Age-Related Alterations in Peripheral Leukocyte Population of Healthy Holstein Dairy Cows during the Pre-Calving Period

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 γδT cells and B cells in older cows compared with heifer during pre-calving period.