The pervasive welfare problem of keel bone fractures in commercial laying hens, their causes, welfare impacts, and evidence-based strategies for reduction.
Keel bone fractures in laying hens represent a welfare paradox of significant moral importance: the most welfare-progressive housing system (cage-free) produces dramatically higher rates of a painful welfare problem than the system it was designed to replace (conventional cage). This does not mean cage-free housing is worse overall for hen welfare — the behavioral freedoms it provides are genuine and significant — but it does mean that cage-free housing as currently designed and managed delivers its welfare potential incompletely. Hens with keel bone fractures experience chronic pain that affects their movement, behavior, and daily experience throughout the production period. The fracture rate of 50-80% means that in a well-managed cage-free system, the majority of hens are experiencing chronic pain from this cause alone. Addressing keel bone fracture welfare requires a multi-level approach: genetic selection for skeletal integrity alongside productivity traits; perch design that reduces fall risk and provides soft landing substrates; aviary design that creates gradual rather than abrupt height transitions; and selective breeding programs that breed for keel bone durability. The welfare science is clear that solving the keel bone fracture problem is one of the highest welfare priorities for cage-free laying hen production.