In the last issue of the MSU Pork Quarterly, Jerry May wrote an excellent article about using carbon dioxide to euthanise pigs. He pointed out that many farms are currently seeking to improve their euthanasia standard operating procedures to ensure that animals experience minimal stress and are rendered unconscious very rapidly (less than one minute).

Since the article went to print, members of the Pork Area-of-Expertise Team, faculty at the MSU College of Veterinary Medicine, and Michigan pork producers have continued to discuss euthanasia practices. So here are a few additional thoughts shared recently.

Employee Considerations

It is important to consider the employees who perform euthanasia and 'set the tone' for the procedure. It should be performed in a respectful, calm manner. Personnel training should include an explanation of how carbon dioxide affects the animal and causes death. Carbon dioxide is a gas which, when inhaled at the concentration being delivered into a closed chamber, causes an animal to lose consciousness. Once unconscious, all sensations are lost. An animal cannot see, hear or feel and essentially, is asleep. This first step usually occurs in less than one minute. During this time, the operator may hear animal movement for a very brief period. The chamber lid should not be removed since this will cause the concentration of carbon dioxide to drop and may prolong the time to unconsciousness. Within 5 to 10 minutes, the heart and lungs can no longer function, and the animal dies. Animals are then removed from the chamber by 'pouring' them out. It is unsafe for the operator to reach into the chamber because he/she may inhale the carbon dioxide. Once the animal is 'poured' out of the chamber, check to determine that the animal is truly dead and not just unconscious. Lightly tap on its eye. If there is no eyelid blink, the animal is dead.

Recognize that performing euthanasia can be distressing for the operator, especially if many animals are euthanised over a short period of time. This can be especially true if there is only one person who is always assigned to this task, or if the person who is responsible for euthanasia is also the caretaker in the farrowing house or nursery area. Animal caretakers who always are assigned the responsibility of euthanasia may experience a sense of failure and may need to be reassured about their skills and expertise.

Equipment Considerations

Chambers can be made from different containers. A picture of a mobile unit is shown below. Do not try to make them bigger for bigger pigs. The carbon dioxide chamber is the suggested euthanasia method for nursery pigs less than 10 weeks of age and 70 pounds. It is less practical for older and heavier pigs. Do not forget to properly vent the chamber. The 'inlet' for the carbon dioxide hose may be placed near the bottom of the container, since carbon dioxide is heavier than air. As Jerry May mentioned, be sure to have an 'outlet' at the top to allow air to escape and to avoid pressure causing the lid to blow off.

As stated in the previous article, use a control valve and the guidelines of its manufacturer to correctly provide the amount of carbon dioxide flowing into the chamber. Generally, one pound of carbon dioxide in the cylinder equals 8.7 cubic feet of gas in the chamber. It is best to provide enough carbon dioxide to completely displace 100 per cent of the chamber space (cubic feet).

Do not use dry ice as a source of carbon dioxide. In a few of the older publications, dry ice is sometimes mentioned as an economical alternative for very small animals. However, it is not an acceptable source of carbon dioxide for on-farm euthanasia of young swine, as high concentrations of the gas cannot be generated in a short period of time. Euthanasia is best done quickly.

April 2009

Further Reading

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