A Two-Step Process of Nitrous Oxide before Carbon Dioxide for Humanely Euthanizing Piglets: On-Farm Trials

SIMPLE SUMMARY: The current approved method of using carbon dioxide (CO(2)) to euthanize newborn piglets is raising animal welfare concerns on whether the method is truly humane. A new form of euthanasia that is humane, practical, and socially acceptable is needed. Nitrous oxide (N(2)O), also known as laughing gas, has been shown to induce narcosis in piglets. We used a novel two-step system of exposing compromised piglets for six minutes to N(2)O followed by carbon dioxide and compared it to using CO(2) alone. After exposure to nitrous oxide, all piglets lost posture, a sign of the onset of loss of consciousness, before being exposed to CO(2) when they showed behavioral distress. On-farm use of a two-step method reduced the amount of time the piglets were exposed to CO(2) but did not reduce the amount of distressful behaviors. Therefore, the results do not support the hypothesis that using N(2)O in a two-step system is more humane than CO(2) alone. ABSTRACT: Current methods of euthanizing piglets are raising animal welfare concerns. Our experiment used a novel two-step euthanasia method, using nitrous oxide (N(2)O) for six minutes and then carbon dioxide (CO(2)) on compromised 0- to 7-day-old piglets. A commercial euthanasia chamber was modified to deliver two euthanasia treatments: the two-step method using N(2)O then CO(2) (N(2)O treatment) or only CO(2) (CO(2) treatment). In Experiment 1, 18 piglets were individually euthanized. In Experiment 2, 18 groups of four to six piglets were euthanized. In the N(2)O treatment, piglets lost posture, indicating the onset of losing consciousness, before going into CO(2) where they showed heavy breathing and open-mouth breathing; whereas piglets in the CO(2) treatment did not lose posture until after exhibiting these behaviors (p ≤ 0.004). However, piglets in the N(2)O treatment took longer to lose posture compared to the CO(2) treatment (p < 0.001). Piglets in the N(2)O treatment displayed more behavioral signs of stress and aversion: squeals/minute (p = 0.004), escape attempts per pig (p = 0.021), and righting responses per pig (p = 0.084) in a group setting. In these regards, it cannot be concluded that euthanizing piglets for 6 min with N(2)O and then CO(2) is more humane than euthanizing with CO(2) alone.