Japanese black (JB) calves have greater susceptibility to infectious diseases compared to Holstein (Hol) calves. In order to clarify the differences in cellular immune status between JB and Hol calves, the leukocyte population and lymphocyte proliferative ability were analyzed. In total 200 healthy calves, 1 day to 14 weeks of age, were examined: 105 JB and 95 Hol calves. Lower numbers in peripheral blood and percentage in peripheral blood mononuclear cells of CD3(+)TcR1-N12(+) T cells and major histocompatibility complex class-II(+)CD14(-) B cells were observed in the JB compared to the Hol. The percentage of TcR1-N12(+)CD25(+) T cell in the JB was significantly lower than that of the Hol at 4-6, and 8-10 weeks. Interleukin (IL)-2 sensitivity in the JB was lower than that in the Hol, and significant differences were observed in age groups of 6-8 weeks and 10-14 weeks. These findings indicated that the lower numbers of γδ T cells and B cells in the JB compared to the Hol might be associated with the specificity of the immune systems in JB calves.

ABSTRACT. Older cows show a high incidence of infectious diseases during the periparturient period. The periparturient infectious diseases are closely associated with the immune function of dairy cows during the pre-calving period. In order to evaluate the relationship between the immune cell population and age in the cows during the pre-calving period, we obtained blood samples from 170 dairy cows during the pre-calving period. We chose only healthy cows, which did not develop clinical diseases within 2 weeks after the calving in this study. The animals were divided into 4 groups based on their parity: in their 1st pregnancy (Group 1), in their 2nd pregnancy (Group 2), in their 3rd calving (Group 3) and in more than 3rd pregnancy (Group 4). The numbers of the peripheral blood CD3 + TcR1-N12 + and MHC class-II + CD14 -lymphocytes were significantly higher in Group 1 compared to Group 4. This result indicated that the lower T cells and B cells in older cows compared with heifer during pre-calving period.KEY WORDS: dairy cow, leukocyte population, pre-calving period.