Does footpad dermatitis induce a chronic negative welfare state in laying hens?

Footpad dermatitis (FPD) is a common health condition in commercially housed hens. Birds with severe FPD have necrotic lesions on the feet, which are caused by prolonged contact with wet bedding or faeces in the housing environment. FPD is believed to have a negative impact on the welfare of laying hens, and may therefore affect the efficiency and sustainability of egg production. We hypothesise that birds with severe FPD experience chronic stress, and this study aimed to investigate this by comparing neurogenesis between birds which had severe FPD with those in which FPD was absent. Hens managed under semi-commercial conditions were scored on three occasions (May, July, and September) for FPD severity, on a scale of 0-2 (0 = no FPD, 1 = necrosis only, and 2 = necrosis and swelling that was dorsally visible). Only individuals which had a FPD score of 0 on at least two occasions (including September) were selected as control birds (n=9). Birds with the most severe FPD were those which had a score of 2 on all three occasions, or a score of 1 in May and 2 in July and September (n=12). In each of these groups, some birds were reared with a dark brooder while others were not. Selected individuals were culled at 70 weeks of age, and their brains were collected and dissected. One hemisphere of each brain was fixed and then cut to 50μm coronal sections. The sections were immunohistochemically stained against doublecortin (DCX) in order to quantify the density of DCX+ neurons in the rostral and caudal hippocampus, which has previously been validated as a marker of chronic stress. FPD birds reared without a dark brooder had a significantly lower density of bipolar (p<0.001) and multipolar (p=0.049) DCX+ cells than controls. However, in those reared with a dark brooder, FPD had no effect on bipolar cell density (p=0.133) and increased multipolar cell density (p=0.042). A cumulative FPD score was calculated for each bird by adding together their scores from May, July, and September. There was a significant interaction of cumulative FPD score and dark brooder on both bipolar (p<0.001) and multipolar (p=0.015) DCX+ cell densities. These results suggest that the chronic stress experienced by laying hens could be reduced by providing housing conditions and adopting management practices which mitigate the risk of birds developing FPD, and rearing birds with a dark brooder could increase resilience to stress from FPD.