The weaning transition is the most stressful period in a commercial pig's life, involving simultaneous removal from the sow, mixing with unfamiliar pigs, and a dietary change — all at once.
Weaning in commercial pigs represents a welfare crisis concentrated into a few days. The piglet simultaneously loses its mother and the comfort of suckling, encounters unfamiliar pigs leading to aggressive fighting, faces dietary change from milk to solid feed, and moves to a new environment. Each of these stressors individually would be significant; combined they produce a welfare impact visible as post-weaning wasting syndrome, diarrhoea, and increased mortality. Later weaning at 28+ days compared to 21 days significantly reduces welfare impact by allowing greater piglet development and immune maturity. Providing familiar sow-pen litter groups at weaning and high-quality creep feeding that accustoms piglets to solid food before weaning both mitigate the transition stress.