Refinement Alternatives

Humane Killing

Principles for humane killing

For method of killing an animal to be humane:

there should be very rapid (immediate) unconsciousness and subsequent death; and
there should be no pain or distress accompanying the procedure.

Choosing the most humane method of killing an animal for a research study requires consideration of the impact of the method on the research results. The following principles of euthanasia may assist investigators and animal care committees to determine the most humane method to use given the scientific goal of the study:

Whenever an animal’s life is to be taken it should be treated with the highest respect.
The method likely to cause the least pain and distress to the animals should be used whenever possible.
Euthanasia techniques should result in rapid loss of consciousness, followed by cardiac or respiratory arrest and ultimate loss of brain function.
Techniques should require minimum restraint of the animal.
Techniques should be appropriate for the species, age and health of the animal.
Death must be verified following euthanasia.
Personnel should be trained and competent.
Human psychological responses should be taken into account, but should not take precedence over animal welfare considerations.
Animal care committees should be responsible for approval of the method of euthanasia.

(This section has been adapted from the International Council for Laboratory Animal Science International harmonization of guidelines on euthanasia (ICLAS, Nantes, France, 2004), approved in Buenos Aries, Argentina, November 2004, available on Science Online.

Use of carbon dioxide

Some uncertainty exists regarding the humaneness of using carbon dioxide (C0₂) to kill research animals. At the Newcastle Consensus Meeting on Carbon Dioxide Euthanasia of Laboratory Animals (Hawkins et al., 2006), the following problems with use of C0₂ were identified:

There is no “ideal” way of killing animals with C0₂ - both pre-fill and rising concentrations can cause welfare problems.
If animals are placed into a chamber containing a high concentration of C0₂ (above 50%), they will experience at least 10-15 seconds of pain in the mucosa of the upper airways before loss of consciousness. This is a serious welfare problem.
If animals are placed into a chamber with a rising concentration of C0₂, they will find it aversive at a certain level and may experience “air hunger” or dyspnoea which is unpleasant (in humans, it is reported as highly distressing). This may also be a welfare problem..

In addition, the Newcastle Consensus Meeting identified good practices for C0₂ euthanasia:

It is more important to avoid or minimize pain or distress than it is to ensure a rapid loss of consciousness; thus a “gentle” death that takes longer is preferable to a more rapid, but more distressing death.
The optimum chamber filling rate is uncertain. For rats, use of 100% C0₂ at a flow rate of 20% of the chamber volume per minute has been shown to produce loss of consciousness without evidence of pain, but not without evidence of dyspnoea. Reduced flow rates can be increased once the animals have lost consciousness.
It is possible that the addition of oxygen (O₂) to CO₂ may reduce, but not overcome, welfare problems caused by pain or dyspnoea. It is also possible that high concentrations of O₂ would prolong consciousness, which may not be desirable. There is currently insufficient information in the literature to reach a clear conclusion on the appropriate level of O₂.

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For more information on humane killing the following resources may be useful:

Canadian Council on Animal Care (CCAC). (1993) Euthanasia In: CCAC Guide to the Care and Use of Experimental Animals, vol 1, 2nd ed. Section XII. p. 141-153.
- This document describes in detail the various methods used to kill research animals. However, it is currently under revision and will be replaced by the CCAC guidelines on: laboratory animal procedures-adopted guidelines on euthanasia.
Demers G., Griffin G., De Vroey G., Haywood J.R., Zurlo J., and Bédard M. (2006) Harmonization of animal care and use guidance.
Niel, L. (2007) Use of C0₂ as a euthanasia technique. Resource 29.

Online resources

Makowska J.I., Vickers L., Mancell J. & Weary D.M. (2009) Evaluating methods of gas euthanasia for laboratory mice. Applied Animal Behaviour Science 121: 230-235.
American Association of Swine Veterinarians & National Pork Board (2008) On-Farm Euthanasia of Swine: Recommendations for the Producer. Des Moines, USA.
AWIC (2007) Animal Euthanasia.
- This bibliography contains references related to humane euthanasia of animals. It is divided into 8 groups as follows: aquatic animals (mammals and fish); birds; dogs and cats; general; livestock; reptiles; rodents and rabbits; and wildlife, captive and free ranging. The sources of information, published between 1995 and October 2007, include peer-reviewed journals, conference proceedings, theses, annual reports, dissertations, books, monographs, letters, web pages, reviews, and patents

Conlee K., Stephens M.L., Rowan A.N., & King L.A. (2005) Carbon dioxide for euthanasia: concerns regarding pain and distress, with special reference to mice and rats. Laboratory Animals 39:137-161.
Denicourt M. (2008) On-farm euthanasia by electrocution: efficient and safe. Pig PROGRESS 24 (8):28-30.
Hawkins P., Playle L., Golledge H., Leach M., Banzett R., Coenen A., Cooper J., Danneman P., Flecknell P., Kirkden R., Niel L., & Raj M. (2006) Newcastle Consensus Meeting on Carbon Dioxide Euthanasia of Laboratory Animals