Research at Texas Tech University studied the potential use of carbon dioxide (CO2) as a practical method of on-farm euthanasia for young pigs in farrowing as an alternative to blunt force trauma. The pigs’ small size can make the use of captive bolts dangerous and impractical.

For CO2 to become a practical on-farm alternative to blunt force trauma, best management practices must be developed for commercial swine farms, taking into consideration animal welfare and worker safety.

An objective of this study was to compare pre-fill with gradual-fill methods of CO2 euthanasia. The pre-fill method involves filling the euthanasia chamber with 100% CO2 before placing the pig in the chamber. The gradual-fill method involves placing the pig in the euthanasia chamber and then administering the gas.

The euthanasia chamber measured 30.2 x 16.8 x 19.7 in. For the gradual-fill method, 100% CO2 was gradually released at a flow rate of 20% per minute while the pig was in the chamber. For the pre-fill method, the chamber was filled with 100% CO2 prior to placing the pig in the chamber.

To assess the well-being of piglets during CO2 euthanasia, physiological and behavioral measures of stress were recorded. Blood samples were collected prior to euthanasia and just after death to measure cortisol concentrations, a common indicator of stress in animals. Heart rate and brain activity were used to assess time of death. Pig behavior and vocalizations were recorded using a camcorder. Behavior and postures recorded included breathing intensity (heavy, gasping), escape attempts, loss of consciousness and paddling.

Responses differed between methods of gas administration, influencing the time to onset of all behaviors measured.

The time to onset of heavy breathing, gasping, loss of balance, performance of escape behaviors, loss of posture, paddling and the last gasp were quicker in pigs euthanized using the pre-fill method compared with the gradual-fill method.

Most importantly, the time to death was shorter in pigs euthanized using the pre-fill method based on measured brain activity and heart rate.

Based on these results, the pre-fill method of euthanasia appears to be more humane than the gradual-fill method, and best management practices should be written accordingly

Researcher: Mhairi Sutherland, Texas Tech University (where the research was conducted) and Ruakura Research Centre, Hamilton, New Zealand (current address); and Pamela J. Bryer, Lamar University, Beaumont, TX. For more information, contact Sutherland by phone +64 7 838 5503, fax +64 7 856 2836 or e-mail