Keel bone fracture (KBF) is a common injury that affects the behaviour and welfare of laying hens. This study aimed to investigate the impact of KBF on anxiety-like behaviour in laying hens and explore the underlying regulatory mechanisms. Ninety 46-week-old Hy-Line Brown hens were individually housed in furnished cages and divided into two groups based on keel bone diagnosis: the non-fracture group (NF) and the KBF group. Keel bone status was evaluated at 46, 49, and 52 weeks of age using a combination of palpation and X-ray examination. Behavioural data were collected two days after each diagnosis. The open field test (OFT) was conducted at 49 weeks (n = 25 per group), and the attention bias test (ABT) was performed at 52 weeks (NF = 39, KBF=51). Behavioural observations revealed that hens with KBF displayed significantly increased preening and toe pecking behaviours. OFT showed a significant prolongation of the first movement latency and a reduction in exploration time in KBF hens. KBF hens exhibited significantly longer latencies for the first vocalization, first step, and first eating in ABT. Collectively, the OFT and ABT results indicated that hens with keel bone fractures exhibited the anxiety-like behaviour. Physiological indicators (n = 6) revealed elevated serum corticosterone levels and decreased serum serotonin levels in hens with KBF, suggesting that KBF induces a stress response, which contributes to the manifestation of anxiety-like behaviours. Golgi staining (n = 3) revealed a significant reduction in hippocampal neuronal complexity in KBF hens, indicating neuronal damage. qRT-PCR (n = 6) and western blot (n = 3) analysis demonstrated altered expression of genes related to anxiety in the hippocampus, characterized by a notable decrease in the protein levels of DCX, BDNF, and EGR1, suggesting impaired neurogenesis (DCX), reduced stress resilience (DCX and BDNF), and decrease neuroplasticity (BDNF and EGR1), all of which are closely linked to anxiety-like behaviour. Therefore, we suggest that keel bone fracture is associated with anxiety-like behaviour in laying hens, which may result from stress signals generated by the fracture that trigger the expression of anxiety-related genes in the brain.
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