Effects of social disruption on physical parameters, corticosterone concentrations, and immune system in two genetic lines of White Leghorn layers.

Farm management practices such as increasing group size and mixing of unfamiliar chickens may cause social disruption and affect bird well-being. To examine genetic-associated physical and physiological differences in response to social disruption, 2 strains of White Leghorn hens were used in the study [i.e., HGPS (line selected for high group production and survivability) and DXL (DeKalb XL commercial line)]. Social disruption was created when hens were 50 wk of age by increasing group size from 4 hens (control) to 8 hens (experimental) per cage and providing an unstable social environment by moving 2 hens weekly between cages within the same line (experimental hens only). At 58 wk of age, hens were feather-scored. After euthanization, BW and the right adrenal gland weight were collected (n = 10 per treatment). Adrenal gland weight was adjusted for BW, and adjusted adrenal weight was used for analysis. Plasma corticosterone was quantified using RIA. The T-lymphocytes (CD4+ and CD8+) were measured using flow cytometry. Results showed that average feather cover score was greater for DXL hens than HGPS hens in both the unstressed (P < 0.05) and stressed treatment (P < 0.01). There was no difference in BW in DXL and HGPS hens between the control and the social disruption treatments. However, the relative adrenal weight of HGPS hens tended to be lower than control hens after social disruption (0.05 > P < 0.10). Plasma corticosterone was significantly lower in both strains following social disruption (P < 0.01). The T-lymphocyte ratio (CD4+:CD8+) was greater in HGPS hens than DXL hens post social disruption (P < 0.05). The data indicate that the 2 strains of hens reacted differently in terms of the adrenal system and immunity in response to social disruption. Hens selected for longevity with docile behaviors and high productivity, such as HGPS hens, provide a useful tool for improving animal well-being.