Neuroendocrine regulation of social stress in two genetic lines of White Leghorn hens
Social stress resulting from varied group sizes and stocking density in caged systems and social disruption is a common problem that impacts bird welfare in the poultry industry in the United States. To examine whether there is a genetic basis of variations in response to group size and density, and social disruption, two genetic strains of White Leghorn hens were used in this study; a line selected for high group productivity and survivability in multiple-bird cages referred to as HGPS and Dekalb XL (DXL), a commercial line individually selected for production. To examine the effects of increased group size and stocking density effects, birds from each line were housed in either 4-bird cages (542 cm2/bird) or 10-bird cages (434 cm2/bird) from 17 to 60 wk of age. Blood and brain samples and body and organ weights were collected from the birds at 30, 45, and 60 wk. To examine the effects of increased group size and social disruption birds from each line were housed in either 4-bird cages (542 cm2/bird) or 8-bird cages (542 cm2/bird) from 50 to 58 wk of age. Two hens from the 8-bird cages were moved once a week to create social disruption. Blood and brain samples and body and organ weights were collected from the birds at 58 wk of age. In response to increased group size and density, the unique changes of T subpopulations and the ratio of CD4+:CD8 + suggest that the HGPS birds had greater cell-mediated immunity than DXL birds. There were no genetic or genetic-environment interaction effects on the serotonergic system in the hypthothalmus or Raphe nuclei. Increased group size and density altered dopamine turnover. In response social disruption, the HGPS hens had lower mortality and better feather score than the DXL hens. Social disruption increased adrenal weights and stimulated the immune system in both the HGPS and DXL hens. The results indicate that there were no genetic basis of variations in the concentrations of peripheral tryptophan, serotonin, epinephrine, norepinephrine, and dopamine in response to social disruption. In the Raphe nuclei, the HGPS hens may have a higher serotonin turnover. In the hypothalamus, compared with its relative controls, social disruption led to a lower serotonin turnover in the hypothalamus. In the Raphe nuclei, epinephrine increased in the DXL birds, while the HGPS hens had decreased dihydroxyphenylacetic acid and dopamine turnover post social disruption. The data suggest that selection for docile behaviors and productivity in poultry, such as the hens of the HGPS line, alters hens’ serotonergic and catecholamine homeostasis in the central nervous system in response to increased group size and cage density as well as social disruption. These changes are consistent with the line’s unique behavioral characteristics and capability to cope with their housing environments.
Cheng, Purdue University.
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