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

Armstrong, E. A.; Rufener, C.; Toscano, M. J.; Eastham, J. E.; Guy, J. H.; Sandilands, V.; Boswell, T.; Smulders, T. V. (2020). Keel bone fractures induce a depressive-like state in laying hens. Scientific reports, 10(1), p. 3007. Springer Nature 10.1038/s41598-020-59940-1

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In commercial flocks of laying hens, keel bone fractures (KBFs) are prevalent and associated with behavioural indicators of pain. However, whether their impact is severe enough to induce a depressive-like state of chronic stress is unknown. As chronic stress downregulates adult hippocampal neurogenesis (AHN) in mammals and birds, we employ this measure as a neural biomarker of subjective welfare state. Radiographs obtained longitudinally from Lohmann Brown laying hens housed in a commercial multi-tier aviary were used to score the severity of naturally-occurring KBFs between the ages of 21–62 weeks. Individual birds’ transitions between aviary zones were also recorded. Focal hens with severe KBFs at 3–4 weeks prior to sampling (n = 15) had lower densities of immature doublecortin-positive (DCX+) multipolar and bipolar neurons in the hippocampal formation than focal hens with minimal fractures (n = 9). KBF severity scores at this time also negatively predicted DCX+ cell numbers on an individual level, while hens that acquired fractures earlier in their lives had fewer DCX+ neurons in the caudal hippocampal formation. Activity levels 3–4 weeks prior to sampling were not associated with AHN. KBFs thus lead to a negative affective state lasting at least 3–4 weeks, and management steps to reduce their occurrence are likely to have significant welfare benefits.

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