Pen design in commercial pig production significantly influences rates of aggression, lameness, and injury, with major welfare implications for millions of animals.
Pig welfare in intensive systems is substantially shaped by pen design. Animals kept in barren environments with insufficient space and no enrichment display high levels of redirected behaviour, biting, and chronic stress. Evidence-based design improvements include providing deep-litter or semi-solid flooring, enrichment objects (chains, wood, substrate), adequate space allowances, and stable social groups to reduce mixing-related aggression. Whole-system changes are more effective than single-measure interventions. The long-term goal should be housing systems that allow pigs to express natural behaviours.