditions are those techniques that may require certain
conditions to be met to consistently produce humane
death, may have greater potential for operator error or
safety hazard, are not well documented in the scientific
literature, or may require a secondary method to ensure
death. Methods acceptable with conditions are equivalent to acceptable methods when all criteria for application of a method can be met. Unacceptable techniques
are those methods deemed inhumane under any conditions or that the POE found posed a substantial risk to
10
the human applying the technique. The Guidelines also
include information about adjunctive methods, which
are those that should not be used as a sole method of
euthanasia, but that can be used in conjunction with
other methods to bring about euthanasia.
The POE recognized there will be less-than-perfect
situations in which a method of euthanasia that is listed
as acceptable or acceptable with conditions may not be
possible, and a method or agent that is the best under
the circumstances will need to be applied.
As with many other procedures involving animals,
some methods of euthanasia require physical handling of the animal. The amount of control and kind
of restraint required will be determined by the species,
breed, and size of animal involved; the degree of domestication, tolerance to humans, level of excitement, and
prior handling experience of the animal; the presence
of painful injury or disease; the animal’s social environment; and the method of euthanasia and competence of
the person(s) performing the euthanasia. Proper handling is vital to minimize pain and distress in animals,
to ensure the safety of the person performing euthanasia, and, often, to protect other people and animals.
Handling animals that are not accustomed to humans
or that are severely injured or otherwise compromised
may not be possible without inducing stress, so some
latitude in the means of euthanasia is needed in some
situations. The POE discussed the criteria for euthanasia used in the Guidelines as they apply to circumstances when the degree of control over the animal makes it
difficult to ensure death without pain and distress. Premedication with the intent of providing anxiolysis, analgesia, somnolence for easier and safer IV access, and
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
reduction of stage II or postmortem activity that could
be distressing to personnel is strongly encouraged to reduce animal distress and improve personnel safety. This
is particularly important for prey species, nondomesticated species, and animals enduring painful conditions.
Personnel who perform euthanasia must demonstrate proficiency in the use of the technique in a
closely supervised environment. Each facility or institution where euthanasia is performed (whether a clinic,
laboratory, or other setting) is responsible for training
its personnel adequately to ensure the facility or institution operates in compliance with federal, state, and
local laws. Furthermore, experience in the humane
restraint of the species of animal to be euthanized is
important and should be expected, to ensure that animal pain and distress are minimized. Training and experience should include familiarity with the normal
behavior of the species being euthanized, an appreciation of how handling and restraint affect that behavior,
and an understanding of the mechanism by which the
selected technique induces loss of consciousness and
death. Euthanasia should only be attempted when the
necessary drugs and supplies are available to ensure a
smooth procedure.
Selection of the most appropriate method of euthanasia in any given situation depends on the species and
number of animals involved, available means of animal
restraint, skill of personnel, and other considerations.
Information in the scientific literature and available
from practical experience focuses primarily on domesticated animals, but the same general considerations
should be applied to all species.
Euthanasia must be performed in accord with applicable federal, state, and local laws governing drug
acquisition, use, and storage, occupational safety, and
methods used for euthanasia and disposal of animals,
with special attention to species requirements where
possible. The AVMA encourages those responsible for
performing euthanasia of nonhuman animals to review
current federal, state, and local regulations. If drugs
have been used, careful consideration must be given to
appropriate disposal of the animal’s remains and steps
should be taken to avoid environmental contamination
and human and animal exposures to residues.
Circumstances may arise that are not clearly covered by the Guidelines. Whenever such situations arise,
a veterinarian experienced with the species should apply professional judgment, knowledge of clinically acceptable techniques, professional ethos, and social conscience in selecting an appropriate technique for ending an animal’s life.
It is imperative that death be verified after euthanasia and before disposal of the animal. An animal in deep
narcosis following administration of an injectable or inhalant agent may appear to be dead, but might eventually recover. Death must be confirmed by examining
the animal for cessation of vital signs. Consideration
should be given to the animal species and method of
euthanasia when determining appropriate criteria for
confirming death.
Safe handling and disposal of the resulting animal
remains are also critically important when the presence
of zoonotic disease, foreign animal diseases, or other
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
diseases of concern to population health is suspected.
Appropriate diagnostic samples should be collected
for testing, pertinent regulatory authorities should be
notified, and the animal’s body should be incinerated,
if possible. Use of personal protective equipment and
precautions for handling biohazardous materials are
recommended. Animals that have injured humans may
require specific actions to be taken depending on local
and state laws.
I5.1 CONSCIOUSNESS
AND UNCONSCIOUSNESS
Unconsciousness, defined as loss of individual
awareness, occurs when the brain’s ability to integrate
information is blocked or disrupted. In humans, onset of anesthetic-induced unconsciousness has been
functionally defined by loss of appropriate response
to verbal command; in animals, by loss of the righting
reflex.42,43 This definition, introduced with the discovery of general anesthesia more than 160 years ago, is
still useful because it is an easily observable, integrated
whole-animal response.
Anesthetics produce unconsciousness either by
preventing integration (blocking interactions among
specialized brain regions) or by reducing information
(shrinking the number of activity patterns available
to cortical networks) received by the cerebral cortex
or equivalent structure(s). Further, the abrupt loss of
consciousness that occurs at a critical concentration
of anesthetic implies that the integrated repertoire of
neural states underlying consciousness may collapse
nonlinearly.44 Cross-species data suggest that memory
and awareness are abolished with less than half the
concentration required to abolish movement. Thus, an
anesthetic state (unconsciousness and amnesia) can be
produced at concentrations of anesthetic that do not
prevent physical movements.43
Measurements of brain electrical function have
been used to objectively quantify the unconscious state.
At some level between behavioral unresponsiveness
and the induction of a flat electroenencephalogram
(EEG; indicating the cessation of the brain’s electrical
activity and brain death), consciousness must vanish.
However, EEG data cannot provide definitive answers
as to onset of unconsciousness. Brain function monitors based on EEG are limited in their ability to directly
indicate presence or absence of unconsciousness, especially around the transition point44; also, it is not always
clear which EEG patterns are indicators of activation by
stress or pain.25
Physical methods that destroy or render nonfunctional the brain regions responsible for cortical integration (eg, gunshot, captive bolt, cerebral electrocution,
blunt force trauma, maceration) produce instantaneous
unconsciousness. When physical methods directly
destroy the brain, signs of unconsciousness include
immediate collapse and a several-second period of tetanic spasm, followed by slow hind limb movements
of increasing frequency45–47 in cattle; however, there is
species variability in this response. The corneal reflex
will be absent.48 Signs of effective electrocution are loss
of righting reflex, loss of eyeblink and moving object
tracking, extension of the limbs, opisthotonos, down11
ward rotation of the eyeballs, and tonic spasm changing
to clonic spasm, with eventual muscle flaccidity.49,50
Decapitation and cervical dislocation as physical
methods of euthanasia require separate comment. The
interpretation of brain electrical activity, which can persist for up to 30 seconds following these methods,51–54
has been controversial.55 As indicated previously, EEG
methods cannot provide definitive answers as to onset
of unconsciousness. Other studies56–59 indicate such activity does not imply the ability to perceive pain and
conclude that loss of consciousness develops rapidly.
Once loss of consciousness occurs, subsequently
observed activities, such as convulsions, vocalization,
reflex struggling, breath holding, and tachypnea, can be
attributed to the second stage of anesthesia, which by
definition lasts from loss of consciousness to the onset of a regular breathing pattern.60,61 Thus, events observed following loss of the righting reflex are likely not
consciously perceived. Some agents may induce convulsions, but these generally follow loss of consciousness. Agents inducing convulsions prior to loss of consciousness are unacceptable for euthanasia.
I5.2 PAIN AND ITS PERCEPTION
Criteria for painless death can be established only
after the mechanisms of pain are understood. The perception of pain is defined as a conscious experience.43
The International Association for the Study of Pain
(IASP) describes pain as “An unpleasant sensory and
emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Activity induced in the nociceptor and nociceptive
pathways by a noxious stimulus is not pain, which is
always a psychological state, even though we may well
appreciate that pain most often has a proximate physical cause.”62
The perception of pain based on mammalian models requires nerve impulses from peripheral nociceptors
to reach a functioning conscious cerebral cortex and
the associated subcortical brain structures. Noxious
stimulation that threatens to damage or destroy tissue produces activity in primary nociceptors and other
sensory nerve endings. In addition to mechanical and
thermal stimulation, a variety of endogenous substances can generate nociceptive impulses, including prostaglandins, hydrogen ions, potassium ions, substance
P, purines, histamine, bradykinin, and leukotrienes, as
can electrical currents.
Nociceptive impulses are conducted by nociceptor
primary afferent fibers to either the spinal cord or the
brainstem and two general sets of neural networks. Reflex withdrawal and flexion in response to nociceptive
input are mediated at the spinal level while ascending
nociceptive pathways carry impulses to the reticular
formation, hypothalamus, thalamus, and cerebral cortex (somatosensory cortex and limbic system) for sensory processing and spatial localization. Thus, movement observed in response to nociception can be due to
spinally mediated reflex activity, cerebral cortical and
subcortical processing, or a combination of the two.
For example, it is well recognized clinically that spinally mediated nociceptive reflexes may remain intact
distal to a compressive spinal lesion or complete spinal
12
transaction that blocks the ascending nociceptive pathways. In contrast, administration of a local anesthetic
into the epidural space suppresses both spinally mediated nociceptive reflexes and ascending nociceptive
pathways; in either case, noxious stimuli are not perceived as pain in conscious human or nonhuman animals because activity in the ascending pathways, and
thus access to the higher cortical centers, is suppressed
or blocked. It is therefore incorrect to substitute the
term pain for stimuli, receptors, reflexes, or pathways
because the term implies higher sensory processing associated with conscious perception. Consequently, the
choice of a euthanasia agent or method is less critical
if it is to be used on an animal that is anesthetized or
unconscious, provided that the animal does not regain
consciousness prior to death.
Pain is subjective in the sense that individuals can
differ in their perceptions of pain intensity as well as
in their physical and behavioral responses to it. Pain
can be broadly categorized as sensory-discriminative,
where the origin and the stimulus causing pain are
determined, or as motivational-affective, where the severity of the stimulus is perceived and a response to
it determined.63 Sensory-discriminative nociceptive
processing occurs within cortical and subcortical structures using mechanisms similar to those used to process
other sensory-discriminatory input and provides information on stimulus intensity, duration, location, and
quality. Motivational-affective processing involves the
ascending reticular formation for behavioral and cortical arousal, as well as thalamic input to the forebrain
and limbic system for perception of discomfort, fear,
anxiety, and depression. Motivational-affective neural
networks also provide strong inputs to the limbic system, hypothalamus, and autonomic nervous system for
reflex activation of the cardiovascular, pulmonary, and
pituitary-adrenal systems.
Although the perception of pain requires a conscious experience, defining consciousness, and therefore the ability to perceive pain, across many species
is quite difficult. Previously it was thought that finfish,
amphibians, reptiles, and invertebrates lacked the anatomic structures necessary to perceive pain as we understand it in birds and mammals. For example, the invertebrate taxa include animals with no nervous system
(eg, sponges) and nervous systems with no ganglionation or minimal ganglionation (eg, starfish). However,
there are also invertebrate taxa with well-developed
brains and/or complex behaviors that include the ability to analyze and respond to complex environmental
cues (eg, octopus, cuttlefish, spiders,64,65 honeybees,
butterflies, ants). Most invertebrates do respond to
noxious stimuli and many have endogenous opioids.66
Amphibians and reptiles also represent taxa with
a diverse range of anatomic and physiologic characteristics such that it is often difficult to ascertain that an
amphibian or reptile is, in fact, dead. Although amphibians and reptiles respond to noxious stimuli and are
presumed to feel pain, our understanding of their nociception and response to stimuli is incomplete. Nevertheless, there is increasing taxa-specific evidence of the
efficacy of analgesics to minimize the impact of noxious
stimuli on these species.67,68 Consequently, euthanasia
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
techniques that result in “rapid loss of consciousness”
and “minimize pain and distress” should be strived for,
even where it is difficult to determine that these criteria
have been met.
Compelling recent evidence indicates finfish possess
the components of nociceptive processing systems similar to those found in terrestrial vertebrates,55–70 though
debate continues based on questions of the impact of
quantitative differences in numbers of specific components such as unmyelinated C fibers in major nerve bundles. Suggestions that finfish responses to pain merely
represent simple reflexes71 have been refuted by studies72,73 demonstrating forebrain and midbrain electrical
activity in response to stimulation and differing with
type of nociceptor stimulation. Learning and memory
consolidation in trials where finfish are taught to avoid
noxious stimuli have moved the issue of finfish cognition and sentience forward74 to the point where the preponderance of accumulated evidence supports the position that finfish should be accorded the same considerations as terrestrial vertebrates in regard to relief from
pain. The POE was not able to identify similar studies of
Chondrichthyes (cartilaginous finfish), amphibians, reptiles, and invertebrates, but believes that available information suggests that efforts to relieve pain and distress
for these taxa are warranted, unless further investigation
disproves a capacity to feel pain or distress.
While there is ongoing debate about finfishes’, amphibians’, reptiles’, and invertebrate animals’ ability to
feel pain or otherwise experience compromised welfare, they do respond to noxious stimuli. Consequently,
the Guidelines assume that a conservative and humane
approach to the care of any creature is warranted, justifiable, and expected by society. Euthanasia methods
should be employed that minimize the potential for
distress or pain in all animal taxa, and these methods
should be modified as new taxa-specific knowledge of
their physiology and anatomy is acquired.
I5.3 STRESS AND DISTRESS
An understanding of the continuum that represents
stress and distress is essential for evaluating techniques
that minimize any distress experienced by an animal being euthanized. Stress has been defined as the effect of
physical, physiologic, or emotional factors (stressors)
that induce an alteration in an animal’s homeostasis
or adaptive state.75 The response of an animal to stress
represents the adaptive process that is necessary to restore the baseline mental and physiologic state. These
responses may involve changes in an animal’s neuroendocrinologic system, autonomic nervous system,
and mental status that may result in overt behavioral
changes. An animal’s response varies according to its
experience, age, species, breed, and current physiologic
and psychological state, as well as handling, social environment, and other factors.76,77
Stress and the resulting responses have been divided into three phases.78 Eustress results when harmless
stimuli initiate adaptive responses that are beneficial to
the animal. Neutral stress results when the animal’s response to stimuli causes neither harmful nor beneficial
effects to the animal. Distress results when an animal’s
response to stimuli interferes with its well-being and
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
comfort.79 To avoid distress, veterinarians should strive
to euthanize animals within the animals’ physical and
behavioral comfort zones (eg, preferred temperatures,
natural habitat, home) and, when possible, prepare a
calming environment.
I5.4 ANIMAL BEHAVIOR
The need to minimize animal distress, including
negative affective or experientially based states like fear,
aversion, anxiety, and apprehension, must be considered in determining the method of euthanasia. Ethologists and animal welfare scientists are getting better at
discerning the nature and content of these states. Veterinarians and other personnel involved in performing
euthanasia should familiarize themselves with pre-euthanasia protocols and be attentive to species and individual variability. For virtually all animals, being placed
in a novel environment is stressful80–83; therefore, a euthanasia approach that can be applied in familiar surroundings may help reduce stress.
For animals accustomed to human contact, gentle
restraint (preferably in a familiar and safe environment), careful handling, and talking during euthanasia
often have a calming effect and may also be effective
coping strategies for personnel.84 Sedation and/or anesthesia may assist in achieving the best conditions for
euthanasia. It must be recognized that sedatives or anesthetics given at this stage that change circulation may
delay the onset of the euthanasia agent.
Animals that are in social groups of conspecifics or
that are wild, feral, injured, or already distressed from
disease pose another challenge. For example, mammals
and birds that are not used to being handled have higher
corticosteroid levels during handling and restraint compared with animals accustomed to frequent handling by
people.85–87 For example, beef cattle that are extensively
raised on pasture or range have higher corticosteroid levels when restrained in a squeeze chute compared with
intensively raised dairy cattle that are always in close association with people,88,89 and being placed in a new cage
has been shown to be stressful for rodents.90 Because
handling may be a stressor for animals less accustomed
to human contact (eg, wildlife, feral species, zoo animals,
and some laboratory animals), the methods of handling
and degree of restraint (including none, such as for gunshot) required to perform euthanasia should be considered when evaluating various methods.76 When handling
such animals, calming may be accomplished by retaining them (as much as possible) in familiar environments,
and by minimizing visual, auditory, and tactile stimulation. When struggling during capture or restraint may
cause pain, injury, or anxiety to the animal or danger to
the operator, the use of tranquilizers, analgesics, and/or
anesthetics may be necessary. A method of administration should be chosen that causes the least distress in the
animal for which euthanasia must be performed. Various
techniques for oral delivery of sedatives to dogs and cats
have been described that may be useful under these circumstances.91,92
Expressions and body postures that indicate various emotional states of animals have been described for
some species.93–96 Behavioral responses to noxious stimuli in conscious animals include distress vocalization,
13
struggling, attempts to escape, and defensive or redirected aggression. In cattle and pigs, vocalization during handling or painful procedures is associated with
physiologic indicators of stress.97–99 Vocalization is associated with excessive pressure applied by a restraint device.100,101 Salivation, urination, defecation, evacuation
of anal sacs, pupillary dilatation, tachycardia, sweating,
and reflex skeletal muscle contractions causing shivering, tremors, or other muscular spasms may occur in
unconscious as well as conscious animals. Fear can
cause immobility or playing dead in certain species,
particularly rabbits and chickens.102 This immobility
response should not be interpreted as loss of consciousness when the animal is, in fact, conscious. Distress vocalizations, fearful behavior, and release of certain odors
or pheromones by a frightened animal may cause anxiety and apprehension in other animals.103,104 Therefore,
for sensitive species, it is desirable that other animals
not be present when individual animal euthanasia is
performed. Often, simple environmental modifications
can help reduce agitation and stress, such as providing
a nonslip floor for the animals to stand on, reducing
noise, blocking the animal’s vision with a blindfold or a
barrier, or removing distracting stimuli that cause animals to become agitated.101,105–108
I5.5 HUMAN BEHAVIOR
The depth of the emotional attachment between
animals and their owners or caretakers requires an additional layer of professional respect and care beyond
the ethical obligation to provide a good death for the
animal. Human concerns associated with the euthanasia of healthy and unwanted animals can be particularly
challenging, as can situations where the health interests of groups of animals and/or the health interests of
people conflict with the welfare of individual animals
(eg, animal health emergencies).
The human-animal relationship should be respected by discussing euthanasia openly, providing an
appropriate place to conduct the process, offering the
opportunity for animal owners and/or caretakers to be
present when at all possible (consistent with the best
interests of the animal and the owners and caretakers),
fully informing those present about what they will see
(including possible unpleasant side effects), and giving
emotional support and information about grief counseling as needed.109–111 Regardless of the euthanasia
method chosen, it is important to consider the level
of understanding and perceptions of those in attendance as they witness euthanasia. When death has been
achieved and verified, owners and caretakers should be
verbally notified.110
Owners and caretakers are not the only people
affected by the euthanasia of animals. Veterinarians
and their staffs may also become attached to patients
and struggle with the ethics of the caring-killing paradox,112,113 particularly when they must end the lives of
animals they have known and treated for many years.
Repeating this scenario regularly may lead to emotional
burnout, or compassion fatigue. The various ways in
which veterinarians cope with euthanasia have been
discussed elsewhere.114
There are six settings in which the Panel was most
14
aware of the potential for substantive psychological impacts of animal euthanasia on people.
The first setting is the veterinary clinical setting
(clinics and hospitals or mobile veterinary practices)
where owners have to make decisions about whether
and when to euthanize. Although many owners rely
heavily on their veterinarian’s judgment, others may
have misgivings about making a decision. This is particularly likely if an owner feels responsible for an animal’s medical or behavioral problem. Owners choose
euthanasia for their animals for a variety of reasons,
including prevention of suffering from a terminal illness, their inability to care for the animal, the impact of
the animal’s condition on other animals or people, and/
or financial considerations. The decision to euthanize
often carries strong feelings of emotion such as guilt,
sadness, shock, and disbelief.115 As society continues to
pay more attention to questions about the moral status
of animals, loss of animal life should be handled with
the utmost respect and compassion by all animal care
staff. The ability to communicate well is crucial to helping owners make end-of-life decisions for their animals
and is a learned skill that requires training.116
Almost 80% of clients who recently experienced the
death of a pet (87% by euthanasia) reported a positive
correlation between support from the veterinarian and
staff and their ability to handle the grief associated with
their pet’s death.115 Owners should be given the opportunity to be present during euthanasia, when feasible,
and they should be prepared for what to expect.110,115,117
What drugs are being used and how the animal could
respond should be discussed. Behaviors such as vocalization, agonal breaths, muscle twitches, failure of the
eyelids to close, urination, or defecation can be distressing to owners. Counseling services for owners having difficulty coping with animal death are available in
some communities, and veterinarians are encouraged
to seek grief support training to assist their clients.118–120
While good euthanasia practices (ie, client communication and education, compassionate species-appropriate
handling and selection of technique, pre-euthanasia
sedatives or anesthetics as needed to minimize anxiety
and facilitate safe restraint, and careful confirmation of
death) are often applied in the euthanasia of dogs and
cats, they should also be followed for other species that
are kept as pets, including small mammals, birds, reptiles, farm animals, and aquatic animals.
The second setting is in animal care and control
facilities where unwanted, homeless, diseased, and injured animals must be euthanized in large numbers.
The person performing euthanasia must be technically proficient (including the use of humane handling
methods and familiarity with the method of euthanasia
being employed), and must be able to understand and
communicate to others the reasons for euthanasia and
why a particular approach was selected. This requires
organizational commitment to provide ongoing professional training on the latest methods, techniques, and
materials available for euthanasia.
Distress may develop among personnel directly involved in performing euthanasia repeatedly,121 and may
include a psychological state characterized by a strong
sense of work dissatisfaction or alienation, which may
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
be expressed by absenteeism, belligerence, or careless
and callous handling of animals.122 The impact on personnel may be worse when euthanasia is conducted in
frequent, shorter sessions compared with fewer, longer
sessions.123 In addition, animal shelter personnel have
been shown to have more difficulty dealing emotionally with the euthanasia of healthy, unwanted animals
than those that are old, sick, injured, or wild.124 Specific
coping strategies that can make the task more tolerable
include adequate training programs so that euthanasia is performed competently, rotation of duties and
shared responsibilities for staff performing euthanasia,
peer support in the workplace, professional support as
necessary, focusing on animals that are successfully adopted or returned to owners, devoting some work time
to educational activities, and providing time off when
workers feel distressed. Management should be aware
of potential personnel problems related to animal euthanasia and determine whether it is necessary to institute a program to prevent, decrease, or eliminate this
problem.
The third setting is the laboratory. Researchers,
technicians, and students may become attached to animals that must be euthanized in laboratory settings,
even though the animals are often purpose-bred for research.125 The human–research animal bond positively
impacts quality of life for a variety of research animals,
but those caring for the animals often experience euthanasia-related stress symptoms comparable to those
encountered in veterinary clinics and animal shelters.126–128 The same considerations afforded pet owners
or shelter employees should be provided to those working in laboratories, particularly the provision of training to promote grief coping skills.129
The fourth setting is wildlife conservation and
management. Wildlife biologists, wildlife managers,
and wildlife health professionals are often responsible
for euthanizing animals that are injured, diseased, or
in excessive number or those that threaten property
or human safety. Although relocation of some animals
may be appropriate and attempted, relocation is often
only a temporary solution and may be insufficient to
address a larger problem. People who must deal with
these animals, especially under public pressure to save
the animals rather than destroy them, can experience
extreme distress and anxiety. In addition, the perceptions of not only the wildlife professionals, but of onlookers, need to be considered when selecting a euthanasia method.
The fifth setting is livestock and poultry production. As for shelter and laboratory animal workers, onfarm euthanasia of individual animals by farm workers
charged with nurturing and raising production animals
can take a heavy toll on employees both physically and
emotionally.130
The sixth setting is that in which there is broad
public exposure. Because euthanasia of zoo animals,
animals involved in roadside or racetrack accidents,
stranded marine animals, and nuisance or injured wildlife can draw public attention, human attitudes and
responses must be considered whenever these animals
are euthanized. Natural disasters and foreign animal
disease programs also present public challenges. AttenAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
tion to public perceptions, however, should not outweigh the primary responsibility of doing what is in the
animal’s best interest under the circumstances (ie, using
the most appropriate and painless euthanasia method
possible).
In addition to ensuring good care of animals during euthanasia and considering the psychological wellbeing of human participants, the physical safety of personnel handling the animals and performing euthanasia
needs to be protected. The safe use of controlled substances and diversion control to prevent abuse is also
part of the responsibility of those using such substances
in the performance of euthanasia.131
I6. MECHANISMS OF EUTHANASIA
Euthanizing agents cause death by three basic
mechanisms: (1) direct depression of neurons necessary for life function, (2) hypoxia, and (3) physical disruption of brain activity. The euthanasia process should
minimize or eliminate pain, anxiety, and distress prior
to loss of consciousness. As loss of consciousness resulting from these mechanisms can occur at different
rates, the suitability of a particular agent or method
will depend on whether an animal experiences distress
prior to loss of consciousness.
Unconsciousness, defined as loss of individual
awareness, occurs when the brain’s ability to integrate
information is blocked or disrupted (see comments
on unconsciousness for additional information). Ideally, euthanasia methods should result in rapid loss of
consciousness, followed by cardiac or respiratory arrest
and the subsequent loss of brain function. Loss of consciousness should precede loss of muscle movement.
Agents and methods that prevent movement through
muscle paralysis, but that do not block or disrupt the
cerebral cortex or equivalent structures (eg, succinylcholine, strychnine, curare, nicotine, potassium, or
magnesium salts), are not acceptable as sole agents for
euthanasia of vertebrates because they result in distress
and conscious perception of pain prior to death. In contrast, magnesium salts are acceptable as the sole agent
for euthanasia in many invertebrates due to the absence
of evidence for cerebral activity in some members of
these taxa,132,133 and there is evidence that the magnesium ion acts centrally in suppressing neural activity of
cephalopods.134
Depression of the cortical neural system causes loss
of consciousness followed by death. Depending on the
speed of onset of the particular agent or method used,
release of inhibition of motor activity may be observed
accompanied by vocalization and muscle contraction
similar to that seen in the initial stages of anesthesia.
Although distressing to observers, these responses do
not appear to be purposeful. Once ataxia and loss of
righting reflex occurs, subsequent observed motor
activity, such as convulsions, vocalization, and reflex
struggling, can be attributed to the second stage of
anesthesia, which by definition lasts from the loss of
consciousness to the onset of a regular breathing pattern.60,61
Hypoxia is commonly achieved by exposing animals to high concentrations of gases that displace oxygen (O2), such as carbon dioxide (CO2), nitrogen (N2),
15
or argon (Ar), or by exposure to carbon monoxide
(CO) to block uptake of O2 by red blood cells. Exsanguination, an adjunctive method, is another method of
inducing hypoxia, albeit indirectly, and can be a way to
ensure death in an already unconscious or moribund
animal. As with other euthanasia methods, some animals may exhibit motor activity or convulsions following loss of consciousness due to hypoxia; however, this
is reflex activity and is not consciously perceived by the
animal. In addition, methods based on hypoxia will not
be appropriate for species that are tolerant of prolonged
periods of hypoxemia.
Physical disruption of brain activity can be produced through a blow to the skull resulting in concussive stunning; through direct destruction of the brain
with a captive bolt, bullet, or pithing rod; or through
depolarization of brain neurons following electrocution. Death quickly follows when the midbrain centers
controlling respiration and cardiac activity fail. Convulsions and exaggerated muscle activity can follow loss of
consciousness. Physical disruption methods are often
followed by exsanguination. These methods are inexpensive, humane, and painless if performed properly,
and leave no drug residues in the animal’s remains .
Furthermore, animals presumably experience less fear
and anxiety with methods that require little preparatory
handling. However, physical methods usually require a
more direct association of the operator with the animals
to be euthanized, which can be offensive to, and upsetting for, the operator. Physical methods must be skillfully executed to ensure a quick and humane death,
because failure to do so can cause substantial suffering.
In summary, the cerebral cortex or equivalent
structure(s) and associated subcortical structures must
be functional for pain to be perceived. If the cerebral
cortex is nonfunctional because of neuronal depression, hypoxia, or physical disruption, pain is not experienced. Reflex motor activity that may occur following
loss of consciousness, although distressing to observers,
is not perceived by the animal as pain or distress. Given that we are limited to applying euthanasia methods
based on these three basic mechanisms, efforts should
be directed toward educating individuals involved in
the euthanasia process, achieving technical proficiency,
and refining the application of existing methods.135
I7. CONFIRMATION OF DEATH
Death must be confirmed before disposal of any animal remains. A combination of criteria is most reliable
in confirming death, including lack of pulse, breathing,
corneal reflex and response to firm toe pinch, inability to hear respiratory sounds and heartbeat by use of
a stethoscope, graying of the mucous membranes, and
rigor mortis. None of these signs alone, except rigor
mortis, confirms death.
In small animals, particularly in animal shelter settings, verification of death may be supplemented by
percutaneous cardiac puncture after the animal is unconscious. Failure of the needle and attached syringe to
move after insertion into the heart (aspiration of blood
provides evidence of correct location) indicates lack of
cardiac muscle movement and death.136
16
I8. DISPOSAL OF ANIMAL REMAINS
Regardless of the euthanasia method chosen, animal remains must be handled appropriately and in accord with state and local law. Regulations apply not only
to the disposition of the animal’s remains (eg, burial,
incineration, rendering), but also to the management
of chemical residues (eg, pharmaceuticals [including
but not limited to barbiturates, such as pentobarbital]
and other residues, such as lead) that may adversely affect scavengers or result in the adulteration of rendered
products used for animal feed.
Use of pentobarbital invokes legal responsibilities
for veterinarians, animal shelters, and animal owners
to properly dispose of animal remains after death. Animal remains containing pentobarbital are potentially
poisonous for scavenging wildlife, including birds (eg,
bald and golden eagles, vultures, hawk species, gulls,
crows, ravens), carnivorous mammals (eg, bears, martens, fishers, foxes, lynxes, bobcats, cougars), and
domestic dogs.137 Federal laws protecting many of
these species apply to secondary poisoning from animal remains containing pentobarbital. The Migratory
Bird Treaty Act, the Endangered Species Act, and the
Bald and Golden Eagle Protection Act may carry civil
and criminal penalties, with fines in civil cases up to
$25,000 and in criminal cases up to $500,000 and incarceration for up to 2 years.137 Serious repercussions
may occur when veterinary health professionals who
should be well-informed about the necessity for proper
disposal of animal remains fail to provide it, or fail to
inform their clients how to provide it, whether there
was intent to cause harm or not.138,139 Cases of suspected wildlife death from animal remains containing pentobarbital are investigated by the regional US Fish and
Wildlife Service law enforcement office.
Recommendations by the US Fish and Wildlife Service for prevention of secondary poisoning from pentobarbital are to (1) incinerate or cremate animal remains whenever possible, (2) immediately bury deeply
according to local laws and regulations, (3) securely
cover or store animal remains if the ground is frozen
until such time as deep burial is practical, (4) review
and modify local landfill practices to prevent access of
scavengers to legally disposed animal remains, (5) educate clients about proper disposal, (6) include a warning regarding disposal of animal remains on the euthanasia consent form, and (7) tag animal remains and
outer bags or containers with prominent poison tags.137
Rendering is an important means of disposal of
dead livestock and horses, and since many horses are
euthanized with barbiturates, related residues can be
hazardous. Rendered protein is used in animal feed for
cattle, swine, poultry, finfish, aquatic invertebrates, and
companion animals, but products rendered from ruminants are prohibited by law for use in ruminant feed.
Many pet food manufacturers have lowered their acceptance thresholds for barbiturate concentrations in rendered product. Advances in analytical chemistry have
spawned increasingly sensitive assays, and pet food
manufacturers are using these techniques to ensure
the purity of the rendered protein incorporated in their
products. Accordingly, increased analytic sensitivity
has led many renderers to reconsider accepting horses
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
euthanized using barbiturates. This places renderers
and those wishing to employ rendering as a means of
disposal for animals euthanized using pentobarbital in
a difficult position, and may result in renderers being
reluctant to accept more animal remains than they can
reasonably manage without creating residue concerns.
Alternatives for disposal of animal remains must be
considered in advance, in case the renderer cannot or
will not accept animal remains containing barbiturate
residues.
Composting is another means of disposing of animal remains that is becoming increasingly common.
Studies examining the persistence of barbiturate residues in composted animal remains are few, but those
that do exist suggest the persistence of the drugs in
composted material. While the implications of this are
still unclear, it does raise questions about potential environmental impacts in the case of animal health emergencies or mass mortality events.
Alternatives to the use of pentobarbital that may reduce the risk of secondary toxicity include general anesthesia followed by nontoxic injectable agents such as
potassium chloride, or the application of physical methods such as penetrating captive bolt or gunshot. These
alternatives, however, are not risk free. For example,
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
pharmaceutical residues in animal remains other than
barbiturates (eg, xylazine) may affect scavengers and can
reduce the acceptability of the animal remains for renderers. Unfortunately, specific guidance from regulators
regarding the use of such alternatives is limited.
The persistence of antimicrobials in animal remains
presents parallel concerns, particularly for animal remains that will be rendered. While many antimicrobials
may be inactivated or destroyed through the rendering
process, public health concerns associated with antimicrobial resistance, coupled with the enhanced sensitivity of chemical assays and limited regulatory guidance
for renderers, further complicate veterinarians’ responsibilities for safe remediation.
Safe handling and disposal of the resulting animal
remains are also critically important when zoonotic diseases, foreign animal diseases, or diseases of concern to
population health are suspected. Appropriate diagnostic samples should be collected for testing, regulatory
authorities must be contacted, and the animal remains
must be incinerated (if possible). Personal protective
equipment and precautions for handling biohazardous
materials are recommended. Animals that have injured
humans may require specific actions to be taken depending on local and state laws.
17
Part II—Methods of Euthanasia
M1. INHALED AGENTS
M1.1 COMMON CONSIDERATIONS
Inhaled vapors and gases require a critical concentration within the alveoli and blood for effect; thus, all
inhaled methods have the potential to adversely affect
animal welfare because onset of unconsciousness is not
immediate. Distress may be created by properties of the
agent (eg, pungency, hypoxia, hypercarbia) or by the
conditions under which the agent is administered (eg,
home cage or dedicated chamber, gradual displacement
or prefilling of the container), and may manifest itself
behaviorally (eg, overt escape behaviors, approachavoidance preferences [aversion]) or physiologically
(eg, changes in heart rate, sympathetic nervous system
[SNS] activity, hypothalamic-pituitary axis [HPA] activity). Although SNS and HPA activation are well accepted as markers of a stress response, these systems are activated in response to both physical and psychological
stressors and are not necessarily associated with higherorder CNS processing and conscious experience by the
animal. Furthermore, use of SNS and HPA activation to
assess distress during inhalation of euthanasia agents is
complicated by continued exposure to the agents during the period between loss of consciousness and death.
Distress during administration of inhaled agents
has been evaluated by means of both behavioral assessment and aversion testing. While overt behavioral signs
of distress have been reported in some studies, others have not consistently found these effects. Through
preference and approach-avoidance testing, all inhaled
agents currently used for euthanasia have been identified as being aversive to varying degrees. Aversion is
a measure of preference, and while aversion does not
necessarily imply that the experience is painful, forcing
animals into aversive situations creates stress. The conditions of exposure used for aversion studies, however,
may differ from those used for stunning or killing. In
addition, agents identified as being less aversive (eg, Ar
or N2 gas mixtures, inhaled anesthetics) can still produce overt signs of behavioral distress (eg, open-mouth
breathing) in some species under certain conditions
of administration (eg, gradual displacement). As previously noted in the section on consciousness, one of
the characteristics of anesthesia in people is feeling as
if one is having an out-of-body experience, suggesting
a disconnection between one’s sense of self and one’s
awareness of time and space.140 Although we cannot
know for certain the subjective experiences of animals,
one can speculate similar feelings of disorientation may
contribute to the observed signs of distress.
As for physical methods, the conditions under
which inhaled agents are administered for euthanasia
can have profound effects on an animal’s response and,
thus, agent suitability. Simply placing Sprague-Dawley
rats into an unfamiliar exposure chamber containing
room air produces arousal, if not distress.141 Pigs are
social animals and prefer not to be isolated from one
another; consequently, moving them to the CO2 stun18
ning box in groups, rather than lining them up single
file as needed for electric stunning, improves voluntary
forward movement, reduces handling stress and electric prod use, and improves meat quality.142
That inhaled agents can produce distress and aversion in people raises concerns for their use in animals,
in that the US Government Principles for the Utilization and Care of Vertebrate Animals Used in Testing,
Research, and Training143 state “Unless the contrary is
established, investigators should consider that procedures that cause pain or distress in human beings may
cause pain or distress in other animals.” Interestingly,
more than 40% of human children 2 to 10 years old
display distress behaviors during sevoflurane induction, with 17% displaying significant distress and more
than 30% physically resisting during induction.144 Fear
in children undergoing anesthesia may be due to odor,
feel of the mask, or a true phobia of the mask.145 Despite
evidence of distress and aversion, inhaled anesthetics
continue to be administered because the benefits associated with their use greatly outweigh any distress and/
or aversion they may cause.
The suitability of any particular inhaled agent for
euthanasia therefore depends largely on distress and/
or pain experienced prior to loss of consciousness. Distress can be caused by handling, specific agent properties, or method of administration, such that a onesize-fits-all approach cannot be easily applied. Suffering
can be conceptualized as the product of severity, incidence, and duration. As a general rule, a gentle death
that takes longer is preferable to a rapid, but more distressing death25; however, in some species and under
some circumstances, the most humane and pragmatic
option may be exposure to an aversive agent or condition that results in rapid unconsciousness with few or
no outward signs of distress. Our goal is to identify best
practices for administering inhaled agents, defining the
optimal conditions for transport, handling, and agent
selection and delivery to produce the least aversive and
distressing experience for each species.
The following contingencies are common to all inhaled euthanasia agents:
(1) Time to unconsciousness with inhaled agents is
dependent on the displacement rate, container volume,
and concentration. An understanding of the principles
governing delivery of gases or vapors into enclosed
spaces is necessary for appropriate application of both
prefill and gradual displacement methods.
(2) Loss of consciousness will be more rapid if animals are initially exposed to a high concentration of the
agent. However, for many agents and species, forced exposure to high concentrations can be aversive and distressing, such that gradual exposure may be the most
pragmatic and humane option.
(3) Inhaled agents must be supplied in purified
form without contaminants or adulterants, typically
from a commercially supplied source, cylinder, or tank,
such that an effective displacement rate and/or concentration can be readily quantified. The direct application
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
of products of combustion or sublimation is not acceptable due to unreliable or undesirable composition and/
or displacement rate.
(4) The equipment used to deliver and maintain
inhaled agents must be in good working order and in
compliance with state and federal regulations. Leaky or
faulty equipment may lead to slow, distressful death and
may be hazardous to other animals and to personnel.
(5) Most inhaled agents are hazardous to animal
workers because of the risk of explosions (eg, ether,
CO), narcosis (eg, halocarbon anesthetics, CO2, asphyxiating gases), hypoxia (eg, asphyxiating gases,
CO), addiction or physical abuse (eg, nitrous oxide
[N2O], halocarbon anesthetics), or health effects resulting from chronic exposure (eg, N2O, CO, possibly halocarbon anesthetics).
(6) In sick or depressed animals where ventilation
is decreased, agitation during induction is more likely
because the rise in alveolar gas concentration is delayed.
A similar delayed rise in alveolar gas concentration can
be observed in excited animals having increased cardiac
output. Suitable premedication or noninhaled methods
of euthanasia should be considered for such animals.
(7) Neonatal animals appear to be resistant to hypoxia, and because all inhaled agents ultimately cause
hypoxia, neonatal animals take longer to die than
adults.146 Inhaled agents can be used alone in unweaned
animals to induce loss of consciousness, but prolonged
exposure time or a secondary method may be required
to kill the unconscious animal.
(8) Reptiles, amphibians, and diving birds and
mammals have a great capacity for holding their breath
and for anaerobic metabolism. Therefore, induction of
anesthesia and time to loss of consciousness when inhaled agents are used may be greatly prolonged. Noninhaled methods of euthanasia should be considered for
these species and a secondary method is required to kill
the unconscious animal.
(9) Rapid gas flows can produce noise or cold
drafts leading to animal fright and escape behaviors. If
high flows are required, equipment should be designed
to minimize noise and gas streams blowing directly on
the animals.
(10) When possible, inhaled agents should be administered under conditions where animals are most
comfortable (eg, for rodents, in the home cage; for pigs,
in small groups). If animals need to be combined, they
should be of the same species and compatible cohorts,
and, if needed, restrained or separated so that they will
not hurt themselves or others. Chambers should not
be overloaded and need to be kept clean to minimize
odors that might cause distress in animals subsequently
euthanized.
(11) Because some inhaled agents may be lighter
or heavier than air, layering or loss of agent may permit
animals to avoid exposure. Mixing can be maximized
by ensuring incoming gas or vapor flow rates are sufficient. Chambers and containers should be as leak free
as possible.
(12) Death must be verified following administration of inhaled agents. This can be done either by examination of individual animals or by adherence to validated exposure processes proven to result in death.147
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
If an animal is not dead, exposure must be repeated or
followed with another method of euthanasia.
M1.2 PRINCIPLES GOVERNING
ADMINISTRATION
Changes in gas concentration within any enclosed
space involve two physical processes: (1) wash-in of
new gas (or washout of existing gas) and (2) the time
constant required for that change to occur within the
container for a known flow rate. These processes are
commonly combined in the practice of anesthesia to
predict how quickly a change in concentration of an
inhaled anesthetic will occur within a circle rebreathing circuit.148 An understanding of how these processes
work together is critical for the appropriate application
of both gradual displacement and prefill immersion euthanasia methods.149
The rate of change of gas concentration within any
enclosed space is a special form of nonlinear change
known as an exponential process, and as such can be
derived from the wash-in and washout exponential
functions.150 Briefly, for the wash-in exponential function the quantity under consideration rises toward a
limiting value, at a rate that progressively decreases in
proportion to the distance it still has to rise. In theory, the quantity approaches, but never reaches, 100%.
Conversely, for the wash-out exponential function the
quantity under consideration falls at a rate that progressively decreases in proportion to the distance it still has
to fall. Again, in theory, the quantity approaches, but
never reaches, zero.
The exponential wash-in and washout equations
are used to derive the time constant (τ) for an enclosed volume or space. This constant is mathematically equal to the enclosed volume or space undergoing wash-in or wash-out divided by the rate of flow, or
displacement, into that space, where τ = volume / flow
rate.150,151 Thus, the time constant represents the time
at which the wash-in or washout process would have
been complete had the initial rate of change continued
as a linear function rather than an exponential function.150 As such, the time constant is similar in concept
to the half-life, although they are neither identical nor
interchangeable.151
For the wash-in function, 1(τ) is required for the
concentration of the inflowing gas to rise to 63.2% of
the inflowing gas concentration, 2(τ) are required for
the concentration to rise to 86.5%, and 3(τ) are required for the concentration to rise to 95%, with `(τ)
required for the gas concentration within the container
to equal the inflowing gas concentration. Conversely,
for the washout function, 1(τ) is required for the remaining gas concentration to fall to 36.8% of the original value, 2(τ) are required for gas concentration to
fall to 13.5%, 3(τ) are required for gas concentration
to fall to 5%, with `(τ) required for gas concentration
to fall to 0% (Figure 3). The flow, or displacement rate,
therefore determines the time constant for any given
enclosed volume, such that increasing the flow rate will
result in a proportional reduction of the wash-in and
washout time constants for any size chamber (and vice
versa).
Based on Figure 3, it can be shown that a gradual
19
rates that can lead to delivery of freezing gas and dry
ice snow to the animals as well as regulator icing and
cylinder freezing.
A distinction must be made between immersion,
where animals are directly placed into a gas or vapor
contained within a container, and the process of controlled atmospheric stunning (CAS) as employed for
the commercial stunning of poultry and hogs. Although
a complete description of the operation of the commercial CAS systems currently in use is beyond the scope of
this document, typically the entry point is open to the
atmosphere with negligible concentrations of stunning
gas present. Unlike immersion, animals are introduced
at a controlled rate into a tightly controlled stunning
atmospheric gradient, such that CAS can be considered
to be a gradual displacement method.
M1.3 INHALED ANESTHETICS
Figure 3—Graphic representation of the wash-in and wash-out
exponential functions, using a hypothetical example of a closed
container, originally filled with gas A into which gas B is introduced. The wash-in and wash-out functions are used to determine the time constant for the enclosed volume or space. The
gas concentration within the container can be readily determined
from the time constant, which is calculated by dividing the container volume by the gas displacement rate. Figure taken from
Meyer RE, Morrow WEM. Carbon dioxide for emergency on-farm
euthanasia of swine. Journal of Swine Health and Production
2005;13(4): 210–217, 2005. Reprinted with permission.
inflow or displacement rate of 20% of the chamber volume per minute represents a time constant (τ) value of
5 minutes (1 divided by 0.2/min) regardless of chamber
volume. For example, CO2 displacement rate equivalent
to 20% of the chamber volume/min, as recommended
by Hornett and Haynes152 and Smith and Harrap,153 is
predicted to increase CO2 concentration from zero to
63.2% in 5 minutes (1τ), to 86.5% in 10 minutes (2τ),
and to 95% in 15 minutes (3τ). An examination of the
published experimental data of Smith and Harrap confirms this, where CO2 supplied at a displacement rate of
22% of chamber volume increased the CO2 concentration to approximately 64% in 4.5 minutes (1τ for their
chamber). Similarly, Niel and Weary154 reported 65% after 340 seconds (1τ) and 87% after 600 seconds (2τ) for
a CO2 displacement rate of 17.5% of chamber volume/
min. Prefill methods will require displacement rates of
3τ to attain 95% of the inflow gas concentration within
the chamber.
Thus, gas displacement rate is critical to the humane application of inhaled methods, such that an appropriate pressure-reducing regulator and flow meter
combination or equivalent equipment with demonstrated capability for generating the recommended displacement rate for the size container being utilized is
absolutely necessary when compressed gases are used
for euthanasia. Nitrogen, Ar, and CO are all commercially supplied in cylinders under high pressure, but
CO2 is unique in that it is supplied as a liquefied gas
under high pressure. By reducing high pressure at the
cylinder valve, gas flow is made constant to the flow
meter as cylinder pressure decreases during use. With
CO2, the regulator also acts to prevent high gas flow
20
Overdoses of inhaled anesthetics (eg, ether, halothane, methoxyflurane, isoflurane, sevoflurane, desflurane, enflurane) have been used to euthanize many
species.155 Presently, only isoflurane, enflurane, sevoflurane, and desflurane are clinically available in the United States, although halothane and methoxyflurane are
still available elsewhere in the world. Halothane induces anesthesia rapidly and is an effective inhaled agent
for euthanasia. Enflurane is less soluble in blood than
halothane, but, because of its lower vapor pressure and
lower potency, induction rates may be similar to those
for halothane. At deep anesthetic planes, convulsions
may occur. Enflurane is an effective agent for euthanasia, but the associated seizure activity may be disturbing to personnel. Isoflurane is less soluble than halothane, and it induces anesthesia more rapidly. However,
it has a pungent odor and onset of unconsciousness
may be delayed due to breath holding. Due to lower potency, isoflurane also may require more drug to kill an
animal, compared with halothane. Sevoflurane is less
potent than either isoflurane or halothane and has a
lower vapor pressure. Anesthetic concentrations can be
achieved and maintained rapidly but more drug will be
required to kill the animal. Although sevoflurane is reported to possess less of an objectionable odor than isoflurane, some species may struggle violently and experience apnea when sevoflurane is administered by face
mask or induction chamber.156 Like enflurane, sevoflurane induces epileptiform electrocortical activity.157
Desflurane is currently the least soluble potent inhaled
anesthetic, but the vapor is quite pungent, which may
slow induction. This drug is so volatile that it could
displace O2 and induce hypoxemia during induction
if supplemental O2 is not provided. Both diethyl ether
and methoxyflurane are highly soluble, and may be accompanied by agitation because anesthetic induction is
quite slow. Diethyl ether is irritating to the eyes, nose,
and respiratory airways; poses serious risks due to flammability and explosiveness; and has been used to create
a model for stress.158–161
Although inhaled anesthetics are routinely used
to produce general anesthesia in humans and animals,
these agents may be aversive and distressful under certain conditions. Flecknell et al156 reported violent struggling accompanied by apnea and bradycardia in rabbits
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
administered isoflurane, halothane, and sevoflurane
by mask or induction chamber, and concluded these
agents were aversive and should be avoided whenever
possible. Leach et al162–164 found inhaled anesthetic vapors to be associated with some degree of aversion in
laboratory rodents, with increasing aversion noted as
concentration increased; halothane was least aversive
for rats, while halothane and enflurane were least aversive for mice. Makowska and Weary165 also reported
halothane and isoflurane to be aversive to male Wistar
rats, but less so than CO2.
Anesthetic vapor is inhaled until respiration ceases and death ensues. Because the liquid state of most
inhaled anesthetics is irritating, animals should be exposed only to vapors. With inhaled anesthetics, animals
can be placed in a closed receptacle containing cotton
or gauze soaked with an appropriate amount of liquid
anesthetic166 or anesthetic vapor can be introduced from
a precision vaporizer.167 Precision anesthetic vaporizers
typically are limited to 5% to 7% maximum output between 0.5 and 10 L/min O2 flow rate. Induction time
will be influenced by dial setting, flow rate, and size
of the container; time to death may be prolonged because O2 is commonly used as the vapor carrier gas.
The amount of liquid anesthetic required to produce
a given concentration of anesthetic vapor within any
closed container can be readily calculated168; in the case
of isoflurane, a maximum of 33% vapor can be produced at 20°C. Sufficient air or O2 must be provided
during the induction period to prevent hypoxia.166 In
the case of small rodents placed in a large container,
there will be sufficient O2 in the chamber to prevent
hypoxia. Larger species placed in small containers may
initially need supplemental air or O2.166
Nitrous oxide is the least potent of the inhalation
anesthestics. In humans, the minimum alveolar concentration (defined as the median effective dose) for N2O
is 104%; its potency in other species is less than half
that in humans (ie, approx 200%). Because the effective
dose for N2O is above 100% it cannot be used alone at 1
atmosphere of pressure in any species without producing hypoxia prior to respiratory or cardiac arrest. As a
result, animals may become distressed prior to loss of
consciousness. Up to 70% N2O may be combined with
other inhaled gases to speed the onset of anesthesia;
however, the anesthetic contribution of N2O will be
only half (20% to 30%) of that expected in humans due
to its reduced potency in animals.169
Effective procedures should be in place to reduce
animal worker exposure to anesthetic vapors.170 Human
workplace recommended exposure limits were issued
in 1977 by the National Institute of Occupational Safety
and Health (NIOSH); concentrations for halogenated
inhaled anesthetics are not to exceed 2 ppm (1-hour
ceiling) when used alone, or 0.5 ppm for halogenated
anesthetics combined with 25-ppm N2O (time-weighted average during use). The American Conference
of Government Industrial Hygienists has assigned a
threshold limit value time-weighted average of 50 ppm
for N2O, 50 ppm for halothane, and 75 ppm for enflurane for an 8-hour time-weighted exposure. These concentrations were established because they were found
to be attainable utilizing clinical scavenging techniques
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
and there are no controlled studies proving exposure at
these concentrations are safe. No NIOSH recommended
exposure limits exist for the three most currently used
anesthetics (isoflurane, desflurane, and sevoflurane),
and, at present, the Occupational Safety and Health Administration has no permissible exposure limits regulating these specific agents.
Advantages—(1) Inhaled anesthetics are particularly useful for euthanasia of smaller animals (< 7 kg
[15.4 lb]) or for animals in which venipuncture may
be difficult. (2) Inhaled anesthetics can be administered by several different methods depending on the
circumstances and equipment available (eg, face mask,
open drop where the animal is not permitted to directly
contact the anesthetic liquid, precision vaporizer, rigid
or nonrigid containers). (3) Halothane, enflurane, isoflurane, sevoflurane, desflurane, methoxyflurane, and
N2O are nonflammable and nonexplosive under usual
clinical conditions. (4) Inhaled anesthetics can be useful as the sole euthanasia agent or as part of a 2-step
process, where animals are first rendered unconscious
through exposure to inhaled anesthetic agents and subsequently killed via a secondary method.
Disadvantages—(1) Inhaled anesthetics are aversive to rabbits and laboratory rodents and the same
may be true for other species. Animals may struggle
and become anxious during induction of anesthesia, with some animals exhibiting escape behaviors
prior to onset of unconsciousness. Should apnea or
excitement occur, time to loss of consciousness may
be prolonged. (2) Ether is irritating, flammable, and
explosive. Explosions have occurred when animals,
euthanized with ether, were placed in an ordinary
(not explosion-proof) refrigerator or freezer and when
bagged animals were placed in an incinerator. (3) Induction with methoxyflurane is unacceptably slow in
some species. (4) Because of design limits on vapor
output, precision anesthetic vaporizers may be associated with a longer wash-in time constant and, thus,
longer induction time; time to death may be prolonged as O2 is commonly used as the vapor carrier
gas. (5) Nitrous oxide used alone will create a hypoxic
atmosphere prior to loss of consciousness and will
support combustion. (6) Personnel and animals may
be injured by exposure to these agents. There is recognized potential for human abuse of inhaled anesthetics. (7) Because large amounts of inhaled anesthetics
are absorbed and substantial amounts remain in the
body for days,171use of inhaled anesthetics for euthanasia is challenging for food-producing animals due to
potential for tissue residues.
General recommendations—Inhaled anesthetics are
acceptable with conditions for euthanasia of small animals (< 7 kg) where the following contingencies can be
met: (1) In those species where aversion or overt escape
behaviors have not been noted, exposure to high concentrations resulting in rapid loss of consciousness is
preferred. Otherwise, gradual fill methods can be used,
keeping in mind the effect that chamber volume, flow
rate, and anesthetic concentration will have on the time
21
constant and rate of rise of anesthetic concentration.
Inhaled anesthetics can be administered as the sole
euthanasia agent or as part of a 2-step process, where
animals are first rendered unconscious through inhaled
anesthetic agent exposure and then subsequently killed
by a secondary method. (2) Order of preference is isoflurane, halothane, sevoflurane, enflurane, methoxyflurane, and desflurane, with or without N2O. Nitrous oxide should not be used alone. Methoxyflurane is acceptable with conditions only if other agents or methods
are not available. Ether is not acceptable for euthanasia.
(3) Although acceptable, inhaled anesthetics are generally not used for larger animals because of cost and
difficulty of administration. (4) Exposure of workers to
anesthetics must comply with state and federal occupational health and safety regulations.
M1.4 CARBON MONOXIDE
Carbon monoxide is a colorless, odorless gas that
is nonflammable and nonexplosive at concentrations
< 12%. Carbon monoxide is a cumulative poison that
produces fatal hypoxemia; it readily combines with hemoglobin and blocks uptake of O2 by erythrocytes by
forming carboxyhemoglobin.172,173 Precisely because it
is insidious, difficult to detect, and highly toxic even
at low concentrations, the lethal properties of CO have
long been recognized; indeed, approximately 50,000
emergency room visits for human CO poisoning occur
in the United States annually.174
In people, the clinical presentation for CO inhalation is nonspecific, with headache, dizziness, and
weakness the most common symptoms of low-level
CO toxicosis. As concentrations of CO increase, these
signs may be followed by decreased visual acuity, tinnitus, nausea, progressive depression, confusion, and
collapse.175 With higher-level exposure, coma, convulsions, and cardiorespiratory arrest may occur.173 Carbon monoxide stimulates motor centers in the brain,
such that loss of consciousness may be accompanied by
convulsions and muscular spasms. Distinct signs of CO
toxicosis are not evident until the CO concentration is
0.05% in air, and acute signs do not develop until CO
concentration is approximately 0.2% in air. In humans,
exposure to 0.32% CO and 0.45% CO for 1 hour will
induce loss of consciousness and death, respectively.176
Chronic exposure to low concentrations of CO may be
a health hazard, especially with regard to cardiovascular
disease and teratogenic effects.173,174,177–179 An efficient
exhaust or ventilation system is essential to prevent accidental exposure of humans.
In the past, mass euthanasia was accomplished by
use of three different methods for generating CO: (1)
chemical interaction of sodium formate and sulfuric
acid, (2) exhaust fumes from gasoline internal combustion engines, and (3) commercially compressed CO
in cylinders. The first 2 techniques are associated with
substantial problems such as production of other gases,
inadequate production of CO, inadequate gas cooling,
inability to quantify delivery rate, and maintenance of
equipment.
Ramsey and Eilmann180 found that a concentration of 8% CO caused guinea pigs to collapse in 40
seconds to 2 minutes, and death occurred within 6
22
minutes. When used with mink and chinchillas, CO
caused collapse in 1 minute, cessation of breathing in
2 minutes, and cardiac arrest in 5 to 7 minutes.181,182
Chalifoux and Dallaire183 evaluated the physiologic and
behavioral characteristics of dogs exposed to 6% CO
in air, and could not determine the precise time of loss
of consciousness. Electroencephalographic recordings
revealed 20 to 25 seconds of abnormal cortical function, and during this period the dogs became agitated
and vocalized. It is not clear whether these behavioral
responses are indicative of animal distress; however,
humans in this phase reportedly are not distressed.172
Subsequent studies184 have revealed that tranquilization
with acepromazine significantly decreases behavioral
and physiologic responses of dogs euthanized with CO.
Carbon monoxide is noted to be aversive to laboratory
rats, but not as aversive as CO2.185
In one study on cats,186 CO from gasoline engine
exhaust was compared with a combination of 70%
CO2 plus 30% O2. Signs of agitation before loss of consciousness were greater for the CO2-plus-O2 combination. Time to complete immobilization was greater with
CO2 plus O2 (approx 90 seconds) than with CO alone
(approx 56 seconds).186 In another study in neonatal
pigs,187 excitation was less likely to precede loss of consciousness if animals were exposed to a slow rise in CO
concentration.
A study of an epidemic of avian influenza in the
Netherlands in 2003 compared the use of CO2 with CO
for gassing whole houses of poultry.188 The researchers noted that more convulsions were observed in the
presence of CO and recommended that CO2 was the
preferred agent for this application due to safety regulations required for the use of CO.
Advantages—(1) Carbon monoxide induces loss of
consciousness without pain and with minimal discernible discomfort, depending on species. (2) Hypoxemia
induced by CO is insidious. (3) Death occurs rapidly if
concentrations of 4% to 6% are used.
Disadvantages—(1) Carbon monoxide is an aversive agent for laboratory rodents and the same may be
true for other species. (2) Safeguards must be taken to
prevent and monitor exposure of personnel. (3) Electrical equipment exposed to CO (eg, lights and fans) must
be spark free and explosion proof.
General recommendations—Carbon monoxide is
acceptable with conditions for euthanasia, provided all
of the following contingencies are met: (1) Personnel
using CO must be instructed thoroughly in its use and
must understand its hazards and limitations. (2) The
CO chamber must be of the highest-quality construction and should allow for separation of individual animals. If animals need to be combined, they should be of
the same species, and, if needed, restrained or separated
so that they will not hurt themselves or others. Chambers should not be overloaded and need to be kept
clean to minimize odors that might distress animals
that are subsequently euthanized. (3) The CO source
and chamber must be located in a well-ventilated environment, preferably out-of-doors. (4) The chamber
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
must be well lighted and must allow personnel direct
observation of animals. (5) The CO flow rate should
be adequate to rapidly achieve a uniform CO concentration of at least 6% after animals are placed in the
chamber, except for those species (eg, neonatal pigs)
where it has been shown that less agitation occurs with
a gradual rise in CO concentration.187 (6) If the chamber is inside a room, CO monitors must be placed in
the room to warn personnel of hazardous concentrations. (7) It is essential that CO use be in compliance
with state and federal occupational health and safety
regulations. (8) Carbon monoxide must be supplied in
a precisely regulated and purified form without contaminants or adulterants, typically from a commercially
supplied cylinder or tank. The direct application of
products of combustion or sublimation is not acceptable due to unreliable or undesirable composition and/
or displacement rate. As gas displacement rate is critical
to the humane application of CO, an appropriate pressure-reducing regulator and flow meter combination or
equivalent equipment with demonstrated capability for
generating the recommended displacement rate for the
size container being utilized is absolutely necessary.
M1.5 NITROGEN, ARGON
Nitrogen and Ar are odorless, colorless and tasteless
gases that are inert, nonflammable, and nonexplosive.
Nitrogen normally comprises 78% of atmospheric air,
whereas Ar comprises less than 1%. These gases function in the current context by displacing air (and the O2
it contains), causing anoxia. Exposure of Sprague-Dawley rats to severe hypoxic conditions (< 2% O2) using
either gas leads to unconsciousness around 90 seconds
and death after 3 minutes using Ar or 7 minutes using N2141; similar findings have been reported for dogs,
rabbits, and mink.181,182,189,190 Male Sprague-Dawley rats
become hyperpneic, but can survive for more than 20
minutes in Ar or N2 at an O2 concentration of 4.9%.191
Rats are sensitive to even small changes in the
concentration of O2, and are able to detect concentrations both lower and higher than the 20.9% normally
found in air.192 Rats and mice allowed to travel between chambers containing different gases spent most
of their time in the control chamber (containing air),
but preferred a hypoxic chamber (containing Ar) to a
chamber containing CO2; however, the animals stayed
only a few seconds in either gas.162–164 Even when rats
were trained to enter a chamber for a food reward they
typically refused to enter, or left immediately after entering, when the atmosphere was hypoxic (< 2% O2,
90% Ar).193 When rats were exposed to gradually decreasing concentrations of O2 and increasing concentrations of Ar, they always left the chamber before losing consciousness (typically when O2 declined to about
7%).194 With N2 flowing at a rate of 39% of chamber
volume/min (τ = 2 minutes 34 seconds), rats collapsed
in approximately 3 minutes and stopped breathing in
5 to 6 minutes; regardless of flow rate, signs of panic
and distress were evident before the rats collapsed and
died.152 During forced exposure to Ar gradually filling a
chamber at a rate of 50% of the chamber volume/min (τ
= 2 minutes), male Sprague-Dawley rats showed openmouthed breathing and seizure-like behavior prior to
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
loss of consciousness, suggesting similar potential for
distress.195 These observations are not surprising, as
gradual displacement methods using N2 or Ar, alone or
mixed with other gases, are predicted by the wash-in
and washout functions to result in prolonged exposure
to hypoxic conditions.
In contrast, hypoxia produced by inert gases such
as N2 and Ar appears to cause little or no aversion in
turkeys196 or chickens197; these animals freely entered a
chamber containing < 2% O2 and > 90% Ar. When Ar
was used to euthanize chickens, exposure to a chamber
prefilled with Ar, with an O2 concentration of < 2%, led
to EEG changes and collapse in 9 to 12 seconds. Birds
removed from the chamber at 15 to 17 seconds failed
to respond to comb pinching. Continued exposure led
to convulsions at 20 to 24 seconds. Somatosensoryevoked potentials were lost at 24 to 34 seconds, and
the EEG became isoelectric at 57 to 66 seconds.198 With
turkeys, immersion in 90% Ar with 2% residual O2 led
to EEG suppression in 41 seconds, loss of SEP in 44
seconds, and isoelectric EEG in 101 seconds, leading
the authors to conclude exposure times > 3 minutes
were necessary to kill all birds.199 Failure to maintain
< 2% O2 prolongs survival.200,201 Gerritzen et al202 also
reported that chickens did not avoid chambers containing < 2% O2; birds gradually became unconscious
without showing signs of distress. Chickens202–205 and
turkeys196 killed by hypoxia show less head shaking and
open-beak breathing than birds exposed to CO2.
Hypoxia produced by N2 and Ar appears to reduce, but not eliminate, aversive responses in pigs. Pigs
chose to place their head in a hypoxic (< 2% O2, 90%
Ar) chamber containing a food reward, remained with
their head in the chamber until they became ataxic, and
freely returned to the chamber once they regained posture.206 In contrast, exposure to 90% Ar, 70% N2/30%
CO2, and 85% N2/15% CO2 all resulted in signs of aversion, defined by the authors as escape attempts and
gasping; however, the proportion of pigs showing these
behaviors was lowest with Ar.207 Early removal from the
stunning atmosphere results in rapid regaining of consciousness, such that exposure times > 7 minutes are
needed to ensure killing with these gases.208
Mink will also enter into a hypoxic chamber (< 2%
O2, 90% Ar), but will not remain until the point of unconsciousness. The duration of hypoxic exposure freely
chosen is similar to the average duration of a dive for
mink, suggesting they are able to detect hypoxia and
modify their behavior to avoid detrimental effects.209
Advantages—(1) Nitrogen and Ar do not appear
to be directly aversive to chickens or turkeys, and the
resulting hypoxia appears to be nonaversive or only
mildly aversive to these species. Similarly, N2 and Ar
gas mixtures do not appear to be directly aversive to
pigs and appear to reduce, but not eliminate, the behavioral responses to hypoxia. (2) Nitrogen and Ar are
nonflammable, nonexplosive, and readily available as
compressed gases. (3) Hazards to personnel are minimal when used with properly designed equipment. (4)
Argon and N2-CO2 gas mixtures are heavier than air and
can be contained within an apparatus into which animals and birds can be lowered or immersed.207
23
Disadvantages—(1) Hypoxia resulting from exposure to these gases is aversive to rats, mice, and
mink. (2) Based on the wash-in and washout functions, gradual displacement methods using N2 or Ar,
alone or mixed with other gases, may result in exposure to hypoxic conditions prior to loss of consciousness. Loss of consciousness will be preceded by openmouth breathing and hyperpnea, which may be distressing for nonavian species. (3) Reestablishing a low
concentration of O2 (ie, 6% or greater) in the chamber
before death will allow immediate recovery.206,208,210
(4) Exposure times > 7 minutes are needed to ensure
killing of pigs. (5) As with CO2, rats euthanized with
Ar demonstrate alveolar hemorrhage consistent with
terminal asphyxiation.195 (6) Argon costs about three
times as much as N2. (7) These gases tend to cause
more convulsive wing flapping in poultry than CO2 in
air mixtures.
General recommendations—Hypoxia resulting from
exposure to Ar or N2 gas mixtures is acceptable with
conditions for euthanasia of chickens and turkeys.
Likewise, hypoxia resulting from Ar or N2-CO2 gas
mixtures is acceptable with conditions for euthanasia
of pigs, provided animals can be directly placed into a
< 2% O2 atmosphere and exposure times > 7 minutes
are used. Use of Ar or N2 is unacceptable for other
mammals. These gases create an anoxic environment
that is distressing for some species and aversive to laboratory rodents and mink; other methods of euthanasia
are preferable for these species. Argon or N2 hypoxia,
defined as O2 < 2%, could be used to kill these animals
after they are rendered unconscious via an acceptable
method, although prolonged exposure may be necessary to ensure death.
Nitrogen, Ar, and gas mixtures containing these
gases must be supplied in a precisely regulated and purified form without contaminants or adulterants, typically from a commercially supplied cylinder or tank.
The direct application of products of combustion or
sublimation is not acceptable due to unreliable or undesirable composition or displacement rate. As gas displacement rate is critical to the humane application of
these gases, an appropriate pressure-reducing regulator
and flow meter combination or equivalent equipment
with demonstrated capability for generating the recommended displacement rate for the size container being
utilized is absolutely necessary.
M1.6 CARBON DIOXIDE
Inhalation of CO2 causes respiratory acidosis and
produces a reversible anesthetic state by rapidly decreasing intracellular pH.211 Both basal and evoked neural activity are depressed soon after inhalation of 100%
CO2.211–214 Inhalation of CO2 at a concentration of 7.5%
increases pain threshold, and concentrations of 30%
and higher cause deep anesthesia and death with prolonged exposure.153,154,215–217 Methods to administer CO2
include placing animals directly into a closed, prefilled
chamber containing CO2, or exposure to a gradually increasing concentration of CO2.
Carbon dioxide has the potential to cause distress
in animals via three different mechanisms: (1) pain due
24
to formation of carbonic acid on respiratory and ocular
membranes, (2) production of so-called air hunger and
a feeling of breathlessness, and (3) direct stimulation of
ion channels within the amygdala associated with the
fear response.
Carbon dioxide may cause pain due to the formation of carbonic acid when it contacts moisture on the
respiratory and ocular membranes. In humans, rats,
and cats, most nociceptors begin to respond at CO2 concentrations of approximately 40%.218–221 Humans report
discomfort begins at 30% to 50% CO2, and intensifies
to overt pain with higher concentrations.222–224 Inhaled
irritants are known to induce a reflex apnea and heart
rate reduction, and these responses are thought to reduce transfer of harmful substances into the body.225 In
rats, 100% CO2 elicits apnea and bradycardia, but CO2
at concentrations of 10%, 25%, and 50% does not,226
suggesting gradual displacement methods are less likely to produce pain prior to unconsciousness in rodents.
Carbon dioxide has a key role as a respiratory
stimulant, and elevated concentrations are known to
cause profound effects on the respiratory, cardiovascular, and sympathetic nervous systems.227–229 In humans,
air hunger begins at concentrations as low as 8% and
this sensation intensifies with higher concentrations,
becoming severe at approximately 15%.230–232 With mild
increases in inspired CO2, increased ventilation results
in a reduction or elimination of air hunger, but there
are limits to this compensatory mechanism such that
air hunger may reoccur during spontaneous breathing
with moderate hypercarbia and hypoxemia.233–235 Adding O2 to CO2 may or may not preclude signs of distress.224,236–238 Supplemental O2 will, however, prolong
time to hypoxemic death and may delay onset of unconsciousness.
Although CO2 exposure has the potential to produce a stress response, interpretation of the subjective experiences of animals is complicated. Borovsky239
found an increase in norepinephrine in rats following
30 seconds of exposure to 100% CO2. Similarly, Reed240
exposed rats to 20 to 25 seconds of CO2, which was
sufficient to render them recumbent, unconscious, and
unresponsive, and observed 10-fold increases in vasopressin and oxytocin concentrations. Indirect measures
of sympathetic nervous system activation, such as elevated heart rate and blood pressure, have been complicated by the rapid depressant effects of CO2 exposure.
Activation of the hypothalamic pituitary axis has also
been examined during CO2 exposure. Prolonged exposure to low concentrations of CO2 (6% to 10%) has
been found to increase corticosterone in rats241,242 and
cortisol in dogs.243 In a single-blind study in healthy human volunteers, a single breath of 35% CO2 was found
to result in elevated cortisol concentrations and exposure was associated with an increase in fear.244 It has
been suggested that responses to systemic stressors associated with immediate survival, such as hypoxia and
hypercapnia, are likely directly relayed from brainstem
nuclei and are not associated with higher-order CNS
processing and conscious experience.245 In fact, Kc et
al246 found that hypothalamic vasopressin-containing
neurons are similarly activated in response to CO2 exposure in both awake and anesthetized rats. As stated
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
previously, assessment of the animal’s response to inhaled agents, such as CO2, is complicated by continued
exposure during the period between loss of consciousness and death.
Distress during CO2 exposure has also been examined by means of behavioral assessment and aversion testing. Variability in behavioral responses to CO2
has been reported for rats and mice,152–154,195,237,247–249
pigs,206,250–253 and poultry.196,202–205,254–257 While signs of
distress have been reported as occurring in animals in
some studies, other researchers have not consistently
observed these effects. This may be due to variations
in methods of gas exposure and types of behaviors assessed, as well as strain variability.
Using preference and approach-avoidance testing,
rats and mice show aversion to CO2 concentrations
sufficient to induce unconsciousness,162,163 and are
willing to forgo a palatable food reward to avoid exposure to CO2 concentrations of approximately 15% and
higher165,193 after up to 24 hours of food deprivation.236
Mink will avoid a chamber containing a desirable novel
object when it contains 100% CO2.258 In contrast to
other species, a large proportion of chickens and turkeys will enter a chamber containing moderate concentrations of CO2 (60%) to gain access to food or social
contact.197,202,250 Following incapacitation and prior to
loss of consciousness, birds in these studies show behaviors such as open-beak breathing and head-shaking;
these behaviors, however, may not be associated with
distress because birds do not withdraw from CO2 when
these behaviors occur.203 Thus, it appears that birds are
more willing than rodents and mink to tolerate CO2
at concentrations that are sufficient to induce loss of
posture, and that loss of consciousness follows shortly
afterwards.
Genetics may play a role in CO2 response variability. Panic disorder in humans is genetically linked to
enhanced sensitivity to CO2.259 The fear network, comprising the hippocampus, the medial prefrontal cortex,
the amygdala, and its brainstem projections, appears to
be abnormally sensitive to CO2 in these patients.260 The
genetic background of some pigs, especially excitable
lines such as the Hampshire and German Landrace, has
been associated with animals that react poorly to CO2
stunning, while calmer lines combining the Yorkshire
or Dutch Landrace conformations show much milder
reactions.261 Given a choice, Duroc and Large White
pigs will tolerate 30% CO2 to gain access to a food reward, but will forgo the reward to avoid exposure to
90% CO2, even after a 24-hour period of food deprivation.206,250 A shock with an electric prod, however,
is more aversive to Landrace X Large White pigs than
inhaling 60% or 90% CO2, with pigs inhaling 60% CO2
willing to reenter the crate containing CO2.251 Until further research is conducted, one can conclude that use
of CO2 may be humane for certain genetic lines of pigs
and stressful for others.261
Recent studies involving mice have found regions
of the amygdala associated with fear behavior to contain acid-sensing ion channels (ASICs) sensitive to elevated CO2.262 Fear behaviors and aversion in response
to CO2 exposure were reduced in mice in which the
ASIC receptors were eliminated or inhibited, suggestAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
ing that aversive responses to CO2 in rodents, and potentially other species, are mediated in part by an innate
fear response. Further studies defining the presence of
ASICs and their role in CO2-induced fear in other rodent strains, as well as other animal species, are warranted.
As with other inhaled agents, time to unconsciousness with CO2 is dependent on the displacement rate,
container volume, and concentration used. In rats, unconsciousness is induced in approximately 12 to 33
seconds with 80% to 100% CO2 and 40 to 50 seconds
with 70% CO2.237,263 Similarly, a rapidly increasing concentration (flow rate > 50% of the chamber volume per
minute) induces unconsciousness in only 26 to 48 seconds.153,154,195,238,247 Leake and Waters217 found that dogs
exposed to 30% to 40% CO2 were anesthetized in 1 to
2 minutes. For cats, inhalation of 60% CO2 results in
loss of consciousness within 45 seconds, and respiratory arrest within 5 minutes.264 For pigs, exposure to
60% to 90% CO2 causes unconsciousness in 14 to 30
seconds,210–212,250 with unconsciousness occurring prior
to onset of signs of excitation.210,214 Euthanasia via exposure to CO2 has been described for individual birds
and small groups,265 and its application to euthanasia of
chickens, turkeys, and ducks has been studied extensively, resulting in information about times to collapse,
unconsciousness and death, loss of somatosensory
evoked potentials, and changes in EEG. Leghorn chicks
7 days of age collapsed in 12 seconds after exposure to
97% CO2.248 Raj201 found that 2 minutes’ exposure to
90% CO2 was sufficient to kill day-old chicks exposed
in batches. Broilers 5 weeks of age collapsed an average
of 17 seconds after entering a tunnel filled with 60%
CO2.202
Unlike N2 and Ar, which must be held within a
very tight range of concentration for effective euthanasia, CO2 can render poultry unconscious and kill over
a wide range of concentrations. In tests where it took 8
seconds to achieve the target gas concentration, broilers
and mature hens collapsed in 19 to 21 seconds at 65%
CO2 and 25 to 28 seconds at 35% CO2.266 In a gradualfill study, ducks and turkeys lost consciousness before
25% CO2 was reached and died after the concentration
reached 45%.254 At 49% CO2, EEG suppression, loss of
somatosensory evoked potentials (SEPs), and EEG silence occurred in 11, 26, and 76 seconds in chickens.267
In turkeys, EEG suppression took place in an average of
21 seconds at 49% CO2, but was reduced to 13 seconds
at 86% CO2. In the same report, time to loss of SEPs was
not affected by gas concentration, averaging 20, 15, and
21 seconds, but time to EEG silence was concentration
dependent (ie, 88, 67, and 42 seconds for 49%, 65%,
and 86% CO2, respectively).268
As a general rule, a gentle death that takes longer
is preferable to a rapid, but more distressing death.25
Gradual-fill CO2 exposure causes aversion in rodents
beginning at approximately a 15% concentration and
lasting to onset of unconsciousness. If an appropriate
gradual displacement rate is used, animals will lose
consciousness before CO2 concentrations become painful.195 A 20%/min gradual displacement produces unconsciousness in 106 seconds at a CO2 concentration of
30%152,154,224,238; a slower 10%/min displacement increas25
es time to onset of unconsciousness to 156 seconds at
a CO2 concentration of 21%.195 For poultry, immersion
into relatively low concentrations or exposure to CO2
concentrations producing a gradual induction of unconsciousness reduces convulsions compared with immersion into N2 or Ar.204,269 Carbon dioxide may invoke
involuntary (unconscious) motor activity in birds, such
as flapping of the wings or other terminal movements,
which can damage tissues and be disconcerting for observers248,270; wing flapping is less with CO2 than with
N2 or Ar.269
Due to respiratory adaptations in immature animals, reptiles, amphibians, and some burrowing and
diving species (eg, lagomorphs, mustelids, aquatic
birds, nonhatched birds, newly hatched chicks), high
CO2 concentrations, combined with extended exposure times, follow-up exposure to hypoxemia, or a secondary euthanasia method, may be required to ensure
unconsciousness and death. High CO2 concentrations
(> 60%) and extended exposure times (> 5 minutes)
are required for effective euthanasia of newly hatched
chickens.201,271 On the day of birth, rats and mice exposed to 100% CO2 required exposure times of 35 and
50 minutes, respectively, to ensure death. By 10 days of
age, exposure times of 5 minutes were sufficient to ensure death.272,273 For adult mink, 5 minutes of exposure
is sufficient to ensure death using 100% CO2, but not
using 70% CO2.181 Rabbits of the genus Oryctolagus also
have prolonged survival times when exposed to CO2.274
Inhaled halocarbon anesthetics have been proposed as alternatives to CO2 for rodent euthanasia.25,165,167 However, inhaled anesthetics also produce
varying degrees of aversion in rodents,162–165 and are associated in other animals and humans with aversion,
distress, and escape behaviors during anesthetic induction. Uncertainty exists as to the feasibility of substituting inhaled anesthetic agents for CO2 with respect
to animal welfare and human health and safety.25 Time
to death may be prolonged as O2 is commonly used as
the vapor carrier gas with precision anesthetic vaporizers. Because large amounts of inhaled anesthetics are
absorbed and substantial amounts remain in the body
for days, even after apparent recovery,171 euthanasia via
inhaled anesthetics is unsuitable for food-producing
animals because of the potential for tissue residues. Effective procedures should be in place to reduce worker
exposure to anesthetic vapors. Careful and deliberate
consideration of the consequences associated with this
proposal is warranted before this recommendation can
be made.
Advantages—(1) The rapid depressant, analgesic,
and anesthetic effects of CO2 are well established. (2)
Carbon dioxide is readily available in compressed gas
cylinders. (3) Carbon dioxide is inexpensive, nonflammable, and nonexplosive and poses minimal hazard to
personnel when used with properly designed equipment. (4) Carbon dioxide does not result in accumulation of toxic tissue residues in animals from which food
is produced.
Disadvantages—(1) Substantial and conflicting differences in response to CO2 inhalation exist between and
26
within species, strains, and breeds, making broad generalizations difficult. (2) Carbon dioxide, whether administered by prefill or gradual displacement methods, can
be aversive to some species, and therefore potential exists to cause distress. (3) Because CO2 is heavier than air,
layering of gas or incomplete filling of a chamber may
permit animals to climb or raise their heads above the
effective concentrations and avoid exposure. (4) Immature individuals and some aquatic and burrowing species
may have extraordinary tolerance for CO2. (5) Reptiles
and amphibians may breathe too slowly for the use of
CO2. (6) Euthanasia by exposure to CO2 with O2 supplementation may take longer than euthanasia by other
means.224,237,238 (7) Induction of loss of consciousness at
concentrations < 80% may produce postmortem pulmonary and upper respiratory tract lesions.224,275 (8) Dry ice
and liquid CO2 are potential sources of distress or injury
if permitted to directly contact animals.
General recommendations—Carbon dioxide is acceptable with conditions for euthanasia in those species
where aversion or distress can be minimized. Carbon dioxide exposure using a gradual fill method is less likely
to cause pain due to nociceptor activation by carbonic
acid prior to onset of unconsciousness; a displacement
rate from 10% to 30% of the chamber volume/min is
recommended.25,152,193,195 Whenever gradual displacement methods are used, CO2 flow should be maintained
for at least 1 minute after respiratory arrest.153 If animals need to be combined, they should be of the same
species and, if needed, restrained so that they will not
hurt themselves or others. Immature animals must be
exposed to high concentrations of CO2 for an extended
period of time to ensure death. Oxygen administered
together with CO2 appears to provide little advantage
and is not recommended for euthanasia.
The practice of immersion, where conscious animals are placed directly into a container prefilled with
100% CO2, is unacceptable. A 2-step process, where animals are first rendered unconscious and then immersed
into 100% CO2, is preferred when gradual displacement
methods cannot be used. Immersion of poultry in lesser
concentrations is acceptable with conditions as it does
not appear to be distressing.
Carbon dioxide and CO2 gas mixtures must be supplied in a precisely regulated and purified form without
contaminants or adulterants, typically from a commercially supplied cylinder or tank. The direct application
of products of combustion or sublimation is not acceptable due to unreliable or undesirable composition and/
or displacement rate. As gas displacement rate is critical
to the humane application of CO2, an appropriate pressure-reducing regulator and flow meter or equivalent
equipment with demonstrated capability for generating
the recommended displacement rates for the size container being utilized is absolutely necessary.
M2. NONINHALED AGENTS
M2.1 COMMON CONSIDERATIONS
Noninhaled agents of euthanasia include chemical agents that are introduced into the body by means
other than through direct delivery to the respiratory
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
tract. The primary routes of their administration are
parenteral injection, topical application, and immersion. When it is being determined whether a particular
drug and route of administration are appropriate for euthanasia, consideration needs to be given to the species
involved, the pharmacodynamics of the chemical agent,
degree of physical or chemical restraint required, potential hazards to personnel, consequences of intended
or unintended consumption of the animal’s remains by
humans and other animals, and potential hazards to the
environment from chemical residues. Many noninhaled
euthanasia agents can induce a state of unconsciousness during which minimal vital functions are evident
but from which some animals may recover. Therefore,
as for any euthanasia method, death must be confirmed
prior to final disposition of the animal’s remains.
M2.1.1 Compounding
While several euthanasia agents (eg, barbiturates,
barbiturate combinations, Tributameb [not currently being manufactured in the United States due to concerns
with the manufacturing process, although the approved
New Animal Drug Application has been retained], and
T-61c [withdrawn from the market in the United States
in 1991; consequently, it is no longer commercially
available in this country]) have been approved or are
in review by the FDA Center for Veterinary Medicine
(FDA-CVM), some commonly used injectable euthanasia drugs are not approved, but are compounded from
bulk drugs. These include chloral hydrate, magnesium
sulfate, and some formulations of potassium chloride.
The FDA-CVM’s most recent version of the Compliance
Policy Guide on compounding of drugs for use in animals states that compounding from bulk drugs, except
those specifically addressed for regulatory discretion by
the FDA, raises concerns and may result in regulatory
oversight.276 Use of compounded euthanasia drugs that
may create human or animal health risks (eg, unintentional ingestion by other animals) is of concern.
M2.1.2 Residue/Disposal Issues
Animals euthanized by chemical means must never
enter the human food chain and should be disposed of
in accord with local, state, and federal laws. Disposal of
euthanized animals has become increasingly problematic
because most rendering facilities will no longer take animals euthanized with agents that pose residue hazards
(eg, barbiturates). The potential for ingestion of euthanasia agents is an important consideration in the euthanasia of animals that are disposed of in outdoor settings
where scavenging by other animals is possible277 or when
euthanized animals are fed to zoo and exotic animals.278
Veterinarians and laypersons have been fined for causing
accidental deaths of endangered birds that ingested animal remains that were poorly buried.138 Environmental
warnings must now be included on animal euthanasia
drugs approved by the FDA-CVM.279
M2.2 ROUTES OF ADMINISTRATION
M2.2.1 Parenteral Injection
The use of injectable euthanasia agents is one of
the most rapid and reliable methods of performing euAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
thanasia. It is usually the most desirable method when
it can be performed without causing fear or distress in
the animal. When appropriately administered, acceptable injectable euthanasia agents result in smooth loss
of consciousness prior to cessation of cardiac and/or
respiratory function, minimizing pain and distress to
the animal. However, heightened awareness for personnel safety is imperative when using injectable euthanasia agents because needle-stick injuries involving
these drugs have been shown to result in adverse effects
(41.6% of the time); 17% of these adverse effects were
systemic and severe.280
Intravenous injections deliver euthanasia agents
directly into the vascular system, allowing for rapid
distribution of the agent to the brain or neural centers, resulting in rapid loss of consciousness (for some
invertebrates with closed circulatory systems, intrahemolymph injection is considered analogous to IV
injection).281 When the restraint necessary for giving
an animal an IV injection is likely to impart added distress to the animal or pose undue risk to the operator,
sedation, anesthesia, or an acceptable alternate route
or method of administration should be used. Aggressive or fearful animals should be sedated prior to restraint for IV administration of the euthanasia agent.
Paralytic immobilizing agents (eg, neuromuscular
blocking agents) are unacceptable as a sole means of
euthanasia, because animals under their influence remain awake and able to feel pain. Having said this,
there may be select circumstances (eg, for wild or feral
animals) where the administration of paralytic agents
(eg, neuromuscular blocking agents) may be the most
rapid and humane means of restraint prior to euthanasia due to their more rapid onset compared with other
immobilizing agents.282 In such situations, paralytic
immobilizing agents may only be used if the chosen
method of euthanasia (eg, captive bolt, IV injection of
euthanasia solution) can be applied immediately following immobilization. Paralytic immobilizing agents
must never be used as a sole means of euthanasia, nor
should they be used if delay is expected between immobilization and euthanasia.
When intravascular administration is considered
impractical or impossible, IP or intracoelomic administration of a nonirritating283 barbiturate or other approved
solution is acceptable. Intracoelomic administration of
buffered tricaine methanesulfonate (MS 222d,e) is acceptable for some poikilotherms. When injectable euthanasia agents are administered into the peritoneal or coelomic cavities, vertebrates may be slow to pass through
stages I and II of anesthesia.284 Accordingly, they should
be placed in small enclosures in quiet areas to minimize
excitement and trauma. Intra-abdominal administration
of euthanasia agents is an acceptable means of delivery in
invertebrates with open circulatory systems.
In anesthetized mice, retrobulbar injection of no
more than 200 µL of injectable anesthetic solution
(ketamine:xylazine) is acceptable with conditions, resulting in death within 5 seconds of cessation of injection.285 Intraosseous administration of some euthanasia
solutions to awake animals may cause pain due to the
viscosity of the agent, chemical irritation, or other reasons.286 Administration of analgesics, slower injection of
27
euthanasia agent, and other strategies that may reduce
discomfort should be used where possible when administering euthanasia agents through pre-existing intraosseous catheters.287 Placement of intraosseous (greater
trochanter of the femur, greater tubercle of the humerus,
medial aspect of the proximal tibia) catheters for administration of euthanasia agents and intracardiac, intrahepatic, intrasplenic, or intrarenal injections are acceptable
only when performed on anesthetized or unconscious
animals (with the exception of intrahepatic injections in
cats as discussed in the Companion Animals section of
the text). These routes are not acceptable in awake mammals and birds due to the difficulty and unpredictability
of performing the techniques accurately with minimal
discomfort. In some poikilotherms for which intracardiac puncture is the standard means of vascular access (eg,
some snakes and other reptiles), intracardiac administration of euthanasia solutions in awake animals is acceptable. With the exceptions of IM delivery of ultrapotent
opioids (ie, etorphine and carfentanil) and IM delivery of
select injectable anesthetics, IM, SC, intrathoracic, intrapulmonary, intrathecal, and other nonvascular injections
are not acceptable routes of administration for injectable
euthanasia agents in awake animals.
M2.2.2 Immersion
Euthanasia of finfish and some aquatic amphibians
and invertebrates must take into account the vast differences in metabolism, respiration, and tolerance to
cerebral hypoxia among the various aquatic species.
Because aquatic animals have diverse physiologic and
anatomic characteristics, optimal methods for delivery
of euthanasia agents will vary. In many situations, the
immersion of aquatic animals in water containing euthanasia agents is the best way to minimize pain and
distress. The response of aquatic animals to immersion
agents can vary with species, concentration of agent,
and quality of water; consideration of these factors
should be made when selecting an appropriate euthanasia agent. Immersion agents added to water may be
absorbed by multiple routes, including across the gills,
via ingestion, and/or through the skin.
Ideally, immersion agents added to water will be
nonirritating to skin, eyes, and oral and respiratory tissues and will result in rapid loss of consciousness (often,
but not always, measured as a loss of righting response)
with minimal signs of distress or avoidance behavior.
Currently there are no US FDA-approved drugs for the
euthanasia of aquatic animals. United States Environmental Protection Agency (EPA)–registered agents for
poisoning finfish (eg, rotenone, antimycin) are not recommended as euthanasia agents, because their mechanisms of action and times to death do not fit the criteria
for euthanasia. Additionally, the use of these agents requires a restricted pesticide applicator’s license and extralabel use of these agents is a violation of federal law.
Agents approved by the FDA as tranquilizers and anesthetics for finfish (eg, Finquel,d Tricaine-Se) have been
used extralabel as euthanasia agents for aquatic animals.
M2.2.3 Topical Application
Absorption of topically applied agents is slow and
variable, making topical application an unacceptable
28
means of efficient delivery of euthanasia agents for
most animals. Exceptions include animals with highly
permeable skin to which nonirritating, rapidly absorbed agents are applied (eg, amphibians euthanized
with benzocaine gel). Currently there are no topical
euthanasia agents that are US FDA approved for any
species.
M2.2.4 Oral Administration
The oral route has several disadvantages when considered for administration of euthanasia agents, including lack of established drugs and doses, variability in
agent bioavailability and rate of absorption, potential
difficulty of administration (including potential for aspiration), and potential for loss of agent through vomiting or regurgitation (in species that are capable of these
functions). For these reasons, the oral route is generally
unacceptable as a sole means of euthanasia, but may be
an appropriate way to deliver sedatives prior to administration of parenteral euthanasia agents.
M2.3 BARBITURIC ACID DERIVATIVES
Barbiturates depress the CNS in descending order, beginning with the cerebral cortex, with loss of consciousness progressing to anesthesia. With an overdose, deep
anesthesia progresses to apnea due to depression of the
respiratory center, and this is followed by cardiac arrest.
All barbituric acid derivatives used for anesthesia are
acceptable for euthanasia when administered IV. There is
a rapid onset of action, and loss of consciousness induced
by barbiturates results in minimal or transient pain associated with venipuncture. Desirable barbiturates are
those that are potent, nonirritating, long acting, stable in
solution, and inexpensive. Sodium pentobarbital best fits
these criteria and is most widely used, although others
such as secobarbital are also acceptable.
Advantages—(1) A primary advantage of barbiturates is speed of action. This effect depends on the
dose, concentration, route, and rate of the injection. (2)
Barbiturates induce euthanasia smoothly, with minimal
discomfort for the animal. (3) Barbiturates are less expensive than many other euthanasia agents. (4) Food
and Drug Administration–approved barbiturate-based
euthanasia solutions are readily available for dogs and
horses (use for other species is extralabel).
Disadvantages—(1) Intravenous injection is necessary for best results and this requires trained personnel.
(2) Each animal must be appropriately restrained. (3)
Current federal drug regulations require strict accounting for barbiturates, and these must be used under the
supervision of personnel registered with the US Drug
Enforcement Administration (DEA). Extralabel use requires the drug be used by or under the supervision of
a veterinarian. (4) An aesthetically objectionable terminal gasp may occur in unconscious animals. (5) Some
animals may go through an excitatory phase that may
be distressing to observers. (6) These drugs tend to persist in the animal’s remains and may cause sedation or
even death of animals that consume the body. (7) Tissue
artifacts (eg, splenomegaly) may occur in some species
euthanized with barbiturates.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
General recommendations—The advantages of using barbiturates for euthanasia in dogs and cats far
outweigh the disadvantages. Intravenous injection of
a barbituric acid derivative is the preferred method
for euthanasia of dogs, cats, other small animals, and
horses. Barbiturates are also acceptable for all other
species of animals if circumstances permit their use.
Intraperitoneal or intracoelomic injection may be used
in situations when an IV injection would be distressful,
dangerous, or difficult due to small patient size. Intracardiac (in mammals and birds), intrasplenic, intrahepatic, and intrarenal injections must only be used if the
animal is unconscious or anesthetized (with the exception of intrahepatic injections in cats as discussed in the
Companion Animals section of the text).
M2.4 PENTOBARBITAL COMBINATIONS
Several euthanasia products combine a barbituric
acid derivative (usually sodium pentobarbital) with local
anesthetic agents, other CNS depressants (eg, phenytoin,
ethanol), or agents that metabolize to pentobarbital. Although some of the additives are slowly cardiotoxic, euthanasia makes this pharmacologic effect inconsequential. These combination products are listed by the DEA
as schedule III drugs, making them somewhat simpler to
obtain, store, and administer than schedule II drugs such
as sodium pentobarbital. The pharmacologic properties
and recommended use of euthanasia products that combine sodium pentobarbital with agents such as lidocaine
or phenytoin are interchangeable with those of pure barbituric acid derivatives.
Mixing of pentobarbital with a neuromuscular
blocking agent in the same injection apparatus is not an
acceptable approach to euthanasia because of the potential for the neuromuscular blocking agent to induce
paralysis prior to onset of unconsciousness.
M2.5 TRIBUTAME
Tributame euthanasia solution is an injectable, nonbarbiturate euthanasia agent with each milliliter containing 135 mg of embutramide, 45 mg of chloroquine phosphate USP, and 1.9 mg lidocaine USP dissolved in water
and ethyl alcohol. The final formulation has a teal blue
color with the bittering agent, denatonium benzoate,
added to minimize the risk of the solution being ingested accidentally. Tributame was approved by the FDA in
2005 as an IV agent for euthanasia of dogs, and embutramide was classified as a schedule III controlled substance
in 2006, making Tributame a C-III controlled agent.288–290
Embutramide is a derivative of γ-hydroxybutyrate
that was investigated as a general anesthetic in the late
1950s, but was never used as a pharmaceutical agent
due to a poor margin of safety, with severe cardiovascular effects including hypotension, myocardial depression, and ventricular dysrhythmias.291 Embutramide
can be injected alone to cause death, but the time until
death can exceed 5 minutes. Subsequently, chloroquine
phosphate, an antimalarial drug with profound cardiovascular depressant effects, was added to embutramide,
and studies verified a significantly shorter time until
death.291,292 Studies on dogs showed this combination
of two drugs to be effective, but when tested for euthanasia of cats, a substantial response to IV injection
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
via peripheral vein was evident. This effect was almost
completely eliminated by addition of lidocaine. The addition of chloroquine and lidocaine also lowers the dosage of embutramide required for euthanasia.291 Death
from Tributame results from severe CNS depression,
hypoxia, and circulatory collapse.
Tributame produces unconsciousness in dogs in
fewer than 30 seconds, with death occurring within 2
minutes; agonal breathing may occur in 60% to 70% of
patients.293 Injection is to be given IV over a period of
10 to 15 seconds through a preplaced catheter or hypodermic needle at a dosage of 1 mL for each 5 lbs (0.45
mL/kg [0.2 mL/lb]).
Advantages—(1) Tributame has a rapid onset of action. This effect depends on the dose, concentration,
route, and rate of the injection. (2) Tributame induces
euthanasia smoothly, with minimal discomfort to the
animal. (3) Schedule III status makes Tributame somewhat simpler to obtain, store, and administer than
Schedule II drugs such as sodium pentobarbital.
Disadvantages—(1) At the time of compilation of
this report, while Tributame is FDA approved for use in
dogs, it is not currently being manufactured. (2) Intravenous injection by trained personnel is necessary. (3)
Each animal must be individually restrained. (4) Aesthetically objectionable agonal breathing may occur in
unconscious animals. (5) The component drugs tend to
persist in the animal’s remains and may cause sedation
or even death of animals that consume the body.
General recommendations—If it becomes available,
Tributame is an acceptable euthanasia drug for dogs
provided that it is administered IV by a highly skilled
person at recommended dosages and at proper injection rates. If barbiturates are not available, its extralabel
use in cats may be considered; however, adverse reactions (ie, agonal breathing) have been reported and the
current FDA-approved Tributame label recommends
against its use in cats. Routes of administration of Tributame other than IV injection are not acceptable.
M2.6 T-61
T-61 is an injectable, nonbarbiturate, nonnarcotic
mixture of embutramide, mebozonium (mebenzonium) iodide, and tetracaine hydrochloride.293 Embutramide induces narcosis and respiratory depression,
while mebozonium causes nondepolarizing muscular
paralysis.294 Concern has been expressed that the paralytic effect of mebozonium occurs before embutramideinduced unconsciousness, creating a potential for animal distress prior to loss of consciousness, as manifested by muscular activity and/or vocalization during
injection. However, electrophysiologic studies in dogs
and rabbits have shown that loss of consciousness and
loss of motor activity occur simultaneously following
T-61 injection.295 Although many consider the aesthetically unpleasant reactions of dogs to T-61 injection
to be similar to dysphoria seen during the induction
phases of anesthesia, the behavior demonstrated during these reactions can cause distress in personnel witnessing euthanasia. Because of these concerns, T-61 has
29
been voluntarily withdrawn from the market by the
manufacturer and is no longer manufactured or commercially available in the United States, although it is
available in Canada and other countries. T-61 should be
administered only IV and at carefully monitored rates
of injection to avoid dysphoria during injection.
Advantages—(1) T-61 has a rapid onset of action
and has been used to euthanize dogs, cats, horses, laboratory animals, birds, and wildlife. (2) Terminal (agonal) gasps that can occur in animals euthanized by IV
barbiturates are not seen with use of T-61.
Disadvantages—(1) T-61 is currently not being manufactured in the United States. (2) Slow IV injection is
necessary to avoid dysphoria prior to unconsciousness.
(3) Each animal must be appropriately restrained and
the agent must be administered by trained personnel. (4)
Secondary toxicosis may occur in animals that consume
remains of animals euthanized with T-61. (5) Because
T-61 contains embutramide, a schedule III controlled
drug, it is subject to the same restrictions in acquisition,
storage, and use as other schedule III agents.
General recommendations—T-61 is acceptable as an
agent of euthanasia provided it is administered appropriately by trained personnel. Routes of administration
of T-61 other than IV are not acceptable.
M2.7 ULTRAPOTENT OPIOIDS
Etorphine hydrochloride and carfentanil citrate
are ultrapotent opioids (10,000 times as potent as morphine sulfate) that are FDA approved for the immobilization of wildlife.296 These opioids have been used as
immobilization and extralabel euthanasia drugs primarily for large animals, particularly wildlife. Carfentanil has been used transmucosally in a lollipop form
to euthanize captive large apes.297 These drugs act on
µ opioid receptors to cause profound CNS depression,
with death secondary to respiratory arrest.
Advantages—(1) Etorphine and carfentanil can be
delivered IM or transmucosally in situations where IV
administration is unfeasible or dangerous. (2) These
drugs have a rapid onset of action.
Disadvantages—(1) These drugs are strictly regulated, require special licensing to obtain and use, and are not
FDA approved for use as agents of euthanasia. (2) There is
substantial risk for humans handling the drugs, which can
be absorbed through broken skin or mucous membranes.
(3) These opioids may pose a risk of secondary toxicosis if
the remains of euthanized animals are ingested; therefore
proper disposal of animal remains is essential.
General recommendations—Etorphine or carfentanil is acceptable with conditions for euthanasia only
in situations where use of other euthanasia methods is
impractical or dangerous. Personnel handling the drugs
must be familiar with their hazards, and a second person should be standing by and be prepared to summon
medical support and administer first aid in case of accidental human exposure.
30
M2.8 DISSOCIATIVE AGENTS AND
α2-ADRENERGIC RECEPTOR AGONISTS
Injectable dissociative agent and α2-adrenergic receptor agonists induce rapid loss of consciousness, and
sometimes muscle relaxation, prior to surgery, dentistry,
or other procedures. These agents are sometimes given
prior to administration of euthanasia solutions to minimize animal distress, facilitate restraint, and/or provide
a more aesthetic euthanasia environment for owner-attended euthanasia. In overdose situations, these agents
can cause death; however, doses that consistently will
produce death have not been established for most species. In mice, injection of 100 µL of a 10:1 (mg:mg)
solution of ketamine:xylazine resulted in death within
3 to 5 seconds after completion of the injection.285 Intraperitoneal injection of dissociative agents in combination with α2-adrenergic receptor agonists at 5 times
the anesthetic dose has been used as a means of euthanizing laboratory animals.298
Advantages—(1) These agents are readily available.
(2) The combination of these agents causes rapid loss
of consciousness. (3) Although IV injection for euthanasia is preferred, these combinations can be delivered
IM in situations where IV administration is not feasible
or is dangerous.
Disadvantages—(1) These agents are not FDA approved for use as agents of euthanasia. (2) Doses that
consistently produce rapid death have not been established for most drugs and species. (3) The cost of the
higher doses of agents required to cause death may substantially exceed that of an approved euthanasia agent.
(4) Many dissociative agents are controlled substances
and their acquisition, storage, and use are restricted. (5)
Some injectable agents can be hazardous for human personnel if accidental exposure occurs. (6) The environmental impact of residues of injectable anesthetics in the
remains of euthanized animals has not been determined.
General recommendations—In species for which
effective euthanasia doses and routes have been established, overdose of dissociative agent–α-2-adrenergic
combinations is an acceptable method of euthanasia.
These agents are acceptable with conditions in situations where approved euthanasia drugs are not available or as secondary means of euthanasia in already
anesthetized animals provided utmost care is taken to
ensure that death has occurred prior to disposing of animal remains. These combinations are also acceptable
as the first step in a 2-step euthanasia method. Until the
environmental impact of tissue residues is determined,
special care must be taken in the disposal of animal remains. Injectable anesthetics should not be used in animals intended for consumption.
M2.9 POTASSIUM CHLORIDE
AND MAGNESIUM SALTS
Although unacceptable when used in conscious
vertebrate animals, a solution of potassium chloride,
magnesium chloride, or magnesium sulfate injected IV
or intracardially in an animal that is unconscious or under general anesthesia is an acceptable way to induce
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
cardiac arrest and death. The potassium ion is cardiotoxic, and rapid IV or intracardiac administration of 1
to 2 mmol/kg (0.5 to 0.9 mmol/lb) of body weight (1
to 2 mEq K+/kg; 75 to 150 mg/kg [34.1 to 68.2 mg/lb]
of potassium chloride) will cause cardiac arrest.299 This
is an injectable technique for euthanasia of livestock or
wildlife species that may reduce the risk of toxicosis for
predators or scavengers in situations where the remains
of euthanized animals may be consumed.300,301 Potassium chloride injected IV at 3 mEq/kg (1.4 mEq/lb) into
parrots anesthetized with isoflurane caused mild vocalization in 1 of 6 birds and resulted in asystole in 68
seconds.302 Use of 10 mEq/kg (4.5 mEq/lb) IV in anesthetized parrots resulted in involuntary muscle tremors
in 5 of 6 birds and caused asystole in 32.8 seconds. Neither dosage resulted in histologic artifacts.
Magnesium salts may also be mixed in water for
use as immersion euthanasia agents for some aquatic
invertebrates. In these animals, magnesium salts induce
death through suppression of neural activity.134
sium sulfate and sodium pentobarbital as an economical anesthesia and euthanasia agent for large animals,
but now is rarely used for this application in veterinary
medicine. α Chloralose is a longer-acting derivative of
chloral hydrate that has been used for anesthesia of
laboratory animals, particularly for study of cerebrovasculature.303,304 When administered IV, these agents
have almost immediate sedative action, but unless
combined with other anesthetics, the onset of anesthesia is delayed. Death is caused by hypoxemia resulting
from progressive depression of the respiratory center,
and may be preceded by gasping, muscle spasms, and
vocalization.
Advantages—(1) Potassium chloride and magnesium salts are not controlled substances and are easily
acquired, transported, and mixed in the field. (2) Potassium chloride and magnesium salt solutions, when
administered after rendering an animal unconscious,
result in animal remains that are potentially less toxic
for scavengers and predators and may be a good choice
in cases where proper disposal of animal remains (eg,
rendering, incineration) is impossible or impractical.
Disadvantages—(1) Chloral hydrate depresses the
cerebrum slowly; therefore, restraint may be a problem for some animals. (2) Chloral hydrate is no longer available as an FDA-approved drug in the United
States, so it must be compounded from bulk drug. This
is problematic because of the lack of manufacturing
controls, tests for potency, and illegality of compounding from bulk drugs.
Disadvantages—(1) Rippling of muscle tissue and
clonic spasms may occur upon or shortly after injection. (2) Potassium chloride and magnesium salt solutions are not approved by the FDA for use as euthanasia
agents. (3) Saturated solutions are required to obtain
suitable concentrations for rapid injection into large
animals.
General recommendations—Personnel performing
this technique must be trained and knowledgeable in
anesthetic techniques, and be competent in assessing
the level of unconsciousness that is required for administration of potassium chloride and magnesium
salt solutions IV. Administration of potassium chloride
or magnesium salt solutions IV requires animals to be
in a surgical plane of anesthesia characterized by loss
of consciousness, loss of reflex muscle response, and
loss of response to noxious stimuli. Use in unconscious
animals (made recumbent and unresponsive to noxious
stimuli) is acceptable in situations where other euthanasia methods are unavailable or not feasible. Although
no scavenger toxicoses have been reported with potassium chloride or magnesium salts in combination with
a general anesthetic, proper disposal of animal remains
should always be attempted to prevent possible toxicosis by consumption of animal remains contaminated
with general anesthetics.
M2.10 CHLORAL HYDRATE
AND α CHLORALOSE
Chloral hydrate (1,1,1-trichloro-2,2,-dihydroxyethane) was once used in combination with magneAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Advantages—(1) Historically, chloral hydrate was
an inexpensive anesthetic and euthanasia agent, making it economical for large animals. (2) Schedule IV status makes chloral hydrate somewhat simpler to obtain,
store, and administer than schedule II or III drugs, such
as sodium pentobarbital.
General recommendations—Chloral hydrate and α
chloralose are not acceptable euthanasia agents because
the associated adverse effects may be severe, reactions
can be aesthetically objectionable, and other products
are better choices.
M2.11 ALCOHOLS
Ethanol and other alcohols increase cell membrane
fluidity, alter ion channels within neural cells, and
decrease nerve cell activity.305 Alcohols induce death
through nervous system and respiratory depression, resulting in anesthesia and anoxia. Alcohols have been
used as secondary euthanasia methods for some finfish
species306 and as primary injectable euthanasia agents in
mice used for antibody production.307 In the latter, mice
receiving IP injections of 0.5 mL of 70% ethanol developed gradual loss of muscle control, coma, and death
within 2 to 4 minutes. This method has been proposed
as a potential alternative to barbiturate euthanasia in
mice being used for antibody production, especially “in
developing countries involved in vaccine development,
antibody production and subsequent serological analysis.”307 Tribromoethanol is used as an anesthetic agent
in laboratory rodents.
Advantages—(1) Alcohol is inexpensive and readily available.
Disadvantages—(1) Alcohols produce dose-related
irritation to tissue. (2) Onset of insensibility and death
can be delayed following alcohol administration. (3)
The volume required to euthanize animals larger than
mice renders most alcohols impractical as euthanasia
31
agents. (4) Alcohols are not FDA approved as euthanasia agents. (5) Tribromoethanol is not commercially
available as a pharmaceutical-grade product and must
be compounded.
General recommendations—Ethanol in low concentrations is an acceptable secondary means of euthanasia
in finfish rendered insensible by other means and as a
primary or secondary means of euthanasia of some invertebrates. Immersion in high concentrations (eg, 70%)
of ethanol is not acceptable. Ethanol may be acceptable
with conditions as an agent of euthanasia for mice in
specific situations, but is unacceptable as an agent of euthanasia for larger species. Tribromoethanol is acceptable
with conditions as a method for euthanasia of laboratory
rodents when approved by the IACUC and prepared,
stored, and administered at the appropriate dosage.
M2.12 TRICAINE
METHANESULFONATE (MS 222, TMS)
Tricaine methanesulfonate, commonly referred to
as MS 222, is an anesthetic agent that is FDA approved
(Finquel and Tricaine-S only) for temporary immobilization of finfish, amphibians, and other aquatic, coldblooded animals.308 Tricaine methanesulfonate has been
used for euthanasia of reptiles, amphibians, and finfish.
Tricaine is a benzoic acid derivative and, in water of low
alkalinity (< 50 mg/L as CaCO3), the solution should
be buffered with sodium bicarbonate.309 A 10 g/L stock
solution can be made, and sodium bicarbonate added to
saturation, resulting in a pH between 7.0 and 7.5 for the
solution. The stock solution should be protected from
light and refrigerated or frozen if possible. The solution
should be replaced monthly and any time a brown color
is observed.310 Potency is increased in warm water and
decreased in cold water.309 Immersion of finfish in solutions of MS 222 for 10 minutes following loss of rhythmic opercular movement is sufficient for euthanasia
of most finfish. Due to species differences in response
to MS 222, a secondary method of euthanasia is recommended in some finfish and amphibians to ensure
death.309,311 In the United States, there is a 21-day withdrawal time for MS 222; therefore, it is not appropriate
for euthanasia of animals intended for consumption.
MS 222 rapidly enters the CNS and alters nerve
conduction through blockade of voltage-sensitive sodium channels.311 Additionally, accumulation within
ventricular myocardium results in decreased cardiovascular function. Death is due to decreased nervous and
cardiovascular function.
Studies312 with Xenopus laevis (African clawed frog
or platanna) have shown that the concentrations of MS
222 traditionally used for amphibian euthanasia (0.25
to 0.5 g/L) are not sufficient to induce reliable euthanasia in this species. Immersion of frogs in 5 g/L of MS
222 resulted in deep anesthesia within 4 minutes, but at
least 1 hour of immersion at this concentration was required to reliably euthanize 100% of frogs. The authors
of that study recommended that if a concentration of
MS 222 < 5 g/L or a shorter time frame than 1 hour
is allowed, a secondary euthanasia method should be
used for X laevis. Intracoelomic injection of MS 222 at
the highest possible dosage (2,590 mg/kg [1,177 mg/
32
lb]) did not result in euthanasia, with 6 of 20 frogs regaining mobility within 3 hours after injections. Consequently, intracoelomic injection of MS 222 is not considered to be an acceptable method of euthanasia for X
laevis and possibly other amphibians.
A 2-stage euthanasia method for reptiles using MS
222 has been described.293 The first stage entails intracoelomic injection of 250 to 500 mg/kg (113.6 to 227.3
mg/lb) of a pH-neutralized solution (0.7% to 1.0% MS
222), which results in rapid loss of consciousness (< 30
seconds to 4 minutes). Once unconsciousness occurs,
a second intracoelomic injection of unbuffered 50% MS
222 is administered.
Advantages—(1) MS 222 is soluble in both fresh
and salt water and can be used for a wide variety of
finfish, amphibians, and reptiles. (2) MS 222 is commercially available and is not a controlled substance,
which increases ease of acquisition, storage, and administration.
Disadvantages—(1) MS 222 is expensive and may be
cost prohibitive for use for large finfish, amphibians, and
reptiles or for large populations. (2) There appears to be
substantial species variability in response to MS 222, with
some species requiring higher doses or secondary measures to ensure death. (3) Injection of MS 222 is not appropriate for finfish as rapid excretion via the gills renders
it ineffective by this route.309 (4) MS 222 cannot be used
in animals intended for human consumption. (5) Occupational exposure to MS 222 has been associated with retinal
toxicity in humans.313 (6) MS 222 is not FDA approved
for use as an agent of euthanasia. (7) The impact of MS
222 residues in euthanized finfish on the environment or
scavenger species has not been determined.
General recommendations—MS 222 is an acceptable
method of euthanasia for finfish and for some amphibians and reptiles. When used for large finfish and some
amphibians (eg, Xenopus spp), a secondary method
should be used to ensure death. By itself, intracoelomic injection of MS 222 is not an acceptable euthanasia method for X laevis and possibly other amphibians.
Animals euthanized with MS 222 should not be used as
food sources for humans or other animals.
M2.13 BENZOCAINE HYDROCHLORIDE
Benzocaine base, a compound similar to tricaine
methanesulfonate, is not water soluble and therefore is
prepared as a stock solution (100 g/L) with acetone or
ethanol; the presence of these solvents can be irritating to tissues. Conversely, benzocaine hydrochloride is
water soluble and can be used directly for either anesthesia or euthanasia of finfish and amphibians.293,310
Benzocaine-containing products should be protected
from light and protected from freezing or excessive
heat (> 40°C). Topical application of 7.5% or 20% benzocaine hydrochloride gel on an amphibian’s ventrum
is effective and does not require buffering. Similarly to
MS 222, benzocaine acts through blockade of voltagesensitive sodium channels within the CNS and heart,
resulting in depression of the nervous and cardiovascular systems.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
The application of benzocaine hydrochloride gel
to the ventral abdomen of amphibians (20% concentration; 2.0-cm X 1.0-mm application) is an effective means
of anesthesia and euthanasia for some species.312,314,315
Following application of the gel to the ventrum of X
laevis and placement in a wet bucket, righting and withdrawal reflexes subsided within 7 minutes, and death
occurred within 5 hours.312 No evidence of dermal injury, loss of dermal hydration, or difficulty breathing
was associated with topical application of benzocaine
hydrochloride gel to amphibians. A recent investigation
on euthanasia of adult X laevis describes a dose of 182
mg/kg (82.7 mg/lb) of benzocaine hydrochloride gel as
effective.312 A comparison of benzocaine hydrochloride
application with ice-slurry immersion for euthanasia of
bony bream (Nematalosa erebi) indicated that, for certain warm water finfish species, an ice-slurry elicits less
motor response than benzocaine overdose as a method
of euthanasia, but additional work is needed to determine the most humane method.316
Advantages—(1) Benzocaine hydrochloride is a
relatively fast-acting and effective euthanasia agent for
finfish and amphibians. (2) Benzocaine hydrochloride
is not a controlled substance. (3) Benzocaine hydrochloride has low toxicity for humans at concentrations
used to euthanize finfish. (4) Benzocaine hydrochloride
poses little environmental risk as it is readily filtered
by use of activated carbon and breaks down in water
within approximately 4 hours.
Disadvantages—(1) Benzocaine hydrochloride is
not FDA approved for use as an agent of euthanasia.
(2) Benzocaine hydrochloride may be cost prohibitive
for euthanasia of larger finfish, amphibians, and reptiles
or large populations. (3) Benzocaine hydrochloride solutions must be carefully buffered to avoid tissue irritation. (4) The impact of benzocaine residues in euthanized finfish on the environment or scavenger species
has not been determined.
General recommendations—Benzocaine hydrochloride gel and solutions are acceptable agents for
euthanasia for finfish and amphibians. Benzocaine hydrochloride is not an acceptable euthanasia agent for
animals intended for consumption.
induction, prolonged recovery, and narrow margin of
safety, as it can cause rapid onset of ventilatory failure at
high concentrations (> 400 mg/L).321
The anesthetic mechanism of clove oil and its derivatives has been poorly studied, but they appear to
act similarly to other local anesthetics by inhibition of
voltage-sensitive sodium channels within the nervous
system.296 Studies322–324 of rodents indicate this class of
agents may cause paralysis in addition to their anesthetic effects.
Advantages—(1) Clove oil and its derivatives are
widely available, are relatively inexpensive, and are not
controlled substances. (2) These agents have a short induction time. (3) Clove oil and its derivatives are effective at a wide range of water temperatures.
Disadvantages—(1) Clove oil and its derivatives are
not FDA approved for use as an agent of euthanasia.
(2) Animals euthanized with clove oil products are not
approved for human consumption. (3) Some clove oil
derivatives are potential carcinogens. (4) The impact of
clove oil residues in euthanized finfish on the environment or scavenger species has not been determined.
General recommendations—Clove oil, isoeugenol,
and eugenol are acceptable agents of euthanasia for
finfish. It is recommended that, whenever possible,
products with standardized, known concentrations of
essential oils be used so that accurate dosing can occur.
These agents are not acceptable means of euthanasia for
animals intended for consumption.
M2.15 2-PHENOXYETHANOL
Immersion in 2-phenoxyethanol has been used
for anesthesia and euthanasia of finfish at concentrations of 0.3 to 0.5 mg/L or higher.309 The solubility
of 2-phenoxyethanol is reduced in colder water. The
mechanism of action of 2-phenoxyethanol is poorly understood, but death is thought to occur from hypoxia
secondary to CNS depression. Finfish should be kept in
the 2-phenoxyethanol solution for at least 10 minutes
after cessation of opercular movement.
Advantages—(1) 2-phenoxyethanol can be used in
a 1-step immersion method for euthanasia of finfish.
(2) 2-phenoxyethanol is not a controlled substance.
M2.14 CLOVE OIL, ISOEUGENOL, AND EUGENOL
Cloves contain a number of essential oils, including eugenol, isoeugenol, and methyleugenol.317 Eugenol
comprises 85% to 95% of the essential oils in cloves, and
has been used as a food flavoring and a local anesthetic
for human dentistry. It is also classified as an exempted
minimum-risk pesticide active ingredient by the US EPA.
Eugenol exhibits antifungal, antibacterial, antioxidant,
and anticonvulsant activity. Some other components of
clove oil, such as isoeugenol, are equivocal carcinogens
based on studies in rodents.318 Clove oil and its extracts
have become popular as anesthetic agents for freshwater
and marine finfish because of their wide availability, low
cost, and shorter induction times when compared with
MS 222.319,320 When compared with MS 222 as an anesthetic agent, eugenol was found to have a more rapid
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Disadvantages—(1) Induction times can be prolonged.
(2) There are species variations in dosage levels and duration of exposure required for euthanasia. (3) Some species exhibit hyperactivity prior to loss of consciousness.
(4) 2-phenoxyethanol is not FDA approved for use as an
agent of euthanasia. (5) The impact of 2-phenoxyethanol
residues in euthanized finfish on the environment or scavenger species has not been determined.
General recommendations—Although there are
probably more efficient immersion agents available,
2-phenoxyethanol is an acceptable method of euthanasia for finfish under certain circumstances. 2-phenoxyethanol is not an acceptable means of euthanasia in animals intended for consumption.
33
M2.16 QUINALDINE (2-METHYLQUINOLINE,
QUINALIDINE SULFATE)
Quinaldine has low solubility in water and therefore must first be dissolved in acetone or alcohol and
then buffered with bicarbonate.309 The potency of quinaldine varies with species, water temperature, water pH,
and mineral content of water. Quinaldine acts through
depression of sensory centers of the CNS.
Advantages—(1) Quinaldine can be used in a
1-step immersion method for euthanasia of finfish. (2)
Quinaldine is not a controlled substance.
Disadvantages—(1) Quinaldine is not FDA approved for use as an agent of euthanasia. (2) The impact of quinaldine residues in euthanized finfish on the
environment or scavenger species has not been determined.
General recommendations—Quinaldine is an acceptable method of euthanasia for finfish under certain
circumstances. Quinaldine is not an acceptable means
of euthanasia in animals intended for consumption.
M2.17 METOMIDATE
Metomidate is a highly water-soluble, nonbarbiturate hypnotic that acts by causing CNS depression.
It is currently listed in the Index of Legally Marketed
Unapproved New Animal Drugs for Minor Species by
the FDA for use in sedation and anesthesia. While it is a
rapidly acting euthanasia compound for certain species
when used at 10 times the upper limit of the recommended anesthetic dose, its listing in the Index makes
extralabel use (eg, its use for euthanasia) illegal. Should
the index status of metomidate change to inclue euthanasia, or should FDA approval be obtained (thereby
allowing extralabel use under AMDUCA), metomidate
would be considered an acceptable agent of euthanasia
for some species of finfish under certain circumstances.
Metomidate is not an acceptable means of euthanasia in animals intended for consumption.
M2.18 SODIUM HYPOCHLORITE
Sodium hypochlorite (bleach) and solutions made
from calcium hypochlorite granules act as solvents and
oxidants in tissue, resulting in saponification of fatty
acids, denaturation of proteins, and derangement of
cellular processes.326 Hypochlorite has been used to
euthanize unhatched and hatched zebrafish up to 7
days after fertilization, after which time hatchlings are
considered developed beyond an embryonic form and
capable of experiencing distress or pain.327 Hypochlorite has also been used to terminate embryos in various
research settings.
Advantages—(1) Sodium hypochlorite and calcium
hypochlorite are inexpensive, are readily available, and,
at the concentrations used for embryonic and larval
stage destruction (1% to 10%), pose minimal hazards
to personnel. (2) These products are not controlled
substances.
Disadvantages—(1) Concentrated hypochlorite so34
lutions are corrosive and pose risk of dermal, ocular,
and respiratory injury to personnel if mishandled. (2)
Sodium hypoclorite is not FDA approved for euthanasia.
General recommendations–When used on early embryonic and larval stages prior to development of nociceptive abilities, application of hypochlorites can be
an acceptable means of euthanasia. Hypochlorites are
unacceptable as the sole means of euthanasia of organisms beyond these embryonic and larval stages. Use of
hypochlorites is unnacceptable for finfish intended for
human consumption.
M2.19 FORMALDEHYDE
Formaldehyde causes cellular damage through
oxidative injury as well as through formation of crosslinkages with DNA, RNA, and proteins.328 Formaldehyde can be used to euthanize and preserve Porifera
(sponges) as these invertebrates lack nervous tissue.
Advantages—(1) Formaldehyde is inexpensive,
easily obtainable, and not a controlled substance. (2)
Formaldehyde rapidly fixes tissues, preserving structure for later study.
Disadvantages—(1) Formaldehyde poses substantial health risks for personnel, including respiratory, dermal, and ocular irritation and hypersensitivity.
Formaldehyde is also a known human carcinogen.329
General recommendations—Formaldehyde is an
acceptable method of euthanasia for Porifera species.
Formaldehyde is acceptable as an adjunctive method
of euthanasia for Coelenterates (comb jellies, corals,
anemones) and Gastropod molluscs (snails, slugs) only
after these animals have been rendered nonresponsive
by other methods (eg, magnesium chloride330). Formaldehyde is unacceptable as a first step or adjunctive
method of euthanasia for other animal species.
M2.20 UNACCEPTABLE AGENTS
Strychnine, nicotine, caffeine, cleaning agents, solvents, pesticides, disinfectants, and other toxicants not
specifically designed for therapeutic or euthanasia use
are unacceptable for use as euthanasia agents under any
circumstances.
Magnesium sulfate, potassium chloride, and neuromuscular blocking agents are unacceptable for use
as euthanasia agents in conscious vertebrate animals.
These agents may be used for euthanasia of anesthetized or unconscious animals as previously described.
M3. PHYSICAL METHODS
M3.1 COMMON CONSIDERATIONS
Physical methods of euthanasia include captive
bolt, gunshot, cervical dislocation, decapitation, electrocution, focused beam microwave irradiation, thoracic compression, exsanguination, maceration, stunning,
and pithing. When properly used by skilled personnel
with well-maintained equipment, physical methods of
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
euthanasia may result in less fear and anxiety and be
more rapid, painless, humane, and practical than other
forms of euthanasia. Exsanguination, stunning, and
pithing are not recommended as a sole means of euthanasia, but may be considered as adjuncts to other
agents or methods.
Some consider physical methods of euthanasia aesthetically displeasing. There are occasions, however,
when what is perceived as aesthetic and what is most
humane are in conflict. Despite their aesthetic challenges, in certain situations physical methods may be the
most appropriate choice for euthanasia and rapid relief
of pain and suffering. Personnel using physical methods of euthanasia must be well trained and monitored
for each type of physical method performed to ensure
euthanasia is conducted appropriately. They must also
be sensitive to the aesthetic implications of the method
and convey to onlookers what they should expect to
observe when at all possible.
Since most physical methods involve trauma, there
is inherent risk for animals and people. If the method
is not performed correctly, personnel may be injured
or the animal may not be effectively euthanized; personnel skill and experience are essential. Inexperienced
persons should be trained by experienced persons and
should practice on euthanized animals or anesthetized
animals to be euthanized until they are proficient in
performing the method properly and humanely. After
the method has been applied, death must be confirmed
before disposal of the remains.
M3.2 PENETRATING CAPTIVE BOLT
Penetrating captive bolts have been used for euthanasia of ruminants, horses, swine, laboratory rabbits, and dogs.331 Their mode of action is concussion
and trauma to the cerebral hemisphere and brainstem.48,332,333 Adequate restraint is important to ensure
proper placement of captive bolts. A cerebral hemisphere and the brainstem must be sufficiently disrupted
by the projectile to induce sudden loss of consciousness
and subsequent death. Appropriate placement of captive bolts for various species has been described.130,332–335
Signs of effective captive bolt penetration and death are
immediate collapse and a several-second period of tetanic spasm, followed by slow hind limb movements
of increasing frequency.46,47 The corneal reflex must be
absent and the eyes must open into a wide blank stare
and not be rotated.45
There are two types of penetrating captive bolts:
a regular penetrating captive bolt and an air injection
penetrating captive bolt. In both cases, the bolts penetrate the brain. In the air injection penetrating captive bolt, air under high pressure is injected through
the bolt into the brain to increase the extent of tissue
destruction. Powder-activated guns that use the traditional captive bolt are available in 9 mm, .22 caliber,
and .25 caliber.130 Captive bolt guns powered by compressed air (pneumatic) are also available in regular and
air injection types. All captive bolt guns require careful
maintenance and cleaning after each day of use. Lack of
maintenance is a major cause of captive bolt gun failure
for both powder-activated and pneumatic captive bolt
guns.101 Cartridges for powder-activated captive bolt
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
guns must be stored in a dry location because damp
cartridges will reduce effectiveness.336
Advantages—(1) Both regular and air injection
penetrating captive bolts may be used effectively for
euthanasia of animals in research facilities and on the
farm, when the use of drugs for this purpose is inappropriate or impractical. (2) They do not chemically
contaminate tissues.
Disadvantages—(1) Euthanasia by captive bolt can
be aesthetically displeasing. (2) Death may not occur
if equipment is not maintained and used properly. (3)
The air injection captive bolt must never be used on
ruminants that will be used for food because of concerns about contamination of meat with specified risk
materials (neurologic tissue). (4) Because the penetrating captive bolt is destructive, brain tissue may not be
able to be examined for evidence of rabies infection or
chronic wasting disease.
General recommendations—Use of the penetrating
captive bolt is acceptable with conditions and is a practical method of euthanasia for horses, ruminants, and
swine. To ensure death, it is recommended that animals
be immediately exsanguinated or pithed (see adjunctive methods) unless a powerful captive bolt gun designed for euthanasia is used. These guns have recently
become available and reduce the need to apply an adjunctive method. Ruminants used for food should not
be pithed to avoid contamination of the carcass with
specified risk materials. Captive bolt guns used for larger species must have an extended bolt.
M3.3 NONPENETRATING CAPTIVE BOLT
The nonpenetrating captive bolt has a wide mushroom-shaped head that does not penetrate the brain of
large mammals, such as adult cattle, slaughter-weight
pigs, sows, and adult sheep. In general, nonpenetrating
captive bolt guns only stun animals and should not be
used as a sole method of euthanasia. Correct positioning is critical for an effective stun of an adult cow. Nonpenetrating captive bolts are not effective for stunning
bulls, adult swine, or cattle with long hair.
Purpose-built pneumatic nonpenetrating captive
bolt guns have recently been developed and successfully used for euthanasia of suckling pigs,c neonatal ruminants,130 and turkeys.337
Advantage—Less damage to the brain.
Disadvantages—(1) Nonpenetrating captive bolt
guns only stun animals and therefore are generally not
effective as a sole means of euthanasia. The exception is
nonpenetrating pneumatic captive bolt guns that have
been purpose-built for euthanasia of suckling pigs,c neonatal ruminants,130 and turkeys.338 (2) Depending on degree of destruction, use of a nonpenetrating captive bolt
may preclude postmortem diagnostics for diseases of the
brain, including rabies and chronic wasting disease.
General recommendations—In general, nonpenetrating captive bolt guns should not be used as a sole
35
method of euthanasia. However, pneumatic purposebuilt nonpenetrating captive bolt guns have been used
successfully to euthanize suckling pigs,c neonatal ruminants,130 and turkeys.339
M3.4 MANUALLY APPLIED
BLUNT FORCE TRAUMA TO THE HEAD
Euthanasia by manually applied blunt force trauma
to the head must be evaluated in terms of the anatomic
features of the species on which it is to be performed,
the skill of those performing it, the number of animals
to be euthanized, and the environment in which it is
to be conducted. Manually applied blunt force trauma
to the head can be a humane method of euthanasia for
neonatal animals with thin craniums if a single sharp
blow delivered to the central skull bones with sufficient
force can produce immediate depression of the CNS and
destruction of brain tissue. When properly performed,
loss of consciousness is rapid. Personnel performing
manually applied blunt force trauma to the head must
be properly trained and monitored for proficiency with
this method of euthanasia, and they must be aware of
its aesthetic implications.
Manually applied blunt force trauma to the head
has been used primarily to euthanize small laboratory
animals with thin craniums.334,340,341 It has also been applied for euthanasia of young piglets. The anatomic features of neonatal calves make manually applied blunt
force trauma to the head unacceptable as a method of
euthanasia for this species.
Personnel who have to perform manually applied
blunt force trauma to the head often find it displeasing and soon become fatigued. Fatigue can lead to inconsistency in application, creating humane concerns
about its efficacious application to large numbers of
animals. For this reason, the AVMA encourages those
using manually applied blunt force trauma to the head
as a euthanasia method to actively search for alternate
approaches.
Advantages—(1) Blunt force trauma applied manually to the head is inexpensive and effective when
performed correctly. (2) Blunt force trauma does not
chemically contaminate tissues.
Disadvantages—(1) Manually applied blunt force
trauma is displeasing for personnel who have to perform it. (2) Repeatedly performing manually applied
blunt force trauma can result in personnel fatigue, loss
of efficacy, and humane concerns. (3) Trauma to the
cranium can damage tissues and interfere with diagnosis of brain diseases.
General recommendations—Replace, as much as
possible, manually applied blunt force trauma to the
head with alternate methods. Manually applied blunt
force trauma is not acceptable for neonatal calves, because of their anatomic features.
M3.5 GUNSHOT
A properly placed gunshot can cause immediate
insensibility and a humane death. Under some conditions, a gunshot may be the only practical method
36
of euthanasia. Shooting should only be performed by
highly skilled personnel trained in the use of firearms
and only in jurisdictions that allow for legal firearm
use. The safety of personnel, the public, and other animals that are nearby should be considered. The procedure should be performed outdoors and in areas where
public access is restricted.
In applying gunshot to the head as a method of
euthanasia for captive animals, the firearm should be
aimed so that the projectile enters the brain, causing
instant loss of consciousness.166,335,342–345 This must take
into account differences in brain position and skull
conformation between species, as well as the energy requirement for penetration of the skull and sinus.332,343
Accurate targeting for a gunshot to the head in various species has been described.343,344,346 For wildlife and
other freely roaming animals, the preferred target area
should be the head. It may, however, not be possible or
appropriate to target the head when killing is attempted
from large distances (missed shots may result in jaw
fractures or other nonfatal injuries) or when diagnostic samples of brain tissue are needed for diagnosis of
diseases (eg, rabies, chronic wasting disease) important
to public health. The appropriate firearm should be selected for the situation, with the goal being penetration
and destruction of brain tissue without emergence from
the contralateral side of the head.130,347 A gunshot to the
heart or neck does not immediately render animals unconscious, but may be required when it is not possible
to meet the POE’s definition of euthanasia.348
M3.5.1 Basic Principles of Firearms
To determine whether a firearm or type of ammunition is appropriate for euthanizing animals, some basic
principles must be understood. The kinetic energy of
an object increases as the speed and weight or mass of
the object increase. In reference to firearms, the bullet’s
kinetic energy (muzzle energy) is the energy of a bullet as it leaves the end of the barrel when the firearm
is discharged. Muzzle energy is frequently used as an
indicator of a bullet’s destructive potential. The heavier the bullet and the greater its velocity, the higher its
muzzle energy and capacity for destruction of objects
in its path.
Muzzle energy (E) can be expressed as the mass of
the bullet (M) times its velocity (V) squared, divided by
2.349 However, to accommodate units of measure commonly used in the United States for civilian firearms,
energy (E) is expressed in foot-pounds. This is calculated by multiplication of the bullet’s weight (W) times
its velocity in feet per second (V) squared, divided by
450,450. The International System of Units expresses
muzzle energy in joules (J).
Representative ballistics data for various types of
firearms are provided in Table 1. The muzzle energy
of commercially available ammunition varies greatly.
For example, the difference in muzzle energy generated from a .357 Magnum handgun loaded with a 180
grain compared with a 110 grain bullet may differ by as
much as 180 foot-pounds.349 Velocity has an even greater impact on bullet energy than bullet mass. Selection
of an appropriate bullet and firearm is critical to good
performance when conducting euthanasia procedures.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Table 1—Average muzzle energies for common handguns and
rifles. (Adapted from USDA, 2004, National Animal Health Emergency Management System Guidelines, USDA, Washington, DC.
Available at: www.dem.ri.gov/topics/erp/nahems_euthanasia.pdf
[Accessed August 27, 2009] and cited by Woods J, Shearer JK,
Hill J. Recommended on-farm euthanasia practices. In: Grandin
T, ed. Improving animal welfare: a practical approach. Wallingford,
Oxfordshire, England: CABI Publishing, 2010; 194–195.)
Muzzle energy
Cartridge/firearm
Handguns
.40 Smith and Wesson
.45 Automatic Colt Pistol
.357 Magnum
.41 Remington Magnum
10-mm Automatic
.44 Remington Magnum
Rifles
.223 Remington
30-30 Winchester
.308
30-06 Springfield
In foot pounds
In joules
408
411
557
607
649
729
553
557
755
823
880
988
1,296
1,902
2,648
2,841
1,757
2,579
3,590
3,852
Lighter-weight, higher-velocity bullets can have high
muzzle energy, but decreased penetration, which can
be an issue when penetrating thick bones.
Whereas most euthanasia using firearms is conducted at close range, calculations of muzzle energy are
useful for determining which firearms are appropriate
for euthanasia of animals of varying sizes. As the bullet travels beyond the muzzle of the firearm its energy
gradually begins to decrease. While this is not a concern for the use of firearms in close proximity to the
animal, when attempting to euthanize an animal from
a distance, to ensure accuracy and that an acceptable
level of muzzle energy is achieved, a high-powered rifle
may be the better choice for conducting euthanasia. In
all cases, the most important factors in ensuring successful euthanasia are the experience and skill of the
shooter.
M3.5.2 Muzzle Energy Requirements
For euthanasia, the combination of firearm and
ammunition350 selected must achieve a muzzle energy
of at least 300 ft-lb (407 J) for animals weighing up to
400 lb (180 kg). For animals larger than 400 lb, 1,000
ft-lb (1,356 J) is required.130 As demonstrated by Table
1, handguns do not typically achieve the muzzle energy required to euthanize animals weighing more than
400 lb (180 kg), and therefore rifles must be used to
euthanize these animals.
Some would argue that the muzzle energies recommended are well beyond what is necessary to achieve
satisfactory results. Anecdotal comment suggests that
the .22 LR is one of the most frequently used firearms
for euthanasia of livestock with varying degrees of success. There is little doubt that success or failure is partially related to firearm and bullet characteristics, but
probably more so to selection of the ideal anatomic site
(ie, a site more likely to affect the brainstem) for conducting the procedure. The Humane Slaughter Association lists multiple firearms for euthanasia of livestock,
including shotguns (12, 16, 20, 28, and .410 gauges),
handguns (.32 to .45 caliber), and rifles (.22, .243,
.270, and .308). In general, when comparing handguns
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
with rifles, the longer the barrel, the higher the muzzle
velocity. Therefore, if a .22 is used for euthanasia it is
best fired from a rifle. The .22 should never be used on
aged bulls, boars, or rams.351
M3.5.3 Bullet Selection
While much of the emphasis in euthanasia by gunshot is placed on choice of the most appropriate firearm,
it should be remembered that the gun is only the means
of delivery. Bullet selection is quite possibly the most
important consideration for euthanasia of livestock by
gunshot. There are three basic types of bullets pertinent
to this discussion: solid points, hollow points, and full
metal jacketed bullets. Solid-point bullets are preferred
for euthanasia since they are designed for greater penetration of their targets. Under ideal conditions this
type of bullet will also undergo moderate expansion to
a mushroom shape that increases its destructive characteristics. Hollow-point bullets are designed with a
hollowed-out tip that causes rapid expansion and fragmentation of the bullet on impact. The hollow-point
design allows maximum transfer of energy without risk
of overpenetration. For applications where it may be
desirable to control or reduce the degree of bullet penetration, hollow-point bullets are preferred. However,
for the purposes of euthanasia of livestock the first requirement is that the bullet possesses sufficient energy
to penetrate the skull and enter the underlying brain
tissue. The concern with hollow-point bullets is that,
since the majority of their energy is released on impact
through fragmentation, they may not have sufficient
energy to traverse the skull. The other extreme is represented by full metal jacket bullets, which do not expand
or fragment on impact with their targets. These bullets
have a lead core with a thin metal jacket cover that
completely covers (surrounds) the bullet. Full metal
jacket bullets generally achieve maximum penetration,
which may have benefits for euthanasia but also creates additional safety hazards for bystanders. Shotguns
loaded with shot shells (number 4, 5, or 6) have sufficient energy to traverse the skull but, unlike the possibility of bullets from either a handgun or rifle, rarely
exit the skull. These are important considerations when
selecting a firearm for on-farm euthanasia. Probably the
most important point to be made relative to the use of
gunshot for euthanasia is that scientific information on
firearm and bullet selection is lacking. This is an area of
urgent need in euthanasia research.
M3.5.4 Firearm Safety
Firearm safety cannot be overemphasized. Guns
are inherently dangerous and must be handled with
caution at all times. This needs to become the mindset
in handling and use of firearms. Common recommendations include the following: (1) assume that all firearms are loaded, (2) always know where the muzzle is
and never allow it to point in the direction of oneself or
bystanders, (3) keep fingers away from the trigger and
out of the trigger guard until ready to fire, (4) be sure
of the target and what lies beyond it, and (5) always be
sure that the gun is unloaded when not in use. Readers
desiring more information or training on proper use of
firearms are advised to contact local hunter safety pro37
grams. These programs offer training in firearm safety
and also provide information on rules and regulations
for firearm use.
Firearms should never be held flush to an animal’s
body. The pressure within the barrel when fired may
cause the barrel of the gun to explode, placing the
shooter and observers at great risk of injury. Ideally, the
muzzle of the firearm should be held within 1 to 2 feet
of the animal’s forehead and perpendicular to the skull
with the intended path of the bullet roughly in the direction of the foramen magnum. This will reduce the
potential for ricochet while directing the bullet toward
the cerebrum, midbrain, and medulla oblongata, which
will assure immediate loss of consciousness and rapid
death.
Advantages—(1) Loss of consciousness is instantaneous if the projectile destroys most of the brain. (2)
Given the need to minimize stress induced by handling
and human contact, gunshot may be the most practical and logical method of euthanasia for wild or freeranging species.
Disadvantages—(1) Gunshot may be dangerous for
personnel. (2) It is aesthetically unpleasant for many.
(3) Under field conditions, it may be difficult to hit
the vital target area. (4) Brain tissue may not be able
to be examined for evidence of brain diseases (eg, rabies infection, chronic wasting disease) when the head
is targeted. (5) Skill in application of firearms and species-specific knowledge of appropriate target sites is required. In some states, firearm use is not permitted if
the operator has been convicted of a felony.
General recommendations—When other methods
cannot be used, an accurately delivered gunshot is acceptable with conditions for euthanasia.344,352 When an
animal can be appropriately restrained, the penetrating
captive bolt, preferably one designed for euthanasia, is
preferred to a gunshot because it is safer for personnel.
Prior to shooting, animals accustomed to the presence
of humans should be treated in a calm and reassuring
manner to minimize anxiety. In the case of wild animals,
gunshots should be delivered with the least amount of
prior human contact necessary. Gunshot should not be
used for routine euthanasia of animals in animal control situations, such as municipal pounds or shelters.
M3.6 CERVICAL DISLOCATION
Cervical dislocation has been used for many years
for euthanasia and, when performed by well-trained
individuals on appropriate animals, appears to be humane. However, there are few scientific studies available to confirm this observation. The method has been
used to euthanize small birds, poultry, mice, immature
rats (< 200 g [7.1 oz]), and rabbits. For mice and rats,
the thumb and index finger are placed on either side of
the neck at the base of the skull or, alternatively, a rod
is pressed at the base of the skull. With the other hand,
the base of the tail or the hind limbs are quickly pulled,
causing separation of the cervical vertebrae from the
skull. For immature rabbits, the head is held in 1 hand
and the hind limbs in the other. The animal is stretched
38
and the neck is hyperextended and dorsally twisted to
separate the first cervical vertebra from the skull.334,353
For poultry and other birds, the legs of the bird should
be grasped (or wings if grasped at the base) and the
neck stretched by pulling on the head while applying
a ventrodorsal rotational force to the skull. Crushing
of cervical vertebrae and spinal cord is not acceptable
unless the bird is first rendered unconscious. Personnel
should be trained on anesthetized and/or dead animals
to demonstrate proficiency.
Data suggest that electrical activity in the brain
persists for 13 seconds following cervical dislocation
in rats,58 and unlike decapitation, rapid exsanguination does not contribute to loss of consciousness.56,57
For some classes of poultry there is evidence that cervical dislocation may not cause immediate unconsciousness.337–339,354
Advantages—(1) Cervical dislocation is a method
that may induce rapid loss of consciousness.58,275 (2) It
does not chemically contaminate tissue. (3) It is rapidly
accomplished.
Disadvantages—(1) Cervical dislocation may be
aesthetically displeasing to personnel performing or
observing the method. (2) Cervical dislocation requires
mastering technical skills to ensure loss of consciousness is rapidly induced. (3) Its use for euthanasia is limited to small birds, poultry, mice, immature rats (< 200
g), and rabbits.
General recommendations—Manual cervical dislocation is acceptable with conditions for euthanasia of
small birds, poultry, mice, rats weighing < 200 g, and
rabbits when performed by individuals with a demonstrated high degree of technical proficiency. In lieu of
demonstrated technical competency, animals must be
unconscious or anesthetized prior to cervical dislocation. For heavy rats and rabbits, the large muscle mass
in the cervical region makes manual cervical dislocation physically more difficult.355 When performed on
poultry, cervical dislocation must result in luxation
of the cervical vertebrae without primary crushing of
the vertebrae and spinal cord. In some classes of poultry, there is evidence that cervical dislocation may not
cause immediate unconsciousness.337–339,354 In these cases, other physical methods such as blunt force trauma
or decapitation may be more humane356 and should be
employed when available or practicable.
Those responsible for the use of this method must
ensure that personnel performing cervical dislocation
have been properly trained and consistently apply it
humanely and effectively.
M3.7 DECAPITATION
Decapitation can be used to euthanize rodents and
small rabbits in research settings. It provides a means
to recover tissues and body fluids that are chemically
uncontaminated. It also provides a means of obtaining
anatomically undamaged brain tissue for study.357
Although it has been demonstrated that electrical
activity in the brain persists for 13 to 14 seconds following decapitation,59 more recent studies and reports56–58
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
indicate this activity does not imply that pain is perceived, and in fact conclude that loss of consciousness
develops rapidly. Visually evoked potentials in mice
were reduced more quickly after cervical dislocation
compared with decapitation.51
Guillotines designed to accomplish decapitation of
adult rodents and small rabbits in a uniformly instantaneous manner are commercially available. Guillotines
are not commercially available for neonatal rodents, but
sharp blades can be used for this purpose.
Advantages—(1) Decapitation appears to induce
rapid loss of consciousness.56–58 (2) It does not chemically contaminate tissues. (3) It is rapidly accomplished.
Disadvantages—(1) Handling and restraint required to perform decapitation may be distressful for
animals.358 (2) The interpretation of the presence of
electrical activity in the brain following decapitation
has created controversy, and its importance may still
be open to debate.56–59 (3) Personnel performing this
method should recognize the inherent danger of the
guillotine and take precautions to prevent personal injury. (4) Decapitation may be aesthetically displeasing
to personnel performing or observing the method.
General recommendations—This method is acceptable with conditions if performed correctly, and it may
be used in research settings when its use is required
by the experimental design and approved by the IACUC. Decapitation is justified for studies where undamaged and uncontaminated brain tissue is required.
The equipment used to perform decapitation must be
maintained in good working order and serviced on a
regular basis to ensure sharpness of blades. The use
of plastic cones to restrain animals appears to reduce
distress from handling, minimizes the chance of injury
to personnel, and improves positioning of the animal.
Decapitation of amphibians, finfish, and reptiles is addressed elsewhere in the Guidelines. Those responsible
for the use of this method must ensure that personnel
who perform decapitation have been properly trained
to do so and are monitored for competence.
M3.8 ELECTROCUTION
Alternating current has been used to euthanize
dogs, cattle, sheep, goats, swine, chickens, foxes, mink,
and finfish.45,54,342,345,359–366 Fifty- or 60-cycle electrical
current is more effective than higher frequencies.367,368
Electrocution induces death by cardiac fibrillation,
which causes cerebral hypoxia.365,366,369 However, animals do not lose consciousness for 10 to 30 seconds
or more after onset of cardiac fibrillation. It is imperative that animals be unconscious and insensible to pain
before being electrocuted. Unconsciousness can be induced by any method that is acceptable or acceptable
with conditions, including passing a current through
the brain.370
Parameters for use of electricity to induce unconsciousness are readily available.342,371 When electricity
is used to induce unconsciousness, a current is passed
through the brain, which will induce a grand mal epileptic seizure.106,363,366,372 Signs of effective induction of
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
the seizure are extension of the limbs, opisthotonus,
downward rotation of the eyeballs, and a tonic (rigid)
spasm changing to a clonic (paddling) spasm with
eventual muscle flaccidity.
There are three approaches to the use of electricity
for euthanasia. They are head only, 1-step head to body,
and 2-step head and body. To be effective for euthanasia all three of these methods must induce a grand mal
epileptic seizure.
For the head-only procedure, an electrical current
is passed through the head to induce a seizure. This
causes a temporary loss of consciousness of 15 to 30
seconds’ duration,106,372,373 but does not induce cardiac
fibrillation. For this reason, head-only application must
be immediately followed by a secondary procedure to
cause death. When the head-only procedure is applied,
the grand mal seizure is easily observable. Electrically
induced cardiac fibrillation, exsanguination, or other
appropriate adjunctive methods may be used to achieve
death and should be performed within 15 seconds of
when the animal becomes unconscious.
In the 1-step head-to-body approach an electrical
current is simultaneously passed through both the brain
and the heart. This simultaneously induces a grand mal
seizure and electrocutes the animal by inducing cardiac
arrest.106,359,374–376 Because electricity passes through the
spinal column, clinical signs of the grand mal seizure
may be masked; however, it is usually possible to see a
weak tonic phase and weak clonic phase after a 3-second application. If current is applied for more than 3
seconds, tonic and clonic spasms may be blocked. The
1-step approach must be used with amperage settings
that have been scientifically verified to induce a seizure.
Recommended amperages are 1.25 amps for pigs, 1
amp for sheep, and 1.25 amps for cattle.341,376 Denicourt
et al377 report that 110 V at 60 Hz applied for 3 seconds
was effective for pigs up to 125 kg (275 lb).
In the 2-step method an electrical current is passed
through the head to induce unconsciousness, then a
second current is passed through either the side of the
body or the brisket to induce cardiac arrest.378,379 Applying the second current by an electrode placed on the
side of the body behind the forelimb has been reported
to be effective.49
A common cause of failure to induce unconsciousness is incorrect placement of the electrodes.374 Experiments with dogs revealed that electrode positions
where the brain is bypassed do not cause instantaneous
unconsciousness. When electricity passes only between
the forelimbs and hind limbs or neck and feet, it causes
the heart to fibrillate but does not induce sudden loss of
consciousness.369 The animal will be electrocuted, but
will remain conscious until it dies from cardiac fibrillation.
Three options are available for correct electrode
placement for the head-only method, including on both
sides of the head between the eye and ear, the base of
the ear on both sides of the head, and diagonally below
one ear and above the eye on the opposite side of the
head. For the 1-step (head-to-back) method, the head
electrode may be placed on the forehead or immediately behind the ear. The head electrode should never
be placed on the neck because the brain will be by39
passed.100 Diagonal movement of the electrical current
through the body can be accomplished by placing the
head electrode behind one ear and the body electrode
on the opposite side. When the 2-step procedure is
used, placement of the body electrode behind the forelimb is effective.49 Electrodes consisting of a metal band
or chain around the nose and a band or chain around
the thorax appear to be effective for pigs weighing up
to 125 kg.377
When electrical methods of euthanasia are used,
the following signs of return to consciousness must
be absent: rhythmic breathing, righting reflex, vocalization, eyeblink, and tracking of a moving object.49
Gasping and nystagmus may be present in animals that
have been successfully rendered unconscious with electricity. Gasping should not be confused with rhythmic
breathing, and nystagmus (a rapid vibrating or fluttering of the eye) should not be confused with eyeblink
(complete closure and then complete opening of the
eye, which occurs without touching).
Advantages—(1) Electrocution is humane if the
animal is first rendered unconscious. (2) It does not
chemically contaminate tissues. (3) It is economical.
Disadvantages—(1) Electrocution may be hazardous to personnel. (2) It is not useful for dangerous, intractable animals that are difficult to restrain. (3) It is
aesthetically objectionable because of violent extension
and stiffening of the limbs, head, and neck. (4) It may
not result in death in small animals (< 5 kg [11 lb])
because ventricular fibrillation and circulatory collapse
do not always persist after cessation of current flow. (5)
Sometimes it is not effective in dehydrated animals.371
(6) Personnel must be familiar with appropriate placement of electrodes and use of equipment. (7) Purposebuilt equipment must be used.
General recommendations—Euthanasia by electrocution is acceptable with conditions. It requires special skills and equipment that will ensure passage of
sufficient current through the brain to induce loss of
consciousness and induce tonic and clonic epileptic
spasms. Unconsciousness must be induced before cardiac fibrillation or simultaneously with cardiac fibrillation. Cardiac fibrillation must never occur before the
animal is rendered unconscious. Methods that apply
electric current from head to tail, head to foot, or head
to moistened metal plates on which the animal stands
are unacceptable. The 2-step method should be used
in situations where there may be questions about sufficient current to induce a grand mal seizure with tonic
and clonic spasms. This approach enables observation
of tonic and clonic spasms before a second current is applied to induce cardiac arrest. Although acceptable with
conditions if the aforementioned requirements are met,
the method’s disadvantages outweigh its advantages in
most applications. Electroimmobilization that paralyzes an animal without first inducing unconsciousness is
extremely aversive and is unacceptable.370,371 For both
humane and safety reasons, the use of household electrical cords is not acceptable.
40
M3.9 KILL TRAPS
Mechanical kill traps are used for the collection
and killing of small, free-ranging mammals for commercial purposes (fur, skin, or meat), scientific purposes, to stop property damage, and to protect human
safety. Their use remains controversial and kill traps do
not always render a rapid or stress-free death consistent with the criteria established for euthanasia by the
POE.380 For this reason, use of live traps followed by
other methods of euthanasia is preferred. There are a
few situations when that is not possible (eg, pest control) or when it may actually be more stressful for the
animals or dangerous for humans to use live traps.
Although newer technologies are improving kill trap
performance in achieving loss of consciousness quickly,
individual testing is recommended to be sure the trap is
working properly.381 If kill traps must be used, the most
humane option available must be chosen,382–384 as evaluated by use of International Organization for Standardization testing procedures,385 or by the methods of Gilbert,386 Proulx et al,387,388 or Hiltz and Roy.389
To reach the required level of efficacy, traps may
need to be modified from manufacturers’ production
standards. In addition, as specified in scientific studies, trap placement (ground vs tree sets), bait type, set
location, selectivity apparatus, body placement modifying devices (eg, sidewings, cones), trigger sensitivity,
and trigger type, size, and conformation are essential
considerations that could affect a kill trap’s ability to
reach these standards. Several kill traps, modifications,
and set specifics have been scientifically evaluated and
found to meet standards for various species.387,388,390–403,f
Advantage—(1) Free-ranging small mammals may
be killed with minimal distress associated with handling and human contact. (2) Multiple animals may be
effectively killed in situations where public health, animal behavior, or other constraints exist.
Disadvantages—(1) Traps may not kill within acceptable time periods. (2) Selectivity and efficiency is
dependent on the skill and proficiency of the operator.
(3) Nontarget species may be trapped and injured.
General recommendations—Kill traps do not consistently meet the POE’s criteria for euthanasia, and may
be best characterized as humane killing under some
circumstances. At the same time, it is recognized they
can be practical and effective for scientific animal collection or pest control when used in a manner that ensures selectivity, a swift kill, and no damage to body
parts needed for field research.404,405 Care must be taken
to avoid trapping and injuring nontarget species.
Traps need to be checked at least once daily. In
those instances when an animal is wounded or captured
but not dead, the animal must be killed quickly and humanely. Kill traps should be used only when other acceptable methods are not practical or have failed. Traps
for nocturnal species should not be activated during the
day to avoid capture of diurnal species.404 Trap manufacturers should strive to meet their responsibility of
minimizing pain and suffering in target species. Traps
that entrap a conscious animal in glue or other sticky
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
substance are not acceptable for euthanasia, but may be
required for pest control. Glue traps are acceptable for
insects or spiders.
M3.10 MACERATION
Maceration, via use of a specially designed mechanical apparatus having rotating blades or projections, causes immediate fragmentation and death of
poultry up to 72 hours old and embryonated eggs. A
review406 of the use of commercially available macerators for euthanasia of chicks, poults, and pipped eggs
indicates that death by maceration in poultry up to 72
hours old occurs immediately with minimal pain and
distress. Maceration is an alternative to the use of CO2
for euthanasia of poultry up to 72 hours old. Maceration is believed to be equivalent to cervical dislocation
and cranial compression as to time element, and is
considered to be an acceptable means of euthanasia for
newly hatched poultry by the Federation of Animal Science Societies,407 Agriculture Canada,408 World Organisation for Animal Health,342 and European Union.409
Advantages—(1) Death is almost instantaneous.
(2) The method is safe for workers. (3) Large numbers
of animals can be killed quickly.
Disadvantages—(1) Special equipment is required
and it must be kept in excellent working condition. (2)
Personnel must be trained to ensure proper operation
of equipment. (3) Macerated tissues may present biosecurity risks.
General recommendations—Maceration requires
special equipment that must be kept in excellent working order. Chicks must be delivered to the macerator
in a way and at a rate that prevents a backlog of chicks
at the point of entry into the macerator and without
causing injury, suffocation, or avoidable distress to the
chicks before maceration.
M3.11 FOCUSED BEAM
MICROWAVE IRRADIATION
Heating by focused beam microwave irradiation is
used primarily by neurobiologists to fix brain metabolites in vivo while maintaining the anatomic integrity of
the brain.410 Microwave instruments have been specifically designed for use in euthanasia of laboratory mice
and rats. The instruments differ in design from kitchen
units and may vary in maximal power output from 1.3
to 10 kW. All units direct their microwave energy to
the head of the animal. The power required to rapidly
halt brain enzyme activity depends on the efficiency of
the unit, the ability to tune the resonant cavity, and the
size of the rodent head.411 There is considerable variation among instruments in the time required for loss
of consciousness and euthanasia. A 10-kW, 2,450-MHz
instrument operated at a power of 9 kW will increase
the brain temperature of 18- to 28-g mice to 79°C in
330 milliseconds, and the brain temperature of 250- to
420-g rats to 94°C in 800 milliseconds.412
Advantages—(1) Loss of consciousness is achieved
in < 100 milliseconds, and death in < 1 second. (2) This
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
is the most effective method to fix brain tissue in vivo
for subsequent assay of enzymatically labile chemicals.
Disadvantages—(1) Instruments are expensive. (2)
Only animals the size of mice and rats can be euthanized with commercial instruments that are currently
available.
General recommendations—Focused beam microwave irradiation is a humane method for euthanizing
small laboratory rodents if instruments that induce rapid loss of consciousness are used. Only instruments that
are designed for this use and have appropriate power
and microwave distribution can be used. Microwave
ovens designed for domestic and institutional kitchens
are unacceptable for euthanasia.
M3.12 THORACIC (CARDIOPULMONARY,
CARDIAC) COMPRESSION
Thoracic (cardiopulmonary, cardiac) compression
is a method that has been used by biologists to terminate the lives of wild small mammals and birds, mainly
under field conditions. Although it has been used extensively in the field, data supporting this method are
not available, including degree of distress induced and
time to unconsciousness or death. Based on current
knowledge of the physiology of both small mammals
and birds, thoracic compression can result in substantial pain and distress before animals become unconscious, thus lacking key humane considerations that
can be addressed by other methods. Various veterinary
and allied groups do not support thoracic compression
as a method of euthanasia.413–416 Consequently, thoracic
compression is an unacceptable means of euthanizing
animals that are not deeply anesthetized or insentient
due to other reasons, but is appropriate as a secondary
method for animals that are insentient.
The consensus of veterinarians with field biology
training and expertise is that portable equipment and
alternate methods are currently available to field biologists for euthanasia of wildlife under field conditions,
in accordance with current standards for good animal
welfare. Anesthetics can be administered prior to application of thoracic compression. Depending on taxa,
open-drop methods or injectable agents that do not
require DEA registration can be used. These alternate
methods are generally practical to use with minimal
training and preparation as standard procedures prior
to embarking upon fieldwork.
M3.13 ADJUNCTIVE METHODS
M3.13.1 Exsanguination
Exsanguination can be used to ensure death subsequent to stunning, or in otherwise unconscious animals. Because anxiety is associated with extreme hypovolemia, exsanguination must not be used as a sole
means of euthanasia.417 Animals may be exsanguinated
to obtain blood products, but only when they are sedated, stunned, or anesthetized.418
M3.13.2 Pithing
Pithing is used as an adjunctive procedure to en41
sure death in an animal that has been rendered unconscious by other means.
Pithing in ruminants is performed by inserting a
pithing rod or tool through the entry site produced in
the skull by a penetrating captive bolt or free bullet.419
The operator manipulates the pithing tool to substantially destroy both brainstem and spinal cord tissue.
Muscular activity during pithing can be considerable,
but is followed by quiescence that facilitates exsanguination or other procedures. Pithing is sometimes used in
42
advance of exsanguination to reduce involuntary movement in stunned animals.420 This method should not be
used in ruminants intended for food because of possible
contamination of the meat with specified risk materials.
Disposable pithing rods are available for purchase.
The rod must be somewhat rigid, yet flexible, and of
sufficient length to reach the brain and spinal column
through the access point in the skull.
Pithing of frogs and other amphibians is strongly
discouraged, unless the patient is anesthetized first.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Part III—Methods of Euthanasia
by Species and Environment
S1. COMPANION ANIMALS
Methods acceptable with conditions are equivalent
to acceptable methods when all criteria for application
of a method can be met.
S1.1 GENERAL CONSIDERATIONS
Companion animals for which euthanasia is determined to be necessary are usually encountered in
4 main environments: individually owned animals;
breeding animals (from dams, sires, and single litters
to colonies of breeding animals); populations of animals maintained in animal control facilities, shelters
and rescues, and pet shops; and animals maintained in
research laboratories. Examples of less common venues in which companion animals might be euthanized
include quarantine stations and Greyhound racetracks.
Aquatic companion animals are considered in Section
S6, Finfish and Aquatic Invertebrates, of the Guidelines.
As indicated previously in this document (see Section
I5.5, Human Behavior), the relationships between companion animals and their owners or caretakers vary and
should be carefully considered and respected when selecting an approach to euthanasia for these species.
Euthanasia of companion animals is best conducted
in quiet, familiar environments when practical. The species being euthanized, the reason for euthanasia, and the
availability of equipment and personnel will all contribute to decisions about the most appropriate location.
The professional judgment of the veterinarian conducting or providing oversight for euthanasia is paramount
in making appropriate decisions about euthanasia (eg,
location, agent, route of administration) in species kept
as companions and in the specific environments where
they are encountered. Personnel conducting euthanasia
must have a complete understanding of and proficiency
in the euthanasia method to be used.
For individually owned companion animals, euthanasia will often be conducted in a private room in
a veterinary clinic or in the home, to minimize animal
and owner distress.421 Factors leading to the decision to
euthanize should be discussed openly,109 and the animal’s owner should be permitted to be present during
euthanasia whenever feasible. Owners should be fully
informed about the process they are about to observe,
including the potential for excitation during anesthesia and other possible complications.421,422 If one euthanasia method is proving difficult, another method
should be tried immediately. Euthanasia should only be
attempted when the necessary drugs and supplies are
available to ensure a smooth procedure and, upon verification of death, owners should be verbally notified.110
In animal control, shelter, and rescue situations;
research laboratories; and other institutional settings,
trained technical personnel rather than veterinarians
often perform euthanasia. Training and monitoring of
these individuals for proficiency vary by setting and
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
state (eg, animal control officers, animal care technicians in laboratories, certified euthanasia technicians
in shelters in some states), as does the amount of veterinary supervision required. Euthanizing large numbers of animals on a regular basis can be stressful and
may result in symptoms of compassion fatigue.123 To
minimize the stress and demands of this duty, trained
personnel must be assured that they are performing
euthanasia in the most humane manner possible. This
requires an organizational commitment to provide ongoing professional training on the latest methods and
materials available for euthanasia and effective management of compassion fatigue for all personnel.121 In
addition, personnel should be familiar with methods
of restraint and euthanasia for all species likely to be
encountered in their facility.
Areas where euthanasia is conducted in institutional settings should be isolated from other activities,
where possible, to minimize stress on animals and to
provide staff with a professional and dedicated work
area. A well-designed euthanasia space provides good
lighting with the ability to dim or brighten as required,
ventilation, adaptable fixtures, and adequate space for
at least two people to move around freely in different
types of animal-handling situations.121,423 Attempts
should be made to minimize smells, sights, and sounds
that may be stressors for animals being euthanized. Basic equipment for handling and restraint, a scale, clippers, tourniquets, stethoscope, cleaning supplies, a variety of needles and syringes, and body bags should be
readily available to accommodate the needs of potentially diverse animal populations. In addition, a first-aid
kit should be available to address minor human injuries, and medical attention should always be sought for
bite injuries and more serious human injuries.
Euthanasia protocols for companion animals (usually dogs and cats) in institutional settings (eg, shelters,
large breeding facilities, research facilities, quarantine
facilities, racetracks) may differ from those applied in
traditional companion animal clinical practices due to
situation-specific requirements, including variable access to pharmaceuticals and other equipment, diagnostic and research needs (eg, postmortem tissue samples),
and the number of animals to be euthanized. For this
reason, general recommendations about euthanasia
methods applicable to companion animals are followed
by more specific information as to their applicability in
frequently encountered environments. While protocols
may differ, the interests of the animal must be given
equal consideration whether the animal is individually
owned or not.
S1.2 ACCEPTABLE METHODS
S1.2.1 Noninhaled Agents
Barbiturates and barbituric acid derivatives—Intravenous injection of a barbituric acid derivative (eg,
43
pentobarbital, pentobarbital combination product) is
the preferred method for euthanasia of dogs, cats, and
other small companion animals. Barbiturates administered IV may be given alone as the sole agent of euthanasia or as the second step after sedation or general
anesthesia. Refer to the product label or appropriate
species references424 for recommended doses. Current
federal drug regulations require strict accounting for
barbiturates, and these must be used under the supervision of personnel registered with the US DEA.
When IV access would be distressful, dangerous, or
impractical (eg, small patient size such as puppies, kittens, small dogs and cats, rodents, and some other nondomestic species or behavioral considerations for some
small exotic mammals and feral domestic animals),
barbiturates and barbituric acid derivatives may be administered IP (eg, sodium pentobarbital, secobarbital;
not pentobarbital combination products as these have
only been approved for IV and intracardiac administration). Because of the potential for peritoneal irritation
and pain (observed in rats),425 lidocaine has been used
with some success in rats to ameliorate discomfort.426,427
Lidocaine was also used in combination with sodium
pentobarbital in a laboratory comparison of IP and
intrahepatic injection routes in cats from animal shelters.284 Additional studies are necessary to determine
applicability to and dosing for other species.
Nonbarbiturate anesthetic overdose—Injectable anesthetic overdose (eg, combination of ketamine and xylazine given IV, IP or IM or propofol given IV) is acceptable for euthanasia when animal size, restraint requirements, or other circumstances indicate these drugs are
the best option for euthanasia. Assurance of death is
paramount and may require a second step, such as a
barbiturate, or additional doses of the anesthetic. For
additional information see Section M2, NonInhaled
Agents, and Section S2, Laboratory Animals.
Tributame—While it is not currently being manufactured, Tributame is an acceptable euthanasia drug for
dogs provided it is administered IV by an appropriately
trained individual at recommended dosages and at proper injection rates. If barbiturates are not available, its extralabel use in cats may be considered; however, adverse
reactions (eg, agonal breathing) have been reported and
the current FDA-approved Tributame label recommends
against its use in cats. Routes of administration other
than IV injection are not acceptable. Aesthetically objectionable agonal breathing may occur in unconscious animals and, consequently, the use of Tributame for ownerattended euthanasia is not recommended. While disconcerting for observers, because the animal is unconscious,
agonal breathing has limited impact on its welfare.
T-61—T-61 is acceptable as an agent of euthanasia, provided it is administered appropriately by trained
individuals. Slow IV injection is necessary to avoid
muscular paralysis prior to unconsciousness.295 Routes
other than IV are unacceptable. T-61 is also not currently being manufactured in the United States but is
obtainable from Canada.
Should sodium pentobarbital become unavailable
44
and manufacturing resume in the United States for
Tributame and T-61, more attention may be focused on
the use of the latter two agents for euthanasia of dogs
and cats.
S1.3 ACCEPTABLE WITH
CONDITIONS METHODS
S1.3.1 Noninhaled Agents
Barbiturates and barbituric acid derivatives (alternate routes of administration)—The IP route is not practical for medium or large dogs due to the volume of
agent that must be administered and a prolonged time
to death. A better choice for these animals when IV access is unachievable using manual restraint is general
anesthesia followed by intra-organ injection. In unconscious or anesthetized animals, intra-organ injections
(eg, intraosseous [Figure 4], intracardiac [Figure 5], intrahepatic and intrasplenic [Figure 6], intrarenal [Fig-
Figure 4—One recommended site (greater tubercle of the humerus) for administration of an intraosseous injection in adult dogs,
using a bone injection gun. An alternative is to use a Jamshidi bone
marrow needle or, in very young dogs, a hypodermic needle.
Figure 5—Site for administration of intracardiac injections in the
cat. Intracardiac injection is only appropriate in unconscious or
anesthetized animals.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
section for details). Because of the potential for recovery, care must be taken to ensure death has occurred prior to disposing of animal remains. Inhaled
anesthetics may also be used to anesthetize small
fractious animals prior to administration of an injectable euthanasia agent.
Figure 6—Site for administration of intrahepatic and intrasplenic
injections in the dog. In this figure, the liver is being injected; the
spleen is depicted in red caudal to the liver and stomach. Intrahepatic and intrasplenic injections are only appropriate in unconscious or anesthetized animals with the exception of intrahepatic
injections in cats as discussed in the text.
Figure 7—Site for administration of an intrarenal injection in the
dog. Intrarenal injection is only appropriate in anesthetized or unconscious animals.
ure 7]136,428,g) may be used as an alternative to IV or IP
injection of barbiturates when IV access is difficult.428
Intra-organ injections may speed the rate of barbiturate
uptake over standard IP injections, and when an owner
is present, this approach may be preferred over the IP
route.429 The intrahepatic injection of a combination of
sodium pentobarbital and lidocaine in awake cats from
animal shelters caused rapid unconsciousness and was
more accurately placed than IP injections.284 Therefore,
intrahepatic injection in awake cats may have limited
application in controlled environments when conducted by trained personnel. However, positioning of awake
cats for intrahepatic injection is in an upright position
with the forequarters elevated rather than in lateral recumbency.
S1.3.2 Inhaled Agents
Inhaled anesthetics—Overdoses of inhaled anesthetics administered via chamber (eg, isoflurane,
sevoflurane) are acceptable with conditions for euthanasia of small mammals and some other species
< 7 kg because most vertebrates display aversion
behavior to inhaled anesthetics (see Inhaled Agents
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Carbon monoxide—Carbon monoxide can be used
effectively for euthanasia when required conditions
for administration (see detailed discussion in Inhaled
Agents section of the Guidelines) can be met. These
conditions can be challenging and costly to meet on a
practical basis, and there is substantial risk to personnel
(hypoxia) if safety precautions are not observed. Consequently, CO is acceptable with conditions for use in
institutional situations where appropriately designed
and maintained equipment and trained and monitored
personnel are available to administer it, but it is not
recommended for routine euthanasia of cats and dogs.
It may be considered in unusual or rare circumstances,
such as natural disasters and large-scale disease outbreaks. Alternate methods with fewer conditions and
disadvantages are recommended for companion animals where feasible.
Carbon dioxide—Carbon dioxide can be used effectively for euthanasia when required conditions for administration (see detailed discussion in Inhaled Agents
section of the Guidelines) can be met. However, just
as for use of CO, this can be challenging and costly to
do on a practical basis. Narcosis is a human safety risk
associated with the use of CO2. Carbon dioxide is acceptable with conditions for use in institutional situations where appropriately designed and maintained
equipment and trained and monitored personnel are
available to administer it, but it is not recommended
for routine euthanasia of cats and dogs. It may be considered in unusual or rare circumstances, including but
not limited to, natural disasters and large-scale disease
outbreaks. Alternate methods with fewer conditions
and disadvantages are recommended for companion
animals where feasible.
S1.3.3 Physical Methods
Gunshot—Gunshot should only be performed by
highly skilled personnel trained in the use of firearms
(eg, animal control and law enforcement officers, properly trained veterinarians) and only in jurisdictions that
allow for legal firearm use. A method acceptable with
conditions, use of gunshot may be appropriate in remote areas or emergency situations in which withholding death by gunshot will result in prolonged, unrelieved
pain and suffering of the animal or imminent danger to
human life. Protocols for ensuring a humane death by
gunshot have been described344,430 and preferred anatomic sites for use of gunshot for dogs and cats are provided
in Figures 8 and 9, respectively. Pre-euthanasia sedation
(eg, medication added to food) is recommended, whenever possible, for cats since they may be difficult to shoot
humanely.344 Gunshot is not recommended as a routine
approach to the euthanasia of dogs, cats, or other small
companion animals, and should not be used when other
methods are available and practicable.
45
exposure may be necessary to ensure death. Alternate
methods with fewer conditions and disadvantages are
recommended whenever feasible.
Electrocution—Electrocution using alternating current in dogs rendered unconscious by an acceptable
means (eg, general anesthesia) may be used for euthanasia (see Section M3.8 of the Guidelines for details).
The disadvantages of electrocution outweigh its advantages; therefore it is not recommended for routine use
in companion animals. Alternate methods with fewer
conditions and disadvantages should be used whenever
feasible.
Figure 8—Anatomic site for gunshot in dogs is located midway
between the level of the eyes and base of the ears, slightly off
midline with aim directed across the dog toward the spine.344
S1.5 UNACCEPTABLE METHODS
With the exception of IM delivery of select injectable anesthetics, the SC, IM, intrapulmonary, and intrathecal routes of administration are unacceptable for
administration of injectable euthanasia agents because
of the limited information available regarding their effectiveness and high probability of pain associated with
injection in awake animals.
Household chemicals, disinfectants, cleaning
agents, and pesticides are not acceptable for administration as euthanasia agents.
Other unacceptable approaches to euthanasia include hypothermia and drowning.
S1.6 SPECIAL CONSIDERATIONS
Figure 9—Anatomic site for gunshot in cats is a point slightly
ventral to a line drawn between the medial bases of the ears344 or
the intersection of lines drawn between lateral canthi of the eyes
and medial bases of ears as shown.
Penetrating captive bolt—Use of a penetrating captive bolt by trained personnel in a controlled laboratory
setting has been described as an effective and humane
method of euthanasia for rabbits and dogs.331 The bolt
must be placed directly against the skull; therefore, safe
and effective application of the technique may be facilitated by pre-euthanasia sedation or anesthesia. Penetrating captive bolt is not recommended as a routine
approach to the euthanasia of dogs, cats, or other small
companion animals, and should not be used when other methods are available and practicable.
S1.4 ADJUNCTIVE METHODS
Potassium chloride—Potassium chloride (1 to 2
mmol/kg, 75 to 150 mg/kg, or 1 to 2 mEq K+/kg) administered IV or intracardially may be used to euthanize companion animals when they are unconscious
(unresponsive to noxious stimuli) or under general anesthesia. Use of potassium chloride in awake animals is
unacceptable.
Nitrogen or argon—Gradual displacement methods
using N2 or Ar, alone or with other gases, in awake dogs
and cats may result in hypoxia prior to loss of consciousness (see Inhaled Agents section of the Guidelines for
details). Therefore, administration of N2 or Ar (< 2%
O2) should only be used as an adjunctive method for
unconscious or anesthetized dogs and cats; prolonged
46
S1.6.1 Dangerous or Fractious Animals
Animals that are unable to be safely and humanely
restrained should be sedated by means of drugs delivered orally (eg, gelatin capsules for delivery of drugs
in food,91 liquid formulations squirted into mouths92)
or remotely (eg, darts, pole syringes) before administration of euthanasia agents. Doing so will assist in relieving anxiety and pain for the animal, in addition to
reducing safety risks for personnel. There is a variety
of pre-euthanasia drugs that can be administered PO,
SC, or IM, alone or in combination, to render animals
unconscious with minimal handling in preparation for
euthanasia.431
S1.6.2 Disposal of Animal Remains
Residues of injectable agents commonly used for
euthanasia of companion animals (eg, sodium pentobarbital) tend to persist in the remains and may cause
sedation or even death of animals that consume the
body. For this reason safe handling and appropriate disposal of the remains are critically important. Additional
information is available in Section I8, Disposal of Animal Remains.
S1.7 FETUSES AND NEONATES
Scientific data432 indicate that mammalian embryos
and fetuses are in a state of unconsciousness throughout pregnancy and birth. For dogs and cats, this is
in part due to moderate neurologic immaturity, with
sentience being achieved several days after birth. The
precocious young of guinea pigs remain insentient and
unconscious until 75% to 80% of the way through pregnancy and remain unconscious until after birth due to
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
chemical inhibitors (eg, adenosine, allopregnanolone,
pregnanolone, prostaglandin D2, placental peptide neuroinhibitor) and hypoxic inhibition of cerebrocortical
activity.432 As a consequence, embryos and fetuses cannot consciously experience feelings such as breathlessness or pain. Therefore, they also “cannot suffer while
dying in utero after the death of the dam, whatever the
cause.”432 Information about developing nonmammalian eggs is available in the S5, Avians; S6, Finfish and
Aquatic Invertebrates; and S7, Captive and Free-Ranging Nondomestic Animals sections of the Guidelines.
Euthanasia of dogs, cats, and other mammals in
mid- or late-term pregnancy should be conducted via
an injection of a barbiturate or barbituric acid derivative (eg, sodium pentobarbital) as previously described.
Fetuses should be left undisturbed in the uterus for 15
to 20 minutes after the bitch or queen has been confirmed dead. This guidance is also generally applicable
to nonmammalian species, with euthanasia of eggs per
guidance provided in the S5, Avians; S6, Finfish and
Aquatic Invertebrates; and S7, Captive and Free-Ranging Nondomestic Animals sections of the Guidelines.
Intraperitoneal injections of pentobarbital should be
avoided whenever possible during the later stages of
pregnancy due to the likelihood of inadvertently entering the uterus, rendering the injection ineffective.
Altricial neonatal and preweanling mammals are
relatively resistant to euthanasia methods that rely on
hypoxia as their mode of action. It is also difficult, if not
impossible, to gain venous access. Therefore, IP injection of pentobarbital is the recommended method of
euthanasia in preweanling dogs, cats, and small mammals. Intraosseous injection may also be used, if strategies are used to minimize discomfort from injection by
using intraosseous catheters that may be in place (see
Section M2, NonInhaled Agents, of the Guidelines), or
if the animal is anesthetized prior to injection.
During ovariohysterectomy of pregnant dogs and
cats and small mammals with altricial neonates, ligation of the uterine blood vessels with retention of the
fetuses inside the uterus will result in death of the fetuses. The resistance of altricial neonates (eg, cats, dogs,
mice, rats) to euthanasia methods whose mechanisms
rely on hypoxia suggests that the uterus should not be
opened for substantially longer periods than for precocial neonates,433 perhaps 1 hour or longer. In the case
of caesarian section in late-term pregnancy, IP injection
of pentobarbital is recommended for fetuses that must
be euthanized for congenital deformities or illness and
that have been removed from the uterus (creating the
potential that successful breathing may have occurred).
S1.8 EUTHANASIA
IN SPECIFIC ENVIRONMENTS
S1.8.1 Individual Animals
in Presence of Owners
Pre-euthanasia sedation or anesthesia should be
provided whenever practicable, either before or after
the owner(s) has had the opportunity to spend some
final moments with his or her pet. Once the animal is
calm, either direct venipuncture or use of an IV catheter is acceptable for IV injection of the euthanizing
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
agent. Use of an IV catheter prevents repeat injections
and minimizes the need for restraint while pet owners
are present. When circulation is compromised by the
animal’s condition and sedation or anesthesia may reduce the likelihood of successful injection, it may be
necessary to proceed with IV injection in the awake
animal, or another route of administration of euthanizing agent might be considered. Alternatively, general
anesthesia may be induced, followed by administration
of a euthanasia agent.
S1.8.2 Breeding Facilities
Euthanasia protocols in large breeding facilities
may differ from those utilized in a clinical practice setting. Indications for euthanasia in breeding facilities
include neonates with congenital defects, acquired abnormalities or diseases within any segment of the population, or other conditions that render animals unsuitable for breeding or sale. Euthanasia may be performed
on an individual-animal basis, or in groups. Euthanasia
method is determined by animal species, size, age, and
number of animals to be euthanized. Barbiturates are
commonly administred IV or IP for individual euthanasia of any species, and for all ages of dogs and cats. Carbon dioxide euthanasia is commonly utilized for individual or group euthanasia of small animals, including
ferrets, rodents, and rabbits. Regardless of method and
number of animals being euthanized, procedures must
be performed in a professional, compassionate manner
by trained individuals under veterinary oversight. Appropriate techniques for assuring death must be applied
individually, regardless of the number of animals being
euthanized.
S1.8.3 Animal Control, Sheltering,
and Rescue Facilities
The preferred method of euthanasia in these facilities is injection of a barbiturate or barbituric acid
derivative with appropriate animal handling. When
euthanizing animals that are well socialized without
pre-euthanasia sedation or anesthesia, appropriate handling usually involves two trained people. One individual restrains the animal and the other administers the
euthanasia agent.434
When euthanizing distressed, dangerous, or fractious animals, a sedative or anesthetic should be administered prior to attempting euthanasia. When the
necessary restraint can be performed safely (appropriate handling techniques and equipment must be used),
a pre-euthanasia sedative or anesthetic can be delivered
IM or PO. After administration of the sedative or anesthetic, the animal is released so that it can return to a
comfortable low-stress location (eg, dimly lighted cage
or area) while the drug takes effect.431 Because of the
diversity of animals received by shelters, technicians
performing euthanasia must have a good understanding of animal behavior and restraint, the proper use of
equipment, and the variety of euthanasia drugs available and their effects.435
S1.8.4 Laboratory Animal Facilities
Euthanasia for companion animals in scientific settings must be approved by the IACUC. The IACUC has
47
mandatory veterinary input and considers animal welfare, requirements for postmortem tissue specimens,
and interference of euthanasia agents or methods with
study results. Scientific and husbandry staff form strong
emotional bonds with companion animals in scientific
settings, so sensitivity to grief and compassion fatigue
is necessary.
tions or pheromones that other animals in the room
could hear or smell may be best performed in another
location, if transportation distress can be minimized.
Similarly, wild-caught animals should be handled and
euthanized in the manner least stressful to the animals.
S2. LABORATORY ANIMALS
Methods acceptable with conditions are equivalent
to acceptable methods when all criteria for application
of a method can be met.
S2.2.1.1 Noninhaled Agents
S2.1 GENERAL CONSIDERATIONS
General comments about companion animals,
farm animals, poikilotherms, and birds are provided
elsewhere in the Guidelines, and usually apply to these
species in the laboratory setting. Some other commonly
used laboratory animal species are addressed later in
the text. Most laboratory mammals currently used in
biomedical research are small rodents that are maintained in large numbers. Venous access is typically difficult and injectable agents are usually delivered via the
IP route.
In addition to humane outcomes, an important
consideration in the choice of method for euthanasia
of laboratory animals is the research objectives for the
animals being euthanized. Euthanasia methods can
lead to metabolic and histologic artifacts that may affect research outcomes. For example, isoflurane may
artificially elevate blood glucose concentrations, while
IP injection of barbiturates can create artifacts in intestinal tissues and/or result in alterations in reproductive
hormones.436–438 Euthanasia by inhalation of CO2 elevates serum potassium concentrations.439 Time elapsed
between euthanasia and tissue collection can also be a
critical factor affecting choice of euthanasia method.440
Research needs may also require the use of an adjunctive method (eg, bilateral thoracotomy, exsanguination,
perfusion with fixatives, injection of potassium chloride). The application of such adjunctive methods is acceptable when the animal is fully anesthetized. Animals
used in infectious disease studies may require special
handling for animal and human health and safety.
S2.2 SMALL LABORATORY AND WILD-CAUGHT
RODENTS (MICE, RATS, HAMSTERS, GUINEA
PIGS, GERBILS, DEGUS, COTTON RATS)
All activities related to the euthanasia of rodents
deserve consideration equivalent to the euthanasia
method itself, and may factor into the choice of method. Laboratory rodents to be euthanized are often removed from the home room and/or home cage, placed
in unfamiliar groups, and then held for a period of time
before euthanasia. Activities that contribute to distress
in rodents include transport, handling (in animals not
accustomed to it), disruption of compatible groups,
and elimination of established scent marks.441–451 While
eliminating all sources of distress may not be practical
or possible, the selected method of euthanizing rodents
should minimize these sources of potential distress.
Methods of euthanasia likely to elicit distress vocaliza48
S2.2.1 Acceptable Methods
Barbiturates and barbituric acid derivatives—Injectable barbiturates act quickly and smoothly to render
rodents unconscious. If there is vascular access, IV
administration is preferred. The IP route is, however,
most practical. Pain may be associated with injections
given via the IP route,426,427 but the degree of pain and
the methods for controlling pain have yet to be defined.
The euthanasia dose is typically three times the anesthetic dose. Pentobarbital is the most commonly used
barbiturate for laboratory rodents because of its long
shelf life and rapidity of action.
Injectable barbiturate combinations—Injectable
barbiturates are often used in combination with local
anesthetics and anticonvulsants. An adequate dose of
barbiturate is the most important component in these
combinations.
Dissociative agent combinations—Lethal doses of
dissociative agents such as ketamine are commonly
used in laboratory settings. In some species, ketamine
alone can result in stimulatory activity prior to sedation and loss of consciousness. In conscious rodents,
ketamine and similar dissociative agents should be
used in combination with an α2-adrenergic receptor
agonist such as xylazine or benzodiazepines such as
diazepam.452
S2.2.2 Acceptable With Conditions Methods
S2.2.2.1 Inhaled Agents
Inhaled anesthetics—Halothane, isoflurane, sevoflurane, or desflurane, with or without N2O, are acceptable with conditions for euthanasia of laboratory
rodents. Nitrous oxide should not be used alone for
euthanasia. These agents may be useful in cases where
physical restraint is difficult or impractical. When used
as a sole euthanasia agent delivered via vaporizer or
anesthetic chamber (open-drop technique), animals
may need to be exposed for prolonged time periods to
ensure death.453 All other caveats as discussed in this
and other sections should be followed, including recommended flow rates, maintaining compatible groups,
and chamber maintenance. The use of inhaled anesthetics for preanesthesia removes the necessity for slow filling of the chamber with CO2; however, it is important
to verify that an animal is dead when inhaled agents
are used for euthanasia. Death may be confirmed by
physical examination, ensured by adjunctive physical
method, or obviated by validation of euthanasia chambers and process.147
Carbon dioxide—Carbon dioxide, with or without premedication with inhaled anesthetics, is acceptAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
able with conditions for euthanasia of small rodents.
Compressed CO2 gas in cylinders is the recommended
source of CO2 because gas inflow to the chamber can
be precisely regulated. An optimal flow rate for CO2
euthanasia systems should displace 10% to 30% of the
chamber or cage volume/min.152,238 Prefilled chambers
are unacceptable. If euthanasia cannot be conducted
in the home cage, chambers should be emptied and
cleaned between uses. It is important to verify that an
animal is dead after exposure to CO2.147 Death may be
confirmed by physical examination, ensured by an adjunctive physical method, or obviated by calibration
and validation of the euthanasia chamber and process.
If an animal is not dead, CO2 narcosis must be followed
with another method of euthanasia. Addition of O2 to
CO2 will prolong the time to death and may complicate
determination of consciousness. There appears to be
no advantage to combining O2 with CO2 for euthanasia.238,427
Decapitation—Decapitation is used in laboratory
settings because it yields tissues uncontaminated by
chemical agents. Loss of cortical function following decapitation is rapid and occurs within 5 to 30 seconds
as measured by a significant reduction in amplitude
recordings of visual evoked responses and EEG changes.51,58,59 Specialized rodent guillotines are available
and must be kept clean, in good condition with sharp
blades. If handled correctly, rats do not show evidence
of hypothalamic-pituitary-adrenal axis activation from
decapitation, or from being present when other rats are
decapitated.455 Decapitation is acceptable with conditions for mice and rats. Personnel should be trained on
anesthetized and/or dead animals to demonstrate proficiency.
Focused beam microwave irradiation—Focused
beam microwave irradiation, using a machine professionally designed for animal euthanasia (see Physical
Methods), is acceptable with conditions for euthanizing mice and rats. It is the preferred method when immediate fixation of brain metabolites is required for research purposes.
Carbon monoxide—Although not commonly used
in a laboratory animal setting, CO administration is acceptable with conditions as a method of rodent euthanasia when the conditions for effective and safe use can
be met (see Inhaled Agents).
S2.2.3 Unacceptable Methods
S2.2.2.2 Noninhaled Agents
S2.2.3.1 Inhaled Agents
Tribromoethanol—Although unavailable as a commercial or pharmaceutical-grade (United States Pharmacopeia/National Formulary/British Pharmacopeia)
product, tribromoethanol is a commonly used rodent
anesthetic. Its use is controversial due to its reported
adverse effects (peritonitis and death).324 However,
many biomedical IACUC have approved its use in rodents. Tribromoethanol is acceptable with conditions
as a method for euthanasia when prepared, stored, and
administered at the appropriate dosage.
Nitrogen and argon—Administration of N2 or Ar is
only acceptable in anesthetized mammals, as a coexisting O2 concentration of < 2% is necessary to achieve
unconsciousness and death. Achieving that condition
is difficult. In addition, Ar has been shown to be highly
aversive to rats.195 With heavy sedation or anesthesia,
it should be recognized that death may be delayed. Although N2 and Ar are effective, other methods of euthanasia are preferable.
S2.2.3.2 Noninhaled Agents
Ethanol—It has been suggested that IP injections of
70% ethanol might be an appropriate method of euthanasia for mice when physical methods are not desired
or other euthanasia agents are unavailable.454 Mice injected with 0.5 mL of 70% ethanol demonstrated gradual loss of muscle control, coma, and death in 2 to 4
minutes.307 While ethanol is acceptable with conditions
for certain applications (antibody production in mice),
other methods discussed as being acceptable and acceptable with conditions in the laboratory setting are
much preferred. Its use in larger species is unacceptable.
Potassium chloride—Intravenous or intracardiac
administration of potassium chloride is not acceptable
as a sole approach to euthanasia.
Neuromuscular blocking agents—Paralytic agents
are unacceptable for use as sole euthanasia agents.
Injectable barbiturates and neuromuscular blocking
agents—Combining injectable barbiturates and neuromuscular blocking agents in the same syringe for administration is unacceptable because the neuromuscular blocking agents may take effect before the animal is
anesthetized.
S2.2.2.3 Physical Methods
Cervical dislocation—Cervical dislocation is used
in laboratory settings. Cervical dislocation requires
neither special equipment nor transport of the animal
and yields tissues uncontaminated by chemical agents.
Loss of cortical function following cervical dislocation
is rapid and occurs within 5 to 10 seconds as measured
by a significant reduction in amplitude recordings of
visual evoked responses and EEG.51,58 Cervical dislocation is acceptable with conditions for mice and rats
< 200 g. Personnel should be trained on anesthetized
and/or dead animals to demonstrate proficiency.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Opioids—Opioids are unacceptable for euthanasia
of laboratory animals as they are not rapidly acting, require high doses, and are not true anesthetic agents.
Urethane—Urethane is a human carcinogen and
has a slow onset of action. It is unacceptable as a sole
euthanasia agent.
α Chloralose—α Chloralose is unacceptable as a
sole agent of euthanasia.
49
S2.2.4 Fetuses and Neonates
Rodents with altricial young, such as mice and
rats, must be differentiated from rodents with precocial
young, such as guinea pigs. Precocial young should be
treated as adults.
S2.2.4.1 Acceptable Methods
Euthanasia of the dam and fetuses—Rodent fetuses
along with other mammals are unconscious in utero
and hypoxia does not evoke a response.456 Therefore,
it is unnecessary to remove fetuses for euthanasia after
the dam is euthanized.
S2.2.4.1.1 Noninhaled Agents
Injectable barbiturates alone and in combination with
local anesthetics and anticonvulsants; dissociative agents
combined with α2-adrenergic receptor agonist or benzodiazepines—These agents are acceptable for use in fetuses
or neonates. See discussion on the use of these agents
in adult rodents.
S2.2.4.2 Acceptable With Conditions Methods
S2.2.4.2.1 Inhaled agents
Inhaled anesthetics—Nonflammable volatile anesthetic agents are effective for both in utero fetuses and
neonatal rodents. Neonatal mice may take up to 50
minutes to die from CO2 exposure.273 Adequate exposure time should be provided, or an adjunctive method
(eg, cervical dislocation, or decapitation) should be
performed after a neonate is nonresponsive to painful
stimuli.
S2.2.4.2.2 Physical Methods
Hypothermia—The gradual cooling of fetuses and
altricial neonates is acceptable with conditions. As cold
surfaces can cause tissue damage and presumably pain,
the animals should not come in direct contact with ice
or precooled surfaces. Hypothermia for anesthesia is
not recommended after approximately 7 days of age.457
Therefore, it is also an unacceptable euthanasia method in animals older than this age.458 Fetuses that are
believed to be unconscious and altricial neonates < 5
days of age that do not have sufficient nervous system
development to perceive pain may be quickly killed by
rapidly freezing in liquid N2.432,459
Decapitation—Decapitation using scissors or sharp
blades is acceptable with conditions for altricial neonates (< 7 days of age). Some rodent neonates, whether
atricial or precocial, may have a tissue mass that is too
large for some scissors. Consideration should be given
to the potential of pain from tissue crushing as well as
to personnel safety. When appropriate, another method
should be selected or an adult decapitator used.
Cervical dislocation—Cervical dislocation by
pinching and disrupting the spinal cord in the high cervical region is acceptable with conditions for fetal and
neonatal mice and rats.
S2.3 LABORATORY FARM ANIMALS, DOGS,
CATS, FERRETS, AND NONHUMAN PRIMATES
S2.3.1 General Considerations
The research goals will often influence the choice
of method of euthanasia for farm animals, dogs, cats,
and ferrets. Generally, sedation (as needed) followed by
IV injectable barbiturates will be the preferred method.
Tributame administered IV by trained personnel may be
an appropriate replacement for dogs if injectable barbiturates are not available. For more information on other
methods of euthanasia of farm and companion species,
consult the appropriate sections of the guidelines.
For nonhuman primates and other wild-caught or
nondomesticated animals used in the laboratory, some
general principles apply. Again, the research being conducted may influence the choice of euthanasia method,
and if the institutional animal care and use program staff
is unfamiliar with a species, researchers working with
the species may provide valuable guidance. Appropriate
restraint for the species must always be applied. Stress in
animals unfamiliar with handling should be minimized.
Venous access should be established or IM agents may be
used (delivered via remote injection equipment if necessary) for sedation. These animals are preferentially euthanized with an injectable barbiturate.
S2.3.2 Special Cases
When animals to be euthanized are fully anesthetized, adjunctive methods such as bilateral thoracotomy, exsanguination, perfusion, and IV or intracardiac
injection of potassium chloride are acceptable.
S2.4 LABORATORY RABBITS
S2.4.1 General Considerations
Rabbits will struggle and breath-hold when confronted with any unpleasant or unfamiliar odors. This
makes most inhaled methods difficult to use in rabbits
without premedication. Wild-caught animals should be
handled and euthanized in the manner least stressful to
the animals.
S2.4.2 Acceptable Methods
S2.4.2.1 Noninhaled Agents
Barbiturates and barbituric acid derivatives—If rabbits are used to handling, venous access may be obtained
via the ear. In the case of fractious rabbits, sedation may
be necessary to gain venous access for administration of
an injectable barbiturate or injectable barbiturate combination. Barbiturates may also be administered IP. As
indicated previously, pain may be associated with injections given via the IP route426,427; however, the degree of
pain and methods to control it have yet to be defined.
These approaches are acceptable for companion rabbits
as well.
S2.4.3 Acceptable With Conditions Methods
S2.4.3.1 Inhaled Agents
Inhaled anesthetics—Although rabbits breath-hold
when confronted with unpleasant odors,156,298,460 ani50
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
mals already under anesthesia may be euthanized by an
overdose of anesthetic.
Carbon dioxide—While CO2 is an effective method
of euthanasia, its use as the sole agent in rabbits results
in apparent distress to the rabbit. Premedication with
sedative agents will allow for the administration of CO2
for euthanasia.
S2.4.3.2 Physical Methods
Cervical dislocation—Cervical dislocation is acceptable with conditions for rabbits when performed by
individuals with a demonstrated high degree of technical proficiency. The need for technical competency
is great in heavy or mature rabbits in which the large
muscle mass in the cervical region makes manual cervical dislocation more difficult. Commercial devices designed to aid in rabbit cervical dislocation are available
and should be evaluated for their effectiveness.
Penetrating captive bolt—The use of rabbit-sized
penetrating captive bolts to euthanize rabbits in laboratory or production facilities is acceptable with conditions. The captive bolt must be maintained in clean
working order, positioned correctly, and operated safely
by trained personnel.
S2.4.4 Special Cases
When rabbits to be euthanized are in a surgical
plane of anesthesia, adjunctive methods such as delivery of potassium chloride, exsanguination, or bilateral
thoracotomy are acceptable.
S2.5 LABORATORY FINFISH, AQUATIC
INVERTEBRATES, AMPHIBIANS, AND REPTILES
Recommending euthanasia methods for finfish,
aquatic invertebrates, amphibians, and reptiles used
in biomedical research is challenging due to the enormous number of species and variations in biological
and physiologic characteristics. Methods for euthanizing species commonly used in research are discussed
in detail in the relevant sections of the Guidelines. See
these sections for additional information.
As described in the aquatics section it is acceptable
for zebrafish (Danio rerio) to be euthanized by rapid
chilling (2° to 4°C) until loss of orientation and operculum movements and subsequent holding times in
ice-chilled water, specific to finfish size and age.316,461,462
Adult zebrafish should be exposed for a minimum of
10 minutes and fry 4 to 7 days after fertilization (dpf)
for at least 20 minutes following loss of operculum
movement. Rapid chilling (as well as MS 222) has
been shown to be an unreliable euthanasia method for
embryos < 3 dpf. To ensure embryonic lethality these
methods should be followed with another agent such
as diluted sodium or calcium hypochlorite solution.462
If necessary to ensure death of other life stages, rapid
chilling may be followed by either an approved adjunctive euthanasia method or a humane killing method.
Until further research is conducted, rapid chilling is acceptable with conditions for other small-bodied tropical and subtropical stenothermic species.
Amphibian species commonly used in research
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
include the African clawed frog (X laevis) and leopard
and bull (Rana spp) frogs. These species are best euthanized via a physical method while fully anesthetized.
S3. ANIMALS FARMED
FOR FOOD AND FIBER
Methods acceptable with conditions are equivalent
to acceptable methods when all criteria for application
of a method are met.
3.1 GENERAL CONSIDERATIONS
While some methods of slaughter and depopulation might meet the criteria for euthanasia identified by
the POE, others will not and comments in this document
are limited to methods used for euthanasia. The following
section relates to species of animals domesticated for agricultural purposes, specifically cattle, sheep, goats, swine,
and poultry, regardless of the context in which that animal
is being kept or the basis for the decision to euthanize it.
Handling of animals prior to euthanasia should be
as stress free as possible. This is facilitated by ensuring
that facilities are well designed, appropriate equipment
is available, and animal handlers are properly trained
and their performance monitored.101,105–108
Regardless of the method of euthanasia used, death
must be confirmed before disposal of the animal’s remains. The most important indicator of death is lack
of a heartbeat. However, because this may be difficult
to evaluate or confirm in some situations, animals can
be observed for secondary indicators of death, which
might include lack of movement over a period of time
(30 minutes beyond detection of a heart beat) or the
presence of rigor mortis.
S3.2 BOVIDS AND SMALL RUMINANTS
S3.2.1 Cattle
S3.2.1.1 Acceptable Methods
S3.2.1.1.1 Noninhaled Agents
Barbiturates and barbituric acid derivatives—Barbiturates act rapidly and normally induce a smooth
transition from consciousness to unconsciousness and
death—a desirable outcome for the operator and observers. Although cost may be a deterrent to the use
of barbiturates for euthanasia of large and large numbers of animals, these agents tend to be less expensive
than other injectable pharmaceuticals. Drawbacks to
the use of barbiturates are that their administration requires adequate restraint of the animal, personnel who
are registered with the US DEA (and other appropriate
state authority where required), use by under the supervision of a veterinarian (because their use in food is
extralabel), strict control over the drug with accounting
of the amount used,463 and fewer options for disposal of
animal remains because of potential residues.
S3.2.1.2 Acceptable With Conditions Methods
S3.2.1.2.1 Physical Methods
Gunshot—Gunshot is the most common method
used for on-farm euthanasia of cattle.464 Death is caused
51
by destruction of brain tissue and the degree of brain
damage inflicted by the bullet is dependent on the firearm, type of bullet (or shotshell for shotguns), and accuracy of aim.
Handguns—Handguns or pistols are short-barreled
firearms that may be fired with one hand. For euthanasia, use of handguns is limited to close-range shooting
(within 1 to 2 feet or 30 to 60 cm) of the intended target. Calibers ranging from .32 to .45 are recommended
for euthanasia of cattle.351 Solid-point lead bullets are
preferable to hollow-point bullets because they are
more likely to traverse the skull. Hollow-point bullets
are designed to expand and fragment on impact with
their targets, which reduces the depth of penetration.
Under ideal conditions and good penetration of the
skull, hollow-point bullets are able to cause extensive
damage to neural tissues; however, because penetration
of the skull is the first criterion in euthanasia, a solid
lead bullet is preferred. The .22 caliber handgun is generally not recommended for routine euthanasia of adult
cattle regardless of bullet used, because of the inability
to consistently achieve desirable muzzle energies with
standard commercial loads.351
Rifles—A rifle is a long-barreled firearm that is
usually fired from the shoulder. Unlike the barrel of a
shotgun, which has a smooth bore for shot shells, the
bore of a rifle barrel contains a series of helical grooves
(called rifling) that cause the bullet to spin as it travels
through the barrel. Rifling imparts stability to the bullet and improves accuracy. For this reason, rifles are the
preferred firearm for euthanasia when it is necessary to
shoot from a distance.
Rifles are capable of delivering bullets at much
higher muzzle velocities and energies and thus are not
the ideal choice for euthanasia of animals in indoor or
short-range conditions. General recommendations on
rifle selection for use in euthanasia of cattle include
.22, .223, .243, .270, .308, and others.130,350,351 Results
of at least one study350 suggest that the .22 LR may
not be the best selection of a firearm for euthanasia
of adult cattle because of poor penetration, deflection,
and fragmentation of the bullet. Standard- and highvelocity bullets fired from a .22 caliber rifle at a range
of 25 m failed to penetrate skulls of steers and heifers studied. On the other hand, the .223 and .30-06
performed satisfactorily (eg, traversed the skull and
caused sufficient brain damage to cause death) when
fired from a distance of 25 m.350 This is in agreement
with similar information indicating that .22 Magnum
or larger-caliber firearms provide higher muzzle energies and more consistent results when delivered to the
proper anatomic site.130
When the most appropriate firearm is being chosen
for the purpose of euthanasia, there are several factors
to be considered, including caliber of the firearm, type
of bullet or shotshell, distance from the target, age of
the animal (aged animals have harder skulls), sex of the
animal (bull or cow), and accuracy of aim. Based upon
available information, if a .22 LR is to be used the following conditions apply: (1) the firearm of choice is a
rifle, (2) a solid-point bullet should be used, (3) it must
52
be fired within close range of the skull (within 1 to 3
feet), and (4) the bullet must be directed so that proper
anatomic placement on the skull is assured.347
Shotguns—Shotguns loaded with birdshot (lead or
steel BBs) or slugs (solid lead projectiles specifically designed for shotguns) are appropriate from a distance of 1
to 2 yards (1 to 2 m). Although all shotguns are lethal at
close range, the preferred gauges for euthanasia of cattle
are 20, 16, or 12. Number 6 or larger birdshot or shotgun slugs are the best choices for euthanasia of cattle.351
Birdshot begins to disperse as it leaves the end of the gun
barrel; however, if the operator stays within short range
of the intended anatomic site, the birdshot will strike the
skull as a compact bolus or mass of BBs with ballistic
characteristics on entry that are similar to a solid lead
bullet. At close range, penetration of the skull is assured
with massive destruction of brain tissue from the dispersion of birdshot into the brain that results in immediate
loss of consciousness and rapid death.
The Canadian study350 cited previously evaluated
several firearms, including the .410 and 12-gauge shotguns. The .410 loaded with either number 4 or number
6 birdshot fired from a distance of 1 m was very effective and had the advantage of less recoil compared with
other firearms used. The 12-gauge shotgun loaded with
number 7 1/2 birdshot fired from a distance of 2 m from
its target was effective but considered to be more powerful than necessary. Results of a 1-oz rifled slug fired
from a 12-gauge shotgun at a distance of 25 m failed to
penetrate the brain not because it lacked power, rather
because of faulty shot placement. Researchers concluded that the rail sighting system on the shotgun was not
sufficient for accurate shot placement if it was necessary to shoot from a distance. They also believed that
recoil from this firearm would likely make it unpleasant
to use if it were necessary to euthanize a large number
of animals.350
One advantage of euthanasia using a shotgun is
that when properly directed the birdshot will have sufficient energy to penetrate the skull but is unlikely to
exit the skull. In the case of a free bullet or shotgun slug
there is always the possibility of the bullet or slug exiting the skull, creating an injury risk for operators and
observers. For operator and bystander safety, the muzzle of a shotgun (or any other firearm) should never be
held directly against the animal’s head. Discharge of the
firearm results in development of enormous pressure
within the barrel that can result in explosion of the barrel if the muzzle end is obstructed or blocked.
Penetrating captive bolt—Penetrating captive bolts
are used for euthanasia of mature cattle in field situations. Styles include in-line (cylindrical) and pistol grip
(resembling a handgun) versions. Pneumatic captive
bolt guns (air powered) are limited to use in slaughter
plant environments. Models using gunpowder charges
are more often used in farm environments. They consist
of a steel bolt and piston at one end, housed within a
barrel. Upon firing, the rapid expansion of gas within
the breech and barrel propels the piston forward driving the bolt through the muzzle. A series of cushions
are strategically located within the barrel to dissipate
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
excess energy of the bolt. Depending upon model, the
bolt may automatically retract or require manual placement back into the barrel through the muzzle. Accurate placement over the ideal anatomic site, energy (ie,
bolt velocity), and depth of penetration of the bolt determine effectiveness of the device to cause a loss of
consciousness and death. Bolt velocity is dependent on
maintenance of the captive bolt gun (cleaning and replacement of worn parts), as well as proper storage of
the cartridge charges. Bolt velocities of 55 to 58 m/s
are desirable for effective captive bolt use in slaughter
plants.332,333,465,466 Recommended minimum bolt velocities proposed for shooting bulls are as high as 70 m/s.
In slaughter plants where bolt velocity is of particular
concern, bolt velocity is routinely monitored to assure
proper function of these devices.467
In general, captive bolt guns, whether penetrating
or nonpenetrating, induce immediate loss of consciousness, but death is not always assured with the use of
this device alone. In a study of 1,826 fed steers and heifers only 3 (0.16%) had signs of a return to sensibility or
consciousness.336 Results were similar in observations
of 692 bulls and cows where 8 (1.2%) animals had signs
consistent with a return to consciousness.336 Failure to
achieve a 100% loss of consciousness with no return
to a conscious mental state was attributed to storage of
the captive bolt charges in a damp location, poor maintenance of firing pins, inexperienced personnel operating the captive bolt (use of the incorrect anatomic
site), misfires associated with a dirty trigger on the captive bolt, and use of the device on cows and bulls with
thick, heavy skulls.336
At the present time, an adjunctive method such as
exsanguination, pithing, or the IV injection of a saturated solution of potassium chloride is recommended to
ensure death when penetrating captive bolt is used.347 A
newer version of penetrating captive bolt has emerged
in recent years.130 This device is equipped with an extended bolt with sufficient length and cartridge power
to increase damage to the brain, including the brainstem. This device is being studied at the present time
and may offer a euthanasia option with the penetrating
captive bolt that does not require the need for an adjunctive method.
Captive bolt guns are attractive options for euthanasia because they offer a greater degree of safety to
the operator and bystanders; but they should only be
used by trained people. The muzzle should always be
pointed toward the ground and away from the body or
bystanders in case of accidental discharge. Protective
gear for both ears and eyes is strongly recommended.
Unlike techniques described for gunshot, the animal must be restrained for accurate placement of the
captive bolt. And, unlike use of a firearm, proper use of
the captive bolt requires that the muzzle of the device be
held firmly against the animal’s head. Once the animal
is restrained, discharge of the captive bolt should occur
with little or no delay so that animal distress is minimized. Adjunctive methods should be implemented as
soon as the animal is rendered unconscious to avoid a
possible return to sensibility. Thus, when conducting
euthanasia by captive bolt, preplanning and preparation improves the likelihood of a successful outcome.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Visual indicators that an animal has been rendered
unconscious from captive bolt or gunshot include the
following: immediate collapse; brief tetanic spasms followed by uncoordinated hind limb movements; immediate and sustained cessation of rhythmic breathing;
lack of coordinated attempts to rise; absence of vocalization; glazed or glassy appearance to the eyes; and
absence of eye reflexes.101 Nervous system control of
the blink or corneal reflex is located in the brainstem;
therefore, the presence of a corneal reflex is highly suggestive that an animal is still conscious.
Anatomic landmarks for use of the penetrating captive bolt and gunshot—In cattle, the point of entry of the
projectile should be at the intersection of two imaginary lines, each drawn from the outside corner of the
eye to the center of the base of the opposite horn, or
an equivalent position in polled animals (Figure 10).342
Figure 10—Anatomic site for gunshot or placement of a captive
bolt and desired path of the projectile in cattle. The point of entry
of the projectile should be at the intersection of two imaginary
lines, each drawn from the outside corner of the eye to the center of the base of the opposite horn, or an equivalent position
in polled animals. (Adapted with permission from Shearer JK,
Nicoletti P. Anatomical landmarks. Available at: www.vetmed.iastate.edu/vdpam/extension/dairy/programs/humane-euthanasia/
anatomical-landmarks. Accessed Jun 24, 2011.)
53
Firearms should be positioned so that the muzzle is
perpendicular to the skull to avoid ricochet. Proper positioning of the firearm or penetrating captive bolt is
necessary to achieve the desired results.
Use of the poll (bony protuberance on the top of
the skull) for application of the penetrating captive
bolt in slaughter plants is not allowed by regulations
in the European Union because the depth of concussion in this region is less than that observed in frontal
sites.468 Conversely, for large bulls and water buffalo use
of the frontal site for administration of a captive bolt
is not always effective because of the thickness of the
hide and skull in this region. Use of the poll position
can be effective if the appropriate captive bolt gun is
used and when the muzzle is directed so that the discharged bolt will enter the brain;469 however, in most
cases the poll position is not preferred. Research has
demonstrated that use of the penetrating captive bolt
at the poll is prone to operator error and misdirection
of the bolt into the spinal cord instead of the brain.469
More animals were not properly rendered unconscious
(ie, depth of concussion was shallow) using the poll
position as compared with frontal sites.
Placement of the captive bolt is critical to ensure
that the bolt enters the brain and not the spinal cord.
Shots from the poll should be directed toward the base
of the tongue unless brainstem tissues are needed for
diagnostic reasons. Whether poll shooting is conducted
by penetrating captive bolt or gunshot, there is substantial potential for misdirection of the bullet or bolt
and damage to the brain to achieve unconsciousness or
death is not assured. This will result in delays in loss of
consciousness and a greater likelihood of variable periods of extreme distress.
S3.2.1.3 Adjunctive Methods
S3.2.1.3.1 Noninhaled Agents
Potassium chloride and magnesium sulfate—While
not acceptable as a sole method of euthanasia, rapid IV
injection of potassium chloride may assist in ensuring
death after cattle have been rendered unconscious by
penetrating captive bolt, gunshot, or administration of
general anesthetics (α-2-adrenergic agents such as xylazine alone are insufficient; see comments under Unacceptable methods). Normally, injection of 120 to 250
mL of a saturated solution of potassium chloride is sufficient to cause death; however, the potassium chloride
solution should be administered until death is assured.
When conducting euthanasia of cattle that may require
subsequent administration of potassium chloride, the
operator should prepare at least 3 to four 60-mL syringes of solution (equipped with 14- or 16-gauge needles)
in advance. This will facilitate rapid administration and
ensure the animal does not regain consciousness. Any
available vein may be used; however, it is important to
position oneself out of the reach of limbs and hooves
that may cause injury during periods of involuntary
movement. In most cases, it is safest to kneel down near
the animal’s back and close to the animal’s head where
one can reach over the neck to administer the injection
into the jugular vein. Once the needle is in the vein, the
injection should be delivered rapidly.
54
Magnesium sulfate may be administered similarly
to potassium chloride. Death may not occur as rapidly,
but similar to administration of potassium chloride,
residue risks for predators and scavengers are low (see
Noninhaled Agents).
S3.2.1.3.2 Physical Methods
Second shot—Although one well-placed bullet or
shot from a penetrating captive bolt usually results in
immediate loss of consciousness with little likelihood of
return to consciousness, one should always be prepared
to deliver a second or even a third shot if necessary. The
additional injury to brain tissue along with increased
hemorrhage and edema creates substantial intracranial
pressure. Compression resulting from this increase in
pressure interrupts centers in the brain that control respiratory and cardiac functions and leads to death.
Exsanguination—Exsanguination may be performed as an adjunctive measure to ensure death when
necessary in an unconscious animal. Exsanguination
is usually accomplished via an incision of the ventral
aspect of the throat or neck transecting skin, muscle,
trachea, esophagus, carotid arteries, jugular veins, and
a multitude of sensory and motor nerves and other
vessels. This procedure is not recommended as a sole
method of euthanasia; rather it is reserved for use as an
adjunctive method to ensure death since information
in the literature is inconsistent as to the length of time
between the neck cut and loss of consciousness. Some
studies418,470 demonstrate a rapid loss of brain activity
(measured by EEG) with little variation between individual animals. In contrast, direct observation of time
to collapse and EEG data indicate that the time from
ventral-neck incision to unconsciousness is variable
and may be quite prolonged in animals killed by exsanguination.417,471–474
Uncertainty in the time from the neck incision to
loss of consciousness raises obvious questions: Does
the animal feel pain during the neck cut? Does the drop
in blood pressure cause discomfort or distress? Opinions on these questions remain divided. Some hold the
view that when the knife (sakin in Hebrew) is of appropriate size, exceptionally sharp, completely free of
blemishes or imperfections, and used in such manner
as to create a rapid clean incision (such as performed
by a shochet), exsanguination is relatively painless.475
Others contend that tissues of the neck are well innervated with nocioceptive nerve fibers such that transection leads to significant pain and distress sufficient to
cause shock at the time of incision.476–478
In recognition that this issue remains controversial
and that people conducting these procedures for the
purposes of euthanasia are not likely to have a sakin
or the skills of a shochet, the recommendation is that
exsanguination only be used in unconscious animals
as an adjunctive method to assure death. It should be
performed with a pointed, very sharp knife with a rigid
blade at least 6 inches long and conducted as soon as
the loss of consciousness is confirmed.
Exsanguination can be disturbing to observe due to
the large volume of blood loss; this also raises biosecurity concerns. When only the carotid arteries and jugular
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
veins are cut, bleeding may persist at variable rates for
several minutes. Severing these vessels closer to the thoracic inlet where the vessels are larger will increase blood
flow rate. Some evidence suggests that restricted blood
flow may be caused by the formation of false aneurysms
in the severed ends of arteries in cattle.474
Pithing—Pithing is a technique designed to cause
death by increasing destruction of brain and spinal
cord tissue. It is performed by inserting a pithing rod
through the entry site produced in the skull by a bullet
or penetrating captive bolt. The operator manipulates
the pithing tool to destroy brainstem and spinal cord
tissue to ensure death (see Physical Methods). Muscular activity during the pithing process is often quite
violent, but is followed by quiescence that facilitates
exsanguination or other procedures.420
the gun never be held flush with the skull. Instead, the
muzzle of the gun should be aimed in the desired direction and held no closer than 6 to 12 inches from the
target.
Penetrating and nonpenetrating captive bolts—The
principal anatomic sites for application of captive bolts
in small ruminants are the frontal and poll positions
(Figure 11). In sheep with horns, the poll position is
S3.2.2 Sheep and Goats
Euthanasia of small ruminants may be necessary
for reasons ranging from traumatic injury to incurable
disease. Methods include barbiturate overdose, gunshot, or captive bolt followed by an adjunctive method
such as exsanguination, IV administration of potassium
chloride or magnesium sulfate, or pithing. Electrocution is another option, but this method requires specialized equipment to restrain the animal for proper
placement of the electrodes. Because electricity and the
necessary equipment are unlikely to be available for
euthanasia under field conditions, electrocution is not
considered to be practical for routine use.
S3.2.2.1 Acceptable Methods
S3.2.2.1.1 Noninhaled Agents
Barbiturates and barbituric acid derivatives—Barbiturates act by depression of the CNS, which progresses
from a state of consciousness to unconsciousness, deep
anesthesia, and eventually death. Although use of these
agents requires restraint and involves mild discomfort
(ie needle placement) for administration, observers
generally find this a more acceptable method of euthanasia because death comes about more peacefully.
In the companion animal setting, these attributes are
highly desirable. In production settings, concerns for
cost and disposal of animal remains make this method
a less attractive euthanasia option.
S3.2.2.2 Acceptable With Conditions Methods
S3.2.2.2.1 Physical Methods
Gunshot—Firearms recommended for euthanasia
of adult small ruminants include the .22 LR rifle; .38
Special, .357 Magnum, and 9 mm or equivalent handguns; and shotguns. Some prefer hollow-point bullets
to increase brain destruction and reduce the chance of
ricochet. However, operators are reminded that bullet
fragmentation may substantially reduce the potential
for brain destruction because of reduced penetration,
particularly when used in large-horned adult rams.
Shotguns or higher-caliber firearms loaded with solidpoint bullets are preferred in these conditions. When
firearms are used for euthanasia it is important that
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Figure 11—Anatomic sites for gunshot or placement of captive
bolts and desired path of the projectile in sheep and goats. For
polled sheep (top), the proper site is at or slightly behind the poll
aiming toward the angle of the jaw (ie, base of tongue). For heavily horned rams or ewes (bottom), the proper site is high on the
forehead aiming toward the foramen magnum (or spinal canal) or,
alternatively, at or slightly behind the poll (i.e., behind the bony
ridge between the horns) aiming toward the angle of the jaw or
base of the tongue. The brain of a mature goat lies in a more caudal position in the skull than one would expect. The proper site for
use of the penetrating captive bolt or free bullet is from behind
the poll aiming toward the muzzle and lower part of the chin. In
mature horned sheep and goats the hardness of the skull may
deflect some projectiles. (Adapted with permission from Shearer
JK, Nicoletti P. Anatomical landmarks. Available at: www.vetmed.
iastate.edu/vdpam/extension/dairy/programs/humane-euthanasia/anatomical-landmarks. Accessed Jun 24, 2011.)
55
often preferred. Use of a captive bolt in the poll position
was evaluated, using 8 anesthetized sheep.468 Projection
of the shot was on a line running between the bases of
the ears and aiming toward the throat. Cortical visual
evoked responses (ie, measures of light flash–evoked
responses in the electrocorticogram) were evaluated to
determine effectiveness. Visual evoked responses were
abolished in all animals immediately following shooting with the captive bolt. However, in 5 of the 8 sheep,
visual evoked responses were recovered after approximately 50 seconds. These results indicate that using the
poll position for application of captive bolts to sheep
may be associated with rapid recovery of brain function. Therefore, adjunctive methods to ensure death
should be applied immediately following loss of consciousness in small ruminants.
Effective application of the captive bolt in sheep
and goats is indicated by immediate loss of consciousness lasting until death by exsanguination or another
adjunctive method. While it is presumed that penetration of the bolt causes insensibility, research into the
determinants of effective captive bolt use indicates that
the impact of the bolt on the cranium is a principal
contributor to the loss of consciousness.333 The use of
concussive methods (nonpenetrating captive bolt) has
been determined to be an effective means of inducing
insensibility that will persist until death caused by exsanguination.465
Anatomic landmarks for captive bolts and gunshot—
The location for placement of a captive bolt or entry
of a free bullet for euthanasia is similar for both sheep
and goats. The optimal position for hornless sheep and
goats is the top of the head on the midline.342 An alternate site is the frontal region.342 For heavily horned
sheep and goats, the optimal site is behind the poll aiming toward the angle of the jaw.342
S3.2.2.3.2 Physical Methods
Second shot—Although one well-placed bullet or
shot from a penetrating captive bolt usually results in
immediate loss of consciousness with little likelihood
of return to consciousness, one should always be prepared to deliver a second or even a third shot if necessary. The additional injury to brain tissue along with
increased hemorrhage and edema creates sufficient
intracranial pressure to cause death in most cases, but
damage to the brainstem should always be the objective
in euthanasia.
Exsanguination—Exsanguination may be performed as an adjunctive step to ensure death when necessary in small ruminants. It may be accomplished via
an incision of the ventral aspect of the throat or neck
transecting skin, muscle, trachea, esophagus, carotid
arteries, and jugular veins. Exsanguination should be
performed with a pointed, very sharp knife with a rigid
blade at least 6 inches long.
Exsanguination can be disturbing for bystanders
because of the large volume of blood loss, which also
raises biosecurity concerns. When only the carotid arteries and jugular veins are cut, bleeding may persist at
variable rates for several minutes. Severing these vessels closer to the thoracic inlet where the vessels are
larger will increase blood flow rate.
Pithing—Pithing is a technique designed to cause
death by increasing destruction of brain and spinal
cord tissue. It is performed by inserting a pithing rod
through the entry site produced in the skull by a bullet
or penetrating captive bolt. The operator manipulates
the pithing tool to destroy brainstem and spinal cord
tissue to ensure death (see Physical Methods). Muscular activity during the pithing process is often quite
violent, but is followed by quiescence that facilitates
exsanguination or other procedures.420
S3.2.2.3 Adjunctive Methods
S3.2.2.4 Unacceptable Methods
S3.2.2.3.1 Noninhaled Agents
Potassium chloride and magnesium sulfate—Although not acceptable as a sole method of euthanasia,
the rapid IV injection of potassium chloride is an effective method to ensure death in sheep and goats previously rendered unconscious by penetrating or nonpenetrating captive bolt, gunshot, or administration
of anesthetics. When conducting euthanasia of sheep
and goats that may require subsequent administration
of potassium chloride, the operator should prepare at
least one or two 30-mL syringes of solution (equipped
with an 18-gauge needle) in advance. This will facilitate
rapid administration and ensure the animal does not
regain consciousness. Any available vein may be used;
however, it is important to position oneself out of the
reach of limbs and hooves that may cause injury during
periods of involuntary movement. Once the needle is in
the vein, the injection should be delivered rapidly.
Magnesium sulfate may be administered similarly
to potassium chloride. Death may not occur as rapidly,
but similar to administration of potassium chloride,
residue risks for predators and scavengers are low (see
Noninhaled Agents).
56
The following methods are unacceptable for euthanasia of cattle and small ruminants: manually applied
blunt trauma to the head; injection of chemical agents
into conscious animals (eg, disinfectants, electrolytes
such as potassium chloride and magnesium sulfate,
nonanesthetic pharmaceutical agents); administration
of xylazine or any other α2 adrenergic receptor agonist followed by IV potassium chloride or magnesium
sulfate (although large doses of α2 adrenergic receptor
agonists can produce a state resembling general anesthesia, they are recognized as being unreliable for that
purpose479), drowning, or air embolism (ie, injection
of air into the vasculature); and electrocution with a
120-V electrical cord, drowning, and exsanguination in
conscious animals.
S3.2.2.5 Neonates
Neonatal calves, lambs, and kids—Neonatal calves
present special challenges for euthanasia. Methods include barbiturate overdose, gunshot, and captive bolt
(penetrating or nonpenetrating) with an adjunctive
method applied to ensure death. Manually applied blunt
force trauma to the head is not acceptable for calves
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
because their skulls are too hard to achieve immediate
destruction of brain tissue leading to unconsciousness
and death. Manually applied blunt force trauma is also
difficult if not impossible to apply consistently because
of the degree of restraint required and complications in
positioning calves, lambs, and kids for conducting this
procedure.
Barbiturate overdose may be used for euthanasia
of neonatal calves, lambs, and kids. In noncommercial
situations, this method may be preferred over physical
methods. Drawbacks include temporary animal distress
associated with restraint and needle placement, challenges associated with disposal of remains (residue
concerns), a requirement for DEA registration, and because the use of barbituates is extralabel for these species, administration by or under the supervision of a
veterinarian. Assuming these conditions can be met,
barbiturate overdose is generally less objectionable to
owners and observers than other methods.
Use of a penetrating or purpose-built nonpenetrating captive bolt (controlled blunt force trauma) is acceptable with conditions for calves, lambs, and kids.
Controlled blunt force trauma differs from manually
applied blunt force trauma because captive bolts deliver an appropriate and uniform amount of force each
time they are fired, and structural brain damage is more
consistent. Studies480 using controlled blunt force trauma methods found that focal as well as diffuse injury
caused by penetrating and nonpenetrating captive bolt
pistols was similar and sufficient for both to be considered as effective for euthanasia of lambs. Based on electrophysiologic evidence,333 researchers determined that
the primary determinant of effective shooting is the
impact of the bolt and not penetration of the bolt into
brain tissues. In contrast, one report481 credits structural changes including focal damage adjacent to the
wound track and damage to peripheral tissues of the
cerebrum, cerebellum, and brainstem as the predominant factors affecting the loss of respiratory function
and consciousness.
Because calves’, lambs’, and kids’ skulls and craniums are smaller, physical methods such as gunshot
and captive bolt require accurate placement and direction of the bullet or bolt to assure penetration of the
brain and brainstem. The captive bolt device should
be placed on the intersection of two lines each drawn
from the lateral canthus of the eyes to the site of horn
formation on the contralateral (opposite) side. Directing the bolt toward the foramen magnum increases
likelihood of damaging the brainstem; but this may
be difficult since this structure is a relatively small
target in neonates. This highlights the reason why an
adjunctive method such as exsanguination, pithing, or
the rapid IV administration of a saturated solution of
potassium chloride or magnesium sulfate is necessary
in neonates.
S3.2.2.6 Dams and Fetuses
Prerequisites for the sensation of pain, distress, or
pleasurable experiences are sentience and consciousness. Both are necessary for animals to experience either positive or negative states. Behavioral and EEG
evidence indicates that mammalian fetuses are insenAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
tient and unconscious throughout the first 75% to 80%
of gestation.432 As neuronal pathways between the cerebral cortex and thalamus become better established,
the fetus develops the capacity for sentience. However,
while maintained within the protected environment of
the animal’s uterus it remains in an unconscious state
due to the presence of eight or more neuroinhibitors
that act on the cerebral cortex of the fetus to maintain it
in the sleep-like state of unconsciousness. At birth, the
combined effects of reduced neuroinhibition and onset
of neuroactivation contribute to gradual arousal of the
mammalian newborn into a state of consciousness that
occurs within minutes to several hours after birth.432
These observations indicate that the fetus does not
suffer as if drowning in amniotic fluid when the dam is
euthanized; nor is it likely to experience pain associated with other types of invasive procedures in utero.
These studies also support the rationale for international guidelines on the handling of fetuses suggesting that
fetuses should not be removed from the uterus before
the EEG is most likely to be isoelectric. For example,
when animals are euthanized by physical methods that
include exsanguination, delaying removal of the fetus from the uterus for a minimum of 5 minutes after
hemorrhaging has ceased generally assures a substantial amount of anoxia-induced damage to the cerebral
cortex that will normally prevent progression toward
a return to sensibility.482 If there is any doubt as to the
fetus’s level of consciousness, it should be euthanized
immediately by captive bolt and adjunctive methods as
appropriate.
The unconscious state of the fetus also addresses
the welfare concerns of those who fear that the collection of tissues (in particular, fetal calf blood by intracardiac puncture) from live fetuses in the immediate postslaughter period creates undue suffering. Although the
heart may continue to beat (which is necessary for the
successful collection of fetal blood), in the absence of
breathing there is little likelihood of return to a state of
consciousness.482 These are by no means insignificant
concerns as there is high demand for fetal tissues to
support laboratory research. A 2002 report483 suggests
that world demand for fetal calf serum was 500,000 L/y
and growing, a need that would require the harvest of
at least 1,000,000 fetuses/y.
The information derived from these observations
also has application for fetal rescue situations that may
involve euthanasia of late-term pregnant dams by physical methods. The reason why one might attempt this
is to avoid remains disposal complications from drug
residues as would occur if the fetus were to be delivered
by caesarian section using standard surgical methods.
Although respiration is interrupted, the heart continues
to beat in animals rendered unconscious using physical methods. Therefore, it may be possible to rescue a
fetus from an unconscious dam by caesarian section if
the procedure can be performed before the fetus suffers irreversible effects of anoxia. Once the fetus is successfully delivered, euthanasia of the dam may be confirmed via any of the previously described adjunctive
methods. It is important to understand that there are
significant risks to fetal welfare if rescue is attempted.
Welfare complications associated with fetal rescue at57
tempts would include impaired brain function caused
by anoxia occurring during the rescue attempt, compromised respiratory function and body heat production resulting from fetal immaturity, and greater risk of
infection as a consequence of failure of passive transfer
of immunity.432,484,485 When the value of the fetus justifies the effort to secure a successful live delivery, the
preferred approach to assure fetal health and welfare
is by caesarian section using standard surgical procedures.
Barbiturates and barbituric acid derivatives—Pentobarbital readily crosses the placenta resulting in fetal
depression in pregnant animals. However, death of the
dam normally precedes the death of the fetus. In one
study486 cardiac arrest in lambs was delayed for as long
as 25 minutes beyond the death of the dam. Similar observations in mice demonstrated that death of the fetuses could only be achieved by the use of doses well
in excess of those normally required for euthanasia.487
Based on these observations, one could offer a similar
recommendation to that provided previously for death
by exsanguination whereby fetuses should be retained
within the uterus for at least 15 to 20 minutes after maternal death has occurred to prevent the delivery of viable fetuses.
S3.3 SWINE
Methods of euthanasia commonly applied to swine
include CO2, Ar, N2, gas mixtures, gunshot, nonpenetrating and penetrating captive bolts, overdose of an anesthetic administered by a veterinarian, electrocution,
and blunt force trauma (in suckling piglets only). Selection of the most appropriate method for each situation
is dependent upon size and weight of the animal, availability of equipment and facilities, operator skill and
experience with the procedure, aesthetic concerns, human safety, and options for disposal of remains. Certain
physical methods of euthanasia may require adjunctive
methods such as exsanguination or pithing to ensure
death. A brief description of each method and appropriate candidates for it are described. Detailed information on inhaled, noninhaled, and physical methods of
euthanasia may be found in the respective sections of
this document.
S3.3.1 Mature Sows, Boars, and
Grower-Finisher Pigs
Methods usually used for euthanasia of sows, boars,
and grower-finisher pigs include gunshot, penetrating
captive bolt, electrocution, and barbiturate overdose.
Use of physical methods of euthanasia requires
direct contact with the animal, and therefore restraint
is necessary. Use of a snare is the most common form
of restraint for adult swine. Studies488–495 demonstrate
varying degrees of stress associated with restraint by
snaring techniques. To minimize stress associated
with snaring, personnel conducting euthanasia of
swine are advised to make advance preparations (eg,
prepare the site, load the gun or captive bolt) so that
the time during which the animal must be restrained
is minimized.
58
S3.3.1.1 Acceptable Methods
S3.3.1.1.1 Noninhaled Agents
Barbiturates and barbituric acid derivatives—Mature sows, boars, and grower-finisher pigs may be
euthanized by IV administration of euthanasia solutions containing barbiturates.496 A dosage of 1 mL/5 kg
(0.45 mL/2.3 lb) up to 30 kg (66 lb), then 1 mL/10 kg
(0.45 mL/4.5 lb) thereafter, has been recommended.497
This method may not cause death if a lethal dose is not
administered IV. Barbituates are not commonly used
in field conditions, but may be applicable in some settings. Because these drugs are controlled substances
they must be administered by personnel who are registered with the US DEA, and extralebel use requires
administration by or under the supervision of a veterinarian. Strict record keeping is required of all who use
and store these drugs.
Many find euthanasia by the IV administration of
a barbituate less displeasing than gunshot, captive bolt,
or electrocution. Therefore, it is preferred in some settings. A disadvantage of this method of euthanasia is
that tissues from animals euthanized with barbiturates
may not be suitable for diagnostic evaluation. Furthermore, options for disposal of animals euthanized with
barbiturates are complicated by concerns for residues
that create risks for scavengers and other domesticated
animals that may consume portions of the animal’s remains, and renderers may not accept animal remains
contaminated with barbiturate residues.
S3.3.1.2 Acceptable With Conditions Methods
S3.3.1.2.1 Inhaled Agents
Carbon dioxide, nitrogen, and argon—Studied gas
mixtures include N2 with CO2; Ar, alone and with
CO2; and CO. Inhaled agents are most commonly used
as a method of euthanasia in slaughter plants, and are
considered to be acceptable with conditions. Inhaled
agents have greater application for pigs weighing 70
lb or less, rather than grower-finisher pigs or mature
sows and boars. Gas combinations (eg, CO2 and Ar)
have been shown to be effective alternatives to CO2
alone, and when the concentration of CO2 is high,
duration of exposure ensures unconsciousness is followed by death. These methods are described in greater detail for the euthanasia of nursery pigs and in the
section on Inhaled Agents.
S3.3.1.2.2 Physical Methods
Gunshot—Gunshot is commonly used for euthanasia of growing and adult swine. When properly conducted using the appropriate firearm, euthanasia by
gunshot produces immediate loss of consciousness and
rapid death. There are three possible sites for conducting euthanasia in swine: frontal, temporal, and from behind the ear toward the opposite eye (Figure 12). The
frontal site is in the center of the forehead slightly above
a line drawn between the eyes. The projectile should be
directed toward the spinal canal. The temporal site is
slightly anterior and below the ear. Specific sites may
vary slightly according to breed.351,352,498
Because of the thickness of the pig’s skull, muzzle
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
may be captured in an earthen surface. Shotguns may
be used at short range and offer the advantage of less
potential for bullet ricochet. Twelve-, 16- or 20-gauge
shotguns are recommended for mature pigs. The muzzle should never be held flush to the skull.
Gunshot is an effective, low-cost method of euthanasia when properly performed. Firearms are readily
available in most areas. Human safety is the primary
concern with the use of gunshot for euthanasia. Proper
training on firearm safety and use is imperative and
gunshot should only be performed by personnel who
have had appropriate training.
Figure 12—There are three possible sites for conducting euthanasia in swine: frontal, temporal and from behind the ear toward
the opposite eye. The frontal site is in the center of the forehead
slightly above a line drawn between the eyes. The bolt or bullet
should be directed toward the spinal canal. The temporal site is
slightly anterior and below the ear. The ideal target location and
direction of aim may vary slightly according to breed and the age
of the animal (due to growth of the frontal sinuses). (Adapted
with permission from Shearer JK, Nicoletti P. Anatomical landmarks. Available at: www.vetmed.iastate.edu/vdpam/extension/
dairy/programs/humane-euthanasia/anatomical-landmarks.
Accessed Jun 24, 2011.)
energies of 300 ft-lb or more are required for euthanasia
of adult sows, boars, and growing-finishing pigs. When
the alternate site behind the ear is chosen, a .22 caliber
firearm loaded with a solid-point bullet may be used.
Wadcutters and fragmenting bullets should not be used
for euthanasia of adult swine. Potential for ricochet is
reduced when euthanasia by gunshot can be conducted
outdoors where bullets that pass through the animal
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Penetrating captive bolt—Use of well-maintained
penetrating captive bolt guns with ammunition appropriately selected for the size of the animal is acceptable
with conditions as a method of euthanasia for growing
and adult swine.499,500 Proper application of the penetrating captive bolt requires restraint of the animal
because the device must be held firmly against the forehead over the site described for gunshot (Figure 12).
When performed correctly, the pig drops to the floor
immediately, exhibiting varying amounts of tonic and
clonic muscle movements. Confirmation that the animal has been rendered insensible includes observation
of the following: rhythmic breathing stops, no righting
reflex is observed, vocalization is absent, and no palpebral reflexes or responses to noxious stimuli are present. All pigs should be observed for evidence of these
responses until death has been confirmed.
Death following use of the penetrating captive
bolt is commonly achieved, but is not assured depending upon bolt length and depth of the frontal sinus in
mature sows and boars. Therefore, secondary steps to
ensure death (eg, a second application of the penetrating captive bolt, exsanguination, pithing) should be applied as necessary. Breed differences result in variable
skull shapes making determination of the best anatomic site for conducting euthanasia in mature sows and
boars difficult.352
Penetrating captive bolts offer safety advantages
compared with firearms. Properly applied, the method
is very effective and costs associated with its use are
minimal. However, it is important that penetrating captive bolt guns be maintained regularly (cleaning and
replacement of worn parts) and that cartridge charges
be stored properly to ensure appropriate bolt velocity.
Bolt length and ammunition requirements for effective
single-step euthanasia vary for different sizes and maturities of pigs. Using a captive bolt of inappropriate
length or with insufficient charge reduces effectiveness.
Personnel must be trained in the proper use of penetrating captive bolts to ensure effective euthanasia.
Electrocution—Electrocution as a sole method of euthanasia can achieve death via 2-step or single-step processes.359,373,501–508 Electrical current must pass through
the brain to achieve loss of consciousness, but then must
cross the heart to cause fibrillation and cardiac arrest. As
a 2-step process, electrode placements are head-head,
followed by head to flank, for the appropriate time. For a
single-step process for euthanasia, head to opposite flank
is an example of appropriate placement.
59
Head-only electrocution induces a grand mal seizure and immediate unconsciousness, but death does
not occur unless followed by head-to-heart electrocution or the application of an adjunctive method to ensure death such as exsanguination373,509 or pithing. The
secondary step, whether head-to-heart electrocution or
another method, must be performed within 15 seconds
of onset of unconsciousness; otherwise, the animal may
regain consciousness. Head-only electrocution is performed by placement of the electrodes in one of three
positions: between the eyes and base of the ears on either
side of the head; below the base of the ears on either side
of the head; or diagonally, below one ear to above the
opposite eye. Placement of electrodes for head-to-heart
electrocution is on the head in front of the brain (some
use the base of the ear) with a secondary electrode attached to the body behind the heart on the opposite side.
This assures diagonal movement of current through the
animal’s body. With specific electrode placement, current
of 110 V at a minimum frequency of 60 Hz applied for
a minimum of 3 seconds is sufficient for euthanasia of
pigs up to 125 kg.510 Systems used for electrocution must
be capable of meeting minimum current requirements to
ensure insensibility in the head-only method, and insensibility and cardiac fibrillation in the head-heart method.
Electrocution is effective as a single-step process
with appropriate tong or clamp placement. However,
proper training and special equipment must be used to
ensure adequate and safe euthanasia. While electrocution is commonly used to render animals insensible in
slaughter plants and safety precautions in that environment are routine, for implementation on-farm where use
of the method is less common, extra precautions may
need to be taken to ensure human safety. Agonal gasping
may be evident after current is withdrawn and may be
aesthetically unacceptable for observers and operators.
S3.3.1.3 Adjunctive Methods
Exsanguination—While not appropriate as a sole
method of euthanasia, exsanguination may be performed
as a secondary step to ensure death when necessary.
Pithing—While not appropriate as a sole method of
euthanasia, pithing may be performed as a secondary
step to ensure death when necessary.
More information about these methods is available
in the Physical Methods section of the Guidelines.
S3.3.2 Nursery Pigs (70 lb or Lighter)
Nursery pigs may be euthanized by use of CO,
CO2, gunshot, penetrating captive bolt, purpose-built
nonpenetrating captive bolt, electrocution, or anesthetic overdose. Descriptions of the use of CO2 and
nonpenetrating captive bolt for euthanasia of young
pigs follow. For details on other methods please see the
preceding information in this section or the Physical
Methods section of the Guidelines.
S3.3.2.1 Acceptable Methods
S3.3.2.1.1 Noninhaled Agents
Bartiburates and barbituric acid derivatives—Nursery pigs may be euthanized by IV administration of
60
euthanasia solutions containing barbiturates. Because
these drugs are controlled substances they must be administered by personnel who are registered with the US
DEA. Strict record keeping is required of all who use
and store these drugs.
Many find euthanasia by the IV administration of
an anesthetic less aesthetically displeasing than administration of CO2, captive bolt, or electrocution. Therefore, it is preferred in some settings. A disadvantage of
this method is that tissues from animals euthanized with
barbiturates may not be suitable for diagnostic evaluation and cannot be used for food. Furthermore, options
for disposal of animals euthanized with barbiturates are
complicated by concerns for residues that create risks
for scavengers and other domesticated animals that
may consume portions of the animal’s remains.
S3.3.2.2 Acceptable With Conditions Methods
S3.3.2.2.1 Inhaled Agents
Carbon dioxide—Carbon dioxide alone or in combination with N2 or Ar has been used successfully for
euthanasia.206,208,212,250,252,511 Properly applied, inhalation
of CO2 is an effective method of euthanasia. On the
other hand, if air exchange rates are not carefully controlled and monitored, animals may suffer substantial
stress from suffocation prior to loss of consciousness
and death (see Inhaled Agents section of Guidelines).
Conducting this procedure on small pigs requires
a container large enough for the size and number of
pigs to be euthanized. Pigs may be exposed to CO2 by
gradually displacing ambient gases (introducing CO2
into the container) or by introducing the animals into a
prefilled environment. In the gradual-fill approach, pigs
are placed in an enclosed container and CO2 flow is initiated at a rate and for a time to reach a level sufficient
to achieve euthanasia. In the prefill approach, a concentrated environment of CO2 is created, pigs are placed in
that environment, and CO2 flow is resumed to maintain
effective euthanasia concentrations. In both methods,
exposure of pigs with normal respiration to a constant
supply of 80% to 90% CO2 for a minimum of 5 minutes
is necessary for effective euthanasia.211,214,251,512–518
Carbon dioxide offers advantages for euthanasia,
including that it is relatively inexpensive, nonflammable and nonexplosive, and clean (no blood loss).
Drawbacks to the use of CO2 are that it requires special
equipment and training for efficient and safe application, and that there is little published research on appropriate techniques for euthanizing young (neonatal
and growing) pigs. Systems must be able to achieve a
level of anesthesia while not causing hypothermia. An
appropriate pressure-reducing regulator and flow meter
capable of generating the recommended displacement
rates for the size container being utilized is absolutely
necessary. Death must be verified following administration of CO2. This can be done by examination of individual animals or adherence to validated exposure
processes proven to result in death.352 If an animal is
not dead, exposure must be repeated or followed with
another method of euthanasia.
For young pigs, movement during the induction
phase has caused some to question the degree of stress
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
that may be induced with this method. Some interpret
these movements as indications of aversion. While this
may be the case in systems that are not functioning properly, there is evidence that such reactions may be normal
for pigs in an unconscious state.214,515,516 Small or incapacitated piglets have low tidal volumes and will not die
as rapidly as larger, more viable pigs. Carbon dioxide
euthanasia in chamber settings has not been extensively
studied for larger pigs. Meyer and Morrow148 recommend
that chamber volume be exchanged at least 2.5 times to
accommodate the wash-in–washout principle regardless of the size of swine to be euthanized. Monitoring of
equipment and gas must be routine and consistent to ensure there is always sufficient gas to accomplish the objective of euthanasia. Carbon dioxide containers should
never be placed in an unventilated area due to risks associated with an overdose of gaseous CO2 for humans.
S3.3.2.2.2 Physical Methods
Nonpenetrating captive bolt—A purpose-built nonpenetrating captive bolt may be used for euthanasia of
young pigs. The concussive impact of the bolt induces
an immediate loss of consciousness that when followed
by an adjunctive method to ensure death meets the criteria for euthanasia. The nonpenetrating captive bolt
works best in younger pigs before the frontal bones are
fully developed and hardened.
Use of a proper functioning nonpenetrating captive
bolt with appropriate charges offers the advantage of
delivering a uniform concussive force to the skull (controlled blunt force trauma). This reduces the potential
for ineffective stunning and euthanasia that may occur
more often with the use of manually applied blunt force
trauma. However, this method requires immediate application of an adjunctive method to ensure euthanasia.
Electrocution—Electrocution is acceptable with
conditions for swine weighing more than 10 lb. Details
are provided earlier in this section and in the Physical
Methods section of the Guidelines.
S3.3.3 Suckling Pigs
Options for the euthanasia of suckling pigs include
CO2; Ar, N2 and CO2 mixtures; CO; inhaled anesthetics; purpose-built nonpenetrating captive bolt; electrocution (for pigs over 10 lb); anesthetic overdose; and
blunt force trauma. Described are the application of
barbituates, nonpenetrating captive bolt, manually applied blunt force trauma, and CO2. See previous sections of the Guidelines for more detailed information
on the application of other euthanasia techniques.
S3.3.3.1 Acceptable Methods
S3.3.3.1.1 Injectable Agents
Bartiburates and barbituric acid derivatives—Suckling pigs may be euthanized by IV administration of
euthanasia solutions containing barbiturates. Because
these drugs are controlled substances they must be administered by personnel who are registered with the US
DEA, and extralabel use requires administration by or
under the supervision of a veterinarian. Strict record
keeping is required of all who use and store these drugs.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Many find euthanasia by the IV administration of
an anesthetic less displeasing than administration of
CO2, captive bolt, manually applied blunt force trauma,
or electrocution. Therefore, it is preferred in some settings. A disadvantage of this method is that tissues from
animals euthanized with barbiturates may not be suitable for diagnostic evaluation. Furthermore, options
for disposal of animals euthanized with barbiturates
are complicated by concerns about residues that create risks for scavengers and other domesticated animals
that may consume portions of the animal’s remains
S3.3.3.2 Acceptable With Conditions Methods
S3.3.3.2.1 Inhaled Agents
Carbon dioxide—Carbon dioxide may be effective
as a method of euthanasia for small groups of neonatal
piglets; however, the parameters of the technique need
to be optimized and published to ensure consistency
and repeatability. In particular, the needs of piglets with
low tidal volumes must be explored.
S3.3.3.2.2 Physical Methods
Nonpenetrating captive bolt—The purpose-built
nonpenetrating captive bolt can be an effective method
of euthanasia for young piglets.519–521 Loss of consciousness and death are caused by a severe nonpenetrating
concussive force applied to the forehead of the piglet.
The utility of the nonpenetrating captive bolt is focused
on the unique condition in suckling and young pigs
where the frontal bones are not fully developed, leaving the brain susceptible to blunt, high-velocity impact.
When used in appropriately sized and aged pigs
a secondary step to ensure death is unnecessary. Use
of the nonpenetrating captive bolt (controlled blunt
force trauma) is currently being studied with positive
results for use in young swine. The nonpenetrating captive bolt can be powered pneumatically or through the
use of appropriate ammunition. Some brands of captive
bolt guns have been made versatile by providing different heads (varying length of bolt and penetrating or
nonpenetrating end), and ammunition for various-size
pigs, which allows the same gun to be used in different
situations. Current research indicates that euthanasia
using a nonpenetrating captive bolt is effective assuming sufficient power afforded by gun design and the use
of appropriate ammunition.519,520
Manually applied blunt force trauma—Manually applied blunt force trauma, when performed correctly,
meets the definition of euthanasia, namely causing minimal distress with rapid loss of consciousness leading to
death. As for the nonpenetrating captive bolt, the utility
of manually applied blunt force trauma is based on the
unique condition in suckling and young pigs where the
frontal bones are not fully developed, leaving the brain
susceptible to blunt, high-velocity impact. This method
is less aesthetically acceptable than other alternatives,
but when properly performed, death is rapid. Uncertainty of success often causes repeated application or
selection of an alternative euthanasia method.520 The
AVMA encourages those using manually applied blunt
force trauma to the head as a euthanasia method to ac61
tively search for alternatives to ensure that criteria for
euthanasia can be consistently met.
S3.4 POULTRY
Euthanasia methods for poultry (domesticated
birds used for egg, meat, or feather production [eg,
chickens, turkeys, quail, pheasants, ducks, geese]) include gas inhalation, manually applied blunt force trauma, cervical dislocation, decapitation, electrocution,
gunshot, captive bolt, and injectable agents. Where appropriate, additional comments are included to address
physiologic differences among avian species, variations
in environment, and the size or age of birds.
S3.4.1 Acceptable Methods
S3.4.1.1 Noninhaled Agents
Overdoses of injectable anesthetics, including barbiturates and barbituric acid derivatives—Poultry may be
euthanized by IV injection of overdoses of anesthetics,
including barbiturate and barbituric acid derivatives.
Because these drugs are controlled substances they
must be administered by personnel who are registered
with the US DEA, and extralabel use requires administration by or under the supervision of a veterinarian.
Strict record keeping is required of all who use and
store these drugs.
Many find administration of an anesthetic less displeasing than administration of CO2, CO, captive bolt,
manually applied blunt force trauma, cervical dislocation, decapitation, or electrocution. Therefore, it may be
preferred in some settings. A disadvantage of this method
is that tissues from animals euthanized with barbiturates
may not be used for food and may not be suitable for
diagnostic evaluation. Furthermore, options for disposal
of animals euthanized with barbiturates are complicated
by concerns for residues that create risks for scavengers,
other domesticated animals that may consume portions
of the animal’s remains, and humans.
S3.4.2 Acceptable With Conditions Methods
S3.4.2.1 Inhaled Agents
Inhaled gases may be used satisfactorily for euthanasia of poultry, and detailed information about the
various types of inhaled gases is available in the Inhaled Agents section of the Guidelines. When inhaled
gases are used for euthanasia, birds should be checked
to verify death because they may appear dead but can
regain consciousness if the exposure time or the concentration of the agent is insufficient. Gases must be
supplied in purified forms without contaminants or
adulterants, typically from a commercially supplied cylinder or tank. The gas-dispensing system should have
sufficient capacity and control to maintain the necessary gas concentrations in the container being utilized,
and the container itself should be sufficiently airtight to
hold the gas at appropriate levels.
Carbon dioxide—The most common gas used for
euthanasia of poultry is CO2, and its application has
been extensively studied for chickens, turkeys, and
ducks with information available about behavioral re62
sponses, times to collapse, unconsciousness, death,
loss of somatosensory evoked potentials, loss of visually evoked responses, and changes in EEG and ECG
(see Inhaled Agents section of the Guidelines). Carbon
dioxide has successfully been applied for euthanasia
of nonhatched eggs (pips), newly hatched poultry in
hatcheries, and adult birds (including routine euthanasia of large commercial laying hen flocks356,522) and
on farms keeping birds for research or elite genetics.
Because neonatal birds may be more accustomed to
high concentrations of CO2 (incubation environments
typically include more CO2), concentrations necessary
to achieve rapid euthanasia of pipped eggs or newly
hatched chicks may be substantially greater (as high as
80% to 90%) than for adults of the same species.
Carbon dioxide may invoke involuntary (unconscious) motor activity in birds, such as flapping of the
wings or other terminal movements, which can damage
tissues and be disconcerting for observers.248,270 Slower
induction of euthanasia in hypercapnic atmospheres
reduces the severity of convulsions after loss of consciousness.204,205 Death normally occurs within minutes, depending on the species and the concentration
of CO2 present in the closed chamber.
Carbon monoxide—Carbon monoxide may also be
used for euthanasia of poultry. More convulsions may
be observed in the presence of CO than normally occur when CO2 is used for euthanasia.188 The CO flow
rate should be sufficient to rapidly achieve a uniform
concentration of at least 6% after birds are placed in
the chamber (see Inhaled Agents section). Only pure,
commercially available CO should be used. The direct
application of products of combustion or sublimation
is not acceptable due to unreliable or undesirable composition and or displacement rate. Appropriate precautions must be taken to ensure human safety because CO
has a cumulative effect in binding hemoglobin.
Nitrogen or argon—Nitrogen or Ar, mixed or used
alone, with approximately 30% CO2 is acceptable with
conditions for euthanasia of poultry provided the residual atmospheric O2 level can be reduced to and held
at sufficiently low levels (eg, 2% to 3%).267,523 These
agents tend to cause more convulsions (eg, wing flapping) than CO2 in air (see Inhaled Agents section of
the Guidelines).204,269 It has also been noted that convulsions may start when consciousness, at least to some
degree, may still be a possibility.256,524
S3.4.2.2 Physical Methods
The following methods are acceptable with conditions
for euthanasia of poultry. Euthanasia methods should be
chosen based on the welfare of the bird, human safety, skill
and training of personnel, availability of equipment, and
the ability to adequately restrain the bird.
Cervical dislocation—When performed on conscious poultry, cervical dislocation must result in luxation of the cervical vertebrae without primary crushing
of the vertebrae and spinal cord. Manual or mechanical
cervical dislocation may be used for poultry of an appropriate size and species when performed by compeAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
tent personnel who correctly apply the technique. In
some classes of poultry there is evidence that cervical
dislocation may not cause immediate unconsciousness.337–339,354 The legs of the bird should be grasped (or
wings if grasped at the base) and the neck stretched by
pulling on the head while applying a ventrodorsal rotational force to the skull. Crushing of cervical vertebrae
and spinal cord is not acceptable unless the bird is first
rendered unconscious.
Decapitation—Decapitation is acceptable with conditions for the euthanasia of poultry when performed
by competent personnel. Decapitation should be executed with a sharp instrument, ensuring rapid and unobstructed severing of the head from the neck. Use of a
bleeding cone may facilitate restraint.
Manually applied blunt force trauma—Euthanasia
by manually applied blunt force trauma to the head
is acceptable with conditions for turkeys or broiler
breeder birds that are too large for cervical dislocation.
Manually applied blunt force trauma must be correctly
applied by competent personnel. Operator fatigue can
lead to inconsistency in application, creating concern
that the technique may be difficult to apply humanely
to large numbers of birds. For this reason, the AVMA
encourages those using manually applied blunt force
trauma to the head as a euthanasia method to search
for alternatives.
Electrocution—Electrocution is acceptable with
conditions for euthanasia of individual birds. Birds
subjected to electrocution should be observed to ensure
death or an adjunctive method, such as exsanguination
or cervical dislocation, should be performed immediately afterwards to ensure death. A small percentage of
birds do not develop ventricular fibrillation even when
exposed to high amperage current.
Gunshot—Gunshot is acceptable with conditions
for free-ranging poultry and ratites when capture or restraint would potentially be highly stressful for the animal or dangerous for humans. Gunshot is not recommended for captive poultry where restraint is feasible.
Penetrating and nonpenetrating captive bolt—Captive bolts (penetrating or nonpenetrating) are acceptable
with conditions for euthanasia of large poultry (turkeys,
broiler breeders, ratites, waterfowl, etc) when performed
by competent personnel. The captive bolt pistol must be
used in accordance with the manufacturer’s recommendations and the bird should be appropriately restrained
to avoid injury to personnel. Birds should be observed
following captive bolt administration to ensure that
death occurs. Any bird showing signs of recovery must
receive a second shot or be killed by some other means
that is acceptable for a conscious bird.
S3.4.3 Adjunctive Methods
Potassium chloride or magnesium sulfate—Although
IV or intracardiac administration of potassium chloride or magnesium sulfate to a conscious bird as a sole
method of euthanasia is unacceptable, it is acceptable
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
to administer these agents to a bird that is fully anesthetized or otherwise unconscious as a means to ensure
death.
Exsanguination—Although exsanguination of a
conscious bird is an unacceptable method of euthanasia, it is acceptable to exsanguinate birds that are fully
anesthetized or otherwise unconscious as a means to
ensure death. Biosecurity precautions during and following exsanguination should be observed as part of
appropriate disease control.
S3.4.4 Embryos and Neonates
In addition to methods involving inhaled agents
mentioned previously, the following methods are acceptable with conditions for euthanasia of embryos or
neonates.
Embryonated eggs may be destroyed by prolonged
exposure (20 minutes) to CO2, cooling (4 hours at
40°F), or freezing.52 In some cases inhaled anesthetics
can be administered through the air cell at the large end
of the egg. Egg addling can also be used.416 Embryos in
eggs that may have been opened may be decapitated.
Maceration, via use of a specially designed mechanical apparatus having rotating blades or projections,
causes immediate fragmentation and death of newly
hatched poultry and embryonated eggs.271 A review by
the American Association of Avian Pathologists406 of the
use of commercially available macerators for euthanasia
of chicks, poults, and pipped eggs indicates that death
by maceration in poultry up to 72 hours old occurs
immediately with minimal pain and distress. Maceration is an alternative to the use of CO2 for euthanasia of
poultry up to 72 hours old. Maceration is believed to be
equivalent to cervical dislocation and cranial compression as to time to death, and is considered to be an acceptable means of euthanasia for newly hatched poultry by the Federation of Animal Science Societies,407
Agriculture Canada,408 World Organisation for Animal
Health,342 and European Council.525
Maceration requires special equipment that must
be kept in excellent working order. Newly hatched
poultry must be delivered to the macerator in a way and
at a rate that prevents a backlog at the point of entry
into the macerator and without causing injury, suffocation, or avoidable distress before maceration.
S4. EQUIDS
Methods acceptable with conditions are equivalent
to acceptable methods when all criteria for application
of a method are met.
S4.1 GENERAL CONSIDERATIONS
S4.1.1 Human Safety
When equids are euthanized, consideration should
be given to the unpredictability of a falling or thrashing
equid. Most methods of euthanasia will result in some
degree of exaggerated muscular activity after the equid
falls even if the equid is not experiencing pain or distress. Whatever euthanasia method is used should not
put personnel at unnecessary risk.
63
S4.1.2 Disposal of Remains
For equids euthanized with pentobarbital, disposal
of remains must be carried out promptly through commercial rendering, on-farm burial, incineration or cremation, direct haul to a solid waste landfill, or biodigestion. This will help prevent exposure of wildlife and domestic animals to potentially toxic barbiturate residues.
Disposal of remains must be conducted in accord with
all federal, state, and local regulations.
S4.2 METHODS
S4.2.1 Acceptable Methods
S4.2.1.1 Noninhaled agents
Barbiturates or barbituric acid derivatives—Pentobarbital or a pentobarbital combination is the principal choice for equine euthanasia by chemical means.
Because a large volume of solution must be injected,
use of an IV catheter placed in the jugular vein will facilitate the procedure. To facilitate catheterization of
an excitable or fractious equid, a tranquilizer, such as
acepromazine, or an α2-adrenergic receptor agonist can
be administered, but these drugs may prolong time to
loss of consciousness because of their effect on circulation and may result in varying degrees of muscular
activity and agonal gasping. Opioid agonists or agonistantagonists in conjunction with α2-adrenergic receptor
agonists may further facilitate restraint.
S4.2.2 Acceptable With Conditions Methods
S4.2.2.1 Physical Methods
Penetrating captive bolt and gunshot—Penetrating
captive bolt and gunshot are considered acceptable with
conditions for euthanasia of equids. Both should only
be used by well-trained personnel who are regularly
monitored to ensure proficiency, and firearms must be
well maintained. Appropriate restraint is required for
application of the penetrating captive bolt and special
care should be taken to ensure that personnel are not
injured by ricochet from free bullets.
The correct anatomic site for application of gunshot and penetrating captive bolt is illustrated in Figure
13.526 The site for entry of the projectile is described
as being on the intersection of two diagonal lines each
running from the outer corner of the eye to the base of
the opposite ear.
S4.2.3 Adjunctive Methods
Potassium chloride—Although unacceptable when
used in unanesthetized equids, the use of a saturated
solution of potassium chloride injected IV or intracardially in an equid in a deep surgical plane of general
anesthesia is an acceptable method to invoke cardiac
arrest and death.
S4.2.4 Unacceptable Methods
Chloral hydrate—Chloral hydrate has an almost
immediate sedative action, but unless it is combined
with other anesthetics, onset of anesthesia is delayed.
Associated adverse effects can be severe and aesthetically objectionable, and chloral hydrate also has limited
64
Figure 13—Anatomic site for the application of gunshot or penetrating captive bolt for euthanasia of equids. The point of entry
of the projectile should be at the intersection of two imaginary
lines, each drawn from the outside corner of the eye to the center of the base of the opposite ear. (Adapted with permission
from Shearer JK, Nicoletti P. Anatomical landmarks. Available at:
www.vetmed.iastate.edu/vdpam/extension/dairy/programs/humane-euthanasia/anatomical-landmarks. Accessed Jun 24, 2011.)
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
availability. For these reasons, chloral hydrate is an unacceptable means of euthanizing equids.
S4.3 SPECIAL CASES AND EXCEPTIONS
In emergency situations, such as euthanasia of an
equid with a serious injury at a racetrack or another
equestrian event, it may be difficult to restrain a dangerous equid for IV injection. While administration of
a sedative might be desirable, in some situations it is
possible the equid could injure itself or bystanders before a sedative could take effect. In such cases, a neuromuscular blocking agent (eg, succinylcholine) may
be administered to the equid IM or IV, but the equid
must be euthanized via an appropriate method as soon
as the equid can be controlled. Succinylcholine alone
or without sufficient anesthetic is not acceptable for
euthanasia.
S5. AVIANS
Methods acceptable with conditions are equivalent
to acceptable methods when all criteria for application
of a method are met.
S5.1 GENERAL CONSIDERATIONS
The following comments and recommendations
pertain to pet, aviary, falconry, racing, research, and zoo
birds. Information about appropriate euthanasia methods for wild birds can be found in the Captive and FreeRanging Nondomestic Animals section of the Guidelines, whereas euthanasia of poultry and other birds
used for food is addressed in the Animals Farmed for
Food and Fiber section.
Few peer-reviewed reports are available in the scientific literature about euthanasia of individual or small
groups of birds. The information that does exist comprises anecdotal accounts in book chapters, guidelines
from various associations, and journal roundtable discussions and editorials.63,265,270,413,414,511,527–530 There are
scientific studies337,354,524,531–533 comparing various methods for depopulation of commercial poultry, but these
methods may or may not meet the criteria for euthanasia, and may or may not be applicable to individual
birds or small groups of birds.
Because this taxa comprises more than 8,000 species, the choice of euthanasia method for a particular
bird will depend greatly on its species, size, anatomic
and physiologic characteristics, environment, degree
of domestication, clinical state, and anticipated and
actual response to restraint. Personnel performing euthanasia should be familiar with the species being euthanized, be able to interpret avian behavior indicative
of stress, and use their knowledge and experience to
choose restraint and euthanasia options that alleviate
or minimize distress and result in rapid death. Legal
requirements may apply in cases involving endangered
or migratory species.
S5.1.1 Anatomy and Physiology
Birds differ anatomically and physiologically from
mammals and these differences will affect whether and
how particular euthanasia methods may be acceptably
applied. Because birds lack a diaphragm, they have a
single coelomic cavity, rather than separate thoracic
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
and abdominal cavities. When giving intracoelomic injections care must be taken that material is not injected
into the air sacs, which could potentially drown the bird
or expose its respiratory system to irritating substances.
Air sacs act as a bellows to ventilate birds’ small, nonexpanding lungs.534 Because there is no diaphragm, birds
need to be able to move their sternum ventrally and
cranially to breathe.535 Birds also have hollow, pneumatic bones, such as the humerus and femur, which
communicate directly with the respiratory system. Preeuthanasia and euthanasia drugs should not be administered via the intraosseous route into the humerus or
femur because drowning or irritation to the respiratory
system may occur. Intraosseous catheters can, however,
be safely placed in birds, preferably in the distal ulna or
proximal tibiotarsus.
A bird’s respiratory system has greater capacity to
process air than a mammal’s due to a unique unidirectional flow of air through the lungs (which prevents
mixing of inspired and expired air), more efficient gas
exchange, and a greater surface area over which O2 can
be exchanged (more and smaller air capillaries [3 µm]
than the smallest mammalian alveoli [35 µm]).535 Because of their greater capacity to process air, birds are
more sensitive than mammals to inspired toxicants (eg,
the proverbial canary in the coal mine collapsing before
humans detect the methane in the air).536
S5.1.2 Restraint
Manual restraint for administering pre-euthanasia or euthanasia drugs is possible for many bird species. Nets or other equipment may be required or may
improve conditions for both birds and people when
handling birds less acclimated to human contact (eg,
birds in zoos, wild birds). Multiple personnel may be
required to safely handle larger species, such as ratites,
and at least one additional person should be available to
assist in case of an emergency. Chemical restraint may
be useful in some situations, particularly for dangerous
birds where human safety may be compromised by efforts at manual restraint. Drugs used for chemical restraint that are administered at high doses may serve as
the first step of a 2-step euthanasia process.
S5.2 METHODS
Individual birds in a clinical or research setting
can best be rendered unconscious by use of an inhaled
agent (eg, isoflurane, sevoflurane, or halothane), prior
to IV administration of an acceptable injectable euthanasia agent (eg, sodium pentobarbital). The following
methods are considered to be acceptable or acceptable
with conditions for avian species. For more detailed,
non–species-specific information on various agents
and methods, please refer to the Inhaled Agents, Noninhaled Pharmaceutical Agents, and Physical Methods
sections of the Guidelines.
S5.2.1 Acceptable Methods
S5.2.1.1 Noninhaled Agents
Intravenous injection of an injectable euthanasia
agent is the quickest and most reliable means of euthanizing birds when it can be performed without causing
65
fear or distress. Wild, fearful, or excited birds may require a sedative or anesthesia before IV injection can be
performed. When IV injection is impossible, injectable
euthanasia agents can be administered via intracoelomic, intracardiac, or intraosseous routes only if a bird
is unconscious or anesthetized. If the intracoelomic
route is used for birds, injection into the air sacs must
be avoided, because of the potential for respiratory
compromise, irritation of the respiratory system, and
delayed absorption via the air sacs. Euthanasia agents
should also not be administered via the intraosseous
route into the humerus or femur because of the potential for drowning or irritation to the respiratory system.
Regardless of the route of administration, injectable
agents can precipitate in tissues and can induce artifacts
at necropsy and on histopathologic examination.270,528
Barbiturates and barbituric acid derivatives can be
administered IV for euthanasia of anesthetized or properly restrained unanesthetized birds. Barbiturates commonly used for injection are available as sodium salts
that are alkaline and may be irritating and painful when
injected directly into tissues, rather than IV. Therefore,
when IV injection is impossible, injectable euthanasia
agents can be administered via intracoelomic, intracardiac, or intraosseous routes only if a bird is unconscious, or anesthetized. Concepts regarding barbiturate
use in mammals generally also apply to birds and more
information is available in the Noninhaled Agents section of the Guidelines.
S5.2.2 Acceptable With Conditions Methods
S5.2.2.1 Inhaled Agents
Inhaled anesthetics—Inhaled anesthetics may be
used at high concentrations as a sole method of euthanasia or may be used to render birds unconscious prior
to application of other methods of euthanasia.265,416 Exposure to high concentrations of inhaled anesthetics
(eg, halothane, isoflurane, sevoflurane, with or without
N2O) is acceptable with conditions for euthanasia for
birds. Birds exposed to high concentrations of inhaled
anesthetic gases lose consciousness rapidly. Euthanasia
via inhaled gases may be more practical than use of an
injectable agent if large numbers of birds, such as in
flock or aviary situations, must be euthanized. Euthanasia by exposure to gas anesthetics also induces minimal tissue damage and results in the least amount of
tissue artifact for necropsy.270,528
Carbon dioxide—High (> 40%) concentrations of
CO2 induce anesthesia initially followed by loss of consciousness. Euthanasia via exposure to CO2 has been
described for individual birds and small groups,265 and
its application to euthanasia of chickens, turkeys, and
ducks has been studied extensively, resulting in information regarding times to collapse, unconsciousness,
and death; loss of somatosensory evoked potentials;
loss of visually evoked responses; and changes in EEG
and ECG.255,531–533 Application rate of CO2 needs to be
balanced with situational needs as rapid increases in
CO2 concentration decrease the amount of time to loss
of posture and consciousness, while slower increases
in concentration may cause less aversion or reaction,
66
but increase time of exposure. Field applications of
CO2 for broilers have resulted in stress levels similar
to that invoked via routine handling537 or stress and
distress similar to the handling or restraint required
for other methods of euthanasia.533 In a recent study,
most turkeys would voluntarily enter a feeding chamber filled with Ar (90%), or a mixture of Ar (60%) and
CO2 (30%), compared with only 50% of turkeys that
would voluntarily enter the chamber when filled with
a high concentration of CO2 (72%) alone, suggesting
an aversion to 72% CO2.196 More research is needed to
better understand this comparative aversion in turkeys
(eg, whether it is dose or species dependent and availability of agent).
Concepts regarding the use of CO2 in mammals as
described in the Inhaled Agents section of the Guidelines generally also apply to birds. Exposure to CO2
may cause involuntary (unconscious) motor activity,
such as flapping of the wings, which can damage tissues and be disconcerting to, and potentially dangerous
for, observers.248,270
There are some special considerations for the use
of CO2 for euthanasia of birds. Neonatal birds may be
more acclimated to high CO2 concentrations, because
the unhatched bird’s environment typically has a high
CO2 concentration (as high as 14% in the embryonic
chicken). Consequently, CO2 concentrations required
to achieve euthanasia of newly hatched chicks may be
much higher (as much as 80% to 90%) than those for
adults of the same species.416,533 Diving birds also have
physiologic adaptations to hypercapnia and may require higher CO2 concentrations for euthanasia.
Carbon monoxide—Concepts regarding the use of
CO for euthanasia of mammals also apply to birds. See
the Inhaled Agents section of the Guidelines for details.
Nitrogen and argon—Inert gases such as N2 and
Ar, and gas mixtures involving these gases (including
mixtures with CO2), have been used for euthanasia of
poultry,538 but are not recommended for euthanasia of
companion birds.
Behavioral responses of broiler chickens were examined during short (10 seconds) exposures to 100%
Ar, 100% N2, or mixtures (80% Ar / 20% N2 and 80%
N2 / 20% Ar). Normal feeding and no aversive behaviors were observed.203 Birds appear to not have intrapulmonary chemoreceptors for N2 and Ar, and this may
account for a lack of aversion during their initial exposure to and hypoxia from these gases.538 As a euthanasia agent, Ar gas mixed with < 2% O2 was shown to
induce rapid loss of posture (average, 11 seconds), convulsions (average, 22 seconds), unconsciousness, and
death (isoelectric EEG in 1 minute).198 Convulsions
can occur during euthanasia with these inert gases, but
because these signs occurred after collapse and loss of
consciousness, these gases are considered to be humane
for the birds involved.538
S5.2.2.2 Physical Methods
Physical methods of euthanasia may be necessary
in some field situations if other methods of euthanasia
are impractical or impossible to implement. That said,
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
there is little scientific information available regarding
the effect of various physical methods on electrical activity in the brain of birds, which makes evaluation of
the humaneness of these procedures difficult.
Cervical dislocation—Cervical dislocation has generally been used for small birds (< 200 g) when no
other method is available, but the procedure has been
performed on birds as large as 2.3 kg (5.1 lb). It should
only be performed by well-trained personnel who are
regularly monitored to ensure proficiency. Skilled individuals have been able to humanely perform cervical
dislocation in poultry. There is limited research specific to birds concerning electrical activity in the brain
following cervical dislocation. Cervical dislocation of
chickens (average weight of 2.3 kg) did not result in
loss of visually evoked responses in 90% of cases when
compared with use of a percussion bolt pistol, suggesting that fewer than 10% of cervical dislocations resulted in concussion.354 In 3-week-old turkeys (average
weight of 1.6 kg [3.5 lb]) time to insensibility (based
on nictitating membrane movement) was longer, but
time to death (based on cessation of movement) was
shorter after cervical dislocation compared with use of
a nonpenetrating captive bolt and blunt force trauma.337
Whether pain is perceived is not known. Consciousness
and perception of pain are not necessarily concurrent.
Decapitation—Based on information currently
available, decapitation is considered to be acceptable
with conditions for euthanasia of small (< 200 g) birds.
The AAZV Guidelines for Euthanasia of Nondomestic
Animals416 also lists decapitation as acceptable with
conditions, and suggests the method may be preferred
over cervical dislocation under certain field conditions
due to clear evidence of a successful procedure. One
study54 indicated that several methods of partial, mechanical decapitation of chickens (weighing 2.1 to 3.5
kg [4.6 to 7.7 lb]) did not result in the loss of visually
evoked responses in 90% of cases when compared with
use of a percussion bolt pistol and concluded that fewer
than 10% of cervical dislocations resulted in concussion. In another study decapitation applied to anesthetized chickens resulted in visually evoked responses
up to 30 seconds following decapitation, but because
the responses were obtained from anesthetized chickens it is not possible to conclude any association with
cognitive processes.52–54 As indicated previously (see
discussion of Consciousness and Unconsciousness in
the Guidelines), at some level between behavioral unresponsiveness and the induction of a flat EEG, consciousness must vanish; however, EEG data cannot provide definitive answers as to onset of unconsciousness.
Gunshot—Gunshot is not recommended as a method for captive birds, where restraint is feasible. Its use
for wild birds is addressed in the Captive and FreeRanging Nondomestic Animals section of the Guidelines.
S5.2.3 Adjunctive Methods
Potassium chloride—Although administration of
potassium chloride to a conscious, unanesthetized bird
is considered to be an unacceptable method of euthanaAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
sia, potassium chloride may be administered via the IV
or intracardiac routes if a bird is unconscious or completely anesthetized prior to the injection.
Exsanguination—Although exsanguination of a
conscious, unanesthetized bird is an unacceptable approach to euthanasia, exsanguination may be used for
euthanasia of unconscious or anesthetized birds. This
approach may be appropriate if blood samples are needed for diagnostic or research purposes.
Thoracic compression—Although thoracic compression of a conscious, unanesthetized bird is an unacceptable approach to euthanasia, it may be used as an
adjunctive method for animals that are insentient.
S5.2.4 Unacceptable Methods
Thoracic (cardiopulmonary, cardiac) compression
is a method that has been used by biologists to terminate
the lives of wild, small mammals and birds mainly under field conditions when other methods are not available. Although thoracic compression has been used extensively in the field, data supporting this method, including level of distress and times to unconsciousness
or death, are not available. Based on current knowledge
of avian physiology and euthanasia, thoracic compression can result in significant levels of pain and distress
before animals become unconscious, thus lacking key
humane considerations that can be addressed by other
methods. Various veterinary and allied groups do not
support thoracic compression as a method of euthanasia.413–416 Consequently, thoracic compression is generally an unacceptable means of euthanizing animals that
are not deeply anesthetized or insentient due to other
reasons, but is appropriate as a secondary method for
animals that are insentient. Details are available in the
Physical Methods section of the Guidelines.
S5.3 EGGS, EMBRYOS, AND NEONATES
Bird embryos that have attained > 50% incubation
have developed a neural tube sufficient for pain perception; therefore they should be euthanized by similar methods used in avian neonates such as anesthetic
overdose, decapitation, or prolonged (> 20 minutes)
exposure to CO2.52,132,416 Eggs at < 50% incubation may
be destroyed by prolonged exposure (> 20 minutes) to
CO2,334 cooling (< 4°C for 4 hours), or freezing.52,416 Anesthesia can be used prior to euthanasia and is most
easily accomplished with exposure to inhaled anesthetics via entry into the air cell at the large end of the egg.
Egg addling can also be used to destroy the viability of
embryos.416
S6. FINFISH AND AQUATIC INVERTEBRATES
S6.1 GENERAL CONSIDERATIONS
Finfish and aquatic invertebrates play important
roles as food, pets, research subjects, display animals,
sources of recreation, and key components of healthy
ecosystems. In each of these situations it may be necessary to cause the death of some animals. Considerable
evidence is accumulating suggesting it is appropriate to
consider the possibility of pain perception in these spe67
cies.66,71–73,539–547 The aim is to accomplish death for these
animals rapidly with the minimum amount of pain and
distress practicable. Because the environment associated
with finfish and aquatic invertebrates in each of their
roles is different, and because knowledge about the evolutionary and societal status of poikilothermic animals
(lower vertebrates and invertebrates) is limited, identifying and applying appropriate criteria for euthanasia can
be difficult.
S6.1.1 Terms Applicable to Ending Life
Specific to finfish, the three main terms used to describe the ending of life are euthanasia, slaughter, and
humane killing (Table 2). There is often confusion regarding how these terms and their associated methods
differ. The methods described in the Guidelines serve as
guidance for veterinarians and others who may need to
perform euthanasia. The Guidelines are not intended to
specifically address slaughter or humane killing methods.
Slaughter is used primarily to describe the humane killing
of animals intended for human consumption for food or
other uses (eg, agricultural harvest, commercial fishing).
Humane killing is less specific and can be used to describe
some recreational fishing practices and may also include
activities such as finfish sampling, depopulation, eradication, and control to eliminate unwanted finfish (including
diseased or nonnative finfish) from a water body. A fourth
term, harvest, specifically refers to the act or process of
gathering a crop, as in aquaculture and commercial fishing; however, harvest may also be used to describe finfish
removed from a water body by anglers. Whether harvested
finfish are slaughtered or humanely killed depends on the
context of the activity.548–551 Neither slaughter nor humane
killing is addressed by this document. Addressing euthanasia of invertebrates in some settings is not meant to
discount the necessity for and suitability of slaughter and
pest control techniques that do not meet the definition of
euthanasia. Nor is the intent of this document to advocate
the expansion of coverage of IACUC to invertebrates.
S6.1.2 Human and Animal Considerations
Because of the diversity of physiologic and anatomic
characteristics seen among species of finfish and aquatic
invertebrates, optimal methods for euthanasia will vary.
Euthanasia choices for finfish and aquatic invertebrates
must account for animal stress responses and human
safety concerns associated with handling, as well as differences in metabolism, respiration, and tolerance to cerebral hypoxia. Virtually all methods require that personnel be carefully trained and monitored (although some
carry more risks of human ineffectiveness than others),
some require DEA registration and record keeping, extralabel use requires administration by or under the supervision of a veterinarian, and chemicals regulated by
the EPA can only be legally used according to their label
directions. Intracoelomic injections carry an inherent
risk of organ damage and response time may vary. Intravenous injections require careful handling of finfish, as
well as trained and experienced personnel. Intramuscular injections with ketamine, α2 adrenergic receptor agonists, or Telazolh can be administered via pole syringe or
dart gun to larger finfish to facilitate handling and reduce
handling stress for finfish, but rarely achieve surgical
planes of anesthesia in teleosts. In all cases, veterinarians
and others with expertise relevant to the species of interest should be consulted; professional judgment and relevant expertise should be taken into account when ultimately determining the best method to use. In addition,
it is often more difficult to ascertain when a finfish or an
aquatic invertebrate is dead as compared with birds and
mammals. Some unique aspects of euthanasia for finfish
have been described.552,553
S6.1.3 Preparation and Environment
As a general principle the preparations for euthanasia of finfish should be very similar to the preparations
for anesthesia of finfish.554–556 If possible, withholding
food for 12 to 24 hours prior to euthanasia will reduce
regurgitation, defecation, and nitrogenous waste production. The environment should be as quiet and nonstimulatory as possible given the circumstances. Light
intensity should be reduced if possible, but with adequate lighting for personnel. This can also be achieved
through use of a dark or opaque container and lid, or by
use of less intense lighting, (eg, red light illumination,
as red light does not penetrate water well).
Table 2—Terms used to describe the deliberate ending of the lives of finfish. (Adapted with permission from Yanong RPE, Hartman KH,
Watson CA, et al. Fish slaughter, killing, and euthanasia: a review of major published US guidance documents and general considerations of methods. Publication #CIR1525. Gainesville, Fla: Fisheries and Aquatic Sciences Department, Florida Cooperative Extension
Service, Institute of Food and Agricultural Sciences, University of Florida, 2007. Available at: edis.ifas.ufl.edu/fa150. Accessed May 16,
2011.)
Term
Possible applications
Examples
Slaughter
•Agricultural harvest
•Commercial fisheries
•Catfish, salmon, and tilapia
•Wild-caught grouper and snapper
Humane killing
•Recreational fisheries
•Depopulation or eradication
•Control
•Sampling
•Largemouth bass and red drum
•Nonnative species eradication (eg, walking catfish)
•Population disease control or testing (eg, outbreaks of spring viremia of carp
[SVC*] or viral hemorrhagic septicemia [VHS*])
•Large-scale ecological research, open ocean collection
•Pets
•Zoo animals
•Laboratory research
•Some field research
•Hobbyist koi and goldfish, tropical finfish
•Public aquarium shark
•Small-scale toxicology work in zebra danios
•Some small-scale ecological research
Euthanasia
*Spring viremia of carp (SVC) and viral hemorrhagic septicemia (VHS) are viral diseases that are under international and national regulatory
control and for which depopulation of infected populations is warranted.
68
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Water quality should be similar to that of the environment from which the finfish originated, or optimized for that species and situation, for the duration
of euthanasia. If of acceptable quality for finfish health,
water in which they have been house or captured
should be used, and supplemental aeration and temperature control may be necessary. Either the immersion
euthanasia solution is prepared with water from the
finfish housing system and the finfish are transferred
into it or a concentrated form of the anesthetic agent
as a solution (containing buffering agent if appropriate) is introduced directly into the container of finfish
to minimize stressors. If euthanizing a large population
of finfish, it is important to monitor the anesthetic bath
water quality (temperature, dissolved O2, and organic
loading, in particular). The euthanasia agent may need
to be supplemented or replaced periodically. Euthanasia methods should be tested in one animal or a small
group of animals prior to use in a large population for
an unfamiliar species.325 If handling is required, appropriate equipment (nets, gloves) should be used to minimize stressors.
S6.1.4 Indicators of Death in Finfish
and Aquatic Invertebrates
Because the thousands of species of finfish and
aquatic invertebrates vary greatly in anatomic and
physiologic characteristics, reliable indicators of death
may not be available for some. However, there are some
standard approaches that can be useful for many of the
more commonly encountered species. Loss of movement, loss of reactivity to any stimulus, and initial flaccidity (prior to rigor mortis) may serve as indicators of
death for finfish and some aquatic invertebrates. More
useful indicators for many finfish include respiratory
arrest (cessation of rhythmic opercular activity) for a
minimum of 10 minutes and loss of eyeroll (vestibuloocular reflex, the movement of the eye when the finfish
is rocked from side to side). The latter is no longer present in finfish that have been deeply anesthetized or euthanized.557 The heart can continue to contract even after brain death or removal from the bodies of finfish,558
so the presence of a heartbeat is not a reliable indicator
of life, but sustained absence of heartbeat is a strong
indicator of death. For more sessile, less active organisms, or those with specific anatomic or physiologic adaptations that prevent use of these indicators, it may be
more difficult to assess loss of consciousness and death,
and consultation with species experts is recommended.
S6.1.5 Disposition of Euthanized Animals
Any euthanized finfish or invertebrate should be
promptly removed from its aquarium, pond, or other
vessel and disposed of according to all pertinent federal, state, and local regulations, in a manner that will
reduce the risk of disease spread, prevent pests and
other nontarget species from gaining access to animal
remains, and ensure human and environmental safety.
Preventing environmental contamination by any life
stage of finfish that could hatch and/or survive outside
an acceptable, enclosed body of water is an important
consideration in confirmation of death and disposal of
the animal’s remains.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
S6.1.6 Finfish and Aquatic Invertebrates
Intended for Human Consumption
As previously indicated, the term slaughter is used
primarily to refer to the killing of animals intended for
human consumption (eg, agricultural harvest, commercial fisheries) and these Guidelines are not intended
to address that activity. However, when euthanasia of
animals intended for human consumption is desired,
tissue residues from the use of drugs and other chemicals will make many methods unacceptable unless they
have been approved by the FDA for this purpose and
appropriate withdrawal periods are followed. Use of
any unapproved chemicals for euthanasia prohibits entry of the finfish into the food chain, either by rendering, as fish meal, or as directly consumed product.549
With that said, currently there are no drugs approved
for euthanasia of finfish or aquatic invertebrates. Carbon dioxide is a drug of low regulatory priority317 that
avoids unacceptable residues, but it is not an FDAapproved method for killing aquatic animals used for
food. Physical methods that are acceptable with conditions include manually applied blunt force trauma to
the head, decapitation, and pithing.
S6.2 FINFISH
Common methods used to euthanize finfish include noninhaled methods (ie, immersion and injection) and physical methods. Because of general differences in anatomy and application seen between finfish
and terrestrial animals (especially with regard to primary respiratory organs, and aqueous vs air environment),
techniques involving addition of drugs to the finfish’s
environment (ie, the water), for purposes of this document, are considered noninhaled methods.
Descriptions of methods used to euthanize finfish
follow and include 1-step and 2-step procedures. Each
method is further classified as acceptable, acceptable
with conditions, or unacceptable considering characteristics of the methods and the environments in which
euthanasia is conducted, including veterinary private
practice (eg, companion and ornamental [display] finfish), ornamental (aquarium) finfish wholesale and retail
facilities, research laboratories, and finfish kept outdoors
and in fisheries. An acceptable method reliably meets the
requirements of euthanasia. Methods that are acceptable
with conditions reliably meet the requirements of euthanasia when specified conditions are met. An unacceptable method does not meet the requirements of euthanasia. Because finfishes’ anatomic and physiologic characteristics are quite different from those of mammals and
birds, classification of techniques may vary from what
has been recommended for other species.
S6.2.1 Noninhaled Agents
Immersion (1 step)—Intentional overdose via immersion in anesthetic solutions is a common method
of euthanasia for finfish.325,559–561 Finfish should be left
in the anesthetic solution for a minimum of 10 minutes
after cessation of opercular movement.63,325,559 Options
include the following:
(1) Benzocaine or benzocaine hydrochloride, buffered. Solutions for immersion should be prepared in
concentrations $ 250 mg/L and should be buffered.561
69
(2) Carbon dioxide. Immersion in CO2-saturated
water causes narcosis and loss of consciousness after
several minutes.63,325 Some species may exhibit hyperactivity prior to loss of consciousness.559 Purity and
concentration of CO2 are important for effectiveness.
Only CO2 from a source that allows for careful regulation of concentration, such as from cylinders, is acceptable. Care must be taken when using CO2 to prevent exposure to personnel (ie, euthanasia must be conducted
in well-ventilated areas).
(3) Ethanol. Ethanol has been suggested as an acceptable alternative method for finfish.306 The depressive effects of ethanol on the CNS are well described,562
and exposure of zebrafish via immersion has become
a model for behavioral and molecular responses to
alcohol, at concentrations from 10 to 30 mL of 95%
ethanol/L.563–565 At this dose, alcohol induces anesthesia, and prolonged immersion produces death via respiratory depression causing anoxia. This is not equivalent
to immersing finfish directly into preservative concentrations of ethanol (70%), which is not acceptable as a
euthanasia method.
(4) Eugenol, isoeugenol, and clove oil. Whenever
possible, products with standardized, known concentrations of essential oils should be used so that accurate
dosing is possible. Concentrations required for anesthesia will vary depending on species and other factors,
but may be as low as 17 mg/L for some species. Greater
concentrations will be required for euthanasia.566–568
Finish should be left in the anesthetic solution for a
minimum of 10 minutes after cessation of opercular
movement. These compounds are equivocal or known
carcinogens according to the National Toxicology Program.318 Some studies in rodents indicate this group
of anesthetics may cause paralysis in addition to having anesthetic effects, and analgesic properties are unknown.321–324 Because some clove oil products may contain or include either methyleugenol or isoeugenol, or
both, FDA has expressed concern that the use of clove
oil or its components in finfish may adversely affect human food safety and animal food safety. In addition, because clove oil and its components have not been evaluated for target animal safety, FDA is also concerned
that the use of any of these compounds may adversely
affect finish, including endangered aquatic species.569
Isoeugenol is a potential carcinogen318 so human safety
in the application of that agent is of concern.
(5) Isoflurane, sevoflurane. These concentrated liquid anesthetics can be added to water, although they are
generally not very water soluble.559 Injecting the solution through a syringe and fine gauge needle under the
water in the container used for euthanizing is helpful in
ensuring dispersal in the water. Doses of > 5 to 20 mL/L
can be used (10 times the upper range for anesthesia).
However, because both anesthetics are highly volatile,
human safety is of concern and use in a well-ventilated
area is imperative.
(6) Quinaldine sulfate. Solutions for immersion
should be prepared in concentrations $ 100 mg/L.309
Quinaldine sulfate will acidify water; therefore, buffering is required to prevent distress from acute drop in pH.
(7) Tricaine methanesulfonate, buffered (MS 222,
TMS). Solutions must be buffered, and concentrations
70
required for euthanasia may vary depending upon the
species, life stage, and water chemistry parameters. A
concentration of 250 to 500 mg/L, or 5 to 10 times the
anesthetic dosage, is effective for most species.325,561 MS
222 at a dose of 400 mg/L has been shown to be ineffective for a few species (eg, Gulf of Mexico sturgeon).325
Finfish that are too large for practical or cost-effective
immersion in lethal doses of buffered MS 222 can be
euthanized by applying the concentrated, buffered solution directly to the gills.325,559
(8) 2-phenoxyethanol. Solutions for immersion
should be prepared in concentrations $ 0.5 to 0.6 mL/L
or 0.3 to 0.4 mg/L.309
Injection—Injectable agents have been administered for euthanasia via IV, intracoelomic, IM, and intracardiac routes.306,325
(1) Pentobarbital (1 step). Sodium pentobarbital
(60 to 100 mg/kg [27.3 to 45.5 mg/lb]) can be administered by IV, intracardiac, or intracoelomic routes for
euthanasia.63 Pentobarbital may also be administered
via intracardiac injection for anesthetized animals as
the second step of a 2-step euthanasia procedure. Death
usually occurs within 30 minutes.
(2) Ketamine (2 step). Ketamine may be administered at dosages from 66 to 88 mg/kg568 (30 to 40
mg/lb) via an IM injection followed by a lethal dose of
pentobarbital. Observers should be advised about the
possibility of ketamine-induced muscle spasms during
induction.325
(3) Ketamine:medetomidine (2 step). A combination of ketamine, at dosages of 1 to 2 mg/kg, with medetomidine, at dosages of 0.05 to 0.1 mg/kg (0.02 to
0.05 mg/lb), may be administered via IM injection followed by a lethal dose of pentobarbital.568
(4) Propofol (2 step). A dose of 1.5 to 2.5 mg/kg
(0.7 to 1.1 mg/lb) can be administered IV followed by
an injection of a lethal dose of pentobarbital.568
S6.2.2 Physical Methods
The following methods can be applied for euthanasia, providing they are performed using proper equipment by trained personnel who are regularly monitored
for proficiency.
(1) Decapitation followed by pithing (2 step). Rapid severance of the head and brain from the spinal cord,
followed by pithing of the brain, will cause rapid death
and unconsciousness. Decapitation alone is not considered a humane approach to euthanasia, especially
for species that may be particularly tolerant of low O2
concentrations. Pithing helps ensure rapid loss of brain
function and death for those species.570
(2) Cervical transection using a knife or other
sharp instrument inserted caudal to the skull to sever
the spinal cord and cervical vertebrae, followed by pithing (2 step). The rationale for this approach is similar
to that for decapitation (destruction of connections between brain and spinal cord) and pithing (destruction
of brain tissue), except that the head is still physically
attached by musculature to the body.
(3) Manually applied blunt force trauma (cranial
concussion) followed by pithing (2 step). Manually
applied blunt force trauma (a rapid, accurately placed
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
blow of sufficient energy to the cranium with an appropriate-sized club) can cause immediate unconsciousness and potentially death, but should be followed by
pithing to ensure death. The finfish’s size, species, and
anatomy and characteristics of the blow (including its
accuracy, speed, and club mass) will determine the efficacy of manually applied blunt force trauma. This procedure requires training and monitoring for proficiency.
Anatomic features, such as the location of the eyes, can
help serve as a guide to the location of the brain.570,571
(4) Captive bolt (most commonly nonpenetrating;
1 step). This is a method usually applied to large finfish
species.570
(5) Maceration (1 step). When applied correctly,
using a well-maintained macerator specifically designed for the size of finfish being euthanized, death
is nearly instantaneous.572 The process is aesthetically
unpleasant for some operators and observers.
(6) Rapid chilling (hypothermic shock; 1 step or 2
step). It is acceptable for zebrafish (D rerio) to be euthanized by rapid chilling (2° to 4°C) until loss of orientation and operculum movements316,461,462 and subsequent
holding times in ice-chilled water, specific to finfish
size and age. Zebrafish adults (approx 3.8 cm long) can
be rapidly killed (10 to 20 seconds) by immersion in 2°
to 4°C (36° to 39°F) water. Adult zebrafish should be
exposed for a minimum of 10 minutes and fry 4 to 7
dpf for at least 20 minutes following loss of operculum
movement. Use of rapid chilling and use of buffered MS
222 alone have been shown to be unreliable euthanasia methods for zebrafish embryos < 3 dpf. To ensure
embryonic lethality these methods should be followed
with an adjunctive method such as use of diluate sodium or calcium hypochlorite solution at 500 mg/L.327,462
If necessary to ensure death of other life stages, rapid
chilling may be followed by either an approved adjunctive euthanasia method or a humane killing method.
Until further research is conducted, rapid chilling is acceptable with conditions for other small-bodied, similarly sized tropical and subtropical stenothermic species. Species-specific thermal tolerance and body size
will determine the appropriateness and effectiveness
of rapid chilling for euthanasia of finfish. Finfish size
is important because the rate of heat loss via thermal
conduction from a body is proportional to its surface
area. Based on these 2 factors, it has been suggested that
rapid chilling in water associated with an ice slurry is a
suitable killing method for small tropical and subtropical finfish species 3.8 cm in length (tip of the snout to
the posterior end of the last vertebra) or smaller, having
lower lethal temperatures above 4°C.
To ensure optimal hypothermal shock (ie, rapid
killing), transfer of finfish into ice water must be completed as quickly as possible. This means rapid transitions from acclimatization temperature to 2° to 4°C
must be achieved. This can be accomplished by using
minimal water volume to transfer finfish (ie, using a
net to place finfish in chilled water). In addition, finfish should not be in direct contact with the ice in the
water; rather a depression should be formed in the ice
slurry to expose the entire surface of the finfish to the
chilled water. Full contact with cold water ensures optimal exposure and rapid chilling of the finfish. Water
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
temperature must not exceed 2° to 4°C. Well-insulated
containers, such as coolers, will assist in maintaining
the ice slurry and a probe thermometer can be used to
confirm water temperature.
This method of euthanasia is not appropriate for
temperate, cool, or cold-water–tolerant finfish, such as
carp, koi, goldfish, or other species that can survive at
4°C and below. It is appropriate for zebrafish and other
small-bodied (3.8-cm-long or smaller) tropical and subtropical stenothermic finfish, for which the lower lethal
temperature range is above 4°C.316,461,462 This method
can also be acceptable for small to medium-sized (2.8to 13.5-cm-long) Australian river gizzard shad, as long
as secondary euthanasia methods are applied after finfish are rendered nonresponsive.316 However, because of
surface-to-volume considerations, use of this method is
not appropriate in other medium to large-bodied finfish
until data regarding its applicability to euthanasia for
those species become available.
S6.2.3 Adjunctive Methods
Decapitation, pithing, freezing, and other physical
methods for inducing death may be used as the second step of a 2-step procedure when finfish have been
rendered unconscious prior to their application by an
acceptable or acceptable-with-conditions, first-step
method. If necessary to ensure death, rapid chilling for
specified groups may be followed by either an approved
adjunctive euthanasia method or a humane killing
method. Use of a dilute sodium hypochlorite or calcium hypochlorite solution may be an adjunctive method
for early life stages of finfish, including embryos and
larvae.327,462
S6.2.4 Unacceptable Methods
The following are unacceptable methods of euthanasia in any situation. Flushing of finfish into sewer, septic, or other types of outflow systems is unacceptable for
many reasons. Water chemistry and quality may delay
time to death and result in exposure to noxious compounds. For systems in close proximity to and/or connected to natural waterways, pathogen release or transmission may occur from diseased or carrier animals.
Slow chilling or freezing of unanesthetized animals, including placing finfish into a freezer without prior anesthesia, is also an unacceptable method. Similarly death
by anoxia and dessication after removal from the water
or by anoxia in water; any death due to exposure to caustic chemicals; and death including prolonged traumatic
injury prior to unconsciousness are unacceptable.
While metomidate has been used for euthanasia of
some finfish species, its listing in the Index of Legally
Marketed Unapproved New Animal Drugs for Minor
Species by the FDA (with a specified use for sedation
and anesthesia) means that its extralabel use for euthanasia is currently illegal.
S6.2.5 Life Stage Considerations
The effectiveness of euthanasia methods described
in these guidelines may vary by life stage, as well as
by species. Early stages in the lives of finfish, including
embryos and larvae, may require higher concentrations
of immersion anesthetics or a longer duration of ex71
posure.560 As an example, immersion in a buffered MS
222 solution having a concentration > 1 g/L is not a
reliable method for killing some finfish in younger life
stages.461,462,560 For some species and in some situations,
adjunctive methods to guarantee death may need to be
applied for these animals after anesthesia with buffered
MS 222. Rapid chilling followed by an adjunctive method such as immersion in a dilute sodium hypochlorite
or calcium hypochlorite solution is acceptable for zebrafish embryos and larvae as a 2-step method and is
also acceptable with conditions as a 2-step method for
destruction of other (nonzebrafish) species’ embryos
and larvae.327,462
posure.560 As an example, immersion in a buffered MS
222 solution having a concentration > 1 g/L is not a
reliable method for killing some finfish in early life
stages.461,462,560 For some species and in some situations, adjunctive methods to guarantee death may
need to be applied for these animals after anesthesia
with buffered MS 222.
Rapid chilling followed by immersion in a dilute
sodium hypochlorite or calcium hypochlorite solution is acceptable for zebrafish embryos and larvae as a
2-step method and is also acceptable with conditions as
a 2-step method for destruction of other (nonzebrafish)
species’embryos and larvae.327,462
S6.2.6 Finfish in Particular Environments
S6.2.6.2 Aquarium Finfish
Wholesale and Retail Facilities
S6.2.6.1 Veterinary Private Practice—
Companion and Ornamental (Display) Finfish
Freshwater and marine aquarium finfish are commercially collected from the wild, and are also bred in
captivity. Tropical aquarium finfish are sold at retail pet
shops and finfish stores from systems housing one or
more species of finfish per tank. Individual finfish or
populations of finfish may become injured or diseased
and require euthanasia. Methods of euthanasia used in
this environment need to be applicable to individual
finfish, to all finfish in an aquarium, to finfish held in
multiple aquariums on a central filtration system, or for
finfish kept in ponds. In certain situations euthanasia
may not be feasible and depopulation methods may be
required.
The following methods are acceptable for use in
this environment:
Immersion in solutions of buffered tricaine methanesulfonate (MS 222), buffered benzocaine, and quinaldine sulfate. Finfish should be left in the anesthetic
solution for a minimum of 10 minutes after cessation
of opercular movement.63,325,559
The following methods are acceptable with conditions for use in this environment:
(1) Immersion in CO2-saturated water; eugenol,
isoeugenol, or clove oil; and ethanol.
(2) Decapitation, cervical transection, or manually
applied blunt force trauma as step 1 of a 2-step method,
followed by pithing.
(3) Freezing may be used as an adjunctive method
following anesthesia.
(4) Rapid chilling (hypothermic shock) for smallbodied (3.8-cm-long or smaller) tropical and subtropical stenothermic finfish, for which the lower lethal temperature range is above 4°C.316,461,462
The following methods are not recommended for
use in this environment:
Use of injectable anesthetic drugs including barbiturates, requires the oversight of a veterinarian and
DEA permitting for controlled substances. Therefore,
unless a veterinarian is available on-site to oversee use
of these drugs, this method is not recommended in this
environment.
Early stages in the lives of finfish, including embryos
and larvae, may require higher concentrations of immersion anesthetics or a longer duration of exposure.560 As
an example, immersion in a buffered MS 222 solution
having a concentration > 1 g/L is not a reliable method
for killing some finfish in early life stages.461,462,560 For
Clients with pet or display finfish of any species
often value them as companion animals and share a
human-animal bond similar to that seen between clients and other pets, such as dogs and cats. Therefore,
it is important to consider the perception of the client
when euthanasia methods are chosen. Clients should
be offered the opportunity to be present during euthanasia whenever feasible; however, clients also should be
educated as to what method will be used and what they
may observe during euthanasia. For example, clients
may believe the excitement phase of anesthesia, which
can result in increased motor activity or the appearance
of agitation,559 is unduly painful or stressful for the finfish even when it is not.
The following methods are acceptable for use in
this environment:
(1) Immersion in solutions of buffered tricaine
methanesulfonate (MS 222), buffered benzocaine,
isoflurane and sevoflurane, quinaldine sulfate, and
2-phenoxyethanol.
(2) Injections of pentobarbital, ketamine followed
by pentobarbital, a combination of ketamine and medetomidine followed by pentobarbital, and propofol
followed by pentobarbital. Owners should be advised
about the possibility of ketamine-induced muscle
spasms during induction when using that agent.
The following methods are acceptable with conditions for use in this environment:
(1) Immersion in eugenol, isoeugenol, or clove
oil. Finfish should be left in the solution for a minimum of 10 minutes after cessation of opercular movement.63,325,559
The following methods are not recommended for
use in this environment:
(1) Immersion in CO2-saturated water is not recommended because some finfish exposed to this method may become hyperactive, which can be disconcerting for staff and owners.
(2) Manually applied blunt force trauma to the
head, decapitation, and pithing are not recommended
because their application can be distressing for owners
and staff.
Early stages in the lives of finfish, including embryos and larvae, may require higher concentrations
of immersion anesthetics or a longer duration of ex72
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
some species and in some situations, adjunctive methods to guarantee death may need to be applied for these
animals after anesthesia with buffered MS 222.
Rapid chilling followed by immersion in a dilute
sodium hypochlorite or calcium hypochlorite solution is acceptable for zebrafish embryos and larvae as a
2-step method and is also acceptable with conditions as
a 2-step method for destruction of other (nonzebrafish)
species’embryos and larvae.327,462
S6.2.6.3 Research Facilities
Researchers working in laboratories should have
materials readily available to provide appropriate euthanasia for their research subjects when required, and
should be trained and monitored for proficiency in the
use of chosen techniques. Many facilities using finfish
as research subjects are engaged in biomedical research.
Zebrafish are the most common species used for research and are usually kept in small-scale tank systems;
however, some research facilities may also have largescale housing and production systems and/or keep
other larger species of finfish, and consequently, need
to consider additional options for euthanasia.320 The
expertise of those knowledgeable about these settings
and species should be sought as necessary.
The following methods are acceptable for use in
this environment:
(1) Immersion in solutions of buffered tricaine
methanesulfonate (MS 222), buffered benzocaine,
quinaldine sulfate, and 2-phenoxyethanol. Finfish euthanized with these methods must not enter the food
supply.
(2) Rapid chilling (hypothermic shock) is acceptable for zebrafish (D rerio) and Australian river gizzard
shad (N erebi) as long as transfer from acclimatized
temperatures to water associated with a 2° to 4°C ice
slurry occurs rapidly with as little transfer of warmer
water as possible.
The following methods are acceptable with conditions for use in this environment:
(1) Immersion in CO2-saturated water (as long as
observers are advised and can accept that some finfish
exposed to this method may exhibit hyperactivity and
appears to be in distress), eugenol, isoeugenol, or clove
oil.
(2) Rapid chilling (hypothermic shock) to 2° to 4°C
is acceptable with conditions for small-bodied (3.8-cmlong or smaller) tropical and subtropical stenothermic
finfish, for which the lower lethal temperature range
is above 4°C. Because of surface-to-volume considerations, use of this method is not appropriate for other
medium to large-bodied finfish until additional data for
those species become available.
(3) Maceration is acceptable with conditions when
death is instantaneous using a well-maintained macerator designed for the size of finfish being euthanized.
The process is likely to be aesthetically unpleasant for
those observing it.
(4) Decapitation followed by pithing. Rapid severance of the head and brain from the spinal cord, followed by pithing of the brain, will cause rapid death
and unconsciousness.320
(5) Manually applied blunt force trauma (cranial
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
concussion) followed by pithing.
Early stages in the lives of finfish, including embryos
and larvae, may require higher concentrations of immersion anesthetics or a longer duration of exposure.560 As
an example, immersion in a buffered MS 222 solution
having a concentration > 1 g/L is not a reliable method
for killing some finfish in earlier life stages.461,462,560 For
some species and in some situations, adjunctive methods
to guarantee death may need to be applied for these animals after anesthesia with buffered MS 222.
Rapid chilling followed by immersion in a dilute
sodium hypochlorite or calcium hypochlorite solution is acceptable for zebrafish embryos and larvae as a
2-step method and is also acceptable with conditions as
a 2-step method for destruction of other (nonzebrafish)
species’embryos and larvae.
S6.2.6.4 Finfish Kept Outdoors and in Fisheries
Field research on finfish takes place in a complex
environment that must be understood by both researchers and their respective IACUC.320 Field research is frequently conducted on a scale comparable to commercial
fishing, often with the same equipment, boats, and personnel. The large number of finfish, limited boat space,
adverse environmental conditions, and personnel safety
concerns may justify use of harvest techniques that may
not meet the criteria for euthanasia, but in all situations,
pain and distress should be minimized to the greatest extent possible. Similarly, fisheries biologists may be faced
with situations involving numerous finfish requiring depopulation (eg, invasive species) rather than euthanasia.
Fieldwork on finfish may also be conducted on a
smaller scale under conditions that make euthanasia
feasible. In such cases, the following methods should
be applied and convenience for the researcher should
not be a primary consideration.
The following methods are acceptable for use in
this environment:
(1) Immersion in solutions of buffered tricaine
methanesulfonate (MS 222), buffered benzocaine,
quinaldine sulfate, isoflurane or sevoflurane, quinaldine sulfate, and 2-phenoxyethanol. Although a general concern for all environments and situations, the
potential effects of drug residues and proper disposal of
animal remains should be considered when using any
of these drugs.
(2) An injection of pentobarbital (60 to 100 mg/kg)
can be administered IV or intracoelomically.309 Pentobarbital may also be administered intracardially in anesthetized animals. Two-step injection procedures may
also be used, including ketamine (IM) followed by a
lethal dose of pentobarbital; a combination of ketamine
and medetomidine (IM) followed by a lethal dose of
pentobarbital; and propofol (IV) followed by a lethal
dose of pentobarbital. Although a general concern for
all environments and situations, the potential effects of
drug residues and proper disposal of animal remains
should be considered when using any of these drugs.
The following methods are acceptable with conditions for use in this environment:
(1) Immersion in CO2-saturated water or eugenol,
isoeugenol, or clove oil.
(2) Manually applied blunt force trauma to the
73
head followed by pithing.
(3) Decapitation followed by pithing. Decapitation
alone is not considered a humane form of euthanasia,
especially for species that may be particularly tolerant
of low O2 concentrations. Pithing helps ensure rapid
death for those species.
(4) Cervical transection followed by pithing. The
rationale for this approach is similar to that for decapitation and pithing, except that the head is still physically attached by musculature to the body.
(5) Captive bolt. This method is usually applied to
large finfish species.
(6) Rapid chilling (hypothermic shock) in water
of 2° to 4°C for small-bodied (3.8-cm-long or smaller)
tropical and subtropical stenothermic species (as previously described for zebrafish). Because of surface-tovolume considerations, use of this method is not appropriate in medium to large-bodied finfish until pertinent
data for those species becomes available.
Early stages in the lives of finfish, including embryos and larvae, may require higher concentrations
of immersion anesthetics or a longer duration of exposure.560 As an example, immersion in a buffered MS
222 solution having a concentration > 1 g/L is not a
reliable method for killing some finfish in early life
stages.461,462,560 For some species and in some situations,
adjunctive methods to guarantee death may need to be
applied for these animals after anesthesia with buffered
MS 222. Rapid chilling followed by immersion in a dilute sodium hypochlorite or calcium hypochlorite solution is acceptable for zebrafish embryos and larvae as a
2-step method and is also acceptable with conditions as
a 2-step method for destruction of other (nonzebrafish)
species’ embryos and larvae.327,462
S6.3 AQUATIC INVERTEBRATES
Overdose of a general anesthetic is as appropriate a
euthanasia strategy for aquatic invertebrates as it is for
finfish. And, immersion is an effective route of administration of anesthetic and euthanasia agents.133,330
Because confirming the death of many invertebrates
is difficult, 2-step euthanasia procedures are often recommended in which chemical induction of anesthesia,
nonresponsiveness, or presumptive death is followed
by an adjunctive method that destroys the brain or major ganglia physically (eg, pithing, freezing, boiling) or
chemically (eg, alcohol, formalin). Application of the
latter methods by themselves is generally not considered to meet the criteria established for euthanasia.133,330
S6.3.1 Acceptable First Steps of 2-Step Methods
S6.3.1.1 Noninhaled Agents for Immersion
Magnesium salts—Magnesium salts are a near-universal anesthetic agent, relaxing agent, and euthanasia
agent for aquatic invertebrates, although they are ineffective for crustaceans. A range of concentrations has
been recommended for various phyla. Research suggests the magnesium ion acts centrally in suppressing
neural activity of cephalopods.134
Clove oil or eugenol—Clove oil or eugenol has been
used effectively as an immersion agent for the eutha74
nasia of crustaceans (0.125 mL/L).133,573 Isoeugenol is a
potential carcinogen318 so human safety in the application of that agent is of concern.
Ethanol—Ethanol has been used for euthanasia
of some phyla (at a 1% to 5% concentration as compared with concentrations of > 70% used for preservation), and acts by inhibiting neuronal sodium and
calcium channels in molluscs.562 Initial aversion and/
or excitement has been reported as occurring in cephalopods.134,574
Other agents for euthanasia, while less common,
have been described and may be useful for specific applications.133
S6.3.2 Acceptable Second
Steps of 2-Step Methods
S6.3.2.1 Noninhaled Agents for Immersion
Noninhaled agents that can be administered via
immersion as the second step of a 2-step euthanasia approach include 70% alcohol and neutral-buffered 10%
formalin. These agents are not acceptable, however, for
immersion as a single-step procedure, nor as the first
step of a 2-step procedure.
S6.3.2.2 Physical Methods
Pithing, freezing, and boiling are acceptable as
the second step (adjunctive methods) of a 2-step euthanasia procedure. Pithing requires detailed anatomic
knowledge of the species in question. These methods
are not acceptable, however, as a single-step procedure,
nor as the first step of a 2-step procedure.
S6.3.3 Life Stage Considerations
The effectiveness of euthanasia methods described
in the Guidelines may vary depending on life stage
and species. As for finfish, this should be considered
when euthanizing aquatic invertebrates. Methods used
for different life stages of the same species may require
modification to maximize their effectiveness. Recommendations regarding use of adjunctive methods (as
described previously) may also be necessary to guarantee death.
S6.3.4 Unacceptable Methods
Methods of killing that do not cause rapid death or
that cause trauma prior to loss of consciousness are not
considered humane methods of death, or euthanasia.
These can include removing a finfish or aquatic
invertebrate from the water and allowing it to die by
hypoxia secondary to desiccation of gill tissue; leaving
finfish or aquatic invertebrates in a container of water
without adequate aeration, causing death by anoxia; or
any death due to exposure to caustic chemicals or traumatic injury without first inducing unconsciousness in
the finfish or aquatic invertebrate.
S7. CAPTIVE AND FREE-RANGING
NONDOMESTIC ANIMALS
Methods acceptable with conditions are equivalent
to acceptable methods when all criteria for application
of a method are met.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
S7.1 GENERAL CONSIDERATIONS
The nondomestic captive and free-ranging animals
discussed in the following sections vary substantially
in their anatomic and physiologic characteristics, native environment, behavior, social structure, responses
to humans, and other traits. These variations challenge
the application and effectiveness of euthanasia methods for the many different species. The efficacy of these
methods can be further limited by the circumstances
under which euthanasia is performed. Consequently,
the best means of terminating an animal’s life might
not strictly conform to the definition of euthanasia.
For nondomestic captive or free-ranging animals, the
methods selected will often be situation specific, as a
means of minimizing potential risks to the animal’s
welfare and personnel safety. In addition, challenges associated with disposal of the remains of animals with
drug residues that have been addressed in the section
of the document on Dispoal of Remains (eg, secondary toxicity, environmental contamination, and other
topics) are relevant to disposal of the remains of nondomestic animals, particularly under field conditions.
Given the complexity of issues that euthanasia of nondomestic animals presents, personnel are encouraged
to consult references on anatomy, physiology, natural
history, husbandry, and other disciplines that will aid
in understanding how various methods may impact an
animal’s euthanasia experience.52,53,132,575,576 Consultation with experienced colleagues is recommended, particularly when novel circumstances and/or species are
encountered.
Animals may become distressed due to physical discomfort, anxiety in atypical social settings and
physical surroundings, pheromones or odors from
nearby or previously euthanized animals, and the presence of humans. In addition, human safety, observers’
perceptions, availability of trained personnel, potential
infectious disease concerns, conservation and other
population objectives, regulatory oversight that may be
species specific, available equipment and facilities, options for disposal, potential secondary toxicity, research
objectives, and other factors must be considered. Human safety is of utmost importance for all euthanasia
procedures, and appropriate protocols and equipment
(including supplies for addressing human injury due
to animal handling or exposure to immobilizing drugs)
must be available prior to handling animals.577 Laws
and regulations pertaining to the species being euthanized, the euthanasia methods employed, and disposal
of the remains must be followed.
Euthanasia of captive wild animals requires consideration of basic stewardship, physiologic and behavioral variation, and relief from pain and anxiety. Management can be guided by the physical and social setting the animal is in (eg, small enclosures, seminatural
conditions), the animal’s temperament, seasonal factors
(eg, reproductive stage, physical condition), and differences from similar domestic species. Appropriate handling and modifying the animal’s physical and social
environment to minimize distress, as well as administration of anxiolytics, are recommended. Provision of
preferred bedding, temperature, humidity, and security
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
in the period leading up to euthanasia will allow the
animal to be as comfortable as possible. Most small animals will find security in a dimly lighted, appropriately
bedded and ventilated crate, box, tube, or similar container as this simulates a natural tendency to hide from
perceived threats. Some species respond well to being
left within typical social groups or familiar surroundings as long as possible prior to euthanasia to minimize
anxiety.
Best practice for many captive wild animal species
includes a multistep approach, beginning with administration of a sedative or anesthetic to relieve anxiety
and pain. For wild animals in captivity, physical and/or
chemical restraint is usually required before euthanasia can be performed. Physical restraint is appropriate
when skilled staff, facilities, suitable equipment, and
the animal’s characteristics allow rapid immobilization
with minimal distress.577 References should be consulted for appropriate doses of anesthetics and anxiolytics
and preferred routes of administration.424,578–580 Animals
can be premedicated via IM injection and/or orally. Intravenous administration of drugs is generally difficult
without physical or chemical restraint. Chamber delivery of inhaled agents having little odor, such as sevoflurane, allows for induction of anesthesia in smaller
species with minimal stress. Injectable anesthesia can
be momentarily painful or discomforting during or immediately after administration due to a combination of
volume, formulation, and route of administration, as
well as the distress associated with physical restraint.
The advantages and disadvantages of administering
anxiolytics, anesthetics, or other drugs and applying
physical restraint should be balanced against the benefit of providing a swift death to end suffering. Research
is needed to improve the euthanasia options available
for some taxonomic groups and circumstances.
S7.2 CAPTIVE INVERTEBRATES
Invertebrates comprise more than 95% of the animal kingdom’s species and include unrelated taxonomic
groups: spiders (Araneae),581 centipedes and millipedes
(Myriapoda), insects (Hexapoda),582 and many others.
Terrestrial invertebrates play important roles in laboratory research, as display animals, and as companions in
the home. Despite their varied roles, limited guidance
is available on appropriate methods by which invertebrates may be euthanized.63,132,583–585 This is due, in part,
to a lack of coverage under animal welfare regulations
applicable to animals used for research and other purposes in the United States and other countries.574,586 Diversity in anatomic, physiologic, and other characteristics limits generalizations across taxa.281 Of particular
relevance are differences in innervation and circulatory
systems, some of which do not have close corollaries
in familiar vertebrate systems. This creates challenges
for developing humane means of terminating invertebrates’ lives.
While there is ongoing debate about invertebrates’
abilities to perceive pain or otherwise experience compromised welfare, the Guidelines assume that a conservative and humane approach to the care of any creature
is warranted and expected by society. Consequently,
euthanasia methods should be used that minimize the
75
potential for pain or distress. Most commonly used
methods involve terminal anesthesia, followed by physical destruction of the nervous system, to assure lack
of sensory perception and death of the animal. The diversity of invertebrate taxa may require equally diverse
approaches to euthanasia.
S7.2.1 Acceptable Methods
S7.2.1.1 Noninhaled Agents
Injectable agents—While there is little dosing or outcome data in the peer-reviewed literature, an overdose
of pentobarbital or similar agent, at a dose equivalent
to that used for other poikilotherm vertebrates (piscine,
amphibian, or reptilian) on a weight-to-weight basis will
generally suffice. Ideally these agents will be injected directly into the circulating hemolymph. However, because
many invertebrates have an open circulatory system, true
intravascular application can be difficult if not impossible. In such cases an intracoelomic injection would be
warranted unless otherwise contraindicated. Premedication with an injectable or inhaled agent may facilitate administration of barbiturate overdoses.
S7.2.2 Acceptable With Conditions Methods
S7.2.2.1 Inhaled Agents
Inhaled anesthetics—Overdose of an inhaled anesthetic is acceptable with conditions for terrestrial invertebrates where injectable agents are not available.
Because confirming death of many species of invertebrates can be difficult, subsequent use of an adjunctive
method of euthanasia is recommended.
Carbon dioxide—Carbon dioxide may be useful for
euthanasia of some terrestrial invertebrates, but additional information is needed to confirm its efficacy.
S7.2.2.2 Physical and Chemical Methods
Physical (eg, boiling, freezing, pithing) and chemical (eg, alcohol, formalin) methods act by destroying
the brain or major ganglia. Physical and chemical methods should be applied adjunctively, following pharmaceutical or other chemical induction of anesthesia, nonresponsiveness, or presumptive death. These methods
are not considered to be humane as sole methods of
euthanasia.583,584,587,588
Pithing—This method requires detailed anatomic
knowledge of the species in question.
S7.3 CAPTIVE AMPHIBIANS AND REPTILES
S7.3.1 Anatomy and Physiology
Amphibians and reptiles include caecilians (order Gymnophiona), frogs (order Anura), salamanders
(order Caudata), snakes (suborder Serpentes), lizards
(suborder Lacertilia), crocodilians (order Crocodilia),
and turtles and tortoises (superorder Chelonia). Once
again, these taxonomic groups differ substantially anatomically and physiologically from each other, as well
as from mammals. Of particular concern for amphibians and reptiles are differences in metabolism and high
tolerances to hypoxia, as compared with mammals, that
limit the effectiveness of methods based on anoxia. In
addition, consistent access to the vasculature can be
challenging and, therefore, many conventional methods of euthanasia are less efficacious for these species.
Because it is often difficult to confirm that an amphibian or reptile is dead, the application of two or more euthanasia procedures is usually recommended.552,589–591
Our understanding of amphibians’ and reptiles’
nociception and responses to stimuli is incomplete;
therefore, many recommendations for minimizing pain
and distress are extrapolated from information available about mammals. Where uncertainty exists, erring
to proactively alleviate potential pain and suffering is
recommended as an appropriate approach to euthanizing amphibians and reptiles. Consulting multiple
references on amphibian and reptile euthanasia is advised as a means of identifying methods that are most
appropriate for a given species and set of circumstances.166,312,401,552,553,589–591
S7.3.2 Restraint
Physical restraint—Manual restraint is possible for
many species. Equipment may be required for restraint
of some species in some situations (eg, venomous species). Multiple people may be required for larger species, and at least one additional person should be available for emergencies. Large animals may represent a
proportionately greater risk for personnel.
Chemical restraint—Chemical restraint may be
useful in some situations, particularly for venomous or
large animals where human safety would be compromised by manual restraint. Chemical restraint at high
doses may serve as a first or preparatory step of euthanasia in some situations.
S7.3.3 Verification of Death
Because information on the physiologic responses
of invertebrates to many methods of euthanasia is not
available at this time, comments regarding unacceptable
methods of euthanasia are limited to those that should
not be applied as sole methods of euthanasia (see comments under Acceptable With Conditions Methods).
Methods used to verify death in mammalian species, such as auscultation, ECG, Doppler ultrasound,
or pulse oximetry, can be used for amphibians and reptiles, but it is important to remember that amphibian
and reptilian hearts can beat even after brain death.
Death should always be confirmed by physical intervention.
S7.2.4 Developmental Stages of Invertebrates
S7.3.4 Acceptable Methods
Recommendations for euthanasia of the developmental stages of invertebrates are currently not available.
S7.3.4.1 Noninhaled Agents
S7.2.3 Unacceptable Methods
Injectable agents—Venous access for administra76
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
tion of euthanasia agents can be challenging for some
species. Intracoelomic, subcutaneous lymph spaces,
and lymph sacs are acceptable routes of administration.
Direct injection into the brain through the parietal eye,
while under anesthesia, has been described for some
lizard species.592
Sodium pentobarbital (60 to 100 mg/kg of body
weight) can be administered IV, intracoelomically, in
the subcutaneous lymph spaces, or in the lymph sacs,
although doses vary by species.593 Doses as high as
1,100 mg/kg (500 mg/lb) of sodium pentobarbital with
sodium phenytoin administered intracoelomically may
be required for euthanasia of some species such as X
laevis.312 Time to effect may vary, with death occurring
instantaneously or up to 30 minutes later.77,552,589–591,594
Barbiturates are best administered intravascularly to
minimize the discomfort upon injection.595 However,
where intravascular administration is not possible or
its benefits are outweighed by distress imposed by additional restraint, pain from alternate methods, risk to
personnel, or other similar reasons, intracoelomic administration is an acceptable route for administration
of barbiturates.
Dissociative agents such as ketamine hydrochloride or combinations such as tiletamine and zolazepam;
inhaled agents; and IV administered anesthetics, such
as propofol, or other ultra–short-acting barbiturates,
may be used for poikilotherms to induce rapid general
anesthesia and subsequent euthanasia, although application of an adjunctive method to ensure death is recommended.
External or topical agents—Buffered tricaine methanesulfonate (MS 222) may be administered via water
baths (amphibians), or injected directly into the lymph
sacs (amphibians) or the coelomic cavity (amphibians
and reptiles).596–599 Prolonged immersion (as long as 1
hour) may be required for 5 to 10 g/L water baths.312,593
Tricaine methanosulfonate does not create histopathologic artifacts.596 See the Noninhaled Agents section of
the Guidelines for additional information.
Benzocaine hydrochloride, a compound similar to
MS 222, may be used as a bath or in a recirculation
system at concentrations $ 250 mg/L or applied topically to the ventrum as a 7.5% or 20% gel for euthanasia
of amphibians.600 A dose of 182 mg/kg of benzocaine
gel (20% concentration, 2.0-cm X 1.0-mm application)
has been reported as effective for euthanasia of adult
X laevis.312 Pure benzocaine is not water soluble and
should be avoided for anesthesia or euthanasia because
it requires the use of acetone or ethanol solvents, which
may be irritating to tissues.310
In general, these noninhaled agents are highly effective, their onset of action is rapid, and they are applicable across a range of species and sizes of animals.
However, general anesthesia may be required prior to
administration, some require IV administration for vessels that may be difficult to access, they may produce
undesirable tissue artifacts, a controlled substance license is required for barbiturates and some other products, and there may be environmental pollution and
toxicity concerns depending on method of disposal of
the remains.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
S7.3.5 Acceptable With Conditions Methods
S7.3.5.1 Inhaled Agents
Inhaled anesthetics—Inhaled anesthestics are acceptable with conditions when they are more practical
than the previously mentioned acceptable methods,
and where the limitations of this method are understood and addressed. Many reptiles and amphibians are
capable of breath holding and shunting of their blood,
which permits conversion to anaerobic metabolism for
survival during prolonged periods of anoxia (up to 27
hours for some species).601–606 Because of this, induction
of anesthesia and time to loss of consciousness may be
greatly prolonged when inhaled agents are used. Death
may not occur even with prolonged exposure.552,589–591
Lizards and most snakes do not hold their breath to the
same extent as some of the chelonians, and are therefore more likely to have a clinical response to inhaled
agents. Regardless of the species or taxonomic group,
death must be verified prior to terminating the use of
the inhaled agent, or a second, guaranteed lethal procedure (eg, decapitation) should be performed to ensure
death.
Inhaled anesthetics are effective, have a moderately
rapid onset, appear to induce a painless death, can maximize use of the euthanized animal for analytic studies,
and can minimize the need for animal handling. Caveats include that inhaled anesthetics are most suitable
for smaller species, animals may experience an excitation phase prior to becoming anesthetized, they present
environmental pollution and occupational hazard concerns, some are irritants or are perceived as noxious,
and amphibians and reptiles may be resistant to their
action because of breath holding.
Carbon dioxide—Carbon dioxide may be considered
for euthanasia of amphibians and reptiles if alternate
methods are not practical and where the limitations of
this method are understood and addressed.401,552,553,589–591
Due to the potential lack of response to this method
by many species and the requirement for a prolonged
exposure time, other methods are preferable. Death by
CO2 must be verified, and preferably, assured by application of a secondary lethal procedure.
S7.3.5.2 Physical Methods
Penetrating captive bolt or firearm—Crocodilians
and other large reptiles can be euthanized by a penetrating captive bolt or gunshot (free bullet) delivered to
the brain.166 Line drawings of the head of various amphibians and reptiles, with recommended locations for
captive bolt or firearm projectile penetration, are available.401 Refer to ballistics details in the Physical Methods section and experts for more information on selection and use of firearms.
These methods are moderately rapid (allowing for
restraint), are applicable across a wide range of species
and sizes, and leave no environmental residues other
than lead (in the case of free bullet), which can be sequestered. However, size-appropriate equipment and appropriately trained personnel are required, violent muscle contractions can occur following their application,
77
and they may be aesthetically unpleasant for onlookers.
Manually applied blunt force trauma to the head—
This method is acceptable with conditions, when other
options are unavailable, as long as it is performed by
well-trained and skilled personnel and if an adjunctive
method, such as decapitation or pithing, is promptly
applied to ensure death.52,132,589,591 Further research is
needed to clarify methods, taxa, and size ranges where
this method is effective and humane.
Rapid freezing—Reptiles and amphibians can be
euthanized by rapid freezing when it results in immediate death. Based on rodent models, it is likely that this
can be achieved by placing animals < 4 g (0.1 oz) in
liquid N2.52 The technique should not be used for species that have adapted freeze tolerance strategies, as this
method may not result in instant death.607 Placement of
animals $ 4 g in liquid N2 or other uses of hypothermia
are not acceptable.
S7.3.6 Adjunctive Methods
Decapitation—After animals have been anesthetized, decapitation using heavy shears or a guillotine
is effective for some species. It has been assumed that
stopping blood supply to the brain by decapitation
causes rapid loss of consciousness. However, because
the CNS of reptiles and amphibians is tolerant to hypoxic and hypotensive conditions,401 decapitation must
be followed by pithing or another method of destroying
brain tissue.589,591,595 Decapitation should only be performed as part of a 3-step euthanasia protocol (injectable anesthetic, decapitation, pithing).
Pithing—Pithing can be used as a second-step euthanasia method in unconscious animals when performed by properly trained individuals.589,591 The pithing
site in frogs is the foramen magnum, and it is identified
by a slight midline skin depression posterior to the skull,
midline between the eyes, with the neck flexed.552,590
S7.3.7 Unacceptable Methods
Hypothermia—Hypothermia is an inappropriate
method of restraint or euthanasia for amphibians and
reptiles unless animals are sufficiently small (< 4 g)52
to permit immediate and irreversible death if placed
in liquid N2 (rapid freezing).589,591,595 Hypothermia reduces amphibians’ tolerance for noxious stimuli608,609
and there is no evidence that it is clinically efficacious
for euthanasia.610 In addition, it is believed that freezing
can result in the formation of ice crystals in tissues that
may cause pain.52,401 Consequently, because amphibians
and reptiles lack behavioral or physiologic means of
demonstrating pain or distress while hypothermic, generalized prohibitions on hypothermia for restraint or
euthanasia are appropriate. Localized cooling in frogs
may reduce nociception, but this localized effect is not
appropriately applied to the whole body as a part of euthanasia procedures.611 Freezing of deeply anesthetized
animals may be justified under circumstances where
human safety could be compromised.612
S7.3.8 Special Cases and Exceptions
Intracardiac administration of euthanasia agents is
78
acceptable for captive amphibians and reptiles that are
unresponsive to stimuli because of disease or the application of other euthanasia methods, or in cases where
other routes are not possible.
Neuromuscular blocking agents may be used for
routine anesthetic procedures of crocodilians and some
other taxa and are, therefore, considered acceptable
with conditions for restraint of reptiles if given immediately prior to administration of a lethal agent. These
agents are not acceptable as a sole means of euthanasia.
Injectable agents such as lidocaine hydrochloride,
potassium salts, or magnesium salts may be useful as an
adjunctive method to prevent recovery.591
Perfusion with fixative of a deeply anesthetized animal can be used to euthanize amphibians and reptiles
when scientifically justified.
S7.3.9 Destruction of Viable Eggs
Little information is available on the sensory capacity of amphibians and reptiles at the egg stage of
development.52 Freezing is likely appropriate for newly
oviposited eggs, as would be methods of maceration
that result in instantaneous death. Later stages may be
destroyed using methods that are acceptable for adult
animals. More research needs to be done to determine
the most appropriate methods for disposing of live eggs.
S7.4 CAPTIVE NONMARINE MAMMALS
S7.4.1 General Considerations
The anatomic, physiologic, behavioral, and size
variations of nondomestic mammals far exceed those of
their domestic counterparts. This presents challenges
for the application of conventional methods of euthanasia and the recognition of anxiety and pain. Differences from similar domestic species must be recognized
and addressed as thoroughly as practical when preparing for and performing euthanasia.
In zoos or other captive settings, euthanasia of
wildlife is typically performed in the presence of staff
members who are responsible for caring for these animals. Consequently, sensitivity to the meaning and value to caregivers of animals in this kind of setting is important. This can be addressed, in part, with attention
to stewardship, and relief from pain and anxiety prior
to administration of a euthanasia method. Most euthanasia procedures should include the use of inhaled or
injectable anesthetics to achieve unconsciousness, followed by use of an approved method to end life.
In some cases animals may experience intolerable suffering, or the situation may not allow for ideal
stewardship as a prelude to the act of euthanasia. These
situations typically require a more direct approach to
limit how much an animal is allowed to suffer. Such
situations also require a brief explanation to personnel,
where possible, as well as a more complete explanation
of the choice of method subsequent to completion of
the procedure. Preparing staff ahead of time to be cognizant of the possibility of these kinds of situations will
likewise help to better prepare for situations where a
more ideal procedure is not feasible.
Alternate approved methods of euthanasia might
be applicable if an animal is anesthetized prior to euAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
thanasia. Any candidate method not specifically mentioned in the text that follows should be evaluated conceptually to address good stewardship principles prior
to its use.
Following euthanasia, verification of death is important. Methods that can be used for verification of
cessation of cardiac function include, but may not be
limited to, palpation for a pulse in an appropriate anatomic location based on species, auscultation with a
stethoscope, and use of Doppler ultrasound.
S7.4.2 Restraint
Physical restraint—Manual restraint is possible for
many species. Nets or other equipment may be appropriate for smaller species that do not pose an excessive
risk for personnel. For the largest species (hoofstock
and megavertebrates), chutes or other equipment may
provide sufficient restraint for IM or IV administration
of anesthetics and/or anxiolytics. Brief restraint followed by IV administration of a euthanasia agent may
be possible as an approach to euthanasia in some situations. However, administration of a preanesthetic or
sedatives before administration of a euthanasia agent
should be the default in most cases.
Chemical restraint—Chemical restraint may be useful in some situations, particularly for dangerous animals where human safety would be compromised with
manual restraint, as well as to reduce unnecessary stress
and discomfort for the animal(s). Chemical restraint at
high doses may serve as the first step of euthanasia in
some situations.424,578–580
S7.4.3 Acceptable Methods
S7.4.3.1 Noninhaled Agents
Barbiturates—Barbiturates may be administered
IV or IP. Intracardiac administration must be limited
to animals that are unconscious due to disease or the
effects of anesthetics. Onset of action is slower with
IP administration and premedication with anesthetics
may reduce discomfort due to tissue irritation. Barbiturates are best administered intravascularly to minimize
discomfort upon injection.595 However, where intravascular administration is not possible or its benefits are
outweighed by distress imposed by additional restraint,
pain from alternate methods, risk to personnel, or other
similar reasons, IP administration is an acceptable route
for administration of barbiturates.
Barbiturates are highly effective as euthanasia agents,
have a rapid onset of action, and are applicable across a
wide range of species and sizes of animals. However, they
do have drawbacks, including that individuals must be
trained to correctly administer injections, general anesthesia or sedation with injectable or inhaled agents may
be required prior to their administration (depending on
the animal and the situation), they can produce undesirable tissue artifacts, a controlled substance license is
required for their acquisition, and environmental pollution and toxicity may be of concern depending on the
method used to dispose of animal remains.
Nonbarbiturate anesthetic overdose—Opioids and
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
other anesthetics may be administered IV or IM for euthanasia when animal size, restraint requirements, or
other circumstances indicate these drugs are the best
option for euthanasia.
Intramuscular administration of opioids is advantageous when other routes of administration are not
available. Opioids tend to have a rapid onset of action, and the volume of drug to be administered may
be smaller than for other agents. There are also disadvantages associated with administering an overdose of
opioids, including requirements for DEA licensing and
veterinary oversight for extralabel use, risks to human
safety if exposure to drugs occurs, and the potential for
secondary toxicity if tissues are consumed.
S7.4.4 Acceptable With Conditions Methods
S7.4.4.1 Inhaled Agents
Inhaled anesthetics—Inhaled anesthestics are acceptable with conditions when they are more practical
than acceptable methods, and where the limitations of
this method are understood and addressed. Inhaled anesthetics may be administered via face mask or chambers. Placing an animal’s entire crate into a chamber will
allow anesthesia to be induced with the least amount of
distress. As discussed in the Inhaled Agents section of
the Guidelines, agents with minimal odor are preferred.
Inhaled anesthetics have a moderately rapid onset
of action, do not appear to cause pain on administration, maximize the availability of the animal’s remains
for analytic studies, and can be applied with minimal
handling of the animal. They also, however, have some
disadvantages in that they are most suitable for smaller
species, some are irritants or are perceived as noxious,
animals can experience an excitation phase prior to induction of anesthesia, and they may present environmental pollution and occupational safety concerns.
Carbon monoxide, carbon dioxide, and inert gases—
These agents are acceptable with conditions for application where animal welfare and pragmatic concerns
warrant their use and risks to personnel safety can be
addressed. For more information, please consult the
Guidelines section on Inhaled Agents.
S7.4.4.2 Physical Methods
Penetrating captive bolt or firearm—Use of a penetrating captive bolt or firearm (free bullet) may be
appropriate for some species as a first step or adjunct
method of euthanasia, when there is species-specific
knowledge of target sites and safety considerations can
be met.
Advantages of these methods are that they are
moderately rapid (considering application of any needed restraint), they may be relatively easily implemented
under various conditions, they are applicable across a
wide range of species and sizes, and they leave no environmental residues (other than lead, which may be
sequestered). There are some disadvantages in that they
require appropriate, well-maintained equipment and
well-trained personnel, they are potentially aesthetically displeasing for observers, and they present safety
risks for personnel associated with the keeping and use
79
of firearms. Refer to ballistics details in the section on
Physical Methods and experts for more information on
selection and use of firearms.
S7.4.5 Adjunctive Methods
Potassium chloride—Potassium chloride can be
administered IV or intracardially to stop the heart of
animals that are deeply anesthetized or unconscious.
Potassium chloride does not create artifacts that can
interfere with histopathologic examination and, therefore, its application may be appropriate when accurate
postmortem diagnostic or research results are important. Potassium chloride may also be used adjunctively
for large animals that are first anesthetized with barbiturates, particularly where volume of administration
is a limitation. In many cases significant agonal reflex
activity can be avoided where barbiturates are administered prior to administration of potassium chloride.
Exsanguination—Exsanguination may be useful as
a secondary or tertiary method to ensure death. The
aesthetics of this procedure and its acceptance by personnel must be considered in its application.
Cervical dislocation or decapitation—Applied to
small mammals and birds, this method may be useful
as an adjunct or as a first-step method of euthanasia.
A paucity of data for wildlife and the potential for interspecies variation creates challenges for establishing
specific size recommendations. However, based on domestic animals, manual cervical dislocation may be appropriate for birds < 3 kg (6.6 lb), rodents < 200 g, and
rabbits < 1 kg (2.2 lb).599 A secondary method such as
decapitation or exsanguination should be employed to
ensure death when feasible.
Thoracic compression—Thoracic compression may
be useful in rare circumstances in animals that are deeply anesthetized or otherwise unconscious, or as a final,
confirmatory step when the animal’s status is uncertain.
S7.4.6 Unacceptable Methods
Methods that are classified as being unacceptable
for use in comparable domestic species are unacceptable for use in wild mammals that are not deeply anesthetized.
S7.4.7 Embryos, Fetuses, and Neonates
Euthanasia of embryos, fetuses, and neonates
should be conducted using guidelines appropriate for
taxonomically similar domestic mammals.
S7.5 CAPTIVE MARINE MAMMALS
Due to their unique anatomic and physiologic adaptations for aquatic environments, the large size of
some species, and the challenges associated with performing euthanasia under typical circumstances, marine mammals are considered separately from other
mammals. To facilitate making appropriate recommendations regarding euthanasia, marine mammals have
been divided into physiologically and anatomically distinct groups. These groups follow taxonomic lines to
some extent, though it is appropriate to consider the
80
sea otter (a large mustelid) with small pinnipeds: (1)
pinnipeds, (2) odontocetes, (3) mysticetes, and (4) sirinids. Methods addressed under methods of euthanasia
for captive mammals (nonmarine species) are applicable to polar bears, and will not be addressed in this section. Sizes of the animals vary dramatically among and
within these groups and each group should minimally
be divided into subgroups by size (large and small).
Recommendations for euthanasia of marine mammals
in managed care facilities differ from those used for
free-ranging marine mammals, because of differences
in environment and facilities, restraint capabilities, and
personnel and observers.
S7.5.1 Acceptable Methods
S7.5.1.1 Noninhaled Agents
Intravenous administration of barbiturates and
their derivatives can be a rapid and reliable method of
euthanasia for small pinnipeds, small odontocetes, and
sirinids. Intraperitoneal administration is also acceptable where intravascular administration is not possible
or is outweighed by distress from the requirement of
additional restraint, pain from alternate methods, risk
to personnel, or other similar reasons, although tissue
irritation and variable absorption rates must be considered. Safe and effective IV administration of these
agents may also be possible in anesthetized, moribund,
or unconscious large pinnipeds and in large odontocetes. For the largest odontocetes, drug dilution in
large volumes may limit the effectiveness of euthanasia
agents administered IV. Intracardiac administration is
acceptable only in anesthetized, moribund, or unconscious animals.
The advantage of using barbiturates is that death
is usually rapid. Unfortunately, voluntary peripheral
vasoconstriction by cetaceans or hypovolemic shock
may limit access to peripheral veins. There is also a
risk of injury for personnel attempting venipuncture if
animals are not restrained. Furthermore tissue residues
can present challenges for disposal of the animal’s remains and personnel are responsible for ensuring that
secondary toxicity does not occur.
Intramuscular administration of sedatives or anesthetics may be required to immobilize large, anxious, or
fractious animals to ensure animal and personnel safety
prior to administration of IV euthanasia agents. Agents
that have successfully been used alone or in combination for this purpose include tiletamine-zolazepam,
ketamine, xylazine, meperidine, fentanyl, midazolam,
diazepam, acepromazine, and etorphine.613 Veterinarians should be aware that administration of anesthetics
or sedatives in fat layers can result in prolonged time to
effect and diminished depth of sedation and anesthesia.
In addition, tissue residues, particularly when ultrapotent opioids are administered, need to be considered
when disposing of the animal’s remains.
S7.5.2 Acceptable With Conditions Methods
S7.5.2.1 Inhaled Agents
Inhaled anesthetics (eg, halothane, isoflurane,
sevoflurane, methoxyflurane, enflurane) are uncomAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
monly used to euthanize marine mammals because
these animals’ ability to breath- hold means that extended periods of physical restraint are necessary for
their administration. Extended restraint generally poses unacceptable risks and stress for the animal and for
personnel unless the animal is substantially debilitated,
sedated, or anesthetized. Use of inhaled agents may be
appropriate for small pinnipeds after administration of
an injectable sedative or anesthetic under circumstances where acceptable methods are not practical or appropriate for other reasons.
Inhaled agents present some advantages in that
they do not require phlebotomy skills and may present
minimal concern for tissue residues.171 Disadvantages
include that they are expensive, require an extended
delivery time with associated risks of distress and injury for animals and personnel, and may be noxious to
the animal.
S7.5.2.2 Physical Methods
Physical methods, although used to euthanize freeranging marine mammals, will generally not be used
on captive mammals due to limited efficacy for these
species, risk for personnel, and aesthetics.
to the euthanasia of wildlife. In the United States, management of wildlife is primarily under state jurisdiction.
However, some species (eg, migratory birds, endangered
species, marine mammals) are protected and managed
by federal agencies or through collaboration between
state and federal agencies. Within the context of wildlife
management, personnel associated with state and federal
agencies and Native American tribes may handle or capture individual animals or groups of animals for various
purposes, including research. During the course of these
management actions, individual animals may become injured or debilitated and may require euthanasia; in other
cases, research or collection protocols dictate that some
of them be killed. Sometimes population management
requires the lethal control of wildlife species. And, the
public may identify and/or present individual animals
to state or federal personnel because they are orphaned,
sick, injured, diseased (eg, rabid), or becoming a nuisance. Another aspect of wildlife management is rehabilitation of orphaned or injured wildlife. For the most
part, wildlife rehabilitation is done by private citizens
and requirements for handling these animals vary by
state and species.
S7.6.2 Special Considerations
S7.6 FREE-RANGING WILDLIFE
S7.6.1 General Considerations
Free-ranging wildlife are present in all habitats
across North America including fresh and salt water.
Wildlife includes representatives of all known animal
taxa, but for the purpose of the Guidelines, will be restricted to amphibians, reptiles, birds, and mammals,
including some feral and exotic species. Wildlife are enjoyed and used by people in a number of ways including nonconsumptive uses (wildlife viewing, bird watching, bird feeding) and legal harvest (hunting, fishing,
commercial take). Varied interests and perspectives can
influence what methods are used to terminate the lives
of free-ranging wildlife.614 This section of the Guidelines updates and expands upon previous editions by
recognizing an inherent lack of control over free-ranging wildlife, accepting that firearms may be the most
appropriate approach to their euthanasia, and acknowledging that the quickest and most humane means of
terminating the life of free-ranging wildlife in a given
situation may not always meet all criteria established
for euthanasia (ie, distinguishes between euthanasia
and methods that are more accurately characterized as
humane killing).
Because of the variety of situations that may be
encountered, it is difficult to strictly classify methods
for termination of free-ranging wildlife as acceptable,
acceptable with conditions, or unacceptable. Furthermore, classification of a given method as a means of euthanasia or humane killing may vary by circumstances.
These acknowledgments are not intended to condone
a lower standard for the humane termination of wildlife. The best methods possible under the circumstances must be applied, and new technology and methods
demonstrated to be superior to previously used methods must be embraced.
Multiple federal, state, and local regulations apply
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
The primary factor influencing methods selected
for euthanasia of free-ranging wildlife is lack of control
over the animal. In addition, some species may be too
large to effectively euthanize by conventional means.
Marine mammals are of particular concern due to their
large size and the lack of standardized equipment and
techniques (see Free-Ranging Marine Mammals for
more information). Other species, such as reptiles,
may be refractory to conventional euthanasia agents.
The potential for secondary toxicity and environmental
hazards associated with the remains of animals euthanized by chemical means are of substantial concern, as
is disposal of large or numerous animal remains. Therefore, while some methods described in the taxonomically based sections for nondomestic animals may be
useful for euthanizing free-ranging wildlife, their applicability will vary.
Given that close human contact is stressful and difficult to achieve for most free-ranging animals, these
animals may have to be euthanized or immobilized
from a distance. In some cases (eg, suburban areas),
discharge of a firearm is illegal, is considered a serious threat to human safety, or may be inappropriate for
other reasons. Consequently, free-ranging animals may
need to be killed quickly and efficiently in ways that
may not fulfill the criteria for euthanasia established by
the POE.
Remotely delivered chemical immobilization may
be required when wildlife cannot be captured. If a freeranging animal is within an acceptable range, trained
individuals may use species and situation-specific anesthetic agents and remote injection equipment to
anesthetize that animal to allow handling. Once anesthetized, many wildlife species can be euthanized via
methods similar to those applied to domestic or captive
wild animals of similar species and size. Other techniques used in wildlife management for trapping or
capturing animals may also be applied to allow some
81
degree of control over the animal.
Care must be taken to prevent secondary intoxication of animals or people during disposal of the remains of free-ranging wildlife that contain residues of
euthanasia agents. This is a legal requirement that often requires deep burial, incineration, or rendering. In
other situations, however, natural decomposition may
be desirable. Use of gunshot can minimize concerns for
secondary toxicity, with the exception of lead ballistics.
Alternatives to lead ballistics are recommended where
possible.
Although not typically a part of wildlife management programs, disease outbreaks or overpopulation
may require culling or large-scale killing of animals. In
addition to selecting the most appropriate methods for
minimizing spread of infectious agent, protecting animal welfare, and protecting the environment, such situations must consider the concerns and perceptions of
the general public, as well as impacts upon personnel
who are directly involved in culling, killing, or euthanasia. Detailed information about depopulation methods
is beyond the scope of this document, but will be made
available in the AVMA Guidelines for the Depopulation
of Animals.
Research objectives may limit the use of some euthanasia agents or methods for wildlife species. Nevertheless, termination of life still dictates that the most
humane, rather than the most convenient, methods be
used to meet the study’s objectives.
Within the context of wildlife rehabilitation, euthanasia of individual animals must be considered if a
fully functional animal cannot be returned to the wild,
if the release of such animals would pose a threat to the
health of the free-ranging wildlife population, or if no
alternatives for care or housing exist. While there are
a limited number of nonreleasable animals that can be
used for educational or display purposes, most animals
that are determined to be unfit for release should be euthanized as soon as possible. Because most animals in
rehabilitation facilities are confined, adequate control
through physical or chemical restraint can usually be
achieved that will allow administration of euthanasia
agents as described in the taxonomically based sections
for nondomestic animals.
which euthanasia of free-ranging wildlife may need to
be conducted, choice of the most humane method will
vary by species, situation, and individual animal. Conditions specified for use of various methods in previous sections will generally apply to free-ranging wildlife, but may be modified according to circumstances to
minimize animal distress and pain, as well as emotional
impact and physical risks to personnel.
S7.6.3.1 Acceptable Methods
S7.6.3.1.1 Noninhaled Agents
Chemical methods of euthanasia applicable to freeranging wildlife include overdoses of injectable anesthetic agents (including barbiturates), T-61, or other
agents that are listed as acceptable for domestic animals
or captive wildlife. Premedication with an injectable or
inhaled agent may reduce animal distress and/or human safety risks, under some circumstances.
S7.6.3.2 Acceptable With Conditions Methods
S7.6.3.2.1 Inhaled Agents
Inhaled anesthetics—Inhaled anesthetics are acceptable with conditions for euthanasia of avian and mammalian wildlife species when these methods are more
practical than acceptable methods, and where the limitations of this method are understood and addressed..
Smaller species that can be confined in enclosed containers can be euthanized using open-drop methods of
administration.622 Larger species may be restrained for
face-mask administration, when animal distress associated with restraint can be minimized. Portable equipment is available that can make these methods practical. Preference should be given to the use of alternate
methods for taxa that can breath-hold for extended periods of time.
Carbon dioxide, carbon monoxide, and other inert
gases—These agents, which are classified as being acceptable with conditions for domestic animals, are
also acceptable with conditions for euthanasia of freeranging wildlife. Conditions that must be met for using
these agents are similar to those for domestic animals.
S7.6.3 Methods
S7.6.3.2.2 Physical Methods
Little published information is available regarding
appropriate methods for euthanasia of specific species
of free-ranging wildlife. Schwartz et al282 evaluated immobilization and euthanasia for white-tailed deer, Hyman615 and Needham616 described euthanasia methods
for captive or stranded marine mammals, and the euthanasia of waterfowl was described by Gullett617 and
Franson.265 Methods for euthanasia of wildlife in rehabilitation facilities have also been described.415
While multiple publications describe euthanasia methods for domestic and nondomestic animals,52,53,63,132,575 as well as for wildlife under free-ranging conditions,618–621 their recommendations are inconsistent. Many conventional euthanasia techniques and
methods can be applied to free-ranging wildlife, if the
animals are sufficiently under the control of personnel.
However, because of the variety of conditions under
Gunshot is acceptable with conditions for euthanasia of free-ranging, captured, or confined wildlife,
provided that bullet placement is to the head (targeted
to destroy the brain).575 Gunshot targeted to the heart
(chest) or to the neck (vertebrae, with the intent of severing the spinal cord) presents challenges for accurate
placement, but may be the best option for free-ranging
or other settings where close approach is not possible
or where the head must be preserved for disease testing
(rabies, Chronic Wasting, or other suspected neurologic diseases). Based on domestic animal models (see
section of the Guidelines addressing Farmed Animals
Used for Food and Fiber), gunshot to the chest or neck
may not result in rapid death and may be considered
humane killing, rather than euthanasia. In some environments (eg, urban and suburban areas), discharge of
a firearm may present a serious threat to human safety
82
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
and may be inappropriate. Refer to ballistics details in
the Physical Methods section and experts for more information on selection and use of firearms.
S7.6.3.3 Adjunctive Methods
Potassium chloride—Potassium chloride may be
administered IV or intracardially to stop the heart of
animals that are deeply anesthetized or unconscious.
Administration of potassium chloride can also be preferred for large animals when administered with barbiturates, where volume of administration is a limitation.
Exsanguination—Bleeding may be used as an adjunctive method to ensure the death of animals that are
anesthetized or otherwise unconscious. The aesthetics
of this procedure and its acceptance by personnel and
observers should be considered.
Cervical dislocation or decapitation—Applied to
small mammals and birds, this method may be useful as
an adjunct or as a first-step method of euthanasia. A paucity of data for wildlife and the potential for interspecies
variation create challenges for establishing specific size
recommendations. However, based on domestic animals,
manual cervical dislocation may be appropriate for birds
< 3 kg, rodents < 200 g, and rabbits < 1 kg.599 A secondary method such as decapitation or exsanguination
should be employed to ensure death when feasible.
Thoracic compression—Thoracic compression may
be useful in rare circumstances in animals that are
deeply anesthetized or otherwise unconscious, or as a
final, confirmatory method to ensure death when the
animal’s status is uncertain.
S7.6.3.4 Unacceptable Methods
Approaches to euthanasia that ignore recent advances in technology, and that do not minimize risks to
animal welfare, personnel safety, and the environment
for a particular set of circumstances, are unacceptable.
S7.6.4 Embryos, Fetuses, and Neonates
Methods that are acceptable for euthanasia of domestic or captive wildlife species in developmental or
neonatal stages are generally acceptable for euthanasia
of similar stages of free-ranging wildlife.
S7.7 FREE-RANGING MARINE MAMMALS
Selecting a method of euthanasia for free-ranging
marine mammals can be a substantial challenge because of large body size, environmental constraints, and
concerns for the safety of personnel. It can also be difficult to determine when stranded marine mammals are
unconscious or dead.623 Currently available euthanasia
methods generally have significant limitations that fail
to meet aesthetic or other conventional standards for
euthanasia of marine mammals under field conditions,
particularly for large animals. Nevertheless, the options
available must be evaluated to identify the best option
under a given set of circumstances. Further research is
warranted to identify improved methods of euthanasia.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
S7.7.1 Acceptable Methods
S7.7.1.1 Noninhaled agents
Overdoses of injectable anesthetics can be used
to euthanize marine mammals under field conditions.
Anesthetics that can be used alone or in combination
include tiletamine-zolazepam, ketamine, xylazine, meperidine, fentanyl, midazolam, diazepam, butorphanol,
acepromazine, barbiturates, and etorphine.613,624,625 Intramuscular administration of anesthetics may be required to achieve restraint of conscious animals before
personnel can safely perform euthanasia using injectable agents by an intravascular route. A clear understanding of species anatomy and use of sufficiently long
needles are required to ensure that muscle, rather than
fat, is the site of injection.
Injectable anesthetics may be administered by
multiple routes. Mucocutaneous administration, via
the blowhole, can be an effective method that maximizes personnel safety.625 Intravenous administration
can be rapid and reliable for small pinnipeds, small
odontocetes, and sirinids. For larger animals, safe IV
administration is generally limited to animals that are
anesthetized or unconscious. In addition, drug dilution in large blood volumes of large odontocetes and
mysticetes may limit the effectiveness of IV administered agents. Intraperitoneal administration can be effective for small marine mammals if sufficiently long
needles are available to access the peritoneal cavity.
However, delayed absorption may limit the efficacy of
drugs administered via this route. Intracardiac administration is acceptable only in anesthetized, moribund,
or unconscious animals. This approach requires special, strong, and long needles to ensure that the heart
can be accessed.
Advantages of injectable anesthetics are that they
act rapidly and personnel experienced with these methods are readily available. Their administration is logistically simple and aesthetically acceptable, and public
safety is relatively easy to secure. However, voluntary
peripheral vasoconstriction by cetaceans or hypovolemic shock may limit access to peripheral veins and fat
layers must be bypassed for effective administration.
Large quantities of drug may be required to effectively
euthanize large animals, and administration of single
types of agents, such as α2 adrenergic receptor agonists,
can result in animals passing through aesthetically displeasing and potentially unsafe excitation phases of
anesthesia. There is a risk of injury for personnel attempting to access veins if animals are not appropriately restrained, and personnel may also face self-administration risks (especially for ultrapotent opioids).
Environmental contamination and scavenger exposure
are possible due to residues in the animal’s remains.
S7.7.2 Acceptable With Conditions Methods
S7.7.2.1 Physical Methods
Gunshot—Gunshot is acceptable with conditions
for euthanizing small marine mammals when injectable methods are not practical; conventional projectile
ballistics are not recommended for use in large odontocetes or large mysticetes. References are available to as83
sist in identifying appropriate anatomic landmarks and
caliber of ballistics.348,626–630
Advantages of gunshot include a rapid death and
equipment that is generally readily available. Gunshot
also poses minimal risk for other animals that may
scavenge the animal’s remains. However, its efficacy is
highly dependent on the knowledge, technical expertise, and experience of the operator. Associated noise
can distress other animals (especially in the case of
mass strandings) and ricochet poses a risk to bystanders. Euthanasia by gunshot may also be aesthetically
displeasing and emotionally distressing for personnel
and bystanders. Compliance with firearm regulations is
also required. Refer to details for ballistics in the Physical Methods section and experts for more information
on selection and use of firearms.
Manually applied blunt force trauma—In situations
where other options are not available, a concussive
blow to the head may be an effective method of euthanasia for small juvenile marine mammals.631 The advantages of properly applied manual blunt force trauma are
that it results in rapid death, no special equipment is
required, and there is limited potential for secondary
toxicity for scavengers. However, the efficacy of manually applied blunt force trauma is highly dependent on
knowledge and experience of the operator and it is aesthetically displeasing for personnel and observers.
Implosive decerebration—Decerebration of large mysticetes and odontocetes can be effectively accomplished
through the detonation of properly placed, shaped, and
dimensioned explosive charges.632,633 Advantages of this
technique include a rapid death, limited potential for
exposure of scavengers to toxic residues, and protection
of personnel from injury by tail flukes. Its efficacy, however, is highly dependent on the knowledge, skills, and
experience of the operator; it is aesthetically displeasing;
and personnel and bystanders must be sufficiently distant from the resulting explosion to avoid injury. If these
conditions can be met, implosive decerebration is an acceptable method of euthanasia.
S7.7.3 Adjunctive Methods
Potassium chloride or succinylcholine—While unacceptable as sole agents of euthanasia in awake animals,
potassium chloride or succinylcholine may be used to
ensure the death of animals that are anesthetized or unconscious. Saturated potassium chloride solutions can
be mixed inexpensively in large volumes and can be
administered IV or intracardially, with a low risk of secondary toxicity for scavengers when preferred methods
of disposal of the remains (eg, deep burial, rendering)
are not available.613,634
as a sole method of euthanasia because it requires an
excessively long time to death, is believed to produce
anxiety associated with extreme hypovolemia, and is
aesthetically displeasing to bystanders. It can, however,
be used as an adjunctive method to ensure the death of
unconscious animals.630
a.
b.
c.
d.
e.
f.
g.
h.
References
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10.
11.
12.
13.
14.
15.
S7.7.4 Unacceptable Methods
16.
Inhaled agents—While acceptable with conditions
from an animal welfare standpoint, practical and human and environmental safety constraints generally
prevent use of inhaled agents for euthanasia of marine
mammals under field conditions.
17.
Exsanguination—Exsanguination is inappropriate
84
Anthony R, University of Alaska Anchorage, Anchorage, Alaska:
Personal communication, 2011.
Tributame, TEVA Animal Health Inc, St Joseph, Mo.
T-61, Intervet Canada Corp, Kirkland, QC, Canada.
Finquel, Argent Laboratories Inc, Redmond, Wash.
Tricaine-S, Western Chemical, Ferndale, Wash.
Twitchell C, Roy LD, Gilbert FF, et al. Effectiveness of rotatingjaw killing traps for beaver (Castor Canadensis) (oral presentation). North Am Aquat Furbearer Symp, Starkville, Miss, May
1999.
Mays J. Euthanasia certification (slide presentation). Natl Anim
Control Assoc Euthanasia Certification Workshop, Dayton,
Ohio, September 2011.
Telazol, Fort Dodge Animal Health, Overland Park, Kan.
18.
19.
Sandoe P, Christiansen SB. Ethics of animal use. Chichester, West
Sussex, England: Wiley-Blackwell, 2008;1–14, 15–32, 49–66.
Rollin BE. Animal agriculture and emerging social ethics for
animals. J Anim Sci 2004;82:955–964.
DeGrazia D. Self-awareness in animals. In: Lurz R, ed. The philosophy of animal minds. Cambridge, England: Cambridge University Press, 2009;201–217.
Thompson PB. Ethics on the frontiers of livestock science. In:
Swain DL, Charmley E, Steel JW, et al, eds. Redesigning animal
agriculture: the challenge of the 21st century. Cambridge, Mass:
CABI, 2007;30–45.
Thompson PB. Getting pragmatic about farm animal welfare. In:
McKenna E, Light A, eds. Animal pragmatism: rethinking humannonhuman relationships. Bloomington, Ind: Indiana University
Press, 2004;140–159.
DeGrazia D. Animal ethics around the turn of the twenty-first
century. J Agric Environ Ethics 1999;11:111–129.
DeGrazia D. Taking animals seriously: mental life and moral status. Cambridge, England: Cambridge University Press, 1996.
Thompson PB. Agricultural ethics: research, teaching, and public
policy. Ames, Iowa: Iowa State University Press, 1998.
Varner G. In nature’s interests? Interests, animal rights and environmental ethics. Oxford, England: Oxford University Press, 1998.
AVMA. Veterinarian’s oath. Available at: www.avma.org/KB/
Policies/Pages/veterinarians-oath.aspx. Accessed May 13, 2011.
Pavlovic D, Spassov A, Lehmann C. Euthanasia: in defense of a
good, ancient word. J Clin Res Bioeth [serial online] 2011;2:105.
doi:10.4172/2155-9627.1000105. Accessed August 13, 2012.
AVMA. AVMA animal welfare principles. Available at: www.
avma.org/KB/Policies/Pages/AVMA-Animal-Welfare-Principles.
aspx. Accessed May 7, 2011.
AVMA. Euthanasia of animals that are unwanted or unfit for
adoption. Available at: www.avma.org/KB/Policies/Pages/
Euthanasia-of-Animals-That-Are-Unwanted-or-Unfit-for-Adoption.aspx. Accessed May 7, 2011.
Haynes R. Animal welfare: competing conceptions and their ethical
implications. Dort, The Netherlands: Springer, 2008.
Appleby MC. What should we do about animal welfare? Oxford,
England: Blackwell, 1999.
Fraser D, Weary DM, Pajor EA, et al. A scientific conception
of animal welfare that reflects ethical concerns. Anim Welf
1997;6:187–205.
Duncan IJH. Animal welfare defined in terms of feelings. Acta
Agric Scand A Anim Sci 1996;(suppl 27):29–35.
Yeates J. Death is a welfare issue. J Agric Environ Ethics
2010;23:229–241.
Kamm FM. Morality, mortality. Vol 1. Oxford, England: Oxford
University Press, 1993.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
20. Morton DB. A hypothetical strategy for the objective evaluation
of animal well-being and quality of life using a dog model. Anim
Welf 2007;16(suppl):75–81.
21. Rollin BE. Animal euthanasia and moral stress. In: Kay WJ, Cohen SP, Fudin CE, et al, eds. Euthanasia of the companion animal.
Philadelphia: Charles Press, 1988;31–41.
22. Niel L, Stewart, SA, Weary, DM. Effect of flow rate on aversion
to gradual-fill carbon dioxide euthanasia in rats. Appl Anim Behav Sci 2008;109:77–84.
23. Brown M, Carbone L, Conlee KM, et al. Report of the working group on animal distress in the laboratory. Lab Anim (NY)
2006;35:26–30.
24. Demers G, Griffin G, DeVroey G, et al. Animal research.
Harmonization of animal care and use guidelines. Science
2006;312:700–701.
25. Hawkins P, Playle L, Golledge H, et al. Newcastle consensus
meeting on carbon dioxide euthanasia of laboratory animals.
London: National Centre for the Replacement, Refinement
and Reduction of Animals in Science, 2006. Available at: www.
nc3rs.org.uk/downloaddoc.asp?id=416&page=292&skin=0.
Accessed Jan 20, 2011.
26. AVMA. Principles of veterinary medical ethics of the AVMA.
Available at: www.avma.org/KB/Policies/Pages/Principles-ofVeterinary-Medical-Ethics-of-the-AVMA.aspx. Accessed May
13, 2011.
27. Rollin BE. An introduction to veterinary medical ethics. 2nd ed.
Ames, Iowa: Blackwell, 2006.
28. Croney CC, Anthony R. Engaging science in a climate of values:
tools for animal scientists tasked with addressing ethical problems. J Anim Sci 2010;88(suppl 13):E75–E81.
29. Sandoe P, Christiansen SB, Appleby MC. Farm animal welfare:
the interaction of ethical questions and animal welfare science.
Anim Welf 2003;12:469–478.
30. Fraser D. Animal ethics and animal welfare science: bridging
the two cultures. Appl Anim Behav Sci 1999;65:171–189.
31. Thompson PB. From a philosopher’s perspective, how should
animal scientists meet the challenge of contentious issues? J
Anim Sci 1999;77:372–377.
32. Webster J. Animal welfare: a cool eye towards Eden. Oxford, England: Blackwell, 1994.
33. Anderson E. Animal rights and the values of nonhuman life.
In: Sunstein C, Nussbaum M, eds. Animal rights: current debates
and new directions. Oxford, England: Oxford University Press,
2004;277–298.
34. Regan T. Animal rights, human wrongs: an introduction to moral
philosophy. Lanham, Md: Rowman and Littlefield, 2003.
35. Pluhar E. Beyond prejudice. Durham, NC: Duke University
Press, 1995.
36. Regan T. The case for animal rights. Berkeley, Calif: University of
California Press, 1983.
37. Anthony R. Ethical implications of the human-animal bond on
the farm. Anim Welf 2003;12:505–512.
38. Burgess-Jackson K. Doing right by our animal companions. J
Ethics 1998;2:159–185.
39. Frey R. Rights, killing and suffering. Oxford, England: Blackwell,
1983.
40. Singer P. Practical ethics. Cambridge: Cambridge University
Press, 1978.
41. Rollin BE. The use and abuse of Aesculapian authority in veterinary medicine. J Am Vet Med Assoc 2002;220:1144–1149.
42. Hendrickx JF, Eger EI II, Sonner JM, et al. Is synergy the rule?
A review of anesthetic interactions producing hypnosis and immobility. Anesth Analg 2008;107:494–506.
43. Antognini JF, Barter L, Carstens E. Overview: movement as an
index of anesthetic depth in humans and experimental animals.
Comp Med 2005;55:413–418.
44. Alkire MT, Hudetz AG, Tononi G. Consciousness and anesthesia. Science 2008;322:876–880.
45. Gregory NG. Animal welfare at markets and during transport
and slaughter. Meat Sci 2008;80:2–11.
46. Finnie JW. Neuropathologic changes produced by non-penetrating percussive captive bolt stunning of cattle. N Z Vet J
1995;43:183–185.
47. Blackmore DK, Newhook JC. The assessment of insensibility
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
in sheep, calves and pigs during slaughter. In: Eikelenboom G,
ed. Stunning of animals for slaughter. Boston: Martinus Nijhoff
Publishers, 1983;13–25.
Gregory NG, Lee CJ, Widdicombe JP. Depth of concussion in
cattle shot by penetrating captive bolt. Meat Sci 2007;77:499–
503.
Vogel KD, Badtram G, Claus JR, et al. Head-only followed by
cardiac arrest electrical stunning is an effective alternative to
head-only electrical stunning in pigs. J Anim Sci 2011;89:1412–
1418.
Blackmore DK, Newhook JC. Electroencephalographic studies
of stunning and slaughter of sheep and calves. 3. The duration
of insensibility induced by electrical stunning in sheep and
calves. Meat Sci 1982;7:19–28.
Cartner SC, Barlow SC, Ness TJ. Loss of cortical function in
mice after decapitation, cervical dislocation, potassium chloride
injection, and CO2 inhalation. Comp Med 2007;57:570–573.
Close B, Banister K, Baumans V, et al. Recommendations for
euthanasia of experimental animals: part 2. DGXT of the European Commission. Lab Anim 1997;31:1–32.
Close B, Banister K, Baumans V, et al. Recommendations for euthanasia of experimental animals: part 1. DGXI of the European
Commission.. Lab Anim 1996;30:293–316.
Gregory NG, Wotton SB. Effect of slaughter on the spontaneous
and evoked activity of the brain. Br Poult Sci 1986;27:195–205.
Bates G. Humane issues surrounding decapitation reconsidered.
J Am Vet Med Assoc 2010;237:1024–1026.
Holson RR. Euthanasia by decapitation: evidence that this technique produces prompt, painless unconsciousness in laboratory
rodents. Neurotoxicol Teratol 1992;14:253–257.
Derr RF. Pain perception in decapitated rat brain. Life Sci
1991;49:1399–1402.
Vanderwolf CH, Buzak DP, Cain RK, et al. Neocortical and hippocampal electrical activity following decapitation in the rat.
Brain Res 1988;451:340–344.
Mikeska JA, Klemm WR. EEG evaluation of humaneness of asphyxia and decapitation euthanasia of the laboratory rat. Lab
Anim Sci 1975;25:175–179.
Muir WW. Considerations for general anesthesia. In: Tranquilli
WJ, Thurmon JC, Grimm KA, eds. Lumb and Jones’ veterinary
anesthesia and analgesia. 4th ed. Ames, Iowa: Blackwell, 2007;7–
30.
Erhardt W, Ring C, Kraft H, et al. CO2 stunning of swine for
slaughter from the anesthesiological viewpoint. Dtsch Tierarztl
Wochenschr 1989;96:92–99.
International Association for the Study of Pain. Pain
terms.
Available
at:
www.iasp-pain.org/AM/Template.
cfm?Section=Pain_Definitions&Template=/CM/HTMLDisplay.
cfm&ContentID=1728#Pain. Accessed Feb 7, 2011.
AVMA. AVMA guidelines on euthanasia. June 2007. Available
from AVMA Animal Welfare Division (animalwelfare@avma.
org).
Tarsitano MS, Jackson RR. Araneophagic jumping spiders discriminate between detour routes that do and do not lead to prey.
Anim Behav 1997;53:257–266.
Jackson RR, Carter CM, Tarsitano MS. Trial-and-error solving
of a confinement problem by a jumping spider, Portia fibriata.
Behaviour 2001;138:1215–1234.
Dyakonova VE. Role of opiod peptides in behavior of invertebrates. J Evol Biochem Physiol 2001;37:335–347.
Sladky KK, Kinney ME, Johnson SM. Analgesic efficacy of butorphanol and morphine in bearded dragons and corn snakes. J
Am Vet Med Assoc 2008;233:267–273.
Baker BB, Sladky KK, Johnson SM. Evaluation of the analgesic
effects of oral and subcutaneous tramadol administration in redeared slider turtles. J Am Vet Med Assoc 2011;238:220–227.
Sneddon LU, Braithwaite VA, Gentle JM. Do fish have nociceptors? Evidence for the evolution of a vertebrate sensory system.
Proc Biol Sci 2003;270:1115–1121.
Sneddon LU. Anatomical and electrophysiological analysis of
the trigeminal nerve in a teleost fish, Oncorhynchus mykiss. Neurosci Lett 2002;319:167–171.
Rose JD. The neurobehavioral nature of fishes and the question
of awareness and pain. Rev Fish Sci 2002;10:1–38.
85
72. Nordgreen J, Horsberg TE, Ranheim B, et al. Somatosensory
evoked potentials in the telencephalon of Atlantic salmon
(Salmo salar) following galvanic stimulation of the tail. J Comp
Physiol A Neuroethol Sens Neural Behav Physiol 2007;193:1235–
1242.
73. Dunlop R, Laming P. Mechanoreceptive and nociceptive responses in the central nervous system of goldfish (Carassius auratus) and trout (Oncorhynchus mykiss). J Pain 2005;6:561–568.
74. Braithwaite VA. Cognition in fish. Behav Physiol Fish 2006;24:1–
37.
75. Kitchen N, Aronson AL, Bittle JL, et al. Panel report on the Colloquium on Recognition and Alleviation of Animal Pain and
Distress. J Am Vet Med Assoc 1987;191:1186–1191.
76. Wack R, Morris P, Sikarskie J, et al. Criteria for humane euthanasia and associated concerns. In: American Association of Zoo
Veterinarians (AAZV). Guidelines for euthanasia of nondomestic
animals. Yulee, Fla: American Association of Zoo Veterinarians,
2006;3–5.
77. National Research Committee on Pain and Distress in Laboratory Animals, Institute of Laboratory Animal Resources, Commission on Life Sciences, National Research Council. Recognition
and alleviation of pain and distress in laboratory animals. Washington, DC: National Academy Press, 1992.
78. Breazile JE. Physiologic basis and consequences of distress in
animals. J Am Vet Med Assoc 1987;191:1212–1215.
79. McMillan FD. Comfort as the primary goal in veterinary medical practice. J Am Vet Med Assoc 1998;212:1370–1374.
80. Coppola CL, Grandin T, Enns MR. Human interaction and cortisol: can human contact reduce stress in shelter dogs? Physiol
Behav 2006;87:537–541.
81. Van Reenen CG, O’Connell NE, Van der Werf JT, et al. Response
of calves to acute stress: individual consistency and relations
between behavioral and physiological measures. Physiol Behav
2005;85:557–570.
82. Dantzer R, Mormède P. Stress in farm animals: a need for reevaluation. J Anim Sci 1983;57:6–18.
83. Moberg GP, Wood VA. Effect of differential rearing on the behavorial and adrenocortical response of lambs to a novel environment. Appl Anim Ethol 1982;8:269–279.
84. Baran BE, Allen JA, Rogelberg SG, et al. Euthanasia-related
strain and coping strategies in animal shelter employees. J Am
Vet Med Assoc 2009;235:83–88.
85. Collette JC, Millam JR, Klasing KC, et al. Neonatal handling
of Amazon parrots alters stress response and immune function.
Appl Anim Behav Sci 2000;66:335–349.
86. Grandin T. Assessment of stress during handling and transport.
J Anim Sci 1997;75:249–257.
87. Boandl KE, Wohlt JE, Carsia RV. Effect of handling, administration of a local anesthetic and electrical dehorning on plasma
cortisol in Holstein calves. J Dairy Sci 1989;72:2193.
88. Lay DC, Friend TH, Bowers CL, et al. A comparative physiological and behavioral study of freeze and hot-iron branding using
dairy cows. J Anim Sci 1992;70:1121–1125.
89. Lay DC, Friend TH, Randel RD, et al. Behavioral and physiological effects of freeze and hot-iron branding on crossbred cattle. J
Anim Sci 1992;70:330–336.
90. Duke JL, Zammit TG, Lawson DM. The effects of routine cagechanging in cardiovascular and behavioral parameters in male
Sprague-Dawley rats. Contemp Top Lab Anim Sci 2001;40:17–20.
91. Ramsay EC, Wetzel RW. Comparison of five regimens for oral
administration of medication to induce sedation in dogs prior
to euthanasia. J Am Vet Med Assoc 1998;213:240–242.
92. Wetzel RW, Ramsay EC. Comparison of four regimens for intraoral administration of medication to induce sedation in cats
prior to euthanasia. J Am Vet Med Assoc 1998;213:243–245.
93. Houpt KA. Domestic animal behavior for veterinarians and animal scientists. 3rd ed. Ames, Iowa: Iowa State University Press,
1998.
94. Beaver BV. Canine behavior: a guide for veterinarians. Philadelphia: WB Saunders Co, 1998;.
95. Beaver BV. The veterinarian’s encyclopedia of animal behavior.
Ames, Iowa: Iowa State University Press, 1994;.
96. Schafer M. The language of the horse: habits and forms of expression. New York: Arco Publishing Co, 1975.
86
97. White RG, DeShazer JA, Tressler CJ, et al. Vocalization and
physiological response of pigs during castration with and without a local anesthetic. J Anim Sci 1995;73:381–386.
98. Warriss PD, Brown SN, Adams M. Relationships between subjective and objective assessments of stress at slaughter and meat
quality in pigs. Meat Sci 1994;38:329–340.
99. Dunn CS. Stress reactions of cattle undergoing ritual slaughter
using two methods of restraint. Vet Rec 1990;126:522–525.
100. Grandin T. Cattle vocalizations are associated with handling
and equipment problems in slaughter plants. Appl Anim Behav
Sci 2001;71:191–201.
101. Grandin T. Objective scoring of animal handling and stunning
practices at slaughter plants. J Am Vet Med Assoc 1998;212:36–
39.
102. Jones AB. Experimental novelty and tonic immobility in chickens (Gallas domesticus). Behav Processes 1984;9:255–260.
103. Vieville-Thomas C, Signoret JP. Pheromonal transmission of an
aversive experience in domestic pig. J Chem Ecol 1992;18:1551–
1557.
104. Stevens DA, Saplikoski NJ. Rats’ reactions to conspecific muscle
and blood evidence for alarm substances. Behav Biol 1973;8:75–
82.
105. Grandin T. Effect of animal welfare audits of slaughter plants
by a major fast food company on cattle handling and stunning
practices. J Am Vet Med Assoc 2000;216:848–851.
106. Grandin T. Euthanasia and slaughter of livestock. J Am Vet Med
Assoc 1994;204:1354–1360.
107. Grandin T. Pig behavior studies applied to slaughter-plant design. Appl Anim Ethol 1982;9:141–151.
108. Grandin T. Observations of cattle behavior applied to design of
cattle handling facilities. Appl Anim Ethol 1980;6:19–31.
109. Nogueira Borden LJ, Adams CL, Bonnett BN, et al. Use of the
measure of patient-centered communication to analyze euthanasia discussions in companion animal practice. J Am Vet Med
Assoc 2010;237:1275–1287.
110. Martin F, Ruby KL, Deking TM, et al. Factors associated with
client, staff, and student satisfaction regarding small animal euthanasia procedures at a veterinary teaching hospital. J Am Vet
Med Assoc 2004;224:1774–1779.
111. Guntzelman J, Riegger MH. Helping pet owners with the euthanasia decision. Vet Med 1993;88:26–34.
112. Arluke A. Managing emotions in an animal shelter. In: Manning
A, Serpell J, eds. Animals and human society. New York: Routledge, 1994;145–165.
113. Rhoades RH. The Humane Society of the United States euthanasia training manual. Washington, DC: Humane Society Press,
2002.
114. Manette CS. A reflection on the ways veterinarians cope with
the death, euthanasia, and slaughter of animals. J Am Vet Med
Assoc 2004;225:34–38.
115. Adams CL, Bonnett BN, Meek AH. Predictors of owner response
to companion animal death in 177 clients from 14 practices in
Ontario. J Am Vet Med Assoc 2000;217:1303–1309.
116. Shaw JR, Lagoni L. End-of-life communication in veterinary
medicine: delivering bad news and euthanasia decision making.
Vet Clin North Am Small Anim Pract 2007;37:95–108.
117. Frid MH, Perea AT. Euthanasia and thanatology in small animals. J Vet Behav 2007;2:35–39.
118. AVMA. Pet loss support hotlines (grief counseling). J Am Vet
Med Assoc 1999;215:1805.
119. Hart LA, Mader B. Pet loss support hotline: the veterinary students’ perspective. Calif Vet 1992;Jan-Feb:19–22.
120. Neiburg HA, Fischer A. Pet loss: a thoughtful guide for adults
and children. New York: Harper & Row, 1982.
121. Rogelberg SG, Reeve CL, Spitzmüller C, et al. Impact of euthanasia rates, euthanasia practices, and human resource practices
on employee turnover in animal shelters. J Am Vet Med Assoc
2007;230:713–719.
122. Arluke A. Coping with euthanasia: a case study of shelter culture. J Am Vet Med Assoc 1991;198:1176–1180.
123. Reeve CL, Rogelberg SG, Spitzmuller C, et al. The caring-killing
paradox: euthanasia-related strain among animal shelter workers. J Appl Soc Psychol 2005;35:119–143.
124. White DJ, Shawhan R. Emotional responses of animal shelter
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
workers to euthanasia. J Am Vet Med Assoc 1996;208:846–849.
125. Wolfle T. Laboratory animal technicians: their role in stress reduction and human-companion animal bonding. Vet Clin North
Am Small Anim Pract 1985;15:449–454.
126. Rohlf V, Bennett P. Perpetration-induced traumatic stress in
persons who euthanize nonhuman animals in surgeries, animal
shelters, and laboratories. Soc Anim 2005;13:201–219.
127. Bayne K. Development of the human-research bond and its impact on animal well-being. ILAR J 2002;43:4–9.
128. Chang FT, Hart LA. Human-animal bonds in the laboratory:
how animal behavior affects the perspectives of caregivers. ILAR
J 2002;43:10–18.
129. Overhulse KA. Coping with lab animal morbidity and mortality:
a trainer’s role. Lab Anim (NY) 2002;31:39–42.
130. Woods J, Shearer JK, Hill J. Recommended on-farm euthanasia
practices. In: Grandin T, ed. Improving animal welfare: a practical approach. Wallingford, Oxfordshire, England: CABI Publishing, 2010.
131. Morrow WEM. Euthanasia hazards. In: Langley RL, ed. Animal
handlers. Occupational medicine: state of the art reviews. Philadelphia: Hanley and Belfus, 1999;14(2):235–246.
132. Reilly JS, ed. Euthanasia of animals used for scientific purposes.
Adelaide, SA: Australia and New Zealand Council for the Care
of Animals in Research and Teaching, Department of Environmental Biology, Adelaide University, 2001.
133. Murray MJ. Euthanasia. In: Lewbart GA, ed. Invertebrate medicine. Ames, Iowa: Blackwell, 2006;303–304.
134. Messenger JB, Nixon M, Ryan KP. Magnesium chloride as
an anaesthetic for cephalopods. Comp Biochem Physiol C
1985;82:203–205.
135. Meyer RE, Morrow WEM. Euthanasia. In: Rollin BE, Benson GJ,
eds. Improving the well-being of farm animals: maximizing welfare and minimizing pain and suffering. Ames, Iowa: Blackwell,
2004;351–362.
136. Fakkema D. Operational guide for animal care and control agencies: euthanasia by injection. Denver: American Humane Association, 2010.
137. Krueger BW, Krueger KA. US Fish and Wildlife Service fact
sheet: secondary pentobarbital poisoning in wildlife. Available
at: cpharm.vetmed.vt.edu/USFWS/. Accessed Mar 7, 2011.
138. O’Rourke K. Euthanatized animals can poison wildlife: veterinarians receive fines. J Am Vet Med Assoc 2002;220:146–147.
139. Otten DR. Advisory on proper disposal of euthanatized animals.
J Am Vet Med Assoc 2001;219:1677–1678.
140. Alkire MT. General anesthesia. In: Banks WP, ed. Encyclopedia of
consciousness. San Diego: Elsevier/Academic Press, 2009;296–313.
141. Sharp J, Azar T, Lawson D. Comparison of carbon dioxide, argon, and nitrogen for inducing unconsciousness or euthanasia
of rats. J Am Assoc Lab Anim Sci 2006;45:21–25.
142. Christensen L, Barton Gade P. Danish Meat Institute. Transportation and pre-stun handling: CO2 systems. Available at: www.
butina.eu/fileadmin/user_upload/images/articles/transport.pdf .
Accessed Dec 13, 2010.
143. Interagency Research Animal Committee. US government principles for the utilization and care of vertebrate animals used
in testing, research and training. Available at: grants.nih.gov/
grants/olaw/references/phspol.htm#USGovPrinciples. Accessed
Dec 13, 2010.
144. Chorney JM, Kain ZN. Behavioral analysis of children’s response
to induction of anesthesia. Anesth Analg 2009;109:1434–1440.
145. Przybylo HJ, Tarbell SE, Stevenson GW. Mask fear in children
presenting for anesthesia: aversion, phobia, or both? Paediatr
Anaesth 2005;15:366–370.
146. Glass HG, Snyder FF, Webster E. The rate of decline in resistance to anoxia of rabbits, dogs, and guinea pigs from the onset
of viability to adult life. Am J Physiol 1944;140:609–615.
147. Garnett N. PHS policy on humane care and use of laboratory
animals clarification regarding use of carbon dioxide for euthanasia of small laboratory animals. Release date: July 17, 2002.
Available at: grants.nih.gov/grants/guide/notice-files/NOTOD-02-062.html. Accessed Dec 14, 2010.
148. Meyer RE, Morrow WEM. Carbon dioxide for emergency onfarm euthanasia of swine. J Swine Health Prod 2005;13:210–217.
149. Meyer RE. Principles of carbon dioxide displacement. Lab Anim
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
(NY) 2008;37:241–242.
150. Nunn JF. Nunn’s applied respiratory physiology. 4th ed. Oxford,
England: Butterworth-Heinemann, 1993;583–593.
151. Davis PD, Kenny GNC. Basic physics and measurement in
anaesthesia. 5th ed. Edinburgh: Butterworth-Heinemann,
2003;57–58.
152. Hornett TD, Haynes AP. Comparison of carbon dioxide/air
mixture and nitrogen/air mixture for the euthanasia of rodents:
design of a system for inhalation euthanasia. Anim Technol
1984;35:93–99.
153. Smith W, Harrap SB. Behavioural and cardiovascular responses of rats to euthanasia using carbon dioxide gas. Lab Anim
1997;31:337–346.
154. Niel L, Weary DM. Behavioural responses of rats to gradual-fill
carbon dioxide euthanasia and reduced oxygen concentrations.
Appl Anim Behav Sci 2006;100:295–308.
155. Booth NH. Inhalant anesthetics. In: Booth NH, McDonald LE,
eds. Veterinary pharmacology and therapeutics. 6th ed. Ames,
Iowa: Iowa State Univeristy Press, 1988;181–211.
156. Flecknell PA, Roughan JV, Hedenqvist P. Induction of anaesthesia with sevoflurane and isoflurane in the rabbit. Lab Anim
1999;33:41–46.
157. Voss LJ, Sleigh JW, Barnard JP, et al. The howling cortex: seizures
and general anesthetic drugs. Anesth Analg 2008;107:1689–
1703.
158. Knigge U, Søe-Jensen P, Jorgensen H, et al. Stress-induced release of anterior pituitary hormones: effect of H3 receptor-mediated inhibition of histaminergic activity or posterior hypothalamic lesion. Neuroendocrinology 1999;69:44–53.
159. Tinnikov AA. Responses of serum corticosterone and corticosteroid-binding globulin to acute and prolonged stress in the rat.
Endocrine 1999;11:145–150.
160. Zelena D, Kiem DT, Barna I, et al. Alpha-2-adenoreceptor subtypes regulate ACTH and beta-endorphin secretions during
stress in the rat. Psychoneuroendocrinology 1999;24:333–343.
161. van Herck H, Baumans V, de Boer SF, et al. Endocrine stress response in rats subjected to singular orbital puncture while under diethyl-ether anesthesia. Lab Anim 1991;25:325–329.
162. Leach MC, Bowell VA, Allan TF, et al. Aversion to gaseous euthanasia agents in rats and mice. Comp Med 2002;52:249–257.
163. Leach MC, Bowell VA, Allan TF, et al. Degrees of aversion shown
by rats and mice to different concentrations of inhalational anaesthetics. Vet Rec 2002;150:808–815.
164. Leach MC, Bowell VA, Allan TF, et al. Measurement of aversion
to determine humane methods of anaesthesia and euthanasia.
Anim Welf 2004;13:S77–S86.
165. Makowska LJ, Weary DM. Rat aversion to induction with inhaled anaesthetics. Appl Anim Behav Sci 2009;119:229–235.
166. Universities Federation for Animal Welfare. Humane killing of
animals. 4th ed. South Mimms, Potters Bar, Hertfordshire, England: Universities Federation for Animal Welfare, 1988;16–22.
167. Makowska IJ, Vickers L, Mancell J, et al. Evaluating methods
of gas euthanasia for laboratory mice. Appl Anim Behav Sci
2009;121:230–235.
168. Schmid RD, Hodgson DS, McMurphy RM. Comparison of anesthetic induction in cats by use of isoflurane in an anesthetic
chamber with a conventional vapor or liquid injection technique. J Am Vet Med Assoc 2008;233:262–266.
169. Steffey EP, Mama KR. Inhalation anesthetics. In: Tranquilli WJ,
Thurmon JC, Grimm KA, eds. Lumb and Jones’ veterinary anesthesia and analgesia. 4th ed. Ames, Iowa: Blackwell, 2007;355–
393.
170. Occupational Safety and Health Administration. Anesthetic
gases: guidelines for workplace exposures. Available at: www.
osha.gov/dts/osta/anestheticgases/index.html#A. Accessed Dec
5, 2010.
171. Lockwood G. Theoretical context-sensitive elimination times
for inhalational anaesthetics. Br J Anaesth 2010;104:648–655.
172. Haldane J. The action of carbonic oxide in man. J Physiol
1895;18:430–462.
173. Raub JA, Mathieu-Nolf M, Hampson NB, et al. Carbon monoxide poisoning—a public health perspective. Toxicology
2000;145:1–14.
174. Hampson NB, Weaver LK. Carbon monoxide poisoning: a new in87
cidence for an old disease. Undersea Hyperb Med 2007;34:163–168.
175. Lowe-Ponsford FL, Henry JA. Clinical aspects of carbon
monoxide poisoning. Adverse Drug React Acute Poisoning Rev
1989;8:217–240.
176. Bloom JD. Some considerations in establishing divers’ breathing gas purity standards for carbon monoxide. Aerosp Med
1972;43:633–636.
177. Norman CA, Halton DM. Is carbon monoxide a workplace teratogen? A review and evaluation of the literature. Ann Occup
Hyg 1990;34:335–347.
178. Wojtczak-Jaroszowa J, Kbow S. Carbon monoxide, carbon disulfide, lead and cadmium—four examples of occupational
toxic agents linked to cardiovascular disease. Med Hypotheses
1989;30:141–150.
179. Fechter LD. Neurotoxicity of prenatal carbon monoxide exposure. Res Rep Health Eff Inst 1987;12:3–22.
180. Ramsey TL, Eilmann HJ. Carbon monoxide acute and
chronic poisoning and experimental studies. J Lab Clin Med
1932;17:415–427.
181. Enggaard Hansen N, Creutzberg A, Simonsen HB. Euthanasia of
mink (Mustela vison) by means of carbon dioxide (CO2), carbon
monoxide (CO) and nitrogen (N2). Br Vet J 1991;147:140–146.
182. Vinte FJ. The humane killing of mink. London: Universities Federation for Animal Welfare, 1957.
183. Chalifoux A, Dallaire A. Physiologic and behavioral evaluation
of CO euthanasia of adult dogs. Am J Vet Res 1983;44:2412–
2417.
184. Dallaire A, Chalifoux A. Premedication of dogs with acepromazine or pentazocine before euthanasia with carbon monoxide.
Can J Comp Med 1985;49:171–178.
185. Weary DM, Makowska IJ. Rat aversion to carbon monoxide.
Appl Anim Behav Sci 2009;121:148–151.
186. Simonsen HB, Thordal-Christensen AA, Ockens N. Carbon
monoxide and carbon dioxide euthanasia of cats: duration and
animal behavior. Br Vet J 1981;137:274–278.
187. Lambooy E, Spanjaard W. Euthanasia of young pigs with carbon
monoxide. Vet Rec 1980;107:59–61.
188. Gerritzen MA, Lambooij E, Stegeman JA, et al. Slaughter of
poultry during the epidemic of avian influenza in the Netherlands in 2003. Vet Rec 2006;159:39–42.
189. Herin RA, Hall P, Fitch JW. Nitrogen inhalation as a method of
euthanasia in dogs. Am J Vet Res 1978;39:989–991.
190. Noell WK, Chinn HI. Time course of failure of the visual pathway in rabbits during anoxia. Fed Proc 1949;8:1–19.
191. Altland PD, Brubach HF, Parker MG. Effects of inert gases on
tolerance of rats to hypoxia. J Appl Physiol 1968;24:778–781.
192. Arieli R. Can the rat detect hypoxia in inspired air? Respir Physiol 1990;79:243–253.
193. Niel L, Weary DM. Rats avoid exposure to carbon dioxide and
argon. Appl Anim Behav Sci 2007;107:100–109.
194. Makowska IJ, Niel L, Kirkden RD, et al. Rats show aversion to
argon-induced hypoxia. Appl Anim Behav Sci 2008;114:572–
581.
195. Burkholder TH, Niel L, Weed JL, et al. Comparison of carbon dioxide and argon euthanasia: effects on behavior, heart
rate, and respiratory lesions in rats. J Am Assoc Lab Anim Sci
2010;49:448–453.
196. Raj ABM. Aversive reactions to argon, carbon dioxide and a mixture of carbon dioxide and argon. Vet Rec 1996;138:592–593.
197. Webster AB, Fletcher DL. Assessment of the aversion of hens
to different gas atmospheres using an approach-avoidance test.
Appl Anim Behav Sci 2004;88:275–287.
198. Raj ABM, Gregory NG, Wotton SB. Changes in the somatosensory evoked potentials and spontaneous electroencephalogram of hens during stunning in argon-induced anoxia. Br Vet J
1991;147:322–330.
199. Raj M, Gregory NG. Time to loss of somatosensory evoked potentials and onset of changes in the spontaneous electroencephalogram of turkeys during gas stunning. Vet Rec 1993;133:318–
320.
200. Mohan Raj AB, Gregory NG, Wotton SB. Effect of carbon dioxide stunning on somatosensory evoked potentials in hens. Res
Vet Sci 1990;49:355–359.
201. Raj ABM, Whittington PE. Euthanasia of day-old chicks with
88
carbon dioxide and argon. Vet Rec 1995;136:292–294.
202. Gerritzen MA, Lambooij E, Hillebrand SJW, et al. Behavioral responses of broilers to different gaseous atmospheres. Poult Sci
2000;79:928–933.
203. McKeegan DEF, McIntyre J, Demmers TGM, et al. Behavioural
responses of broiler chickens during acute exposure to gaseous
stimulation. Appl Anim Behav Sci 2006;99:271–286.
204. Webster AB, Fletcher DL. Reactions of laying hens and broilers to different gases used for stunning poultry. Poult Sci
2001;80:1371–1377.
205. Lambooij E, Gerritzen MA, Engel B, et al. Behavioural responses
during exposure of broiler chickens to different gas mixtures.
Appl Anim Behav Sci 1999;62:255–265.
206. Raj ABM, Gregory NG. Welfare implications of the gas stunning
of pigs: 1. Determination of aversion to the initial inhalation of
carbon dioxide or argon. Anim Welf 1995;4:273–280.
207. Dalmau A, Llonch P, Rodriguez P, et al. Stunning pigs with different gas mixtures: gas stability. Anim Welf 2010;19:315–323.
208. Raj AB. Behaviour of pigs exposed to mixtures of gases and the
time required to stun and kill them: welfare implications. Vet
Rec 1999;144:165–168.
209. Raj M, Mason G. Reaction of farmed mink (Mustela vison) to
argon-induced hypoxia. Vet Rec 1999;145:736–737.
210. Dalmau A, Rodriguez P, Llonch P, et al. Stunning pigs with different gas mixtures: aversion in pigs. Anim Welf 2010;19:325–
333.
211. Martoft L, Lomholt L, Kolthoff C, et al. Effects of CO2 anaesthesia on central nervous system activity in swine. Lab Anim
2002;36:115–126.
212. Raj AB, Johnson SP, Wotton SB, et al. Welfare implications of
gas stunning pigs: 3. the time to loss of somatosensory evoked
potentials and spontaneous electrocorticogram of pigs during
exposure to gases. Vet J 1997;153:329–339.
213. Ring C, Erhardt W, Kraft H, et al. CO2 anaesthesia of slaughter
pigs. Fleischwirtschaft 1988;68:1304–1307.
214. Forslid A. Transient neocortical, hippocampal, and amygdaloid
EEG silence induced by one minute inhalation of high CO2 concentration in swine. Acta Physiol Scand 1987;130:1–10.
215. Mattsson JL, Stinson JM, Clark CS. Electroencephalographic
power-spectral changes coincident with onset of carbon dioxide
narcosis in rhesus monkey. Am J Vet Res 1972;33:2043–2049.
216. Woodbury DM, Rollins LT, Gardner MD, et al. Effects of carbon dioxide on brain excitability and electrolytes. Am J Physiol
1958;192:79–90.
217. Leake CD, Waters RM. The anesthetic properties of carbon dioxid. Curr Res Anesth Anal 1929;8:17–19.
218. Chen X, Gallar J, Pozo MA, et al. CO2 stimulation of the cornea—a comparison between human sensation and nerve activity in polymodal nociceptive afferents of the cat. Eur J Neurosci
1995;7:1154–1163.
219. Peppel P, Anton F. Responses of rat medullary dorsal horn neurons following intranasal noxious chemical stimulation—effects of stimulus intensity, duration and interstimulus interval. J
Neurophysiol 1993;70:2260–2275.
220. Thürauf N, Hummel T, Kettenmann B, et al. Nociceptive and reflexive responses recorded from the human nasal mucosa. Brain
Res 1993;629:293–299.
221. Anton F, Peppel P, Euchner I, et al. Noxious chemical stimulation—responses of rat trigeminal brain stem neurons to CO2
pulses applied to the nasal mucosa. Neurosci Lett 1991;123:208–
211.
222. Feng Y, Simpson TL. Nociceptive sensation and sensitivity
evoked from human cornea and conjunctiva stimulated by CO2.
Invest Ophthalmol Vis Sci 2003;44:529–532.
223. Thürauf N, Günther M, Pauli E, et al. Sensitivity of the negative
mucosal potential to the trigeminal target stimulus CO2. Brain
Res 2002;942:79–86.
224. Danneman PJ, Stein S, Walshaw SO. Humane and practical implications of using carbon dioxide mixed with oxygen for anesthesia or euthanasia of rats. Lab Anim Sci 1997;47:376–385.
225. Widdicombe JG. Reflexes from the upper respiratory tract. In:
Cherniak NS, Widdicombe JG, eds. Handbook of physiology:
the respiratory system. Bethesda, Md: American Physiological
Society, 1986;363–394.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
226. Yavari P, McCulloch PF, Panneton WM. Trigeminally-mediated
alteration of cardiorespiratory rhythms during nasal application
of carbon dioxide in the rat. J Auton Nerv Syst 1996;61:195–200.
227. Moosavi SH, Golestanian E, Binks AP, et al. Hypoxic and hypercapnic drives to breathe generate equivalent levels of air hunger
in humans. J Appl Physiol 2003;94:141–154.
228. Millar RA. Plasma adrenaline and noradrenaline during diffusion respiration. J Physiol 1960;150:79–90.
229. Nahas GG, Ligou JC, Mehlman B. Effects of pH changes on O2
uptake and plasma catecholamine levels in the dog. Am J Physiol
1960;198:60–66.
230. Liotti M, Brannan S, Egan G, et al. Brain responses associated
with consciousness of breathlessness (air hunger). Proc Natl
Acad Sci 2001;98:2035–2040.
231. Dripps RD, Comroe JH. The respiratory and circulatory response of normal man to inhalation of 7.6 percent CO2 and 10.4
percent CO2 with a comparison of the maximal ventilation produced by severe muscular exercise, inhalation of CO2 and maximal voluntary hyperventilation. Am J Physiol 1947;149:43–51.
232. Hill L, Flack M. The effect of excess of carbon dioxide and of
want of oxygen upon the respiration and the circulation. J Physiol 1908;37:77–111.
233. Banzett RB, Lansing RW, Evans KC, et al. Stimulus-response
characteristics of CO2-induced air hunger in normal subjects.
Respir Physiol 1996;103:19–31.
234. Shea SA, Harty HR, Banzett RB. Self-control of level of mechanical ventilation to minimize CO2-induced air hunger. Respir
Physiol 1996;103:113–125.
235. Fowler WS. Breaking point of breath-holding. J Appl Physiol
1954;6:539–545.
236. Kirkden RD, Niel L, Stewart SA, et al. Gas killing of rats: the
effect of supplemental oxygen on aversion to carbon dioxide.
Anim Welf 2008;17:79–87.
237. Coenen AM, Drinkenburg WH, Hoenderken R, et al. Carbon
dioxide euthanasia in rats: oxygen supplementation minimizes
signs of agitation and asphyxia. Lab Anim 1995;29:262–268.
238. Hewett TA, Kovacs MS, Artwohl JE, et al. A comparison of euthanasia methods in rats, using carbon dioxide in prefilled and
fixed flow-rate filled chambers. Lab Anim Sci 1993;43:579–582.
239. Borovsky V, Herman M, Dunphy G, et al. CO2 asphyxia increases plasma norepinephrine in rats via sympathetic nerves. Am J
Physiol 1998;274:R19–R22.
240. Reed B, Varon J, Chait BT, et al. Carbon dioxide-induced anesthesia result in a rapid increase in plasma levels of vasopressin.
Endocrinology 2009;150:2934–2939.
241. Raff H, Roarty TP. Renin, ACTH, and aldosterone during
acute hypercapnia and hypoxia in conscious rats. Am J Physiol
1988;254:R431–R435.
242. Marotta SF, Sithichoke N, Garcy AM, et al. Adrenocortical responses of rats to acute hypoxic and hypercapnic stresses
after treatment with aminergic agents. Neuroendocrinology
1976;20:182–192.
243. Raff H, Shinsako J, Keil LC, et al. Vasopressin, ACTH, and corticosteroids during hypercapnia and graded hypoxia in dogs. Am
J Physiol 1983;244:E453–E458.
244. Argyropoulos SV, Bailey JE, Hood SD, et al. Inhalation of 35%
CO2 results in activation of the HPA axis in healthy volunteers.
Psychoneuroendocrinology 2002;27:715–729.
245. Herman JP, Cullinan WE. Neurocircuitry of stress: central control of the hypothalamo-pituitary-adrenocortical axis. Trends
Neurosci 1997;20:78–84.
246. Kc P, Haxhiu MA, Trouth CO, et al. CO2-induced c-Fos expression in hypothalamic vasopressin containing neurons. Respir
Physiol 2002;129:289–296.
247. Hackbarth H, Kuppers N, Bohnet W. Euthanasia of rats with
carbon dioxide—animal welfare aspects. Lab Anim 2000;34:91–
96.
248. Blackshaw JK, Fenwick DC, Beattie AW, et al. The behavior of
chickens, mice and rats during euthanasia with chloroform, carbon dioxide and ether. Lab Anim 1988;22:67–75.
249. Britt DP. The humaneness of carbon dioxide as an agent of euthanasia for laboratory rodents. In: Euthanasia of unwanted, injured or diseased animals or for educational or scientific purposes.
Potters Bar Hertfordshire, England: Universities Federation for
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Animal Welfare, 1987;19–31.
250. Raj ABM, Gregory NG. Welfare implications of the gas stunning of pigs: 2. Stress of induction of anaesthesia. Anim Welf
1996;5:71–78.
251. Jongman EC, Barnett JL, Hemsworth PH. The aversiveness
of carbon dioxide stunning in pigs and a comparison of the
CO2 stunner crate vs the V-restrainer. Appl Anim Behav Sci
2000;67:67–76.
252. Troeger K, Woltersdorf W. Gas anesthesia of slaughter pigs. 1.
Stunning experiments under laboratory conditions with fat pigs
of known halothane reaction type—meat quality, animal protection. Fleischwirtschaft 1991;72:1063–1068.
253. Dodman NH. Observations on use of Wernberg dip-lift carbon
dioxide apparatus for pre-slaughter anesthesia of pigs. Br Vet J
1977;133:71–80.
254. Gerritzen MA, Lambooij E, Reimert HG, et al. Susceptibility
of duck and turkey to severe hypercapnic hypoxia. Poult Sci
2006;85:1055–1061.
255. Gerritzen M, Lambooij B, Reimert H, et al. A note on behaviour
of poultry exposed to increasing carbon dioxide concentrations.
Appl Anim Behav Sci 2007;108:179–185.
256. McKeegan DEF, McIntyre JA, Demmers TGM, et al. Physiological and behavioural responses of broilers to controlled
atmosphere stunning: implications for welfare. Anim Welf
2007;16:409–426.
257. Abeyesinghe SM, McKeegan DEF, McLeman MA, et al. Controlled atmosphere stunning of broiler chickens. I. Effects on
behaviour, physiology and meat quality in a pilot scale system
at a processing plant. Br Poult Sci 2007;48:406–423.
258. Cooper J, Mason G, Raj M. Determination of the aversion
of farmed mink (Mustela vison) to carbon dioxide. Vet Rec
1998;143:359–361.
259. Battaglia M, Ogliari A, Harris J, et al. A genetic study of the
acute anxious response to carbon dioxide stimulation in man. J
Psychiatr Res 2007;41:906–917.
260. Nardi AE, Freire RC, Zin WA. Panic disorder and control of
breathing. Respir Physiol Neurobiol 2009;167:133–143.
261. Grandin T. Effect of genetics on handling and CO2 stunning of
pigs (updated July 2008). Meat Focus Int 1992;July:124–126.
Available at: www.grandin.com/humane/meatfocus7-92.html.
Accessed Dec 13, 2010.
262. Ziemann AE, Allen JE, Dahdaleh NS, et al. The amygdala is a
chemosensor that detects carbon dioxide and acidosis to elicit
fear behavior. Cell 2009;139:1012–1021.
263. Kohler I, Moens Y, Busato A, et al. Inhalation anaesthesia for
the castration of piglets: CO2 compared to halothane. Zentralbl
Veterinarmed A 1998;45:625–633.
264. Glen JB, Scott WN. Carbon dioxide euthanasia of cats. Br Vet J
1973;129:471–479.
265. Franson JC. Euthanasia. In: Friend M, Franson JC, eds. Field
manual of wildlife diseases. General field procedures and diseases
of birds. Biological Resources Division information and technology report 1999–001. Washington, DC: US Department of the
Interior and US Geological Survey, 1999;49–53.
266. Mohan Raj AB, Gregory NG. Effect of rate of induction of carbon dioxide anaesthesia on the time of onset of unconsciousness and convulsions. Res Vet Sci 1990;49:360–363.
267. Mohan Raj AB, Wotton SB, Gregory NG. Changes in the somatosensory evoked potentials and spontaneous electoencephalogram of hens during stunning with a carbon dioxide and
argon mixture. Br Vet J 1992;148:147–156.
268. Raj M, Gregory NG. An evaluation of humane gas stunning
methods for turkeys. Vet Rec 1994;135:222–223.
269. Poole GH, Fletcher DL. A comparison of argon, carbon dioxide,
and nitrogen in a broiler killing system. Poult Sci 1995;74:1218–
1223.
270. Latimer KS, Rakich PM. Necropsy examination. In: Ritchie BW,
Harrison GJ, Harrison LR, eds. Avian medicine: principles and application. Lake Worth, Fla: Wingers Publishing Inc, 1994;355–379.
271. Jaksch W. Euthanasia of day-old male chicks in the poultry industry. Int J Study Anim Probl 1981;2:203–213.
272. Pritchett-Corning KR. Euthanasia of neonatal rats with carbon
dioxide. J Am Assoc Lab Anim Sci 2009;48:23–27.
273. Pritchett K, Corrow D, Stockwell J, et al. Euthanasia of neonatal
89
mice with carbon dioxide. Comp Med 2005;55:275–281.
274. Hayward JS, Lisson PA. Carbon dioxide tolerance of rabbits and
its relation to burrow fumigation. Aust Wildl Res 1978;5:253–
261.
275. Iwarsson K, Rehbinder C. A study of different euthanasia techniques in guinea pigs, rats, and mice. Animal response and postmortem findings. Scan J Lab Anim Sci 1993;20:191–205.
276. US Department of Health and Human Services. Compounding
of drugs for use in animals. Compliance policy guide section
608.400. Rockville, Md: US FDS, 2003;1–7. Available at: www.
fda.gov/downloads/ICECI/ComplianceManuals/CompliancePolicyGuidanceManual/UCM200461.pdf. Accessed Mar 26,
2010.
277. Campbell VL, Butler AL, Lunn KF. Use of a point-of-care urine
drug test in a dog to assist in diagnosing barbiturate toxicosis
secondary to ingestion of a euthanized carcass. J Vet Emerg Crit
Care (San Antonio) 2009;19:286–291.
278. Jurczynski K, Zittlau E. Pentobarbital poisoning in Sumatran
tigers (Panthera tigris sumatrae). J Zoo Wildl Med 2007;38:583–
584.
279. US FDA. 21 CFR Part 522. Injectable or implantable dosage
form new animal drugs; euthanasia solution; technical amendment. Fed Regist 2003;68:42968–42969.
280. Wilkins JR III, Bowman ME. Needlestick injuries among female
veterinarians: frequency, syringe contents and side-effects. Occup Med (Lond) 1997;47:451–457.
281. Lewbart GA, ed. Invertebrate medicine. Oxford, England: Blackwell, 2006.
282. Schwartz JA, Warren RJ, Henderson DW, et al. Captive and field
tests of a method for immobilization and euthanasia of urban
deer. Wildl Soc Bull 1997;25:532–541.
283. Bucher K, Bucher KE, Waltz D. Irritant actions of unphysiological pH values. A controlled procedure to test for topical irritancy. Agents Actions 1979;9:124–132.
284. Grier RL, Schaffer CB. Evaluation of intraperitoneal and intrahepatic administration of a euthanasia agent in animal shelter
cats. J Am Vet Med Assoc 1990;197:1611–1615.
285. Schoell AR, Heyde BR, Weir DE, et al. Euthanasia method for
mice in rapid time-course pulmonary pharmacokinetic studies.
J Am Assoc Lab Anim Sci 2009;48:506–511.
286. Philbeck TE, Miller LJ, Montez D, et al. Hurts so good. Easing
IO pain and pressure. JEMS 2010;35(9):58–62, 65–66, 68, 69.
287. Montez D, Miller LJ, Puga T, et al. Pain management with the
use of IO: easing IO pain and pressure. Available at: www.jems.
com/article/intraosseous/pain-management-use-io.
Accessed
Jun 13, 2011.
288. US FDA. Tributame Euthanasia Solution: embutramide/chloroquine phosphate/lidocaine. Freedom of Information summary.
NADA 141-245 Silver Spring, Md: FDA, 2005..
289. US FDA. 21 CFR Part 522. Implantation or injectable dosage
form new animal drugs; embutramide, chloroquine, and lidocaine solution. Fed Regist 2005;70:36336–36337.
290. US FDA. 21 CFR Part 1308. Schedules of controlled substances: placement of embutramide into schedule III. Fed Regist
2006;71:51115–51117.
291. Sodfola OA. The cardiovascular effect of chloroquine in anesthetized dogs. Can J Physiol Pharmacol 1980;58:836–841.
292. Don Michael TA, Alwassadeh S. The effects of acute chloroquine poisoning with special references to the heart. Am Heart J
1970;79:831–842.
293. Webb AI. Euthanizing agents. In: Reviere JE, Papich MG, eds.
Veterinary pharmacology and therapeutics. 9th ed. Ames, Iowa:
Wiley Blackwell, 2009;401–408.
294. Webb AI, Pablo LS. Local anesthetics. In: Reviere JE, Papich
MG, eds. Veterinary pharmacology and therapeutics. 9th ed.
Ames, Iowa: Wiley Blackwell, 2009;381–400.
295. Hellebrekers LJ, Baumans V, Bertens APMG, et al. On the use of
T61 for euthanasia of domestic and laboratory animals; an ethical evaluation. Lab Anim 1990;24:200–204.
296. Park CK, Kim K, Jung SJ, et al. Molecular mechanism for local
anesthetic action of eugenol in the rat trigeminal system. Pain
2009;144:84–94.
297. Kearns KS, Swenson B, Ramsay EC. Dosage trials with transmucosal carfentanil citrate in non-human primates. Zoo Biol
90
1999;18:397–402.
298. Flecknell PA. Laboratory animal anaesthesia. 2nd ed. San Diego:
Elsevier Academic Press, 1996;168–171.
299. Saxena K. Death from potassium chloride overdose. Postgrad
Med 1988;84:97–98, 101–102.
300. Lumb WV. Euthanasia by noninhalant pharmacologic agents. J
Am Vet Med Assoc 1974;165:851–852.
301. Ciganovich E. Barbiturates. In: Field manual of wildlife diseases. General field procedures and diseases of birds. Biological Resources Division information and technology report 1999–001.
Washington, DC: US Department of the Interior and US Geological Survey, 1999;349–351.
302. Raghav R, Taylor M, Guincho M, et al. Potassium chloride as a
euthanasia agent in psittacine birds: clinical aspects and consequences for histopathologic assessment. Can Vet J 2011;52:303–
306.
303. Luckl J, Keating J, Greenberg JH. Alpha-chloralose is a suitable
anesthetic for chronic focal cerebral ischemia studies in the rat:
a comparative study. Brain Res 2008;1191:157–167.
304. Belant JL, Tyson LA, Seamans TW. Use of alpha-chloralose by
the Wildlife Services program to capture nuisance birds. Wildl
Soc Bull 1999;27:938–942.
305. Cobaugh DJ. Ethanol. In: Brent J, Phillips SD,Wallace KL, et al,
eds. Critical care toxicology. Philadelphia: Mosby, 2005;1553–
1558.
306. Harms C. Anesthesia in fish. In: Fowler ME, Miller RE, eds. Zoo
and wild animal medicine: current therapy 4. Philadelphia: WB
Saunders Co, 1999;158–163.
307. Lord R. Use of ethanol for euthanasia of mice. Aust Vet J
1989;66:268.
308. US Food and Drug Administration. ANADA 200-226 TricaineS—original approval. Available at: www.fda.gov/AnimalVeterinary/Products/ApprovedAnimalDrugProducts/FOIADrugSummaries/ucm132992.htm. Accessed May 16, 2011.
309. Noga EJ. Chapter 17: pharmacopoeia. In: Fish disease: diagnosis
and treatment. 2nd ed. Ames, Iowa: Wiley-Blackwell, 2010;375–
420.
310. Stoskopf MK. Anesthesia. In: Brown LA, ed. Aquaculture for veterinarians: fish husbandry and medicine. Oxford, England: Pergamon Press, 1993;161–167.
311. Committee for Veterinary Medicinal Products. Tricaine mesilate:
summary report. EMEA/MRL/586/99-FINAL. London: European
Agency for the Evaluation of Medicinal Products, 1999. Available at www.ema.europa.eu/docs/en_GB/document_library/
Maximum_Residue_Limits_-_Report/2009/11/WC500015660.
pdf. Accessed Sep 9, 2010.
312. Torreilles SL, McClure DE, Green SL. Evaluation and refinement
of euthanasia methods for Xenopus laevis. J Am Assoc Lab Anim
Sci 2009;48:512–516.
313. Bernstein PS, Digre KB, Creel DJ. Retinal toxicity associated
with occupations exposure to the fish anesthetic MS 222 (ethyl-m-aminobenzoic acid methanesulfonate). Am J Ophthalmol
1997;124:843–844.
314. Kaiser H, Green DM. Keeping the frogs still: Orajel is a safe
anesthetic in amphibian photography. Herpetol Rev 2001;32:93–
94.
315. Chen MH, Combs CA. An alternative anesthesia for amphibians: ventral application of benzocaine. Herpetol Rev 1999;30:34.
316. Blessing JJ, Marshal JC, Balcombe SR. Humane killing of fishes
for scientific research: a comparison of two methods. J Fish Biol
2010;76:2571–2577.
317. US FDA Center for Veterinary Medicine. Enforcement priorities for drug use in aquaculture. Silver Spring, Md: US FDA,
2011. Available at www.fda.gov/downloads/AnimalVeterinary/
GuidanceComplianceEnforcement/PoliciesProceduresManual/
UCM046931.pdf. Accessed Jan 10, 2011.
318. National Toxicology Program. NTP technical report on the toxicology and carcinogenesis studies of isoeugenol (CAS No. 97-54-1)
in F344/N rats and B6C3F1 mice (gavage studies). NTP TR 551.
NIH publication No. 08-5892. Washington, DC: US Department
of Health and Human Services, 2008. Available at: ntp.niehs.
nih.gov/files/TR551board_web.pdf. Accessed May 16, 2011.
319. Grush J, Noakes DL, Moccia RD. The efficacy of clove oil as an
anesthetic for the zebrafish, Danio rerio (Hamilton). Zebrafish
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
2004;1:46–53.
320. Borski RJ, Hodson RG. Fish research and the institutional animal care and use committee. ILAR J 2003;44:286–294.
321. Sladky KK, Swanson CR, Stoskopf MK, et al. Comparative efficacy of tricaine methanesulfonate and clove oil for use as
anesthetics in red pacu (Piaractus brachypomus). Am J Vet Res
2001;62:337–342.
322. Brodin P, Roed A. Effects of eugenol on rat phrenic nerve and
phrenic-diaphragm preparations. Arch Oral Biol 1984;29:611–615.
323. Ingvast-Larsson JC, Axén VC, Kiessling AK. Effects of isoeugenol on in vitro neuromuscular blockade of rat phrenic nervediaphragm preparations. Am J Vet Res 2003;64:690–693.
324. Meyer RE, Fish R. Pharmacology of injectable anesthetics, sedatives, and tranquilizers. In: Fish RE, Danneman PJ, Brown M, et
al, eds. Anesthesia and analgesia of laboratory animals. 2nd ed.
San Diego: Academic Press, 2008;27–82.
325. Neiffer DL, Stamper A. Fish sedation, anesthesia, analgesia, and
euthanasia: considerations, methods, and types of drugs. ILAR J
2009;50:343–360.
326. Estrela C, Estrela CR, Barbin EL, et al. Mechanism of action of
sodium hypochlorite. Braz Dent J 2002;13:113–117.
327. National Institutes of Health. Guidelines for use of zebrafish in
the NIH intramural research program. Bethesda, MD: National
Institutes of Health, 2009. Available at: oacu.od.nih.gov/arac/
documents/Zebrafish.pdf. Accessed Nov 25, 2010.
328. Agency for Toxic Substances and Disease Registry. Toxological
profile for formadehyde. July 1999. Available at: www.atsdr.cdc.
gov/toxprofiles/tp111.pdf. Accessed Aug 13, 2012.
329. National Toxicology Program. Report on carcinogens. 12th ed.
Research Triangle Park, NC: US Department of Health and Human Services, Public Health Service, National Toxicology Program, 2011.
330. Murray MJ. Invertebrates. In: American Association of Zoo Veterinarians (AAZV). Guidelines for euthanasia of non-domestic
animals. Yulee, Fla: American Association of Zoo Veterinarians,
2006;25–27.
331. Dennis MB Jr, Dong WK, Weisbrod KA, et al. Use of captive bolt
as a method of euthanasia in larger laboratory animal species.
Lab Anim Sci 1988;38:459–462.
332. Blackmore DK. Energy requirements for the penetration of
heads of domestic stock and the development of a multiple projectile. Vet Rec 1985;116:36–40.
333. Daly CC, Whittington PE. Investigation into the principal determinants of effective captive bolt stunning of sheep. Res Vet Sci
1989;46:406–408.
334. Clifford DH. Preanesthesia, anesthesia, analgesia, and euthanasia. In: Fox JG, Cohen BJ, Loew FM, eds. Laboratory animal
medicine. New York: Academic Press Inc, 1984;528–563.
335. Australian Veterinary Association. Guidelines for humane slaughter and euthanasia. Member’s directory and policy compendium.
Lisarow, NSW: Veritage Press, 1997.
336. Grandin T. Return-to-sensibility problems after penetrating
captive bolt stunning of cattle in commercial beef slaughter
plants. J Am Vet Med Assoc 2002;221:1258–1261.
337. Erasmus MA, Lawlis P, Duncan IJ, et al. Using time to insensibility and estimated time of death to evaluate a nonpenetrating
captive bolt, cervical dislocation, and blunt trauma for on-farm
killing of turkeys. Poult Sci 2010;89:1345–1354.
338. Erasmus MA, Turner PV, Niekamp SG, et al. Brain and skull lesions resulting from use of percussive bolt, cervical dislocation
by stretching, cervical dislocation by crushing and blunt trauma
in turkeys. Vet Rec 2010;167:850–858.
339. Erasmus MA, Turner PV, Widowski TM. Measures of insensibility used to determine effective stunning and killing of poultry. J
Appl Poult Res 2010;19:288–298.
340. Canadian Council on Animal Care. Guide to the care and use of
experimental animals. Vol 1. 2nd ed. Ottawa: Canadian Council
on Animal Care, 1993.
341. Green CJ. Euthanasia. In: Animal anesthesia. London: Laboratory Animals Ltd, 1979;237–241.
342. World Organisation for Animal Health (OIE). Chapter 7.6: killing of animals for disease control purposes. In: Terrestrial animal health code. 20th ed. Paris: OIE, 2011. Available at: www.
oie.int/index.php?id=169&L=0&htmfile=chapitre_1.7.6.htm.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Accessed May 16, 2011.
343. Finnie JW. Neuroradiological aspects of experimental traumatic
missle injury in sheep. N Z Vet J 1994;42:54–57.
344. Longair JA, Finley GG, Laniel MA, et al. Guidelines for the euthanasia of domestic animals by firearms. Can Vet J 1991;32:724–
726.
345. Carding T. Euthanasia of dogs and cats. Anim Regul Stud
1977;1:5–21.
346. Blackmore DK, Bowling MC, Madie P, et al. The use of a shotgun
for the emergency slaughter or euthanasia of large mature pigs.
N Z Vet J 1995;43:134–137.
347. Finnie IW. Traumatic head injury in ruminant livestock. Aust
Vet J 1997;75:204–208.
348. Blackmore DK, Madie P, Bowling MC, et al. The use of a shotgun for emergency slaughter of stranded cetaceans. N Z Vet J
1995;43:158–159.
349. Nelson JM. Bullet Energy in Foot Pounds. Available at: web.
stcloudstate.edu/jmnelson/web/gun/benergy/index.html. Accessed Jun 15, 2011.
350. Baker HJ, Scrimgeour HJ. Evaluation of methods for the euthanasia of cattle in a foreign animal disease outbreak. Can Vet J
1995;36:160–165.
351. Humane Slaughter Association. Humane killing of livestock using
firearms: guidance notes #3. 2nd ed. Wheathampstead, Hertfordshire, England: Humane Slaughter Association, 2005.
352. National Pork Board, American Association of Swine Practitioners. On-farm euthanasia of swine. 2nd edition. Des Moines,
Iowa: National Pork Board, 2009.
353. Hughes HC. Euthanasia of laboratory animals. In: Melby EC,
Altman NH, eds. Handbook of laboratory animal science. Vol 3.
Cleveland, Ohio: CRC Press, 1976;553–559.
354. Gregory NG, Wotton SB. Comparison of neck dislocation and
percussion of the head on visual evoked responses in the chicken’s brain. Vet Rec 1990;126:570–572.
355. Keller GL. Physical euthanasia methods. Lab Anim (NY)
1982;11:20–26.
356. Webster AB, Fletcher DL, Savage SI. Humane on-farm killing of
spent hens. J Appl Poult Res 1996;5:191–200.
357. Feldman DB, Gupta BN. Histopathologic changes in laboratory
animals resulting from various methods of euthanasia. Lab Anim
Sci 1976;26:218–221.
358. Urbanski HF, Kelley ST. Sedation by exposure to gaseous carbon
dioxide-oxygen mixture: application to studies involving small
laboratory animal species. Lab Anim Sci 1991;41:80–82.
359. Anil MH, McKinstry JL. Reflexes and loss of sensibility following head-to-back electrical stunning in sheep. Vet Rec
1991;128:106–107.
360. Hatch RC. Euthanatizing agents. In: Booth NH, McDonald LE,
eds. Veterinary pharmacology and therapeutics. 6th ed. Ames,
Iowa: Iowa State University Press, 1988;1143–1148.
361. Lambooy E, van Voorst N. Electrocution of pigs with notifiable
diseases. Vet Q 1986;8:80–82.
362. Eikelenboom G, ed. Stunning of animals for slaughter. Boston:
Martinus Nijhoff Publishers, 1983.
363. Warrington R. Electrical stunning, a review of the literature. Vet
Bull 1974;44:617–628.
364. Roberts TDM. Electrocution cabinets. Vet Rec 1974;95:241–242.
365. Loftsgard G, Rraathen S, Helgebostad A. Electrical stunning of
mink. Vet Rec 1972;91:132–134.
366. Croft PG, Hume CW. Electric stunning of sheep. Vet Rec
1956;68:318–321.
367. Anil AM, McKinstry JL The effectiveness of high frequency electrical stunning in pigs. Meat Sci 1994;31:481–491.
368. Croft PS 1952. Problems with electric stunning, Vet. Record
64:255–258.
369. Roberts TDM. Cortical activity in electrocuted dogs. Vet Rec
1954;66:561–567.
370. Pascoe PJ. Humaneness of an electroimmobilization unit for
cattle. Am J Vet Res 1986;47:2252–2256.
371. Grandin T, American Meat Institute Animal Welfare Committee. Recommended animal handling guidelines and audit guide: a
systematic approach to animal welfare. Washington, DC: American Meat Institute, 2010;19–22.
372. Lambooy E. Electrical stunning of sheep. Meat Sci 1982;6:123–
91
135.
373. Blackmore DK, Newhook JC. Insensibility during slaughter of pigs in comparison to other domestic stock. N Z Vet J
1981;29:219–222.
374. Grandin T. Solving return-to-sensibility problems after electrical stunning in commercial pork slaughter plants. J Am Vet Med
Assoc 2001;219:608–611.
375. Anil MH. Studies on the return of physical reflexes in pigs following electrical stunning. Meat Sci 1991;30:13–21.
376. Hoenderken R. Electrical and carbon dioxide stunning of pigs
for slaughter. In: Eikelenboom G, ed. Stunning of animals for
slaughter. Boston: Martinus Nijhoff Publishers, 1983;59–63
377. Denicourt M, Klopfenstein C, DuFour V, et al. Developing a safe
and acceptable method for on-farm euthanasia of pigs by electrocution. Final report. Montreal: Faculty of Veterinary Medicine,
University of Montreal, 2009.
378. Vogel KD, Badtram G, Claus JR, et al. Head-only followed by
cardiac arrest electrical stunning is an effective alternative to
head-only electrical stunning in pigs. J Anim Sci 2011;89:1412–
1418.
379. Weaver AL, Wotton SB. The Jarvis Beef Stunner: effect of a prototype chest electrode. Meat Sci 2009;81:51–56.
380. Meerburg BGH, Brom FWA, Kijlstra A. The ethics of rodent
control. Pest Manag Sci 2008;64:1205–1211.
381. Federal Provincial Committee for Humane Trapping. Final report: Committee of the Federal Provincial Wildlife Conference. Ottawa: Canadian Wildlife Service, 1981.
382. Department of Foreign Affairs and International Trade. Agreement on international humane trapping standards between the
European Community, Canada, and the Russian Federation. Ottawa: Department of Foreign Affairs and International Trade,
1997;1–32.
383. Canadian General Standards Board. Animal (mammal) traps—
mechanically powered, trigger-activated killing traps for use on
land. No. CAN/CGSB-144.1–96. Ottawa: Canadian General
Standards Board, 1996;1–36.
384. Nolan JW, Barrett MW. Description and operation of the humane
trapping research facility at the Alberta Environmental Centre.
AECV90–R3. Vegreville, AB, Canada: Alberta Environmental
Centre, 1990.
385. International Organization for Standardization. Animal (mammal) traps-part 4: methods for testing killing trap systems used on
land or underwater. TC 191, ISO/DIS 19009–4E. Geneva: International Organization for Standardization, 2000;1–15.
386. Gilbert FF. Assessment of furbearer response to trapping devices, in Proceedings. Worldw Furbearer Conf 1981;1599–1611.
387. Proulx G, Barrett MW. Evaluation of the Bionic trap to quickly
kill fisher (Martes pennanti) in simulated natural environments.
J Wildl Dis 1993;29:310–316.
388. Proulx G, Barrett MW, Cook SR. The C120 Magnum with pan
trigger: a humane trap for mink (Mustela vison). J Wildl Dis
1990;26:511–517.
389. Hiltz M, Roy LD. Rating of killing traps against humane trapping standards using computer simulations, in Proceedings.
19th Vertebrate Pest Conf 2000;197–201.
390. Association of Fish and Wildlife Agencies. Best management
practices. Available at: jjcdev.com/~fishwild/?section=best_
management_practices Accessed July 22, 2012.
391. International Association of Fish and Wildlife Agencies. Summary of progress. 1999–2000 field season: testing restraining and
body-gripping traps for development of best management practices
for trapping in the United States. Washington, DC: International
Association of Fish and Wildlife Agencies, 2003.
392. Warburton B, Gregory NG, Morriss G. Effect of jaw shape in
kill-traps on time to loss of palpebral reflexes in brushtail possums. J Wildl Dis 2000;36:92–96.
393. King CM. The effects of two types of steel traps upon captured
stoats (Mustela erminea). J Zool (Lond) 1981;195:553–554.
394. Proulx G, Kolenosky AJ, Cole PJ, et al. A humane killing trap for
lynx (Felis lynx): the Conibear 330 with clamping bars. J Wildl
Dis 1995;31:57–61.
395. Warburton B, Hall JV. Impact momentum and clamping force
thresholds for developing standards for possum kill traps. N Z J
Zool 1995;22:39–44.
92
396. Naylor BJ, Novak M. Catch efficiency and selectivity of various
traps and sets used for capturing American martens. Wildl Soc
Bull 1994;22:489–496.
397. Proulx G, Barrett MW. Field testing of the C120 magnum trap
for mink. Wildl Soc Bull 1993;21:421–426.
398. Proulx G, Kolenosky AJ, Badry MJ, et al. Assessment of the
Savageau 2001-8 trap to effectively kill artic fox. Wildl Soc Bull
1993;21:132–135.
399. Proulx G, Kolenosky AJ, Cole PJ. Assessment of the Kania trap
to humanely kill red squirrels (Tamiasciurus hudsonicus) in enclosures. J Wildl Dis 1993;29:324–329.
400. Proulx G, Pawlina IM, Wong RK. Re-evaluation of the C120
magnum and Bionic traps to humanely kill mink. J Wildl Dis
1993;29:184.
401. Cooper JE, Ewbank R, Platt C, et al. Euthanasia of amphibians
and reptiles. London: Universities Federation for Animal Welfare and World Society for the Protection of Animals, 1989.
402. Proulx G, Cook SR, Barrett MW. Assessment and preliminary
development of the rotating jaw Conibear 120 trap to effectively
kill marten (Martes americana). Can J Zool 1989;67:1074–1079.
403. Hill EP. Evaluation of improved traps and trapping techniques.
Project report W-44-6, Job IV-B. Montgomery, Ala: Alabama Department of Conservation and Natural Resources, 1981;1–19.
404. Guidelines of the American Society of Mammalogists for the use
of mammals in research. J Mammal 2011;92:235–253.
405. Improving animal welfare in US trapping programs. Washington,
DC: International Association of Fish and Wildlife Agencies,
1997.
406. American Association of Avian Pathologists (AAAP) Animal
Welfare and Management Practices Committee. Review of mechanical euthanasia of day-old poultry. Athens, Ga: American Association of Avian Pathologists, 2005.
407. Federation of Animal Science Societies (FASS). Guide for the
care and use of agricultural animals in agricultural research and
teaching. Champaign, Ill: Federation of Animal Science Societies, 2010.
408. Agriculture Canada. Recommended code of practice for the care
and handling of poultry from hatchery to processing plant. Publication 1757/E.1989. Ottawa: Agriculture Canada, 1989.
409. European Council. European Council Regulation No. 1099/2009
of 24 December 2009 on the protection of animals at the time of
killing. Brussels: The Council of the European Union, 2009.
410. Stavinoha WR. Study of brain neurochemistry utilizing rapid
inactivation of brain enzyme activity by heating and microwave
irradiation. In: Black CL, Stavinoha WB, Marvyama Y, eds. Microwave irraditation as a tool to study labile metabolites in tissue.
Elmsford, NY: Pergamon Press, 1983;1–12.
411. Stavinoha WB, Frazer J, Modak AT. Microwave fixation for the
study of acetylcholine metabolism. In: Jenden DJ, ed. Cholinergic mechanisms and psychopharmacology. New York: Plenum
Publishing Corp, 1978;169–179.
412. Ikarashi Y, Marvyama Y, Stavinoha WB. Study of the use of the
microwave magnetic field for the rapid inactivation of brain enzymes. Jpn J Pharmacol 1984;35:371–387.
413. Bennett RA. Association disagrees with euthanasia method for
avian species (lett). J Am Vet Med Assoc 2001;218:1262.
414. Ludders JW. Another reader opposing thoracic compression for
avian euthanasia (lett). J Am Vet Med Assoc 2001;218:1721.
415. Chapter 7.3: Acceptable euthanasia methods. In: Miller EA, ed.
Minimum standards for wildlife rehabilitation. 3rd ed. St Cloud,
Minn: National Wildlife Rehabilitators Association, 2000;60–64.
416. Orosz S. Birds. In: American Association of Zoo Veterinarians
(AAZV). Guidelines for euthanasia of nondomestic animals. Yulee, Fla: American Association of Zoo Veterinarians, 2006;46–
49.
417. Blackmore DK. Differences in behavior between sheep and cattle during slaughter. Res Vet Sci 1984;37:223–226.
418. Gregory NG, Wotton SB. Time to loss of brain responsiveness following exsanguination in calves. Res Vet Sci 1984;37:141–143.
419. Appelt M, Sperry J. Stunning and killing cattle humanely and
reliably in emergency situations—a comparison between a
stunning-only and stunning and pithing protocol. Can Vet J
2007;48:529–534.
420. Leach TM, Wilkins LJ. Observations on the physiological effects
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
of pithing cattle at slaughter. Meat Sci 1985;15:101–106.
421. Hart LA, Hart BL, Mader B. Humane euthanasia and companion
animal death: caring for the animal, the client, and the veterinarian. J Am Vet Med Assoc 1990;197:1292–1299.
422. Lagoni L, Butler C. Facilitating companion animal death. Compend Contin Educ Pract Vet 1994;16:70–76.
423. Rhoades RH. The euthanasia area. In: The Humane Society of the
United States euthanasia training manual. Washington, DC: The
Humane Society of the United States, 2002;21–30.
424. Carpenter JW. Exotic animal formulary. 3rd ed. St Louis: WB
Saunders Co, 2005.
425. Wadham JJB, Townsend P, Morton DB. Intraperitoneal injection of sodium pentobarbitone as a method of euthanasia for
rodents. ANZCCART News 1997;10(4):8.
426. Svendsen O, Kok L, Lauritzen B. Nociception after intraperitoneal injection of a sodium pentobarbitone formulation with
and without lidocaine in rats quantified by expression of neuronal c-fos in the spinal cord— a preliminary study. Lab Anim
2007;41:197–203.
427. Ambrose N, Wadham J, Morton D. Refinement of euthanasia.
In: Balls M, Zeller A-M, Halder ME, eds. Progress in the reduction, refinement and replacement of animal experimentation. Amsterdam: Elsevier, 2000;1159–1170.
428. Rhoades RH. Selecting the injection site. In: The Humane Society
of the United States euthanasia training manual. Washington, DC:
The Humane Society of the United States, 2002;41–50.
429. Cooney KA. In-home Pet Euthanasia Techniques: The veterinarian’s guide to helping pets and their families say goodbye
in the comfort of home. Loveland, Colo: Home to Heaven PC,
2011. eBook. www.hometoheaven.net/ebook, 4–155.441.
430. Hanyok PM. Guidelines for police officers when responding to
emergency animal incidents. Anim Welf Inf Center Bull winter
2001–spring 2002;11(3–4). Available at: www.nal.usda.gov/
awic/newsletters/v11n3/11n3hany.htm. Accessed Sep 12, 2011.
431. Rhoades RH. Pre-euthanasia anesthetic. In: The Humane Society
of the United States euthanasia training manual. Washington, DC:
The Humane Society of the United States, 2002;67–80.
432. Mellor DJ. Galloping colts, fetal feelings, and reassuring regulations: putting animal welfare science into practice. J Vet Med
Educ 2010;37:94–100.
433. Leist KH, Grauwiler J. Fetal pathology in rats following uterinevessel clamping on day 14 of gestation. Teratology 1974;10:55–
67.
434. Rhoades RH. Understanding euthanasia. In: The Humane Society
of the United States euthanasia training manual. Washington, DC:
The Humane Society of the United States, 2002;1–10.
435. Rhoades RH. Physical restraint. In: The Humane Society of the
United States euthanasia training manual. Washington, DC: The
Humane Society of the United States, 2002;51–66.
436. Arnold M, Langhans W. Effects of anesthesia and blood sampling techniques on plasma metabolites and corticosterone in
the rat. Physiol Behav 2010;99:592–598.
437. Grieves JL, Dick EJ, Schlabritz-Loutsevich NE, et al. Barbiturate
euthanasia solution-induced tissue artifact in nonhuman primates. J Med Primatol 2008;37:154–161.
438. Artwohl J, Brown P, Corning B, et al. Report of the ACLAM
Task Force on Rodent Euthanasia. J Am Assoc Lab Anim Sci
2006;45:98–105.
439. Traslavina RP, King EJ, Loar AS, et al. Euthanasia by CO2 inhalation affects potassium levels in mice. J Am Assoc Lab Anim Sci
2010;49:316–322.
440. Faupel RP, Seitz HJ, Tarnowski W, et al. The problem of tissue
sampling from experimental animals with respect to freezing
technique, anoxia, stress and narcosis. A new method for sampling rat liver tissue and the physiological values of glycolytic
intermediates and related compounds. Arch Biochem Biophys
1972;148:509–522.
441. Castelhano-Carlos MJ, Baumans V. The impact of light, noise,
cage cleaning and in-house transport on welfare and stress of
laboratory rats. Lab Anim 2009;43:311–327.
442. Crawley J. Agression. In: What’s wrong with my mouse? 2nd ed.
New York: Wiley & Sons, 2007;213–217.
443. Balcombe JP, Barnard ND, Sandusky C, et al. Laboratory routines
cause animal stress. Contemp Top Lab Anim Sci 2004;43:42–51.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
444. Sharp J, Zammit T, Azar T, et al. Are “by-stander” female
Sprague-Dawley rats affected by experimental procedures? Contemp Top Lab Anim Sci 2003;42:19–27.
445. Sharp J, Zammit T, Azar T, et al. Stress-like responses to common procedures in individually and group-housed female rats.
Contemp Top Lab Anim Sci 2003;42:9–18.
446. Sharp J, Zammit T, Azar T, et al. Does witnessing experimental
procedures produce stress in male rats? Contemp Top Lab Anim
Sci 2002;41:8–12.
447. Sharp JL, Zammit TG, Azar T, et al. Stress-like responses to
common procedures in male rats housed alone or with other
rats. Contemp Top Lab Anim Sci 2002;41:8–14.
448. Daev EV, Vorob’ev KV, Zimina SA. Olfactory stress and modification of phagocytosis in peripheral blood cells of adult male mice
[in Russian]. Tsitologiia 2001;43:954–960.
449. Moynihan JA, Karp JD, Cohen N, et al. Immune deviation following stress odor exposure: role of endogenous opioids. J Neuroimmunol 2000;102:145–153.
450. Baines MG, Haddad EK, Pomerantz DK, et al. Effects of sensory
stimuli on the incidence of fetal resorption in a murine model of
spontaneous abortion: the presence of an alien male and postimplantation embryo survival. J Reprod Fertil 1994;102:221–228.
451. Moynihan JA, Karp JD, Cohen N, et al. Alterations in interleukin-4 and antibody production following pheromone exposure:
role of glucocorticoids. J Neuroimmunol 1994;54:51–58.
452. Vaupel DB, McCoun D, Cone EJ. Phencyclidine analogs and
precursors: rotarod and lethal dose studies in the mouse. J Pharmacol Exp Ther 1984;230:20–27.
453. Brunson DB. Pharmacology of inhalation anesthetics. In: Kohn
DF, Wixson SK, White WJ, et al, eds. Anesthesia and analgesia in
laboratory animals. San Diego: Academic Press, 1997;32–33.
454. Lord R. Humane killing. Nature 1991;350:456.
455. Fagin KD, Shinsako J, Dallman MF. Effects of housing and
chronic cannulation on plasma ACTH and corticosterone in the
rat. Am J Physiol 1983;245:E515–E520.
456. Mellor DJ, Diesch TJ, Gunn AJ, et al. The importance of ‘awareness’ for understanding fetal pain. Brain Res Brain Res Rev
2005;49:455–471.
457. Gaertner DJ, Hallman TM, Hankenson FC, et al. Anesthesia
and analgesia for laboratory rodents. In: Fish RE, Brown MJ,
Danneman PJ, et al, eds. Anesthesia and analgesia in laboratory
animals. New York: Elsevier, 2008;278.
458. Vogler G. Anesthesia and analgesia. In: Suckow MA, Weisbroth
SH, Franklin CL, eds. The laboratory rat. 2nd ed. San Diego:
Academic Press, 2006;658.
459. Diesch TJ, Mellor DJ, Johnson CB, et al. Electroencephalographic responses to tail clamping in anaesthetised rat pups.
Lab Anim 2009;43:224–231.
460. Hedenqvist P, Roughan JV, Antunes L, et al. Induction of anaesthesia with desflurane and isoflurane in the rabbit. Lab Anim
2001;35:172–179.
461. Wilson JM, Bunte RM, Carty AJ. Evaluation of rapid cooling
and tricaine methanessulfonate (MS222) as methods of euthanasia in zebrafish (Danio rerio). J Am Assoc Lab Anim Sci
2009;48:785–789.
462. Varga ZM, Matthews M, Trevarrow B, et al. Hypothermic shock is
a reliable and rapid euthanasia method for zebrafish. Final report
to OLAW on euthanasia of zebrafish. Bethesda, Md: Office of
Laboratory Animal Welfare, National Institutes of Health, 2008.
463. Thurmon JC. Euthanasia of food animals. Vet Clin North Am
Food Anim Pract 1986;2:743–756.
464. Fulwider WK, Grandin T, Rollin BE, et al. Survey of management practices on one hundred and thirteen north central and
northeastern United States dairies. J Dairy Sci 2008;91:1686–
1692.
465. Daly CC. Recent developments in captive bolt stunning. In: Humane slaughter of animals for food. Potters Bar, Hertfordshire,
England: Universities Federation for Animal Welfare, 1986;15–
20.
466. Gregory N, Shaw F. Penetrating captive bolt stunning and exsanguination of cattle in abattoirs. J Appl Anim Welf Sci 2000;3:215–
230.
467. Grandin T. Maintenance of good animal welfare standards in
beef slaughter plants by use of auditing programs. J Am Vet Med
93
Assoc 2005;226:370–373.
468. Daly CC, Whittington PE. Concussive methods of pre-slaughter
stunning in sheep: effects of captive bolt stunning in the poll
position on brain function. Res Vet Sci 1986;41:353–355.
469. Gregory NG, Spence JY, Mason CW, et al. Effectiveness of
poll stunning water buffalo with captive bolt guns. Meat Sci
2009;81:178–182.
470. Schulze W, Schultze-Petzold H, Hazem AS, et al. Experiments
on the objective assessment of pain and consciousness in
slaughtering sheep and calves by the conventional method (humane killer stunning) and by ritual slaughtering laws (shechita). Dtsch Tierarztl Wochenschr 1978;85:62–66.
471. Bager F, Devine CE, Gilbert KV. Jugular blood flow in calves
after head-only electrical stunning and throat-cutting. Meat Sci
1988;22:237–243.
472. Daly CC, Kallweit E, Ellendorf F. Cortical function in cattle
during slaughter: conventional captive bolt stunning followed
by exsanguination compared with shechita slaughter. Vet Rec
1988;122:325–329.
473. Newhook JC, Blackmore DK. Electroencephalographic studies
of stunning and slaughter of sheep and calves: part 1— the onset of permanent insensibility in sheep during slaughter. Meat
Sci 1982;6:221–233.
474. Gregory NG, Fielding HR, von Wenzlawowicz M, et al. Time to
collapse following slaughter without stunning in cattle. Meat Sci
2010;85:66–69.
475. Rosen SD. Physiological insights into shechita. Vet Rec
2004;154:759–765.
476. Gregory NG. Physiology of stress, distress, stunning and slaughter. In: Animal welfare and meat science. Wallingford, Oxfordshire, England: CABI Publishing, 1998;64–92.
477. Gibson TJ, Johnson CB, Murrell JC, et al. Components of electroencelphalographic responses to slaughter in halothane-anesthetized calves: effects of cutting neck tissues compared with
major blood vessels. N Z Vet J 2009;57:84–89.
478. Mellor DJ, Gibson TJ, Johnson CB. A re-evaluation of the need
to stun calves prior to slaughter by ventral-neck incision : an
introductory review. N Z Vet J 2009;57:74–76.
479. Evers AS, Crowder CM, Balser JR. General anesthetics. In:
Brunton LL, Lazo JS, Parker KL, eds. Goodman and Gillman’s
the pharmacological basis of therapeutics. 11th ed. New York:
McGraw-Hill Medical Publishing Division, 2006;362.
480. Finnie JW, Blumbergs PC, Manavis J, et al. Evaluation of brain
damage resulting from penetrating and non-penetrating captive
bolt stunning using lambs. Aust Vet J 2000;78:775–778.
481. Finnie JW, Manavis J, Blumberg PC, et al. Brain damage in sheep
from penetrating captive bolt stunning. Aust Vet J 2002;80:67–
69.
482. OIE. Chapter 7.5.5: management of fetuses during slaughter
of pregnant animals. In: Terrestrial animal health code. 17th ed.
Paris: OIE, 2008;284.
483. Jochems CE, van der Valk JB, Stafleu FR, et al. The use of fetal
bovine serum: ethical or scientific problem? Altern Lab Anim
2002;30:219–227.
484. Yan EB, Barburamani AA, Walker AM, et al. Changes in cerebral blood flow, cerebral metabolites, and breathing movements
in the sheep fetus following asphyxia produced by occlusion
of the umbilical cord. Am J Physiol Regul Integr Comp Physiol
2009;297:R60–R69.
485. Mellor DJ. Integration of perinatal events, pathophysiological changes and consequences for the newborn lamb. Br Vet J
1988;144:552–569.
486. Peisker N, Preissel AK, Rechenbach HD, et al. Foetal stress responses to euthanasia of pregnant sheep. Berl Munch Tierarztl
Wochenschr 2010;123:2–10.
487. Klaunberg BA, O’Malley J, Clark T, et al. Euthanasia of mouse
fetuses and neonates. Contemp Top Lab Anim Sci 2004;43:29–34.
488. Küchenmeister U, Kuhn G, Ender K. Preslaughter handling of
pigs and the effect on heart rate, meat quality, including tenderness, and sarcoplasmic reticulum Ca2+ transport. Meat Sci
2005;71:690–695.
489. Küchenmeister U, Kuhn G, Stabenow B, et al. The effect of experimental stress on sarcoplasmic reticulum Ca2+ transport and
meat quality in pig muscle. Meat Sci 2002;61:375–380.
94
490. Geverink NA, Schouten WGP, Gort G, et al. Individual differences in behavioral and physiological responses to restraint
stress in pigs. Physiol Behav 2002;77:451–457.
491. Magnusson U, Wattrang E, Tsuma V, et al. Effects of stress resulting from short-term restraint on in vitro functional capacity
of leukocytes obtained from pigs. Am J Vet Res 1998;59:421–
425.
492. Neubert E, Gurtler H, Vallentin G. Effect of restraining growth
pigs with snare restraints on plasma levels of catecholamines,
cortisol, insulin and metabolic parameters. Berl Munch Tierarztl
Wochenschr 1996;109:409–413.
493. Roozen AW, Magnusson U. Effects of short-term restraint stress
on leukocyte counts, lymphocyte proliferation and lysis of
erythrocytes in gilts. Zentralbl Veterinarmed B 1996;43:505–511.
494. Roozen AWM, Tsuma VT, Magnusson U. Effects of short-term
restraint stress on plasma concentrations of catecholamines,
β-endorphin, and cortisol in gilts. Am J Vet Res 1995;56:1225–
1227.
495. Farmer C, Dubreuil P, Couture Y, et al. Hormonal changes following an acute stress in control and somatostatin-immunized
pigs. Domest Anim Endocrinol 1991;8:527–536.
496. Muir W. Handbook of veterinary anesthesia. 3rd ed. St Louis:
Mosby, 2000.
497. Maisch A, Ritzmann M, Heinritzi K. The humane euthanasia of
pigs with pentobarbital. Tierarztl Umsch 2005;60:679–683.
498. Althen TG, Ono K, Topel DG. Effect of stress susceptibility or
stunning method on catecholamine levels in swine. J Anim Sci
1977;44:985–989.
499. Humane Slaughter Association. Captive bolt stunning of livestock: guidance notes No. 2. 4th ed. Wheathampstead, Hertfordshire, England: Humane Slaughter Association, 2006.
500. Van der Wal PP. Stunning, sticking and exsanguination as stress
factors in pigs, in Proceedings. 2nd Int Symp Cond Meat Qual
Pigs 1971;153–158.
501. McKinstry JL, Anil MH. The effect of repeat application of electrical stunning on the welfare of pigs. Meat Sci 2004;67:121–
128.
502. Humane Slaughter Association. Electrical stunningof red meat
animals: guidance notes No. 4. Wheathampstead, Hertfordshire,
England: Humane Slaughter Association, 2000;1–22.
503. Anil MH, McKinstry JL. Variations in electrical stunning tong
placements and relative consequences in slaughter pigs. Vet J
1998;155:85–90.
504. Anil MH, McKinstry JL. The effectivenss of high-frequency electrical stunning in pigs. Meat Sci 1992;32:481–491.
505. Lambooij B, Merkus GSM, VonVoorst N, et al. Effect of a low
voltage with a high frequency electrical stunning on unconsciousness in slaughter pigs. Fleischwirtschaft 1996;76:1327–
1328.
506. Lambooij E. Stunning of animals on the farm. Tijdschr Diergeneeskd 1994;119:264–266.
507. Troeger K, Woltersdorf W. Electrical stunning and meat quality
in the pig. Fleischwirtschaft 1990;70:901–904.
508. Wotton SB, Gregory NG. Pig slaughtering procedures: time to
loss of brain responsiveness after exsanguination of cardiac arrest. Res Vet Sci 1986;40:148–151.
509. Hoenderken R. Electrical stunning of pigs. In: Fabiansson S, ed.
Hearing on pre-slaughter stunning (report No. 52). Kavlinge, Sweden: Swedish Meat Research Centre, 1978;29–38.
510. Denicourt M, Klopfenstein C, Dufour C, et al. Using an electrical approach to euthanize pigs on-farm: fundamental principles
to know, in Proceedings. 41st Annu Meet Am Assoc Swine Vet
2010;451–468.
511. Channon HA, Walker PJ, Kerr MG, Weston PA. Using a gas
mixture of nitrous oxide and carbon dioxide during stunning
provides only small improvements to pig welfare. In Manipulating pig production X. Proceedings of the Tenth Biennial Conference of the Australasian Pig Science Association (APSA), held in
Christchurch, New Zealand, 27th to 30th November, 2005 2005
pp. 13
512. Velarde A, Cruz J, Gispert M, et al. Aversion to carbon dioxide
stunning in pigs: effect of carbon dioxide concentration and
halothane genotype. Anim Welf 2007;16:513–522.
513. Nowak B, Mueffling TV, Caspari K, et al. Validation of a method
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
for the detection of virulent Yersinia enterocolitica and their
distribution in slaughter pigs from conventional and alternative
housing systems. Vet Microbiol 2006;117:219–228.
514. Channon HA, Payne AM, Warner RD. Halothane genotype,
pre-slaughter handling and stunning method all influence pork
quality. Meat Sci 2000;56:291–299.
515. Forslid A. Muscle spasms during pre-slaughter CO2 anaesthesia
in pigs. Ethical considerations. Fleischwirtschaft 1992;72:167–
168.
516. Forslid A, Augustinsson O. Acidosis, hypoxia and stress hormone release in response to one-minute inhalation of 80% CO2
in swine. Acta Physiol Scand 1988;132:223–231.
517. Gregory NG, Moss BW, Leeson RH. An assessment of carbon
dioxide stunning in pigs. Vet Rec 1987;121:517–518.
518. Overstreet JW, Marple DN, Huffman DL, et al. Effect of stunning
methods on porcine muscle glycolysis. J Anim Sci 1975;41:1014–
1020.
519. Millman S. Mechanical euthanasia methods—process and
physiology, in Proceedings. 41st Annu Meet Am Assoc Swine Vet
2010;443–446.
520. Whiting T, Steele GS, Wamnes S, et al. Evaluation of methods of
rapid mass killing of segregated early weaned piglets. Can Vet J
2011;52:753–758.
521. Widowski T. Effectiveness of a non-penetrating captive bolt for onfarm euthanasia of low viability piglets. Des Moines, Iowa: National Pork Board, 2008.
522. United Egg ProducersAnimal husbandry guidelines for US egg
laying flocks. 2010 edition. Alpharetta, Ga: United Egg Producers, 2010. Available at: www.unitedegg.org/information/pdf/
UEP_2010_Animal_Welfare_Guidelines.pdf.. Accessed Aug 13,
2012.
523. Webster AB, Collett SR. A mobile modified-atmosphere killing
system for small-flock depopulation. J. Appl. Poult. Res. 2012;
21:131–144
524. Coenen AML, Lankhaar J, Lowe JC, et al. Remote monitoring
of electroencephalogram, electrocardiogram, and behavior during controlled atmosphere stunning in broilers: implications for
welfare. Poult Sci 2009;88:10–19.
525. European Council. European Council Directive 93/119/EC of 22
December 1993 on the protection of animals at the time of slaughter
or killing. Annex G: killing of surplus chicks and embryos in hatchery waste. Brussels: European Council, 1993.
526. Shearer JK, Nicoletti P. Anatomical landmarks. Available at:
www.vetmed.iastate.edu/vdpam/extension/dairy/programs/
humane-euthanasia/anatomical-landmarks. Accessed Jun 24,
2011.
527. Mason C, Spence J, Bilbe L, et al. Methods for dispatching backyard poultry. Vet Rec 2009;164:220.
528. Rae M. Necropsy. In: Clinical avian medicine. Vol 2. Palm Beach,
Fla: Spix Publishing, 2006;661–678.
529. Hess L. Euthanasia techniques in birds—roundtable discussion.
J Avian Med Surg 2005;19:242–245.
530. Gaunt AS, Oring LW. Guidelines to the use of wild birds in research. Washington, DC: The Ornithological Council, 1997.
531. Dawson MD, Johnson KJ, Benson ER, et al. Determining cessation of brain activity during depopulation or euthanasia of
broilers using accelerotomers. J Appl Poult Res 2009;18:135–
142.
532. Raj M, O’Callaghan M, Thompson K, et al. Large scale killing of
poultry species on farm during outbreaks of diseases: evaluation
and development of a humane containerised gas killing system.
Worlds Poult Sci J 2008;64:227–244.
533. Raj M. Humane killing of nonhuman animals for disease control
purposes. J Appl Anim Welf Sci 2008;11:112–124.
534. Powell FL. Respiration. In: Whittow GC, ed. Sturkie’s avian
physiology. 5th ed. San Diego: Academic Press, 2000;233–264.
535. King AS, McLelland J. Respiratory system. In: King AS, McLelland J, eds. Birds: their structure and function. 2nd ed. Eastbourne, East Sussex, England: Bailliere Tindall, 1984;110–144.
536. Dumonceaux G, Harrison GJ. Toxins. In: Ritchie BW, Harrison
GJ, Harrison LR, eds. Avian medicine: principles and application.
Lake Worth, Fla:Wingers Publishing, 1994;1030–1052.
537. Benson E, Malone GW, Alphin RL, et al. Foam-based mass
emergency depopulation of floor-reared meat-type poultry opAVMA Guidelines for the Euthanasia of Animals: 2013 Edition
erations. Poult Sci 2007;86:219–224.
538. Raj ABM. Recent developments in stunning and slaughter of
poultry. Worlds Poult Sci J 2006;62:462–484.
539. Elwood RW, Appel M. Pain experience in hermit crabs? Anim
Behav 2009;77:1243–1246.
540. Barr S, Laming PR, Dick JTA, et al. Nociception or pain in a
decapod crustacean? Anim Behav 2008;75:745–751.
541. Ashley PJ, Sneddon LU, McCrohan CR. Nociception in fish:
stimulus response properties of receptors on the head of trout
Oncorhynchus mykiss. Brain Res 2007;1166:47–54.
542. Braithwaite VA, Boulcott P. Pain perception, aversion and fear in
fish. Dis Aquat Organ 2007;75:131–138.
543. Alvarez FA, Rodriguez-Martin I, Gonzalez-Nuñez V, et al. New
kappa opioid receptor from zebrafish Danio rerio. Neurosci Lett
2006;405:94–99.
544. Sneddon LU. Trigeminal somatosensory innervation of the head
of a teleost fish with particular reference to nociception. Brain
Res 2003;972:44–52.
545. Buatti MC, Pasternak GW. Multiple opiate receptors: phylogenetic differences. Brain Res 1981;218:400–405.
546. Finger TE. Fish that taste with their feet: spinal sensory pathways
in the sea robin, Prionotus carolinus. Biol Bull 1981;161:154–
161.
547. Schulman JA, Finger TE, Brecha NC, et al. Enkephalin immunoreactivity in Golgi cells and mossy fibres of mammalian,
avian and teleost cerebellum. Neuroscience 1981;6:2407–2416.
548. Jepson J. A linguistic analysis of discourse on the killing of nonhuman animals. Soc Anim 2008;16:127–148.
549. Yanong RPE, Hartman KH, Watson CA, et al. Fish slaughter,
killing, and euthanasia: a review of major published US guidance
documents and general considerations of methods. Publication
#CIR1525. Gainesville, Fla: Fisheries and Aquatic Sciences Department, Florida Cooperative Extension Service, Institute of
Food and Agricultural Sciences, University of Florida, 2007.
Available at: edis.ifas.ufl.edu/fa150. Accessed May 16, 2011.
550. Hartman KH. Fish. In: American Association of Zoo Veterinarians (AAZV). Guidelines for euthanasia of nondomestic animals. Yulee, Fla: American Association of Zoo Veterinarians,
2006;28–38.
551. Håstein T, Scarfe AD, Lund VL. Science-based assessment of
welfare: aquatic animals. Rev Sci Tech 2005;24:529–547.
552. Burns R. Considerations in the euthanasia of reptiles, fish and
amphibians, in Proceedings. Am Assoc Zoo Vet Wildl Dis Assoc
Am Assoc Wildl Vet Joint Conf 1995;243–249.
553. Zwart P, de Vries HR, Cooper JE. The humane killing of fishes,
amphibia, reptiles and birds [in Dutch]. Tijdschr Diergeneeskd
1989;114:557–565.
554. Brown LA. Anesthesia and restraint. In: Stoskopf MK, ed. Fish
medicine. Philadelphia: WB Saunders, 1993;79–90.
555. Roberts HE. Anesthesia, analgesia and euthanasia. In: Roberts
HE, ed.Fundamentals of ornamental fish health. Ames, Iowa:
Blackwell, 2010;166–171.
556. Saint-Erne N. Anesthesia. In: Advanced koi care. 2nd ed. Glendale, Ariz: Erne Enterprises, 2010;50–52.
557. Standing Committee of the European Convention for the Protection of Animals Kept for Farming Purposes. Recommendations
concerning farmed fish. Strasbourg, France: European Convention for the Protection of Animals Kept for Farming Purposes,
2006.
558. Stetter MD. Fish and amphibian anesthesia. Vet Clin North Am
Exot Anim Pract 2001;4:69–82.
559. Ross LG, Ross B. Anaesthetic and sedative techniques for aquatic
animals. 3rd ed. Oxford, England: Blackwell, 2008.
560. Rombough PJ. Ontogenetic changes in the toxicity and efficacy
of the anaesthetic MS222 (tricaine methanesulfonate) in zebrafish (Danio rerio) larvae. Comp Biochem Physiol A Mol Integr
Physiol 2007;148:463–469.
561. Canadian Council on Animal Care. Guidelines on: the care and
use of fish in research, teaching and testing. Ottawa: Canadian
Council on Animal Care, 2005. Available at: www.ccac.ca/Documents/Standards/Guidelines/Fish.pdf. Accessed Dec 19, 2010.
562. Deitrich RA, Dunwiddie TV, Harris RA, et al. Mechanism of action of ethanol: initial central nervous system actions. Pharmacol Rev 1989;41:489–537.
95
563. Peng J, Wngle M, Mueller T, et al. Ethanol-modulated camouflage response screen in zebrafish uncovers a novel role for
camp and extracellular signal-regulated kinase signaling in behavioral sensitivity to ethanol. J Neurosci 2009;29:8408–8418.
564. Dlugos CA, Rabin RA. Ethanol effects on three strains of zebrafish: model system for genetic investigations. Pharmacol Biochem
Behav 2003;74:471–480.
565. Gerlai R, Lahav M, Guo S, et al. Drinks like a fish: zebra fish
(Danio rerio) as a behavior genetic model to study alcohol effects. Pharmacol Biochem Behav 2000;67:773–782.
566. Gladden JN, Brainard BM, Shelton JL, et al. Evaluation of isoeugenol for anesthesia in koi carp (Cyprinus carpio). Am J Vet Res
2010;71:859–866.
567. Holloway A, Keene JL, Noakes DG, et al. Effects of clove oil and
MS-222 on blood hormone profiles in rainbow trout Oncorhynchus mykiss, Walbaum. Aquaculture Res 2004;35:1025–1030.
568. Lewbart GA. Fish. In: Carpenter JW, ed. Exotic animal formulary. 3rd ed. St Louis: Elsevier Saunders, 2005;5–29.
569. FDA. Concerns related to the use of clove oil as an anesthetic for
fish. Guidance for industry 150. Washington, DC: Department
of Health and Human Services, 2007. Available at: www.fda.gov/
downloads/AnimalVeterinary/GuidanceComplianceEnforcement/GuidanceforIndustry/ucm052520.pdf. Accessed Jan 20,
2011.
570. Davie PS, Kopf RK. Physiology, behaviour and welfare of
fish during recreational fishing and after release. N Z Vet J
2006;54:161–172.
571. van de Vis H, Kestin S, Robb D, et al. Is humane slaughter of fish
possible for industry? Aquaculture Res 2003;34:211–220.
572. Animal Procedures Committee. Report of the Animal Procedures
Committee for 2009. London: The Stationery Office, 2010;27.
573. Waterstrat PR, Pinkham L. Evaluation of eugenol as an anesthetic for the American lobster Homarus americanus. J World
Aquaculture Soc 2005;36:420–424.
574. Gunkel C, Lewbart GA. Invertebrates. In West G, Heard D,
Caulkett N, eds. Zoo animal and wildlife immobilization and anesthesia. Ames, Iowa: Blackwell, 2007;147–158.
575. American Association of Zoo Veterinarians (AAZV). Guidelines
for euthanasia of nondomestic animals. Yulee, Fla: American Association of Zoo Veterinarians, 2006.
576. Canadian Council on Animal Care. Guidelines on: the care and
use of wildlife. Ottawa: Canadian Council on Animal Care,
2003. Available at: ccac.ca/Documents/Standards/Guidelines/
Wildlife.pdf. Accessed Jul 2, 2011.
577. Fowler M. Restraint and handling of wild and domestic animals.
3rd ed. Ames, Iowa: Wiley-Blackwell, 2008.
578. West G, Heard D, Caulkett N. Zoo Animal & wildlife immobilization and anesthesia. Ames, Iowa: Blackwell, 2007.
579. Kreeger TJ, Arnemo J. Handbook of wildlife chemical immobilization. International ed. Fort Collins, Colo: Wildlife Pharmaceuticals Inc, 2002.
580. Clark RK, Jessup DA. Wildlife restraint series. Fort Collins, Colo:
International Wildlife Veterinary Services, 1992.
581. Platnick NI. American Museum of Natural History research
sites.The world spider catalog, version 13.0. Available at: research.amnh.org/entomology/spiders/catalog/index.html. Accessed August 14, 2012.
582. Ruppert E, Fox R, Barnes R. Invertebrate zoology: a functional
evolutionary approach. 7th ed. Thomson Learning, 2007.
583. Murray MJ. Euthanasia. In: Lewbart GA, ed. Invertebrate medicine. 2nd ed. Ames, Iowa: Wiley-Blackwell, 2011;441–444.
584. Braun ME, Heatley JJ, Chitty J. Clinical techniques of invertebrates. Vet Clin North Am Exot Anim Pract 2006;9:205–221.
585. Cooper JE. Anesthesia, analgesia and euthanasia of invertebrates. ILAR J 2011;52:196–204.
586. Gunkel C, Lewbart GA. Anesthesia and analgesia of invertebrates. In: Fish R, Danneman P, Brown M, et al, eds. Anesthesia
and analgesia in laboratory animals. 2nd ed. San Diego: Academic Press, 2008;535–546.
587. Pizzi R. Spiders. In: Lewbart GA, ed. Invertebrate medicine.
Ames, Iowa: Blackwell, 2006;143–168
588. Pizzi R, Cooper JE, George S. Spider health, husbandry, and welfare in zoological collections, in Proceedings. Br Vet Zool Soc
Conf Stand Welf Conserv Zoo Exot Pract 2002;54–59.
96
589. Baier J. Amphibians. In: American Association of Zoo Veterinarians
(AAZV). Guidelines for euthanasia of nondomestic animals. Yulee,
Fla: American Association of Zoo Veterinarians, 2006;39–41.
590. Burns R, McMahan B. Euthanasia methods for ectothermic vertebrates. In: Bonagura JD, ed. Continuing veterinary therapy XII.
Philadelphia: WB Saunders Co, 1995;1379–1381.
591. Baier J. Reptiles. In: American Association of Zoo Veterinarians
(AAZV). Guidelines for euthanasia of nondomestic animals. Yulee,
Fla: American Association of Zoo Veterinarians, 2006;42–45.
592. Mader DR. Euthanasia. In: Mader DR, ed. Reptile medicine and
surgery. St Louis: Saunders/Elsevier, 2006;564–568.
593. Gentz EJ. Medicine and surgery of amphibians. ILAR J
2007;48:255–259.
594. Andrews EJ, Bennet BT, Clark JD, et al. 1993 report of the AVMA
Panel on Euthanasia. J Am Vet Med Assoc 1993;202:229–249.
595. Heard DJ. Principles and techniques of anesthesia and analgesia for exotic practice. Vet Clin North Am Small Anim Pract
1993;23:1301–1327.
596. Conroy CJ, Papenfuss T, Parker J, et al. Use of tricaine methanesulfonate (MS-222) for euthanasia of reptiles. J Am Assoc Lab
Anim Sci 2009;48:28–32.
597. Harrell L. Handling euthanasia in production facilities. In:
Schaeffer DO, Kleinow KM, Krulisch L, eds. The care and use of
amphibians, reptiles and fish in research. Bethesda, Md: Scientists
Center for Animal Welfare, 1992;129.
598. Letcher J. Intracelomic use of tricaine methane sulfonate for anesthesia of bullfrogs (Rana catesbeiana) and leopard frogs (Rana
pipiens). Zoo Biol 1992;11:243–251.
599. Canadian Council on Animal Care. CCAC guidelines on: euthanasia of animals used in science. Ottawa: Canadian Council on
Animal Care, 2010. Available at: www.ccac.ca/Documents/Standards/Guidelines/Euthanasia.pdf. Accessed Jul 2, 2011.
600. Breazile JE, Kitchell RL. Euthanasia for laboratory animals. Fed
Proc 1969;28:1577–1579.
601. Storey KB. Life in a frozen state: adaptive strategies for natural freeze tolerance in amphibians and reptiles. Am J Physiol
1990;258:R559–R568.
602. Brannian RE, Kirk E, Williams D. Anesthetic induction of kinosternid turtles with halothane. J Zoo Anim Med
1987;18:115–117.
603. Jackson OF, Cooper JE. Anesthesia and surgery. In: Cooper JE,
Jackson OF, eds. Diseases of the reptilia. Vol. 2. New York: Academic Press Inc, 1981;535–549.
604. Calderwood HW. Anesthesia for reptiles. J Am Vet Med Assoc
1971;159:1618–1625.
605. Moberly WR. The metabolic responses of the common iguana,
Iguana iguana, to walking and diving. Comp Biochem Physiol
1968;27:21–32.
606. Johlin JM, Moreland FB. Studies of the blood picture of the turtle after complete anoxia. J Biol Chem 1933;103:107–114.
607. Storey KB, Storey JM. Natural freezing survival in animals. Annu
Rev Ecol Syst 1996;27:365–386.
608. Machin KL. Amphibian pain and analgesia. J Zoo Wildl Med
1999;30:2–10.
609. Stevens CW, Pezalla PD. Endogenous opioid system downregulation during hibernation in amphibians. Brain Res
1989;494:227–231.
610. Martin BJ. Evaluation of hypothermia for anesthesia in reptiles
and amphibians. ILAR J 1995;37:186–190.
611. Suckow MA, Terril LA, Grigdesby CF, et al. Evaluation of hypothermia-induced analgesia and influence of opioid antagonists in Leopard frogs (Rana pipiens). Pharmacol Biochem Behav
1999;63:39–43.
612. Schaffer DO. Anesthesia and analgesia in nontraditional laboratory animal species. In: Kohn DF, Wixson SK, White WJ, et al.
eds. Anesthesia and analgesia in laboratory animals. San Diego:
Academic Press Inc, 1997;337–378.
613. Greer LL, Whaley J. Marine mammals. In: American Association of Zoo Veterinarians (AAZV). Guidelines for euthanasia of
nondomestic animals. Yulee, Fla: American Association of Zoo
Veterinarians, 2006;66–74.
614. Drew ML. Wildlife issues. In: American Association of Zoo Veterinarians (AAZV). Guidelines for the euthanasia of nondomestic
animals. Yulee, Fla: American Association of Zoo Veterinarians,
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
2006;19–22.
615. Hyman J. Euthanasia in marine mammals. In: Dierauf LA, ed.
Handbook of marine mammal medicine: health, disease and rehabilitation. Boca Raton, Fla: CRC Press Inc, 1990;265–266.
616. Needham DJ. Cetacean strandings. In: Fowler ME, ed. Zoo and
wild animal medicine: current therapy 3. 3rd ed. Philadelphia:
WB Saunders Co, 1993;415–425.
617. Gullett PA. Euthanasia. In: Friend M, ed. Field guide to wildlife
diseases. Volume 1: general field procedures and diseases of migratory birds. Resource publication #167. Washington, DC: US Department of the Interior, Fish and Wildlife Service, 1987;59–63.
618. Fair JM. Guidelines for the use of wild birds in research. 3rd ed.
Washington, DC: The Ornithological Council, 2010.
619. Sikes RS, Gannon WL. Guidelines of the American Society of
Mammalogists for the use of wild mammals in research. J Mammal 2011;92:235–253.
620. Herptological Animal Care and Use Committee. Guidelines for
use of live amphibians and reptiles in field and laboratory research.
Miami: American Society of Ichthyologists and Herpetologists,
2004.
621. Orlans FB. Field research guidelines: impact on animal care and
use committees. Bethesda, Md: Scientists Center for Animal Welfare, 1988.
622. McClure DN, Anderson N. Rodents and small mammals. In:
American Association of Zoo Veterinarians (AAZV). Guidelines
for euthanasia of nondomestic animals. Yulee, Fla: American Association of Zoo Veterinarians, 2006;61–65.
623. Brakes P, Butterworth A, Donoghue M. Investigating criteria
for insensibility and death in stranded cetaceans in New Zealand.
IWC/58/WKM&AWI 9. Agenda item 5.2.4. Impington, Cambridgeshire, England: International Whaling Commission,
2006.
624. Moore M, Walsh M, Bailey J, et al. Sedation at sea of entangled
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
625.
626.
627.
628.
629.
630.
631.
632.
633.
634.
North Atlantic right whales (Eubalaena glacialis) to enhance
disentanglement. PLoS ONE [serial online] 2010;5:e9597.
doi:10.1371/journal.pone.0009597. Accessed August 14, 2012.
Dunn JL. Multiple-agent euthanasia of a juvenile fin whale,
Balanoptera physalus. Mar Mamm Sci 2006;22:1004–1007.
Øen EO, Knudsen SK. Euthanasia of whales: the effect of .375
and .458 calibre round-nosed, full metal-jacketed rifle bullets
on the central nervous system of common minke whales. J Cetacean Res Manag 2007;9:81–88.
Donoghue, M. IWC 58: workshop on whale killing methods and
associated welfare issues euthanasia of stranded cetaceans in New
Zealand. IWC/58/WKM&AWI 10. Agenda item 4.4. Impington,
Cambridgeshire, England: International Whaling Commission,
2006.
Lawrence K. Euthanasia of stranded whales. Vet Rec 2003;153:
540.
Bonner WN. Killing methods. In: Laws RM, ed. Antarctic seals:
research methods and techniques. Cambridge, England: Cambridge University Press, 1993;150–160.
Sweeney JC. What practitioners should know about whale
strandings. In: Kirk RW, ed. Kirk’s current veterinary therapy 10.
Philadelphia: WBSaunders Co, 1989;721–727.
Daoust PY, Crook A, Bollinger TK, et al. Animal welfare and the
harp seal hunt in Atlantic Canada. Can Vet J 2002;43:687–694.
Coughran D, Stiles I, Fuller PJ. Euthanasia of beached
humpback whales using explosives. J Cetacean Res Manag
2012;12:137–144.
International Whaling Commission. Report of the workshop on
welfare issues associated with the entanglement of large whales.
IWC/62/15. Agenda item 5.2.1. Impington, Cambridgeshire,
England: International Whaling Commission, 2010.
Daoust PY, Ortenburger AI. Successful euthanasia of a juvenile
fin whale. Can Vet J 2001;42:127–129.
97
Glossary
Acceptable: A method considered to reliably meet the
requirements of euthanasia. See EUTHANASIA.
Acceptable With Conditions: A method considered
to reliably meet the requirements of euthanasia
when specified conditions are met. See EUTHANASIA.
Adjunctive Method: A method of assuring death that
may be used after an animal has been made unconscious.
Affect: The external expression of emotion.
Altricial: Immobile, blind, naked young animals (including but not limited to birds and some rodents)
requiring parental care and feeding.
Anesthesia, General: A method used to produce unconsciousness. See UNCONCIOUSNESS.
Animal: Any nonhuman animal (Kingdom: Animalia).
Aversion: A desire to avoid or retreat from a stimulus.
Avian: Relating to birds.
Captive Bolt: A device used to kill or stun animals
where a tethered metal rod is discharged into the
brain of the animal.
Chick: A young bird.
Cremation: To incinerate a dead body. See INCINERATION.
Depopulation: The killing of animals in large numbers in response to an animal health emergency (eg,
catastrophic infectious disease, mass intoxication,
natural disaster) where all due consideration is
given to the terminal experience of the animal, but
the circumstances surrounding the event are understood to be exigent and extenuating. Depopulation
may not meet the requirements of euthanasia due to
situational constraints.
Distress: The effect of stimuli that initiate adaptive responses that are not beneficial to the animal—thus,
the animal’s response to stimuli interferes with its
welfare and comfort.
Ectotherm: An organism that is dependent on environmental heat sources for regulating its body temperature.
Eustress: The effect of stimuli that initiate adaptive
responses that are beneficial to the animal.
Euthanasia: A method of killing that minimizes pain,
distress, and anxiety experienced by the animal
prior to loss of consciousness, and causes rapid loss
of consciousness followed by cardiac or respiratory
arrest and death (see sections I3, I5, I6).
Exsanguination: The action of draining an animal of
blood.
Fear: An unpleasant emotional experience caused by
an awareness of a threat of danger.
Feral: A free-roaming, unowned animal of a domestic
species that has reverted to wild behavior.
Field Conditions: Any situation outside of a controlled or clinical environment.
Finfish: a term used to describe true (vertebrate) fish
as opposed to other non-fish aquatic animals such as
the invertebrates “starfish” and “cuttlefish”
98
Good Death: see EUTHANASIA.
Harvest: The act or process of killing an animal for
food or other products.
Humane Killing: Killing performed in a manner that
minimizes animal distress, but may not meet the
requirements of euthanasia due to situational constraints.
Incineration: To burn completely, to ashes.
Insensible: See UNCONSCIOUS.
Livestock: Domestic animals raised for use, consumption, or profit, typically on a farm.
Mass euthanasia: see DEPOPULATION.
Nociception: Neuronal impulses generated by noxious
stimuli, which threaten to, or actually do, destroy
tissue. Nociception can occur without consequential pain perception.
Pain: A sensation (perception) that results from nociceptive nerve impulses reaching areas of the brain
capable of conscious perception via ascending neural pathways.
Pithing: Physical destruction of the brain with a wire,
air jet, or rod.
Poikilotherm: An animal with a variable internal temperature. These animals are generally ectothermic.
Poult: A young fowl.
Poultry: Domestic fowl raised for meat or eggs, such
as chickens, turkeys, ducks, or geese.
Precocious: Capable of a high degree of independent
activity (ie, mobility, feeding) from birth.
Secondary Method: A euthanasia method employed
subsequent to a primary method to ensure death of
an unconscious animal before it can recover consciousness. See ADJUNCTIVE METHOD.
Sedation: A state of CNS depression in which the animal is awake but calm, and with sufficient stimuli
may be aroused.
Slaughter: Killing animals for the purposes of harvesting commodities such as meat or hides.
Stress: The effect of physical, physiologic, or emotional factors (stressors) that induce an alteration in
an animal’s homeostasis or adaptive state.
Stunning: Rendering an animal unconscious by use of
a physical, gas, or electrical method.
Suffocate: To kill by preventing access to air or oxygen.
Unacceptable: A method that does not meet the requirements of euthanasia. See EUTHANASIA.
Unconsciousness: Unconsciousness, defined as loss of
individual awareness. This occurs when the brain’s
ability to integrate information is blocked or disrupted. Onset of unconsciousness is associated with
loss of the righting reflex. An unconscious animal
is therefore recumbent and, by definition, unable
to perceive pain; however, unconscious animals
may respond to noxious stimulation with spinally
mediated involuntary movements depending on the
degree of CNS depression present.
Wild: A free-roaming animal of a nondomestic species.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Appendix 1
Agents and methods of euthanasia by species.
Methods
Acceptable
Acceptable With Conditions
(for Adjunctive Methods, see text)
Aquatic invertebrates
S6.3: Immersion in anesthetic solution (magnesium
salts, clove oil, eugenol, ethanol)
S6.3: Adjunctive methods (second step) include 70%
alcohol and neutral-buffered 10% formalin, pithing,
freezing, boiling
Amphibians
S7.3: As appropriate by species—Injected
barbiturates, dissociative agents and anesthetics as
specified, topical buffered tricaine methanesulfonate
or benzocaine hydrochloride
S7.3: As appropriate by species—Inhaled anesthetics
as specified, CO2, penetrating captive bolt or firearm,
manually applied blunt force trauma to the head,
rapid freezing
Avians (See also
Poultry)
S5: Intravenous barbiturates
S5: Inhaled anesthetics, CO2, CO, N2, Ar, cervical
dislocation (small birds and poultry), decapitation
(small birds)
S7.5: Gunshot (free-ranging birds)
Cats
S1: Intravenous barbiturates, injected anesthetic
overdose, Tributame, T-61
S1: Barbiturates (alternate routes of administration),
inhaled anesthetic overdose, CO,* CO2,* gunshot*
Cattle
S3.2: Intravenous barbiturates
S3.2: Gunshot, penetrating captive bolt
Dogs
S1: Intravenous barbiturates, injected anesthetic
overdose, Tributame, T-61
S1: Barbiturates (alternate routes of administration),
inhaled anesthetic overdose, CO,* CO2,* gunshot*
Finfish
S6.2: Immersion in buffered benzocaine or benzocaine
hydrochloride, isoflurane, sevoflurane, quinaldine
sulfate, buffered tricaine methanesulfonate,
2-phenoxyethanol, injected pentobarbital, rapid
chilling (appropriate zebrafish/research setting)
S6.2: Eugenol, isoeugenol, clove oil, CO2-saturated
water (aquarium-fish facilities/fisheries),
decapitation/cervical transection/manually applied
blunt force trauma followed by pithing, rapid chilling
followed by adjunctive method (aquarium-fish
facilities), maceration (research setting)
Equids
S4: Intravenous barbiturates
S4: Penetrating captive bolt, gunshot
Marine mammals
S7.5 (captive): Injected barbiturates S7.7 (free ranging):
Injected barbiturates or anesthetic overdose
S7.5 (captive): Inhaled anesthetics
S7.7 (free ranging): Gunshot, manually applied blunt
force trauma, implosive decerebration
Nonhuman primates
S2.3, S7.4: Injected barbiturates or anesthetic overdose
S2.3, S7.4 (as appropriate by species): Inhaled
anesthetic, CO, CO2
Poultry
S3.4: Injected barbiturates and anesthetic overdose
S3.4: CO2, CO, N2, Ar, cervical dislocation (as
anatomically appropriate), decapitation, manual blunt
force trauma, electrocution, gunshot, captive bolt
Rabbits
S2.4: Intravenous barbiturates
S2.4: Inhaled anesthetic overdose, CO2, cervical
dislocation (as anatomically appropriate), penetrating
captive bolt
Reptiles
S7.3: As appropriate by species—Injected
barbiturates, dissociative agents and anesthetics as
specified
S7.3: As appropriate by species—Inhaled anesthetics
as specified, CO2, penetrating captive bolt or firearm,
manually applied blunt force trauma to the head,
rapid freezing for animals < 4 g
Rodents
S2.2: Injected barbiturates and barbiturate
combinations, dissociative agent combinations
S2.2: Inhaled anesthetics, CO2, CO, tribromoethanol,
ethanol, cervical dislocation, decapitation, focused
beam microwave irradiation
Small ruminants
S3.2: Injected barbiturates
S3.2: Gunshot, penetrating captive bolt
Swine
S3.3: Injected barbiturates
S3.3: CO2, CO, N2, Ar, gunshot, electrocution,
nonpenetrating captive bolt, manually applied blunt
force trauma
*Not recommended for routine use.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
99
100
Appendix 2
Some acceptable* agents and methods of euthanasia.
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Ease of
performance
Safety for
personnel
Species
suitability
Rapid onset of
anesthesia
IV injection is
necessary for
best results and
requires trained
personnel; each
animal must be
appropriately
restrained
Safe except human
abuse potential;
DEA-controlled
substance
Most species,
excluding aquatic
invertebrates
Highly effective when
Apply to the use of non-IV routes (see text)
appropriately administered;
when an IV injection would
be distressful, dangerous, or
difficult due to small patient
size, barbituates may be
administered intraperitoneal or
intracoelomic (pentobarbitalal
combination products have
only been approved for IV and
intracardiac administration)
Depression of CNS
and heart
Rapid,
depending on
dose
Easily used
Safe
Smaller finfish
and amphibians
Effective but expensive
Respiratory
acidosis and
produces a
reversible
anesthetic
state followed
by hypoxia
attributable to
depression of vital
centers
Direct depression
of cerebral cortex,
subcortical
structures, and
vital centers; direct
depression of heart
muscle
Moderately
Easily with
rapid, depending appropriate
on protocol
equipment, closed
container, gas
source, and once
protocol are
established
Minimal hazard
with adequate
ventilation
Most birds
and mammals,
excluding
companion
animals
Effective, but time required
may be prolonged in immature
and neonatal animals
May be used only with those species where
aversion or distress can be minimized; gradual
fill method must be used; must be supplied in a
precisely regulated and purified form without
contaminants or adulterants, typically from
a commercially supplied cylinder or tank; an
appropriate pressure-reducing regulator and
flow meter or equivalent equipment must be
used
Carbon monoxide
Hypoxemia
Combines with
hemoglobin and
blocks uptake of O2
Moderate
onset time,
but insidious
so that most
animal species
are unaware of
onset
Extremely
hazardous, toxic,
explosive in high
concentrations, and
difficult to detect
Most small
species,
excluding
companion
animals
Effective
Acceptable only when equipment is properly
designed and operated
Cervical
dislocation
Hypoxia
Direct depression
Variable
of brain and cardiac
fibrillation
Personnel must be Safe
skilled
Decapitation
Hypoxia due to
disruption of vital
centers
Direct depression
of brain
Requires training
and skill
Guillotine poses
Laboratory
potential employee- rodents; small
injury hazard
rabbits; poultry
and birds; and
some finfish,
amphibians, and
reptiles
Electrocution
Hypoxia
Direct depression
Can be rapid
of brain and cardiac
fibrillation
Not easily
performed in
all instances;
requires specialist
equipment and
skilled application
May be hazardous
to personnel
Used primarily
in sheep, swine,
ruminants, and
other animals
> 5 kg
Gunshot
Physical damage
to brain
Direct concussion
of brain tissue
Requires skill
and appropriate
firearm
May be dangerous;
aesthetically
unpleasant for
many
Large domestic
and selected
nondomestic
species
Agent
Classification
Mode of action
Rapidity†
Barbiturates
Hypoxia and
cardiac arrest
attributable to
depression of the
CNS
Depression of the
CNS in descending
order; loss of
consciousness
progressing to
anesthesia, apnea,
and cardiac arrest
Benzocaine
hydrochloride
Hypoxia
attributable to
depression of vital
centers
Carbon dioxide
Rapid
Immediate
Requires
appropriately
maintained
equipment
Efficacy and comments
Small birds,
Variable
poultry, mice,
immature rats (<
200 g), and rabbits
Irreversible; violent muscle
contraction can occur after
decapitation
Conditions
Must meet a performance standard of luxation of
the cervical vertebrae without primary crushing
of the vertebrae and spinal cord—inducing very
rapid unconsciousness
A commercially available guillotine should be
used if available for the species and application.
In lieu of this, a sharp knife and accurate
placement are required.
Current must pass through the brain, and cardiac
fibrillation must never occur before the animal is
rendered unconscious; electroimmobilization is
unacceptable; use of household electrical cords
is unacceptable
Instant loss of consciousness,
but motor activity may
continue
Personnel must be trained in the use of firearms;
only in jurisdictions that allow for legal firearm
use; safety of personnel, the public, and other
animals that are nearby should be considered
Appendix 2 (continued)
AVMA Guidelines for the Euthanasia of Animals: 2013 Edition
Some acceptable* agents and methods of euthanasia.
Ease of
performance
Safety for
personnel
Species
suitability
Moderately
rapid onset of
anesthesia,
excitation may
develop during
induction
Easily performed
with closed
container
(including topical
or immersion as
appropriate by
species); can be
administered to
large animals by
means of a mask
Effective
procedures should
be in place to
reduce animal
worker exposure to
anesthetic vapors
Most animals
excluding
livestock, finfish,
and many
amphibians and
reptiles
Highly effective provided that
subject is sufficiently exposed
Direct concussion
of brain tissue
Immediate
Easily performed
with properly
designed,
commercially
available
equipment and
trained personnel
Generally safe;
macerated tissues
may present
biosecurity risks
Newly hatched
chicks and poults,
and pipped eggs
only
Effective
Specialized equipment in excellent working
order must be used
Brain enzyme
inactivation
Direct inactivation
of brain enzymes
by rapid heating of
brain
Very rapid
Requires training
and highly
specialized
equipment
Safe
Mice and rats
Highly effective for special
needs
Only instruments that are designed for this use
and have appropriate power and microwave
distribution can be used
Nitrogen, argon
Hypoxia
Reduces partial
pressure of oxygen
available to blood
Rapid
Used in closed
chamber with
rapid filling
Safe if used with
ventilation
Chickens, turkeys, Effective except in young
and swine
and neonates; an effective
agent, but other methods are
preferable in species where
aversion is noted
These gases must be supplied in a precisely
regulated and purified form without
contaminants or adulterants; an appropriate
pressure-reducing regulator and flow meter
combination or equivalent equipment must
be used
Potassium chloride
Cardiotoxic
Direct depression
of cerebral cortex,
subcortical
structures, and vital
centers secondary
to cardiac arrest
Rapid
Requires training
and ability to
give IV injection
of potassium
chloride
Anesthetics may
be hazardous with
accidental human
exposure
Most species
Highly effective, some clonic
muscle spasms may be
observed
Intracardially or IV with an animal that is
unconscious or under general anesthesia
only; unacceptable when used in conscious
vertebrate animals
Penetrating captive
bolt
Physical damage
to brain
Direct concussion
of brain tissue
Immediate
Requires skill,
adequate
restraint, and
proper placement
of captive
bolt; can be
aesthetically
displeasing
Safe
Horses,
ruminants, swine
and nondomestic
species, as
appropriate
Instant loss of consciousness,
but motor activity may
continue
Animals be immediately exsanguinated or
pithed unless a powerful captive bolt gun
designed for euthanasia is used; captive bolt
guns used for larger species must have an
extended bolt
Tricaine methane
sulfonate (TMS,
MS 222)
Hypoxia
Depression of CNS
attributable to
decreased nervous
and cardiovascular
function
Rapid,
depending on
dose
Easily used
Associated with
retinal toxicity in
humans
Finfish, some
reptiles,
amphibians, and
cold-blooded
aquatics
Effective but expensive
The solution should be buffered with
sodium bicarbonate; a secondary method of
euthanasia is recommended in some finfish
and amphibians
2-phenoxyethanol
Hypoxia
attributable to
depression of vital
centers
Rapid,
depending on
dose
Easily used
Safe
Finfish
There are probably more
efficient immersion agents
available
There are species variations in dosage
levels and duration of exposure required
for euthanasia. Finfish should be kept in
the 2-phenoxyethanol solution for at least
10 minutes after cessation of opercular
movement
Agent
Classification
Mode of action
Rapidity†
Inhalant
anesthetics
Hypoxia
attributable to
depression of vital
centers
Direct depression
of cerebral cortex,
subcortical
structures, and vital
centers
Maceration
Physical damage
to brain
Focused beam
microwave
irradiation
Depression of CNS
Efficacy and comments
101
*Acceptable, acceptable with conditions, and adjunctive methods have been included in this appendix, with the appropriate qualifications.
†Immediate = Upon application. Very rapid = Typically within seconds. Rapid = Typically within a few minutes.
DEA = Drug Enforcement Agency.
Conditions
Appendix 3
Some agents and methods that are unacceptable as primary methods of euthanasia.
Agent or method
Comments
Air embolism
Air embolism may be accompanied by convulsions, opisthotonos, and vocalization. If used, it
should be done only in anesthetized animals.
Burning
Chemical or thermal burning of an animal is not an acceptable method of euthanasia.
Chloral hydrate
Unacceptable.
Chloroform
Chloroform is a known hepatotoxin and suspected carcinogen and, therefore, is extremely
hazardous to personnel.
Cyanide
Cyanide poses an extreme danger to personnel and the manner of death is aesthetically
objectionable.
Decompression (excluding lowatmospheric-pressure stunning when
it can be demonstrated that it achieves
euthanasia)
Decompression is unacceptable for euthanasia because of numerous disadvantages. (1)
Many chambers are designed to produce decompression at a rate 15–60 times as fast as the
recommended optimum for animals, resulting in pain and distress attributable to expanding
gases trapped in body cavities. (2) Immature animals are tolerant of hypoxia, and longer periods
of decompression are required before respiration ceases. (3) Accidental recompression, with
recovery of injured animals, can occur. (4) Bleeding, vomiting, convulsions, urination, and
defecation, which are aesthetically unpleasant, may develop in unconscious animals.
Diethyl ether
Diethyl ether is irritating, flammable, and explosive. Explosions have occurred when animals,
euthanatized with ether, were placed in a non-explosion-proof refrigerator or freezer and when
bagged animals were placed in an incinerator.
Drowning
Drowning is not a means of euthanasia and is inhumane.
Exsanguination
Because of the anxiety associated with extreme hypovolemia, exsanguination as a sole method
of killing should be used only on unconscious animals.
Formaldehyde
Direct immersion of an animal into formalin, as a means of euthanasia, is inhumane with the
exception of Porifera.
Household products and solvents
Acetone, cleaning agents, quaternary compounds (including CCl4), laxatives, pesticides,
dimethylketone, quaternary ammonium products, antacids, and other toxicants not specifically
designed for therapeutic or euthanasia use are not acceptable.
Hypothermia
Hypothermia is not an appropriate method of euthanasia.
Magnesium sulfate, potassium chloride,
and neuromuscular blocking agents
Unacceptable for use as euthanasia agents in conscious vertebrate animals.
Manually applied blunt force trauma to
the head
Generally unacceptable for most species excluding piglets and small laboratory animals.
Replace, as much as possible, manually applied blunt force trauma to the head with alternate
methods.
Nonpenetrating captive bolt
Unacceptable excluding purpose-built pneumatic nonpenetrating captive bolt guns used on
suckling pigs, neonatal ruminants, and turkeys.
Neuromuscular blocking agents
(nicotine, magnesium sulfate, potassium
chloride, and all curariform agents)
When used alone, these drugs all cause respiratory arrest before loss of consciousness, so the
animal may perceive pain and distress after it is immobilized.
Rapid freezing
Rapid freezing as a sole means of euthanasia is not considered to be humane with the
exception of reptiles and amphibians and < 5-day-old altricial rodents. In all other cases
animals should be rendered dead or unconscious prior to freezing. (Rapid chilling of finfish is
not considered to be rapid freezing.)
Smothering
Smothering of chicks or poults in bags or containers is not acceptable.
Strychnine
Strychnine causes violent convulsions and painful muscle contractions.
Thoracic compression
Not acceptable for use on a conscious animal.
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AVMA Guidelines for the Euthanasia of Animals: 2013 Edition