Effect of body condition score of the dairy cow on the in vitro immune response of peripheral blood mononuclear cells to progesterone stimulation.

Immune function in cows is closely associated with their physical and hormonal conditions. In order to clarify the relationship between the body condition score (BCS) of lactating dairy cows and the immune response to progesterone (P(4)) in vitro, we examined whether lower BCS in dairy cows affects the responsiveness of peripheral blood mononuclear cells (PBMCs) to P(4) added in to culture medium. Forty-two non-pregnant healthy Holstein dairy cows were examined at 61 to 120 days after calving. The cows were divided into the following two groups; Low BCS group (N=20), which had a BCS of less than 2.25, and a Control group (N=22), which had a BCS over 2.75. PBMCs were stimulated with P(4) (1 microg/mL) and/or phytohemagglutinin (PHA), and the levels of cytokine mRNA were analyzed. In the Low BCS group, a significantly lower IFN-gamma level was stimulated by PHA only compared with the Control group. The combination of P(4) and PHA significant decreased the IFN-gamma/IL-4 ratio in the Control group, but this reaction was not found in the Low BCS group. Our data indicated that expression of IFN-gamma mRNA was basically lower in the low BCS dairy cows and that addition of P(4) did not suppress the cellular immune function in these cows. In this study, we observed that P(4) reduced the cellular immune response in the adequate BCS cows, whereas immunosuppression by P(4) was not found in the PBMCs of the low BCS cows, which already had a lower level of immune function.