Z. Li*, K.E. Nestor*1, and Y. M. Saif#
*The Ohio State University Department of Animal Sciences
and #Food Animal Health Research Program
Abstract
Previous research indicated that large-bodied turkey lines were more susceptible to several turkey diseases than small-bodied lines. An experimental line (F) of turkeys selected long-term for increased 16-week body weight was more susceptible than its non-selected randombred control (RBC2) when exposed to Pasteurella multocida (fowl cholera), Erysipelas rhusiopathiae (erysipelas), Newcastle disease virus, and Bordetella avium. Large-bodied commercial sire lines had similar mortality as the F line when exposed to Pasteurella multocida. A series of studies was undertaken to evaluate changes in the immune system that might be responsible for the difference in disease resistance between the F and RBC2 lines.
A difference between the F and RBC2 lines was observed in response to the mitogen concanavalin A with the F line not responding as well as the RBC2 line. No line difference in response to the mitogen phytohemagglutinin M was observed. Serum IgM concentrations were higher in the F line than in the RBC2 line but there was no difference in serum IgG concentrations. Phagocytic activity, as measured by the carbon clearance method, was lower in the F line than in the RBC2 line. At 9 weeks of age, the F line had a greater spleen weight relative to body weight and a greater ratio of spleen to the bursa of Fabricius weight than the RBC2 line but had lower relative weight of the bursa of Fabricius. The F line had more polymorphisms of the CD8 molecules than the RBC2 line. The F line also had a larger CD4+CD8- T cell subpopulation than the RBC2 line. Antibody responses to several antigens were tested. In general, the F line had higher antibody responses than the RBC2 to sheep red blood cells with no consistent line difference in antibody responses to Brucella abortus, Newcastle disease virus, and P. multocida. In summary, the F and RBC2 lines differ in several facets of the immune system all of which may contribute to the line differences in disease resistance. There are indications that lowered cellular immune response was responsible for the differences in disease resistance.