Keel bone fractures affect the majority of laying hens in commercial production, causing chronic pain throughout the laying cycle and representing one of the highest-priority welfare problems in modern egg production.
Keel bone fractures cause chronic pain that affects the welfare of hundreds of millions of laying hens throughout their productive lives. The keel bone, the large ventral projection of the sternum, is the site of attachment for the major flight muscles and is under mechanical stress during wing-flapping, landing, and normal movement. In calcium-depleted hens producing an egg nearly every day, the bone is structurally weakened and vulnerable to fracture. Once fractured, each subsequent wing movement and landing causes further pain at the fracture site. Hens with keel fractures show reduced perch use, altered feeding posture, and cognitive bias test responses consistent with chronic negative affect. The transition from battery cages to cage-free systems, while welfare-positive overall, has increased keel fracture incidence by exposing hens to flight and impact risks absent in cages. Solving this requires design changes, genetic improvement, and potentially different production approaches rather than return to cages.