Pigs are highly social animals that form stable dominance hierarchies and suffer from social isolation and inappropriate grouping practices. Understanding pig social behaviour is essential for designing housing systems that support positive social welfare.
Repeated social mixing is one of the most significant welfare harms in commercial pig production. Each regrouping event — at weaning, at nursery transfer, at grower pen allocation — causes fighting, injury, and stress that can last days. Pigs show clear stress indicators including elevated cortisol, wounds, reduced feeding, and stereotypic behaviour following mixing. The welfare solution is minimising regrouping events and maintaining stable social groups. Pen design that allows subordinate animals to avoid dominant individuals reduces injury severity when mixing cannot be avoided. Eliminating single housing except for medical necessity and providing adequate space for social interaction are key welfare priorities in progressive pig production systems.