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Gas Alternatives to Carbon Dioxide for Euthanasia: A Piglet Perspective

22 May 2013

A two-step procedure in which pigs are anaesthetised with a mixture of nitrous oxide and oxygen before being euthanised by immersion in carbon dioxide appeared to be more humane than carbon dioxide alone, according to new research from West Lafayette, Indiana, US.

The search for alternative methods to euthanise piglets is critical to address public concern that current methods are not optimal, according to Don Lay of the USDA-ARS, Livestock Behavior Research Unit in West Lafayette, Indiana and co-authors there and at Purdue University.

Scientific evidence supports that blunt force trauma is humane when performed correctly but most people find it visually difficult to accept. The use of carbon dioxide is often recommended; at the same time, it is criticised as being aversive to pigs.

Their research, published in Journal of Animal Science, sought to:

  •  identify a method of scientifically determining if piglets find a gas aversive, using an approach-avoidance test, which relies on the perspective of the piglet, and
  •  test different gas mixtures to determine if they are effective and humane for neonatal piglet euthanasia.

Pigs were allowed to walk freely between one chamber filled with air and another chamber either gradually filled with gas mixtures (Experiment 1) or pre-filled with gas mixtures (Experiment 2). Experiment 1 tested carbon dioxide (90 per cent) and air (10 per cent), nitrous oxide (60 per cent) and carbon dioxide (30 per cent), argon (60 per cent) and carbon dioxide (30 per cent), and nitrogen (60 per cent) and carbon dioxide (30 per cent). Because piglets had to be removed when they started to flail, the test was shorter (P<0.01) for the pigs in the carbon dioxide treatment than those in the nitrous oxide/carbon dioxide, argon/carbon dioxide and nitrogen/carbon dioxide treatments, 3.1±0.2, 8.5±0.6, 9.6±0.4 and 9.9±0.1 minutes, respectively. Nonetheless, all gas mixtures adversely affected the pigs, causing the pigs to leave the test chamber.

In Experiment 2, piglets were allowed to enter a chamber pre-filled with nitrogen/carbon dioxide or nitrous oxide/carbon dioxide (both 60/30 per cent). Pigs exposed to the pre-fill chambers started to flail in fewer than 20 seconds - much faster than with the gradual fill method, which supports that this method was more aversive.

In Experiment 3, piglets were euthanised using a two-step procedure. Pigs were first placed in a gradual fill chamber with one of four gas mixtures: 90 per cent carbon dioxide, nitrogen/carbon dioxide, nitrous oxide/carbon dioxide or nitrous oxide/oxygen - the last three mixtures at 60/30 per cent - followed by placement into a 90 per cent carbon dioxide pre-fill chamber when the pigs started to flail or were anaesthetised.

All three gas treatments that contained carbon dioxide killed pigs more quickly than nitrous oxide/oxygen (P<0.05). However, nitrous oxide/oxygen was the only treatment that anaesthetised the pigs instead of causing squeals or flailing although requiring about 12 minutes longer.

Lay and co-authors concluded that although longer, a two-step procedure in which pigs are anaesthetised with a mixture of nitrous oxide and oxygen before being euthanised by immersion in carbon dioxide may prove to be more humane than carbon dioxide alone.

Reference

Rault J-L., K.A. McMunn, J.N. Marchant-Forde and D.C. Lay Jr. 2013. Gas alternatives to carbon dioxide for euthanasia: A piglet perspective. J. Anim. Sci. 91(4):1874-1883.doi: 10.2527/jas.2012-5761

Further Reading

You can view the full report (fee payable) by clicking here.

May 2013

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