How pigs are grouped and managed socially has major welfare implications. Mixing unfamiliar pigs causes aggression, injury, and prolonged stress — but appropriate social management supports positive welfare.
Pig social welfare is shaped primarily by two critical management decisions: how groups are composed and how they are managed when change is unavoidable. Stable groups of pigs that have grown up together develop predictable hierarchies with relatively low ongoing aggression. The welfare crisis occurs when groups are disrupted: weaning, regrouping, market mixing, and transport all bring unfamiliar pigs into contact, triggering fighting to re-establish hierarchy. Injury rates during mixing events can be very high without management intervention. Strategies including temporary darkness, distraction enrichment, and scent blending before mixing reduce initial aggression. Electronic sow feeders allow group-housed sows to be fed individually without competitive conflict, combining the welfare benefits of social housing with individual nutritional management.