Pigs establish stable dominance hierarchies that reduce long-term aggression, but the process of hierarchy establishment causes significant acute welfare harm.
Pig social hierarchies are welfare-relevant in two distinct phases. The acute phase — hierarchy establishment through fighting — causes injuries, stress, and occasionally severe welfare harm. The chronic phase — maintaining a stable hierarchy — actually reduces ongoing aggression relative to unstable or frequently disrupted groups. Management strategies that minimise regrouping maintain more stable hierarchies and reduce cumulative welfare harm from repeated establishment fights. Subordinate pigs that cannot access adequate food in competitive systems experience nutritional deficiency that compounds other welfare deficits. Electronic feeding systems, adequate feeder space, and stable group management address both the fighting and the access dimensions of hierarchy-related welfare harm.