Date of Award
Doctor of Philosophy
Theses & dissertations (Interdisciplinary)
Susan J. Lamont
The immunocompetence of an individual is essential to the disease resistance capabilities of the individual. The goal of this study was to determine the feasibility of a multi-trait index selection approach to improve general immune competence of chickens. The Iowa State University S1 chicken line was used in the first experiment to test the in vivo assays used to measure the immunocompetence of chickens and to determine the influence of the B blood group, antibody response to GAT, and regression of Rous sarcoma virus-induced tumors on immunocompetence measures. A selection experiment was conducted with a random-breeding chicken line (Ottawa strain 7). A total of 467 chicks from 20 sire families (randomly divided into 2 replicates of 10 sire families each) were used as the base population. Three in vivo assays (carbon clearance assay, PHA wing web assay, and ELISA) were used to evaluate phagocytic activity (PI), cell-mediated response (WI) and antibody production to two vaccines, Pasteurella multocida and Mycoplasma gallisepticum ([alpha]-PM and [alpha]-MG), respectively. Heritabilities of humoral immune response were estimated to be from 0.06 to 0.53. Heritability estimates of cell-mediated response and phagocytosis ranged from 0.06 to 0.36. A selection index was constructed with the assumption that genetic correlations between these traits are negligible. The economic values of the traits were calculated to be negatively proportional to their respective heritability estimates in an effort to apply equal selection pressure to each trait. In the first generation, half-sibs were divided into high or low response sublines within each replicate according to their index values. Selections in subsequent generations were restricted within each subline. After two generations of selection for immunocompetence, significant differences were observed between high and low response sublines for [alpha]-MG and WI. Phenotypic correlations between immunological traits measured by in vivo assays were generally low, suggesting that simultaneous improvement of the three facets of the immune system is necessary. Correlations between in vitro assays showed a similar trend. This study suggests that it is possible to improve immunocompetence by multi-trait selection and that this selection may also have beneficial effects on production traits of the high response hens.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Cheng, Shen, "Genetic selection for immunocompetence in chickens " (1990). Retrospective Theses and Dissertations. 9427.