Pigs are highly social animals with complex group dynamics, and management of mixing, hierarchy formation, and group stability significantly affects welfare outcomes.
Group dynamics profoundly affect pig welfare throughout production. Regrouping events cause predictable bouts of aggressive interaction that injure pigs and cause acute stress. Management systems that minimize unnecessary regrouping, provide adequate space at mixing events, use partition pre-mixing, and maintain stable groups reduce this suffering substantially. The welfare of individual pigs in groups depends on both their position in the hierarchy and the stability of the social environment - chronic subordinate stress in unstable groups is a significant and underappreciated welfare concern.