Armstrong, E. A.E. A.ArmstrongRufener, Christina BarbaraChristina BarbaraRufener0000-0003-2690-1520Toscano, Michael JeffreyMichael JeffreyToscano0000-0001-8185-3002Eastham, J. E.J. E.EasthamGuy, J. H.J. H.GuySandilands, V.V.SandilandsBoswell, T.T.BoswellSmulders, T. V.T. V.Smulders2025-01-082025-01-082020https://boris-portal.unibe.ch/handle/20.500.12422/201154In 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.en600 - Technology::630 - Agriculturearticle10.7892/boris.1451263208027110.1038/s41598-020-59940-1