Housing pigs in groups rather than individually is aligned with their social nature but introduces management challenges related to aggression, resource competition, and disease transmission. Understanding the welfare science behind group housing enables systems that provide genuine social benefits while managing associated risks.
Pigs are highly social animals that in natural conditions live in small, stable family groups. They form complex social hierarchies, cooperate in foraging, engage in social play, and show distress when isolated. Individual housing (as historically used for sows in stall systems) denies pigs the opportunity for social interaction, normal investigative behaviour, and expression of their natural behavioural repertoire—causing significant welfare compromise through frustration, boredom, and social deprivation.
Recognition of the welfare harms of individual housing led to the EU ban on sow stalls (gestation stalls) for most of pregnancy, implemented in 2013 (with some exemptions). Sows must now be housed in groups for the period from 4 weeks after service until 1 week before farrowing. This represents a major welfare improvement, though individual sow stalls remain permitted for short periods and in some other jurisdictions globally.
The transition to group housing requires careful management of aggression. Mixing unfamiliar sows causes fighting as hierarchy is established. Aggressive encounters cause injuries (vulvar bites, skin lacerations, lameness). Management strategies to reduce mixing aggression include: mixing at weaning (when reproductive cycling resets hierarchy), gradual mixing in large groups (where hierarchy cannot be fully established), providing escape routes and visual barriers, temporary separation of very aggressive or vulnerable individuals, and ensuring adequate feed access for all pigs without competition.
Feeding systems profoundly affect welfare in group sow housing. Electronic sow feeding (ESF) systems provide individualised rations to sows identified by electronic transponders, reducing competition but requiring sow training and equipment reliability. Floor feeding relies on simultaneous feeding of all sows to reduce competition but risks lower-ranking animals receiving insufficient ration. Trough feeding with adequate space allowance is widely used. Feed access and body condition monitoring are critical welfare indicators in group sow systems.
Growing and finishing pigs are almost universally group housed, but stocking density, space allowance, and enrichment provision profoundly affect welfare. Higher space allowances reduce aggression, improve lying behaviour, and enable more natural social interactions. Mixing pigs from different litters at weaning causes fighting—all-in/all-out management with stable groups reduces aggression and disease. Tail biting—a major welfare problem in intensive pig production—is associated with high stocking density, inadequate enrichment, suboptimal nutrition, and poor air quality.
Key welfare indicators for group-housed pigs include: skin lesion scoring (reflecting fighting and biting), tail lesion prevalence, body condition score, behavioural time budgets (lying, standing, exploring, social behaviour), and mortality rates. Enrichment provision and quality of the social environment are important outcome determinants. Welfare assessment tools like PigSafe and PIGLOW enable systematic on-farm welfare monitoring in group housing systems.