|Kehrli Jr, Marcus - PFIZER, TERRE HAUTE, IN|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2001
Publication Date: N/A
Interpretive Summary: At the time of calving, the dairy cow becomes severely immune-suppressed. There is a decline in the number of lymphocytes, particularly T- lymphocytes, circulating in the blood. Lymphocytes are particularly important to the immune system as they are the cells that help the body recognize a new infection and, more importantly, help the body recognize and fight off an invader it has seen in the past. They are the memory cells of the immune response. The low number of T-lymphocytes observed in the dairy cow around the time of calving is thought to increase their susceptibility to mastitis (an infection of the mammary gland). Cows also begin lactating when they calve, which places a large metabolic demand on their body. The stress of calving or the stress of milk production, or both, may be causing the immune suppression. In this experiment, we examined T-cell numbers in the blood of cows that had been mastectomized, so they would not produce milk but would experience the stress of calving, with T-cell numbers in normal cows. Mastectomy eliminated changes in T- cell numbers typically observed in normal dairy cows. These data suggest that the metabolic challenges imposed by lactation are, to a large degree, responsible for the immune suppression observed in dairy cows at calving. Results of this study will greatly benefit the dairy producers worldwide.
Technical Abstract: There is an increased incidence of infectious disease in periparturient dairy cows. During the periparturient period there is a decline in T- lymphocyte cell subsets, which parallels a reduction in functional capacities of blood lymphocytes and neutrophils. Mechanisms responsible for these changes in immune function during the periparturient period are poorly characterized. Ten mastectomized and 8 intact multiparous Jersey cows were used to determine if the periparturient changes in peripheral blood mononuclear cell populations are the result of the physiological demands associated with the onset of lactation or if they are a result of the act of parturition. Blood mononuclear cells were phenotyped using monoclonal antibodies against T-cell subsets, B-cells, and monocytes. Blood samples were taken frequently from -4 to 4 wk after parturition. In intact cows, all T-cell subset populations (i.e. CD3, CD4, CD8 and N12 positive cells) decreased at the time of parturition while the percentage of monocytes increased. Mastectomy eliminated the changes in leukocyte subsets (CD3, CD4, N12 positive cells and monocytes) observed in intact cows around parturition. These results indicate that the mammary gland and metabolic stresses associated with lactation influence the composition of peripheral blood mononuclear cell populations in dairy cows during the periparturient period.