Variation in cranial and caudal keel bone composition and its association with keel damage severity in laying hens

Keel bone damage is prevalent in commercial laying hen flocks and is commonly associated with reduced mineralization of this bone. The aim of this study was to characterize variation in cranial and caudal keel bone composition and to examine its association with keel damage severity in Bovans Brown laying hens. The cranial region of the keel was significantly more mineralized than the caudal region (mineral content: 53 +/- 4 % vs. 46 +/- 5 %, P < 0.05). Low to moderate correlations (r = -0.27 to 0.55, P < 0.05) were observed between keel bone chemical composition and radiographic measurements of keel shape (cranial depth, keel length, and mid-depth), suggesting that mineral matrix composition contributes to keel structural development. Furthermore, increasing keel damage severity, assessed by callus extent and size, was associated with significant reductions in lipid content (median: 0.06 to 0.03), mineral content (56 % to 52 %), and the mineral-to-organic ratio (1.7 to 1.4) in the cranial keel cortex (P < 0.05). These findings indicate that reduced keel bone mineralization was associated with increased susceptibility to deformation and fracture. Overall, this study enhances our understanding of keel bone biology in laying hens and identifies compositional factors that may contribute to susceptibility to keel damage and fractures.