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Innovative Scientific Techniques to Evaluate Alternatives to the Use of Carbon Dioxide Euthanasia Procedures

13 March 2013

A two-step procedure in which pigs are anesthetised with a mixture of nitrous oxide and oxygen before being euthanised with carbon dioxide may prove to be more humane that carbon dioxide alone, according to Don Lay of the USDA Agricultural Research Service.

The identification and validation of a humane method to euthanize piglets is critical to address the public’s concern that current methods are not acceptable. Blunt force trauma procedure is humane when carried out correctly but most people find it aesthetically repugnant.

The use of carbon dioxide is often recommended, at the same time it is criticized as being aversive to swine. This research sought to: 1) identify a method of scientifically determining if pigs find a specific euthanasia method aversive, and 2) develop an innovative method of gas euthanasia using nitrous oxide. Three projects were conducted to determine the aversiveness and the effectiveness of different mixtures of gas to euthanize piglets. The gases tested included carbon dioxide, argon, nitrogen, and nitrous oxide.

Experiments 1 and 2 allowed pigs to walk freely between one chamber filled with air and another chamber either gradually filled with gas or pre-charged with gas.

These experiments showed that all the gas mixtures adversely affected the pigs but that those with high carbon dioxide content were worse. Pigs exposed to the pre-charge gas rapidly entered a state of panic, in contrast to gas mixtures containing only 30 per cent carbon dioxide for which pigs were slower to panic.

In Experiment 3, pigs were euthanised with four different gas mixtures. This experiment found that pure carbon dioxide or carbon dioxide mixed with nitrous oxide killed pigs more quickly and thus could be more humane than the other treatments. However, euthanasia using nitrous oxide and oxygen was the only treatment that anesthetised the pigs. These pigs did not appear to feel pain.

Thus, a two-step procedure in which pigs are anesthetised with a mixture of nitrous oxide and oxygen before being euthanised by immersion in carbon dioxide may prove to be more humane that carbon dioxide alone. Data on brain activity, such as the use of electroencephalogram (EEG), would help to confirm this finding.

March 2013

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