Euthanizing single or pairs of sick, injured or weak piglets with nitrogen foam : effects on animal welfare

Abstract: In pig production, it is inevitable having to euthanize some piglets due to sickness, injuries or weakness. The methods available for euthanizing piglets that are 0-42 days are blunt force trauma and captive bolt followed by sticking. These are physical methods that could induce psychological stress in the farmer and prolong the piglets’ suffering if the farmer is reluctant to use the available method. The aim of this thesis was to evaluate the effectiveness of nitrogen foam for euthanizing single and pairs of piglets that are sick, injured or weak. In addition, welfare aspects were assessed to evaluate if nitrogen foam could be a more humane euthanasia method compared to traditional methods. A total of 21 crossbreed piglets of Yorkshire'Dutch Yorkshire dams and Hampshire sires were used in this study. Age ranged from 4–38 days with a weight ranging from 1–12 kg. The piglets were either euthanized individually (treatment 1) or with a companion piglet (treatment 2). The initial response, when exposed to the foam, was for piglets to flinch and/or retreat, followed by exploration of the foam. The exploration of foam at the beginning of foam production indicated that the piglets were not fearful of the foam itself and that the nitrogen gas did not cause discomfort. The explorative behaviour decreased as foam levels began to increase and instead the piglets started to avoid the foam by raising their snout above foam level. When the piglets began to be covered with foam, escape attempts increased. There was a significant difference in vocalisation between treatments, where single piglets vocalized more than pairs, but no differences were seen in activity or escape attempts. All piglets were successfully euthanized and no reflexes or regaining of consciousness was seen at observations after 12 minutes of being submerged in foam. Approximately half of the piglets had no heartbeats when taken out of the box and presumed to be already dead. The results prove nitrogen foam to effectively euthanize pairs of piglets and induce moderate levels of aversive behaviours. Nitrogen foam euthanasia could be an important alternative for on-farm euthanasia, especially for small piglets over 14 days. However, research on how the aversiveness towards the foam can be reduced is needed before the method can be recommended for on-farm use.