Weaning age profoundly affects both piglet and sow welfare. Commercial systems wean at 21–28 days — far earlier than the natural 12–17 week weaning age. Early weaning causes post-weaning stress syndrome: piglets show belly-nosing, aggression, reduced feed intake, and gut microbiome disruption. Sows experience abrupt milk cessation discomfort and accelerated reproductive cycling. EU regulations set minimum weaning age at 28 days, with derogations to 21 days. Research consistently shows weaning at 35+ days reduces post-weaning aggression, improves gut health, and lowers antibiotic use. Economic analysis indicates later weaning is cost-neutral when antibiotic savings are factored. Several premium welfare schemes now mandate 35-day minimum weaning as a certification criterion.