The composition of stable pig social groups — including age, sex, and size distribution — significantly affects welfare outcomes, with evidence-based grouping strategies reducing aggression and improving welfare.
Stable social group composition is a foundational welfare management decision with effects that cascade through the entire production cycle. The best welfare outcomes occur when pigs remain with familiar individuals from weaning through to slaughter, maintaining the social bonds formed in early life rather than experiencing repeated regrouping aggression. Within stable groups, composition choices — age uniformity, litter origin, group size within the facility pen design — further affect the quality of social relationships and the frequency of agonistic interactions. Small to moderate group sizes within individual recognition range, homogeneous in age and size, and maintained without disruption from weaning forward, represent the evidence-based ideal for stable group welfare. Implementation requires facility design and production system planning that accommodates these principles.