Bar-biting in gestating sows is a well-documented stereotypic behaviour indicating chronic frustration and poor welfare in confinement systems, and its prevalence tracks housing quality.
Bar-biting in sows is one of the clearest behavioural indicators of chronic welfare deficit in intensive pig production. Stereotypies develop when animals are prevented from performing highly motivated behaviours — in sows, rooting, nesting, and social interaction. Once established, stereotypies are largely irreversible even if housing improves, which means the welfare cost of early confinement persists throughout the animal's life. The transition to group housing for gestating sows has been the main welfare improvement achieved in this area, though group systems introduce aggression management challenges. Further progress requires reducing gestation stall use globally, improving group housing design, and providing enrichment that allows natural behaviour expression.