|Cheng, Heng Wei|
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2008
Publication Date: 12/1/2008
Citation: Fahey, A.G., Cheng, H. 2008. Group size and density effects on physical indices and cell-mediated immunity in two genetic lines of White Leghorn layers.. Poultry Science. 87:2500-2504. Interpretive Summary: Social stress resulting from varied group sizes with density in caging systems is a common problem that impacts bird welfare in the poultry industry in the United States. Chickens from two genetic lines (Dekalb XL, DXL and High Group Productivity and Survivability, HGPS) were housed in groups of 10 (434 cm2/bird) and 4 (542 cm2/bird) between 17 and 60 weeks of age. Body weight, relative adrenal gland and T-lymphocytes (cell-mediated immunity) were used as biomarkers to determine the optimum group size to improve the well-being of the chickens. Results indicate that body weight and relative adrenal gland were not affected by increased group size and density in both genetic lines. However, there was age-related cell-mediated immune suppression in the DXL line (when combining DXL birds from the 10- and 4- bird cages). The genetic basis of variations in immunity may correlate with its line-unique coping ability to social environments and survivability. The finding could be adapted by producers, veterinarians and other scientists to develop animal well-being standards and guidelines for management practices.
Technical Abstract: Social stress resulting from varied group sizes with density in caging systems 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, two genetic strains of White Leghorn hens were used in this study; HGPS, a line selected for high group productivity and survivability in multiple-bird cages and DXL (Dekalb XL), a commercial line individually selected for production. 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 wks of age. Blood samples, and body and adrenal weights were collected from the birds at 30, 45, and 60 wks of age (n=12, respectively) following euthanasia. Subsets of T-cells (CD4+ and CD8+) were measured using flow cytometry. Hematological parameters were collected from blood smears. Results showed that there were no significant differences for body weight, the relative adrenal glands, and heterophil:lymphocyte ratio between and across lines following the treatments (P>0.05, respectively). Compared to DXL birds, the HGPS birds had a greater ratio of CD4+:CD8+ at 30 and 45 wks of age (HGPS vs. DXL, 1.48:1.14 and 1.93:1.35, respectively). There was an age-associated decrease of CD4+ cells in all groups from 45 to 60 wks of age (P<0.05 and P<0.01, for DXL and HGPS, respectively). However, an age-related decrease of CD8+ cells from 30 to 60 wks and 45 to 60 wks (P<0.01 and P<0.05, respectively) was found in the DXL birds only. The unique changes of T subpopulations and the ratio of CD4+:CD8+ may suggest that HGPS birds had a greater cell-mediated immunity than DXL birds. The genetic basis of variations in immunity may correlate with its line-unique coping ability to social environments and survivability.