Keel bone fractures induce a depressive-like state in laying hens

In commercial flocks of laying hens, keel bone fractures are common and associated with behavioural indicators of pain. This study examines whether their impact is severe enough to induce a depressive-like state of chronic stress, measured using the production of new neurons in specific sections of the brain (adult hippocampal neurogenesis or AHN), which has been shown to be reduced in mammals following chronic stress or pain.
Hens were studied in a commercial multi-tier aviary system between the ages of 21 and 62 weeks. At regular intervals within this time period individual mobility was recorded using monitoring devices and keel bones were x-rayed to assess the presence and severity of naturally-occurring keel bone fractures. Brain tissue was collected from the 24 focal hens 3.5-4.5 weeks after the final x-ray.
Focal hens with severe keel bone fractures made fewer movements between tiers in the aviary at the end of the study than they did at the start, this difference was not present in hens with minimal keel bone fractures. Activity levels 3–4 weeks prior to sampling were not associated with the measures of neuron formation however. Hens with severe keel bone fractures at 3–4 weeks prior to sampling (n = 15) had a reduced density of new-born neurons across the hippocampal formation and differences in specific types of neurons when compared with flock-mates with minimal fractures (n = 9). These results suggest that, as with rodents, the avian hippocampal formation is sensitive to the experience of pain as a result of keel bone fractures. This supports the notion that keel bone fractures present a chronic stress and lead to a negative affective state lasting at least 3–4 weeks. Management steps to reduce the occurrence of keel bone fractures are thus likely to have significant welfare benefits.

Armstrong, E.A., Rufener, C., Toscano, M.J. et al. Keel bone fractures induce a depressive-like state in laying hens. Sci Rep 10, 3007 (2020). https://doi.org/10.1038/s41598-020-59940-1

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