Effects of maternal care and selection for low mortality on tyrosine hydroxylase concentrations and cell soma size in hippocampus and nidopallium caudolaterale in adult laying hen.

Feather pecking and cannibalism in farm-kept laying hens are damaging behaviors both in terms of animal welfare and economic loss, and a major challenge in modern poultry farming. Both rearing with a foster hen and genetic selection have been demonstrated to reduce feather pecking in laying hens. We examined the effects of rearing with a foster hen, genetic selection for low mortality from cannibalism, and interactions between both, using cellular morphology and levels of the rate-limiting enzyme in dopamine production, tyrosine hydroxylase, in the hippocampus and nidopallium caudolaterale (NCL) as a potential measure for laying hen welfare. Hens from the second generation of a sib-selection scheme line derived from a pure-bred White Leghorn line, selected for low mortality and for production characteristics, or their control line (CL) selected only for production characteristics, were housed with or without a foster Silky hen for the first 7 wk of life. Aside from the presence or absence of a foster Silky hen during the first 7 wk of life, housing conditions were identical for all hens. The hens were then sacrificed and brains were removed at 52 wk of age. Brains were sectioned and stained using a Nissl staining to reveal cell soma morphology, or using immunocytochemistry for tyrosine hydroxlase. A greater degree of lateralization in the hippocampus was observed in hens reared without a foster hen, as measured by absolute difference in cell soma size between hemispheres (P<0.05). The low mortality line showed decreased concentrations of tyrosine hydroxylase in the NCL compared with the CL (P<0.005). Our results indicate that morphological changes in brain induced in very early life can be detected in adult hens, and that genetic selection against mortality due to cannibalism impacts tyrosine hydroxylase in the NCL of laying hens. These observations strengthen the notion that brain measures may be useful as potential readouts for animal welfare.