Tibia density increases and keel bone damage accumulates gradually; a live laying hen longitudinal study with validated measurement of cortical and medullary bone

1. Bone quality, particularly keel bone damage, has become an important aspect of laying hen welfare. This study investigated bone density changes in individual hens.2. Methods used included 2D live-bird X-ray to assess tibia and keel density longitudinally from 10 to 60 weeks of age. The data were used to estimate medullary and cortical bone components.3. Results showed that tibial bone density increased or remained stable after puberty, rather than declining during the laying cycle. This suggested that bone quality post-puberty requires reconsideration and the term 'osteoporosis' may need redefining.4. Tibial density increased significantly at puberty, primarily due to medullary bone accretion, and remained consistently high through the laying period. Keel bone damage occurred gradually over time, with no sudden increase. Hence, puberty can be crucial for establishing good bone quality and may provide a point where intervention can reduce keel bone damage in commercial flocks.5. The novel methodology of apportioning tibia area under the curve (AUC) for estimating cortical bone density from 2D X-ray demonstrated strong correlations with CT-derived density estimates. This reinforced its validity as a relatively simple way of assessing bone quality in live hens. The medullary bone correlation from 2D X-ray and CT-derived density was weaker, but total density was strongly correlated, so both can have application in understanding genetics, nutritional interventions or management.