Alterations in neutrophil phagocytosis and lymphocyte blastogenesis in dairy cows around parturition

The bovine blood neutrophil phagocytosis and the blood and milk lymphocyte proliferative response upon stimulation with Phytohaemagglutinin, Concanavalin A and Pokeweed mitogens was studied from 3 weeks prior to calving until 3 weeks after calving. Neutrophil phagocytosis and the total and differential blood leukocyte counts were performed by flow cytometry. A gradual increase in the percentage of phagocytized bacteria and the average number of bacteria per phagocyte was observed before calving followed by a sharp fall on the first postpartum. This was followed by a steady increase in the above parameters reaching the highest levels at two weeks postpartum. There was a gradual increase in the number of neutrophils in blood as calving approached followed by a sharp decrease after calving. The number of lymphocytes in blood dropped before calving, being at the lowest level on the day before calving. The proliferative response of blood and milk lymphocytes upon stimulation with the three mitogens was low during the week preceding parturition with the lowest value on the day before calving. The response of blood lymphocytes returned to a higher level the second week after calving while that of milk lymphocytes remained at a low level during the first and the second postpartum weeks.