The weaning transition — removing piglets from their sow at 21-28 days in commercial systems — is one of the most stressful events in a pig's life. The sudden social, nutritional, and environmental change causes a welfare impact measurable in behaviour, physiology, and growth for weeks afterwards.
Weaners separated from their mothers experience multiple simultaneous stressors: loss of maternal social bond, introduction to unfamiliar conspecifics, change from milk to solid feed, and new housing environment. The cumulative stress response suppresses immune function, predisposes to disease, and causes poor feed intake and growth check lasting 5-7 days post-weaning. Post-weaning diarrhoea in immunocompromised weaners causes abdominal pain, dehydration, and in severe cases death. Welfare improvements include later weaning where operationally possible, mixing pigs from the same litter group, providing milk-flavoured transition feeds, and reducing environmental novelty in weaner housing.