Comparison of Adult Neurogenesis and Caecal Microbiota Abundance in the Laying Hen Hippocampal Formation for Birds with Differing Physical Body Conditions On Farm

Adult hens approaching the end of lay (65/66 weeks-of-age) were sampled from a multi-tier aviary with an outdoor range, and an enriched colony cage system, on adjacent sites of a local egg production farm. Body size, feather cover and redness of the comb were used to select 12 birds with good body condition and 12 birds with poor body condition from each system. Using immunohistochemistry, immature neurons expressing doublecortin (DCX) were quantified in serial hippocampal sections. Additionally, expression of mRNA for inflammatory cytokines was quantified in the spleen and contents of the caecal microbiome were sequenced. Data regarding body mass and spleen mass was also recorded.For practical reasons, it was not possible to compare the same strain/genotype of hen between the two housing systems. For this reason, 14-week-old laying hen pullets of each strain were also sampled directly from adjacent barns of the same rearing farm, where they had been housed in almost identical conditions. DCX-positive cells were also quantified in this sample, to provide a baseline for any strain differences which may have existed before the experience of differing adult housing.