Pigs have complex social lives with established hierarchies, long-term bonds, and rich communication — knowledge that illuminates the welfare costs of management practices that disrupt social structures.
The social complexity of pigs means that management practices disregarding social structure impose significant welfare costs. Routine mixing of unfamiliar pigs — during transfers between production phases, at markets, and during transport — causes predictable intense aggression as new hierarchies are established through fighting. The welfare harm of mixing is measurable: skin lesions from bites, physiological stress responses, and elevated mortality in the days following mixing. Stable social groups allowed to maintain consistent membership show dramatically lower aggression and injury rates. Consolation behavior in pigs — approaching stressed conspecifics in ways that reduce their distress — indicates a degree of social sensitivity that challenges the treatment of pigs as indistinguishable production units rather than socially bonded individuals.