Pigs lack functional sweat glands and rely on wallowing in mud or water to regulate body temperature and skin condition. Providing wallowing opportunities is an important welfare provision in outdoor and enriched indoor systems.
Wallowing is a highly motivated natural behaviour in pigs that serves critical thermoregulatory function. Denying pigs access to wallowing in warm weather causes genuine heat stress welfare harm: pigs that cannot cool themselves through wallowing show elevated cortisol, increased panting, prostration, reduced activity, and in severe cases, heat-related mortality. Outdoor pigs with access to natural mud wallows or constructed water pools show markedly better welfare indicators during warm weather compared to those without. Indoor pigs benefit significantly from cooling systems including misting and drippers that partially substitute for wallowing. The growing recognition of wallowing as a welfare-positive behaviour rather than simply a dirty habit has influenced welfare standards, with organic and higher-welfare indoor systems increasingly incorporating wet substrate or cooling water provision.