Group housing of pigs is now mandatory in the EU for most of the production cycle, but how groups are managed significantly affects social stability, injury rates, and individual pig welfare.
Group housing is a necessary but not sufficient condition for good pig social welfare. Simply removing individual crates does not deliver welfare improvement if group mixing is frequent, space allowance is inadequate, and environmental enrichment is absent. The welfare benefit of group housing depends on creating stable social groups that can establish and maintain hierarchies without chronic high-level aggression. Mixing is the most dangerous welfare event in pig social management - new group formations can result in severe injury within the first 24-48 hours. Systems that maintain stable groups from weaning or early growing stage through to slaughter consistently show lower injury rates and better welfare indicators than systems with frequent mixing at different production stages.