Pigs are highly social, cognitively complex animals with strong preferences for conspecific interaction. The evidence for their social needs is robust and has major implications for farm system design.
The scientific evidence for pig social needs is among the strongest in farmed animal welfare research. Isolation causes measurable physiological stress, depressed immune function, and behavioural indicators of negative affective states. Stable social groups with sufficient space show dramatically lower aggression, more play behaviour, and better growth and health outcomes. The transition away from gestation crates to group sow housing is the most significant welfare improvement in the pig industry — mandated in the EU and voluntarily adopted by many major US pork buyers. However, group housing alone does not ensure welfare: mixing unfamiliar pigs at weaning, regrouping, and transfer causes fighting that must be managed with gradual introduction, olfactory familiarisation, and space. Enrichment — straw, rooting substrate, hanging objects — reduces redirected aggression and supports positive social play. Welfare assessments of pig farms should measure social behaviour quality, not just group housing status.