Pigs establish complex social hierarchies when grouped. Minimizing unnecessary regrouping and managing group composition reduces aggression and improves welfare for millions of pigs.
Pig social welfare depends heavily on group stability. The repeated mixing of unfamiliar pigs for management convenience causes predictable waves of aggressive interactions as new hierarchies are established. Each mixing event represents acute welfare harm. Producers who minimize unnecessary regrouping through stable group management from weaning through finishing see dramatically reduced aggression and injury. Where mixing is unavoidable, introducing pigs to new spaces simultaneously (so no resident-intruder dynamic exists), providing complex environments with visual barriers, and ensuring adequate space reduces injury severity. Larger group sizes in some systems provide more individuals for subordinate animals to avoid, reducing chronic stress compared to small, inescapable groups with rigid hierarchies.