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V. Euthanasia

The term euthanasia literally means "good death." When an animal's life must be ended, it can be done with a minimum of pain, and as rapidly with as little distress as possible. Pain and suffering are functions of the brain (see pain and distress section), as it is the brain that interprets the signals sent from the sensory endings of nerve fibers. So preventing that interpretation can minimize pain and suffering (Introduction @1).

If the cerebral cortex already is not functioning due to anesthesia or hypoxia, this can aid the choice of what to use for euthanasia, provided consciousness is not regained before the animal dies. If the animal is conscious, sedation or anesthesia prior to the euthanizing agent can prevent distress. Handlers should be aware, however, that some of these pretreatments can change the cardiovascular function in such a way as to delay the effect of euthanizing drugs (Introduction @1).

To administer euthanasia humanely requires handling an animal. This has to be done in a species-appropriate manner to minimize distress. People who carry out euthanasia must be properly trained, and the process must be done in consultation with a veterinarian experienced with the species (Introduction @ 1).

Some species will react to the handling necessary for euthanasia by defensive behaviors, vocalizations, release of odors, and cardiovascular and autonomic signs of fear or distress. Some species become immobile and can appear to have lost consciousness or life but in fact are fully aware (e.g., rabbits, chickens). Handlers need to recognize these species specific behaviors (Animal Behavioral Considerations @1).

Some species will release odors that can induce stress in other members of their species, so euthanasia should be carried out in isolation (Animal Behavioral Considerations @1).

People who carry out research on animals can become attached to their subjects. The same considerations for pet owners and veterinary or shelter staffers must be available for research staff to keep euthanasia procedures humane for both the animals and for their caretakers (Animal Behavioral Considerations @ 1).


Some agents for euthanasia are better for animals of certain sizes, species, and ages than others. For instance, young or newborn mammals are able to withstand low oxygen longer than older ones. Special consideration for fetal or newborn rodent euthanasia is available2. Reptiles, amphibians, and diving birds can handle longer periods of low or no oxygen.

Some inhalants smell bad, and animals may hold their breath, delaying death and possibly producing suffering. Some agents are a hazard for people, and some lead to reflexive events by the animals that may cause people watching the process to suffer, even if the animal is not suffering. Such considerations need to guide one's choice of the euthanasia agent (Modes of Action; Inhalant Agents @ 1).

A comprehensive guide and recommendations for the best euthanasia techniques with consideration for issues of setting and species is provided by the report by the American Veterinary Medical Association (AVMA) Guidelines on Euthanasia1.

A useful summary with a table is provided in an article by Michael Aprill3. As he writes, barbiturate injection by the intravenous route is, on balance, a humane, cost-effective, and safe method for most research animals and their handlers. As a controlled substance, its use does require documentation and reporting to the Drug Enforcement Agency.

Other methods that can be acceptable include carbon dioxide exposure. Controversy does exist over the use of carbon dioxide, however. Pros and cons for euthanasia agents for larger or less commonly used species are provided in the AVMA Guidelines. In all instances, the guidance of a veterinarian is imperative for humane euthanasia.

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Readings and Resources on Euthanasia

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