Social Support in a Novel Situation Aimed for Stunning and Euthanasia of Pigs May Be Increased by Familiar Pigs—A Behavioural Study with Weaners

SIMPLE SUMMARY: None of the approved methods for stunning pigs prior to slaughter is ideal from an animal welfare viewpoint. A method involving use of high-expansion foam to encapsulate nitrogen gas has recently been proposed as an alternative humane stunning method. The method is effective, but the foam itself induces some distress to individually exposed pigs. This study evaluated the effects of companionship from a familiar or unfamiliar conspecific during air-filled foam exposure on pigs’ behavioural response. Companionship was found to be related to lower activity levels and fewer escape attempts. When comparing companionship with familiar and unfamiliar conspecifics, it was found that pig pairs with familiar individuals spent more time in physical contact during foam exposure, possibly seeking social support. The results highlight the importance of contact with conspecifics when studying animal welfare and demonstrates the potential benefits of maintaining stable familiar pig groups up to the point of stunning at slaughter. ABSTRACT: The common method of stunning pigs using high concentration carbon dioxide prior to slaughter poses an animal welfare issue, as the gas is aversive. Proof of concept for using nitrogen gas encapsulated in high-expansion foam as an alternative non-aversive method for stunning pigs has recently been presented. However, the individually tested pigs showed distress-related responses to foam exposure, regardless of whether it was nitrogen- or air-filled. This study examined the effect of companionship from a familiar or unfamiliar pig on behaviours in 72 nine-weeks old pigs during exposure to air-filled foam. Escape attempts were observed by 75% of solitary pigs, 42% of pigs with unfamiliar conspecifics, and 33% of pigs with familiar conspecifics. Familiar pig pairs clearly preferred social contact during foam exposure, whereas this was not as clear in unfamiliar pig pairs, and their motivation for social contact could have multiple explanations. The results from this study highlight the importance of contact with conspecifics when studying animal welfare and suggest that familiarity between pigs is important for social support, thus emphasizing the importance of maintaining social groups to reduce distress in pigs at slaughter.