Resistibility to Theileria sergenti infection in Holstein and Japanese Black cattle.

To clarify the resistibility against Theileria sergenti infection in Holstein and Japanese Black cattle under controlled conditions in artificial environmental chambers, those breeds of calves were infected with T. sergenti by infestation with the same number of infected ticks. No apparent differences between the two breeds were observed in the feeding numbers and feeding periods of ticks infested. The level and duration of parasitemia were clearly less and shorter in Japanese Black than those in Holstein calves. With progress of parasitemia, packed cell volume (PCV) and erythrocyte number decreased in both breeds. However, the minimum PCV and erythrocyte number recorded in Japanese Black were higher than those in Holstein calves. These results suggest that the Japanese Black shows solider resistance to T. sergenti infection than the Holstein breed does under experimentally controlled condition without external factors.