Pigs are highly social animals that require appropriate group composition and sufficient space to maintain positive social relationships and avoid chronic aggression and stress.
Social housing in pigs is welfare-critical because isolation causes severe psychological distress, but poorly managed group housing causes chronic aggression and physical injury. The greatest welfare challenge is the routine mixing of unfamiliar pigs for management convenience - at weaning, during finisher phase transfers, and transport - which triggers intense fighting. Management strategies that minimise mixing, provide sufficient space for subordinate pigs to avoid dominant animals, and use olfactory familiarity techniques before mixing significantly reduce aggression-related welfare harm. Stable social groups maintained throughout production represent the gold standard for pig social welfare.