Effects of flow rate, gas type and disease status on the welfare of sucking and weaned pigs during gas euthanasia

Gas euthanasia of swine on farms is increasingly common. However, there is controversy regarding pig welfare during gas euthanasia and research must be conducted to establish best practices ensuring minimal pain and distress. The objectives of these studies were to determine pig welfare and efficacy of processes with various gas euthanasia procedures: gas type (carbon dioxide, argon, carbon dioxide:argon mixture), flow rate (20%, 35%, 50%, prefill), age (neonate, weaned) and disease status of the pig (respiratory disease/depression vs. other reasons). Euthanasia with inhalant gases can produce confounding effects on physiologic responses, therefore behavior was chosen as the primary outcome of interest for welfare assessment. The results of these studies indicate a carbon dioxide:argon gas mixture and slower flow rates (20%) should be avoided when euthanizing weaned or neonate pigs. Neonate pigs succumb to the effects of gas euthanasia quicker than weaned pigs and display fewer signs of distress, however differences are not great enough to warrant procedures adapted for specific age groups. When comparing induction of anesthesia between 100% carbon dioxide and 100% argon, with implications for piglet processing, carbon dioxide was associated with superior pig welfare (lower distress calls, escape attempts, ataxia, righting response). However, infrastructure currently in place for on-farm gas euthanasia was not reliable for inducing depth and duration of anesthesia necessary for piglet processing. Depression score in suckling pigs and respiratory disease in nursery pigs did not affect responses associated with efficacy or welfare when carbon dioxide was used. Conversely, with argon suckling pigs with high depression scores displayed longer latencies for loss of posture than pigs euthanized for other reasons and nursery pigs with respiratory disease lost posture faster than pigs euthanized for other reasons. Regardless of disease status, when assessed from behavioral indicators of distress carbon dioxide, relative to argon, was associated with superior pig welfare. Regardless of application method, including all methods tested with carbon dioxide, distress is still observed therefore, ingenuity and research are still needed to identify practical on-farm euthanasia methods that will further reduce pig distress.