Behavioral response of weaned pigs during gas euthanasia with CO2, CO2 with butorphanol, or nitrous oxide

Authors: ÇAVUSOGLU, ENVER - Uludag University; RAULT, JEAN-LOUP - University Of Veterinary Medicine; GATES, RICHARD - Egg Industry Center; Lay Jr, Donald

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2020
Publication Date: 5/1/2020
Citation: Çavusoglu, E., Rault, J., Gates, R., Lay Jr, D.C. 2020. Behavioral response of weaned pigs during gas euthanasia with CO2, CO2 with butorphanol, or nitrous oxide. Animals. https://doi.org/10.3390/ani10050787.
DOI: https://doi.org/10.3390/ani10050787

Interpretive Summary: The pig industry is forced to euthanize a significant number of pigs due to injuries, hernias or unthriftiness. The majority of pigs are euthanized using carbon dioxide gas asphyxiation. However, concerns as to the humaneness of carbon dioxide are prevalent. An alternative is the use of nitrous oxide gas. We conducted this study to compare euthanasia of young pigs using nitrous oxide or carbon dioxide. In addition, we administered a pain relief drug as a third treatment prior to carbon dioxide exposure to determine if we could eliminate behaviors indicative of pain. Pigs experienced the inability to control muscle movement and loss of posture at the same time, regardless of treatment. However, pigs exposed to carbon dioxide made more escape attempts, but fewer squeals. Conversely, pigs euthanized with nitrous oxide made fewer escape attempts, but more squeals. Pigs in both treatments showed heavy breathing and open mouth breathing prior to losing posture. Administration of pain relief prior to exposure to carbon dioxide did not alter behaviors indicative of pain. The findings are inconclusive as to whether using nitrous oxide is significantly better than using carbon dioxide; but the results show that its use is just as effective, and possibly more humane.

Technical Abstract: The swine industry is forced to euthanize pigs in the first few weeks of life due to injuries, hernias or unthriftiness. The majority of pigs are euthanized using CO2 gas asphyxiation. However, concerns as to the humaneness of CO2 are prevalent. This study compared euthanasia of neonatal pigs using N2O (n = 9) or CO2 (n = 9). In addition, we administered an analgesic prior to CO2 (CO2B) as a third treatment (n = 9) to elucidate behaviors indicative of pain. The CO2 and N2O pigs lost posture at similar times (latency of 145.0 ± 17.3 and 162.6 ± 7.0 s respectively, P > 0.10), while the CO2B pigs lost posture the soonest (101.2 ± 4.7 s, P < 0.01). The CO2B pigs had more escape attempts than the CO2 or N2O pigs (16.4 ± 4.2, 4.7 ± 1.6, 0.3 ± 0.2 respectively; P < 0.0004). However, the N2O pigs performed more squeals than either the CO2 or CO2B pigs (9.0 ± 1.6, 2.8 ± 1.2, 1.3 ± 0.6 respectively, P < 0.001).Given similar time to loss of posture, the shorter time displaying open mouth breathing indicates that N2O is less stressful; however, the greater number of squeals for these pigs suggests the opposite. It was not apparent that any behavior measured was indicative of pain. In conclusion, N2O in higher flow rate can be an alternative of CO2 for pig euthanasia.