Osteoporosis and related bone disease is one of the most significant and underappreciated welfare problems in commercial laying hens. The calcium demands of egg productionâeach egg shell requires approximately 2g of calciumâexceeds dietary supply capacity, forcing hens to mobilize calcium from their own bones. The cumulative result is structural bone weakness, fractures, and pain that affect the majority of commercial hens by the end of their laying cycle.
Post-mortem surveys of commercial laying hens consistently find high rates of keel bone fractures (the breastbone)âranging from 15% to over 80% depending on housing system, breed, and age. These fractures occur during normal activityâlanding from perches, moving through pop-holes, or during handling. Research using pain biomarkers confirms that keel bone fractures are painful and affect behavior, gait, and welfare indicators.
Enriched colonies and free-range systems, despite better welfare in other dimensions, actually show higher keel bone fracture rates than battery cagesâthe greater physical activity and perch use that benefit welfare in other respects also increase fracture risk. Cage-free is better for natural behavior but requires keel bone health management strategies. Aviary design (perch height, angle, cushioning) significantly affects fracture incidence.
Breeding for improved bone strength, optimized calcium/phosphorus nutrition, vitamin D supplementation, appropriate dietary calcium particle size (larger particles improve shell gland function), and aviary design modifications all reduce fracture incidence. Body weight management also mattersâheavier birds have more fractures. Research on keel bone welfare is an active and important field.
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