Immune Responses of Cattle to Theileria orientalis Infection and Seasonal Change

The application of a grazing-based system is still challenging in the cattle industry. Little is known about immune responses of cattle to grazing-associated risks. Therefore, the aim of study was to investigate the effects of grazing-associated Theileria orientalis infection and seasonal temperature on immune changes in cattle. Blood samples were collected from cattle before and after grazing, or in the spring and summer. The levels of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and insulin-like growth factor-1 (IGF-1) in the serum were measured. Also, the presence of T. orientalis in the blood was investigated using PCR. Cattle that were positive for T. orientalis were lower than those that were negative for T. orientalis in the level of IFN-gamma (p < 0.05). Grazing triggered IFN-gamma and IGF-1 secretion in cattle in the absence of T. orientalis (p < 0.05). Interestingly, cattle chronically infected with T. orientalis showed a decrease in IGF-1 level after grazing (p < 0.05). Moreover, summer heat resulted in increased IL-6 in cattle. In conclusion, T. orientalis infection and summer heat may disturb cattle grazing activity. These results provide information on the efficient utilization of grazing system in terms of immune activity in cattle.