Keel bone fractures affect the majority of laying hens in commercial systems, causing chronic pain that is frequently unrecognized and untreated.
Keel bone fractures represent one of the most significant and underappreciated welfare problems in modern egg production. The expectation that cage-free systems would solve welfare problems by allowing natural behavior has been complicated by the discovery that fracture rates in aviaries are comparable to or higher than in enriched cages in many studies. The reason appears to be the collision injuries and falls associated with multi-tier aviary systems. Chronic keel bone pain is evident from behavioral changes, pain assessment responses, and cognitive bias tests in affected hens. Solutions require attention to perch design, aviary geometry, lighting, and breed selection simultaneously. The scale of the problem — affecting hundreds of millions of hens — makes this one of the most important active areas of poultry welfare research.