The housing management of weaned piglets during the post-weaning period profoundly affects their welfare, with social mixing and regrouping causing significant aggression and stress.
Post-weaning regrouping aggression is a predictable welfare harm caused by management practice rather than pig behaviour. Pigs have evolved strong dominance hierarchies within stable groups. Forced mixing with strangers triggers intensive aggressive competition that causes injuries, stress, and immune suppression in a period already compromised by weaning stress. Systems that maintain litter group integrity post-weaning prevent this predictable suffering. The economic convenience of mixing litters for uniform batch management creates direct welfare costs that are rarely quantified against the production benefits.