Euthanasia Guidelines, Ethics and Reality
American Association of Zoo Veterinarians Conference 1999
Leah L. Greer, DVM
Office of Laboratory Animal Care, University of California, Berkeley, CA, USA



Euthanasia is defined as “a good death” from literal Greek translation, one that occurs without pain and distress.4 This definition is a classic oxymoron in that death is defined as “the permanent ending of all life, total destruction.”14 This duality poses much discord to the cognizant species that must perform the act. To help veterinary professionals contend with this antipathetic act, guidelines have been developed in the interest of animal welfare, to ensure that “good deaths” are achieved. Following these guidelines is straightforward, as many common species are addressed. However, the decision to carry out, and means of, euthanasia are based on multifaceted criteria, such as the use of the animal, humane concern for the animal, and the human emotions of those directly and indirectly involved.


In 1992 the Executive Board of the American Veterinary Medical Association (AVMA) convened a panel on euthanasia which led to their fifth panel report, 1993 Report of the AVMA Panel on Euthanasia. In this report the panel updated information on ectothermic, aquatic, wildlife, and fur-bearing species, as well as those used in research.4 The panel is planning to reconvene in the fall of 1999 to update these guidelines. The importance of these guidelines is apparent, as they have been adopted and referenced by many scientific organizations and regulatory agencies.

A comparable report is available from the European Commission entitled Recommendations for Euthanasia of Experimental Animals. These guidelines are more extensive than the AVMA guidelines, including comprehensive lists of cited references, literature recommendations, and information on audiovisual materials.8,9

Reports written by the American Ornithologists’ Union, the American Society of Ichthyologists and Herpetologists, and the American Society of Mammalogists, provide various guidelines for field conditions.1-3 Euthanasia is discussed in these reports, however, for the most part they refer to the AVMA guidelines.

General Considerations

There are several important considerations prior to selecting a method of euthanasia. Primarily, those performing the euthanasia must be experienced in handling the animal as well as trained at the method of euthanasia selected. Proper handling is imperative to minimize pain and distress in the animal and to assure the safety of personnel. The amount of control and handling needed must be determined by the size, temperament, and illness or pain the animal may be experiencing.4

Concern for other animals in the vicinity is also important. Studies have shown that distress vocalizations as well as the release of odors or pheromones can cause anxiety and apprehension in other animals. Actions should be taken to euthanatize animals in an area separate from other live animals, especially of their own species.12

Concern for the emotions of personnel performing or observing the euthanasia must also be addressed. People’s attitudes toward euthanasia vary. Dissident employees can unfortunately spread rumors to volunteers, the ill-informed public, and the unrelenting media. Emotionally supportive discussion groups and trained counselors can be useful in dealing with this difficult issue.4,8,9

Electing Euthanasia

The Veterinarian’s Oath states, “I solemnly swear to use my skills for...the relief of animal suffering.” There are no laws against performing euthanasia on animals. In fact, it is encouraged as long as it is done with professional judgement in the interest of the animals’ welfare. The decision for when to perform a “good death” is irrefutable for several areas of animal husbandry. Production animals are slaughtered at the optimal time for profit, laboratory animals are humanely euthanatized at the end of an experiment, and client-owned animals are euthanatized upon the owners’ decision.

Exhibition animals in zoological facilities fall under the scrutiny of the media and the public, making the responsible decision more complex. The decision is obvious when the animal is diagnosed with an untreatable, terminal condition that is causing pain and suffering. However, what if the animal appears to be suffering but has a chance to recover? Or, what if the animal is diagnosed terminal but is not experiencing pain or suffering? This is where professional judgement and ethics may be open to challenge.

The most uncomfortable ethical question that faces zoological facilities is surplus animals. Regardless if it is an aged animal, or an excess of genetically related animals, the disposition of surplus animals is controversial. The American Zoo and Aquarium Association (AZA) code of ethics states in section I–K “...I pledge to make every effort to assure that exotic animals do not find their way into the hands of those not qualified to care for them properly.” The full extent of the dilemmas involved in placing surplus animals is covered elsewhere.5,10,11 Nevertheless, the media is quick to blame AZA institutions for contributing to undesirable fates such as the pet trade, roadside zoos, shooting preserves, and the fur trade, if the institutions cannot account for the animals from ‘cradle to grave.’11,13 This issue was addressed in 1978 by the AAZPA (now AZA) Surplus Committee, “The Committee believes that the need to euthanatize surplus zoo animals (as defined elsewhere) is not a controversial issue, provided that euthanasia is accomplished by recognized humane methods.” This statement was also supported by the director of wildlife protection for the Humane Society of the United States at that time. However, the prospect of individual euthanasia is still too difficult for many zoo directors to face.11 The 1993 Report of the AVMA Panel of Euthanasia avoids the issue by stating that “the ethical considerations that must be made when euthanizing healthy and unwanted animals raises both professional and societal does not believe that the report is the appropriate forum for an in-depth discussion of this topic.”

Selection of Euthanasia Method

Euthanasia agents cause death by three different mechanisms (1) hypoxia, by either direct (e.g., decapitation) or indirect means (e.g., paralytics); (2) direct depression of neurons vital for life function (e.g., chemical anesthetics); (3) physical disruption of brain activity and destruction of neurons vital for life (e.g., concussion, pithing).4 The acceptable agents available to achieve euthanasia are categorized as inhalant, chemical, or physical methods. These agents and the criteria for their use are widely published in detail.4,7-9,12 Methods of euthanasia that are considered unacceptable and conditionally acceptable are summarized in Table 1. For complete information on agents or methods please refer to the guidelines directly.

Table 1. Summary of unacceptable and conditionally acceptable methods of euthanasia3,7



Air embolism

Only in anesthetized animals. Causes convulsions, opisthotonos, vocalization.

Chloroform, ether

Unacceptable. Hazardous to personnel.


Unacceptable. Hazardous to personnel. Aesthetically objectionable.


Can be performed in small mammals <1 kg by trained personnel only. Recommended to be performed on anesthetized animals. Not recommended as sole agent for ectotherms as they can withstand hypoxia for long periods.


Unacceptable. Time to unconsciousness is not known.


Unacceptable, inhumane.

Electric stunning

Must be performed by trained personnel with specialized equipment. Must be exsanguinated immediately to ensure death.


Must be performed on unconscious animals by trained personnel with specialized equipment. Cardiac defibrillation occurs 10–30 sec before unconsciousness.


Only in anesthetized animals. Hypovolemia induces anxiety.


Penetrating captive bolt is preferred. A free bullet shot must be performed in field conditions by trained personnel. Position of weapon differs with each species.


Unacceptable, inhumane. Animals should not be dropped into boiling water.

Nicotine, Mg Sulfate, KCl, all neuromuscular blocking agents

Conditionally acceptable. When used alone they cause respiratory arrest before unconsciousness, so the animal may perceive pain. May be used after approved method of anesthesia.

Nitrous oxide

Alone does not induce anesthesia. Distressful hypoxemia develops before respiratory or cardiac arrest.

Rapid freezing

Only in anesthetized animals. Formation of ice crystal is considered painful in all species. Commonly used as an adjunctive means of euthanasia.


Unacceptable, inhumane. It is not known when unconsciousness will be reached.


Unacceptable. Causes violent convulsions, and painful muscle contractions.


Must be followed by an approved method of euthanasia. Creates only unconsciousness.


It is imperative that death be confirmed after euthanasia and before disposal of the animal. Death should be confirmed only by trained professionals. A cessation of vital signs such as cardiovascular arrest should be confirmed when possible. Cessation of respiration alone is not sufficient, since many species may be in a state of deep anesthesia, while other species and neonates can survive hypoxic conditions for extended periods of time. Professional judgement is necessary to determine if a secondary means of euthanasia (e.g., exsanguination, bilateral pneumothorax, freezing, and double pithing) is needed to confirm death.

Unusual Considerations

Larvae of fish, tadpoles, or newts may be killed effectively by placing them in a concentrated solution of MS-222 or benzocaine. Methods of euthanasia recommended for adult fish are also recommended for fry and fingerlings.8,9

Reptile eggs without an embryo may be frozen. Reptile eggs with an early life form should not be exposed to extreme temperatures because humane death is not guaranteed. These eggs should be injected with barbiturates, an anesthetic overdose, or an appropriate physical method used to destroy the brain. Bird eggs can be terminated by freezing (<4°C for 4 hr) however, if the neural tube has developed into a brain then death must be confirmed by decapitation or an overdose of anesthetic.8,9

Depending on the species of mammal, embryos that have developed a functional brain (30–50% of gestation) should be killed humanely.8,9 In many cases inhalation agents will not anesthetize a fetus.

If the fetus is to be removed from an anesthetized dam an increased amount must be administered for a longer period to ensure the anesthetic has crossed the placenta. The insensitized fetus may then be killed by decapitation or removal of the heart if small in size. If the fetus is from a larger species it should be killed by methods acceptable in adults.8,9 Neonates should be humanely killed by methods similar to their adult species. However, neonatal animals appear to be resistant to hypoxia, therefore, agents utilizing this method should not be used unless exposure is long enough to ensure death or a second method of death is used.4

Invertebrate species such as cephalopods, or mollusks can be humanely euthanatized by terminal anesthesia. The agent of choice is 7.5% magnesium chloride.6

As vertebrate animals vary widely in size and physiology, the method chosen to euthanatize an animal should be chosen from published material for the most similar species. General guidelines are to use an overdose of acceptable anesthesia, followed by professional confirmation of death or a second method of euthanasia to ensure a humane death and no chance for recovery.

Literature Cited

1.  American Ornithologists’ Union. 1988. Report of Committee on Use of Wild Birds in Research. Auk. 105(Suppl. 1):1A–41A.

2.  American Society of Ichthyologists and Herpetologists. The Herpetologists’ League, Society for the Study of Amphibians and Reptiles. 1987. Guidelines for Use of Live Amphibians and Reptiles in Field Research. J. Herpetol. 21(Suppl. 4):1–14.

3.  American Society of Mammalogists. 1987. Acceptable field methods in mammalogy: preliminary guidelines approved by the American Society of Mammalogists. J. Mammalogy. 68(Suppl. 4):1–18.

4.  Andrews EJ, BT Bennet, JD Clark. 1993. Report of the AVMA panel on euthanasia. J. Am. Vet. Med. Assoc. 202:230–247.

5.  Blakely RL. 1983. The alternatives and public relations-surplus animal management: problems and options. Proc. Am. Assoc. Zool. Parks Aquar. Pp. 292–293.

6.  Boyle PR. 1991. The UFAW Handbook on the Care and Management of Cephalopods in the Laboratory. Universities Federation for Animal Welfare. Potters Bar, Herts., England. Pp. 48–50.

7.  Canadian Council on Animal Care. 1984. Guide to the Care and Use of Experimental Animals. Ontario, Canada. Canadian Council on Animal Care. Vol. 2.

8.  Close B, K Banister, V Baumans, et al. 1996. Recommendations for euthanasia of experimental animals. Lab. Animals. 30:293–316.

9.  Close B, K Banister, V Baumans, et al. 1997. Recommendations for euthanasia of experimental animals. Lab. Animals. 31:1–32.

10.  Conway WG. 1976. The surplus problem. Proc. Am. Assoc. Zool. Parks Aquar. Pp. 20–24.

11.  Graham S. 1996. Issue of surplus animals. In: Wild mammals in Captivity Principles and Techniques. The University of Chicago Press, Chicago, Illinois, Pp. 290–296.

12.  National Research Council. 1992. Recognition and Alleviation of Pain and Distress in Laboratory Animals. National Academy Press, Washington D.C., Pp. 102–116.

13.  Goldston L. 1999. The Animal Business, many zoos give away or sell surplus mammals, which often end up exploited or even hunted despite safe guards. San Jose Mercury News. San Jose, California, February 7–10.

14.  Webster’s New World Dictionary. 2nd College Edition. 1986. Simon and Schuster, New York, New York. P. 363.


Speaker Information
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Leah L. Greer, DVM
Office of Laboratory Animal Care
University of California
Berkeley, CA, USA

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