Pigs have a rich repertoire of natural behaviours including rooting, wallowing, socialising, and nest-building, and the degree to which commercial systems allow these behaviours is a core measure of pig welfare.
The inability to express motivated natural behaviours causes chronic frustration and psychological suffering in pigs. Rooting on a hard concrete floor — without substrate to manipulate — provides no outlet for the strong foraging drive, leading to redirected behaviour including pen-mate biting. The frustrated nest-building drive in sows without material causes visible distress — pigs repeatedly attempt to nest-build on bare concrete, scratching and rooting against the floor without satisfaction. Assessing pig welfare requires evaluating the opportunity to express natural behaviour, not just the absence of obvious injury. Higher welfare systems that provide appropriate materials and space allow pigs to express a fuller behavioural repertoire and show measurably better welfare across physiological and behavioural indicators.