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Group Size and Density Effects on Physical Indices and Cell-Mediated Immunity in Two Genetic Lines of White Leghorn Layers

A. G. Fahey^*, and H. W. Cheng^,1

^* Department of Animal Sciences, Purdue University, West Lafayette, IN 47906; and USDA-Agricultural Research Service, Livestock Behavioral Research Unit, West Lafayette, IN 47907

¹ Corresponding author: wcheng{at}purdue.edu

Social stress resulting from varied group sizes with density in caging systems is a common problem that affects bird welfare in the poultry industry in the United States. To examine whether there is a genetic basis for variations in response to group size and density, 2 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 wk of age. Blood samples, BW, and adrenal weight were collected from the birds at 30, 45, and 60 wk of age (n = 12, respectively) after euthanasia. Subsets of T cells (CD4⁺ and CD8⁺) were measured by flow cytometry. Hematological parameters were collected from blood smears. Results showed that there were no significant differences for BW, the relative adrenal glands, and the heterophil:lymphocyte ratio between and across lines after the treatments (P > 0.05, respectively). Compared with DXL birds, the HGPS birds had a greater ratio of CD4⁺:CD8⁺ at 30 and 45 wk of age. There was an age-associated decrease in CD4⁺ cells in all groups from 45 to 60 wk of age. However, an age-related decrease in CD8⁺ cells from 45 to 60 wk was found in the DXL birds only. The unique changes in T-cell 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 the line-unique ability of birds to cope in social environments and their survivability.

Key Words: group size • subpopulation T cell • hematology • body weight • chicken