Keel bone fractures affect the majority of laying hens in cage-free systems and cause chronic pain that represents one of the most significant unresolved welfare problems in commercial egg production.
Keel bone fractures represent a critical welfare paradox: cage-free systems that improve many hen welfare outcomes simultaneously introduce keel bone fracture risk that causes chronic pain for the majority of birds. This does not make cages preferable — the welfare balance still favors cage-free — but it highlights that housing system transitions alone are insufficient without addressing keel bone health through genetics, housing design, and management. The scale of suffering from keel bone fractures, affecting billions of hens globally, makes this one of the highest-priority welfare research areas in animal agriculture.