Influence of parturition and diets enriched in n-3 or n-6 polyunsaturated fatty acids on immune responses of dairy cows during the transition period

The objectives of this study were to evaluate the functional properties of immunocompetent cells in dairy cows fed diets enriched in n-3 or n-6 polyunsaturated fatty acids during the transition period. Six weeks before calving, 21 primiparous and 27 multiparous pregnant Holstein dairy cows were randomly allotted to 1 of 3 dietary fat treatments: calcium salts of palm oil (Megalac), micronized soybeans, or whole flaxseed, which are, respectively, rich in saturated, n-6, or n-3 fatty acids. On wk 6 and 3 before parturition, cows received a subcutaneous injection of ovalbumin to measure the antibody response in colostrum and serum. Colostrum samples were collected at the first milking after calving, and blood samples were taken 6, 3, and 1 wk before the expected calving date and 1, 3, and 6 wk after calving. Blood mononuclear cells were cultured to evaluate the proliferative response to concanavalin A and the in vitro productions of interferon-gamma, tumor necrosis factor-alpha, nitric oxide, and prostaglandin E2. The serum antibody response to ovalbumin was unaffected by dietary fatty acids, but the response was lower in primiparous cows than in multiparous cows. A significant diet x parity interaction indicated that colostral antibody level against ovalbumin was significantly higher in multiparous cows fed soybeans than in those fed flaxseed or Megalac; there was no difference among treatments for primiparous cows. The lymphocyte response to concanavalin A was lower in cows fed soybeans than in those receiving flaxseed or Megalac when the cells were incubated with autologous serum. The proliferative response of mononuclear cells incubated with autologous serum was suppressed in the 1st wk after calving in both primiparous and multiparous cows, and multiparous cows showed a higher response than primiparous cows throughout the experiment. There was a significant interaction between parity and diet as a result of a greater production of interferon-gamma by mononuclear cells incubated with autologous serum in multiparous cows than in primiparous cows fed flaxseed; there was no difference among cows fed the other diets. Interferon-gamma production was reduced around calving while the inverse was observed for productions of nitric oxide and tumor necrosis factor-alpha. Productions of nitric oxide, prostaglandin E2, and tumor necrosis factor-gamma were greater in primiparous cows than in multiparous cows. In conclusion, functional properties of lymphocytes and monocyte/macrophage lineage of dairy cows during the transition period are modulated by parturition and the composition of polyunsaturated fatty acids in the diet.