Dust bathing is a highly motivated behaviour in laying hens that maintains feather condition and psychological wellbeing, yet most commercial hens are denied access to suitable substrate throughout their lives.
Dust bathing deprivation is a chronic welfare problem for billions of caged laying hens. The behaviour serves maintenance functions including removal of ectoparasites, oil redistribution through the plumage, and thermal regulation, but its expression appears intrinsically motivated beyond these functional benefits. Hens deprived of substrate show clear signs of behavioural frustration: vacuum dust bathing on wire floors, which is functionally ineffective, persists because the motivation cannot be suppressed even when the substrate is absent. The ability to fully express dust bathing, with the full sequence of wing-spreading, head-shaking, and resting in substrate, contributes to positive affect in hens assessed through cognitive bias tests. Cage-free and aviary systems that provide appropriate substrate enable this behaviour and represent a meaningful welfare improvement for one of the most numerically significant groups of farmed animals.