Hen individual health traits and their association with keel bone damage

1. Keel bone damage is a major welfare issue in laying hens. In this study, brown layers kept in commercial multi-tier systems were examined individually to gain information on individual health traits associated with keel bone deformations (KBD) and keel bone fractures (KBF).2. Ten laying hen flocks were assessed at six timepoints during the laying period for KBD, KBF and various health traits (n = 2900). On each visit, five hens with and three hens without keel bone damage were selected for further diagnostics (n = 462). This included X‑rays of the keel bone, post-mortem examination with histopathology (liver and intestines) and analysis of the keel bones (incineration) and tubular bones (breaking strength tests).3. Prevalence for KBD and KBF increased continuously with age (p < 0.0001) with highest mean prevalence at 65 weeks of age (KBD 47%, KBF 52%). Factors associated with KBD were presence of foot pad lesions (p = 0.0124) and lower dry matter (p = 0.0201) in dissected hens. Factors associated with KBF on-farm were higher body mass (p = 0.0239).4. After further diagnostics, KBF was associated with lower dry matter of the keel bone (p = 0.0049), lower relative calcium content of the keel bone (p = 0.0296), wing feather damage (p < 0.05) and enteritis (p = 0.0231). Overall, the occurrence of KBF was associated with KBD and vice versa (p < 0.0001). Palpated sharp bends in the keel on-farm were highly indicative for KBF (p < 0.0001).5. There might be a potential of reducing prevalence of KBF by stabilising gut health of laying hens and preventing foot and feather damage.