Keel bone fractures affect the majority of laying hens in cage-free and aviary systems, representing a major unresolved welfare crisis in modern egg production.
Keel bone fractures cause chronic pain that persists for the entire laying period, which may last 12 to 18 months. Hens with fractures show measurable behavioral changes including reduced willingness to use elevated perches, altered gait, and lower egg production. The transition from caged to cage-free systems, while addressing confinement harms, introduced this new welfare challenge at scale. Research into perch design, lighting management, breed selection for bone density, and early-life calcium supplementation offers partial solutions. The scale of this problem — affecting the majority of the hundreds of millions of cage-free hens worldwide — makes keel bone fracture one of the most numerically significant welfare problems in contemporary agriculture.