Immunological effects of altering the concentrate inclusion level in a grass silage-based diet for early lactation Holstein Friesian cows

Concentrate inclusion levels in dairy cow diets are often adjusted so that the milk yield responses remain economic. While changes inconcentrate level on performance is well known, their impact on other biological parameters, including immune function, is less wellunderstood. The objective of this study was to evaluate the effect of concentrate inclusion level in a grass silage-based mixed rationon immune function. Following calving 63 (45 multiparous and 18 primiparous) Holstein Friesian dairy cows were allocated to one ofthree isonitrogenous diets for thefirst 70 days of lactation. Diets comprised of a mixture of concentrates and grass silage, withconcentrates comprising either a low (30%, LC), medium (50%, MC) or high (70%, HC) proportion of the diet on a dry matter (DM)basis. Daily DM intakes, milk yields and BW were recorded, along with weekly body condition score, milk composition and vaginalmucus scores. Blood biochemistry was measured using a chemistry analyzer, neutrophil phagocytic and oxidative burst assessed usingcommercial kits andflow cytometry, and interferon-γproduction evaluated by ELISA after whole blood stimulation. Over the studyperiod cows on HC had a higher total DM intake, milk yield, fat yield, protein yield, fat+protein yield, protein content, mean BW andmean daily energy balance, and a lower BW loss than cows on MC, whose respective values were higher than cows on LC. Cows onHC and MC had a lower serum non-esterified fatty acid concentration than cows on LC (0.37, 0.37 and 0.50 mmol/l, respectively,P=0.005, SED=0.032), while cows on HC had a lower serumβ-hydroxybutyrate concentration than cows on MC and LC (0.42, 0.55and 0.55 mmol/l, respectively,P=0.002, SED=0.03). Concentrate inclusion level had no effect on vaginal mucus scores. At week 3postpartum, cows on HC tended to have a higher percentage of oxidative burst positive neutrophils than cows on LC (43.2% and35.3%, respectively,P=0.078, SED=3.11), although at all other times concentrate inclusion level in the total mixed ration had noeffect on neutrophil phagocytic or oxidative burst characteristics, or on interferon-γproduction by pokeweed mitogen stimulatedwhole blood culture. This study demonstrates that for high yielding Holstein Friesian cows managed on a grass silage-based diet,concentrate inclusion levels in early lactation affects performance but has no effect on neutrophil or lymphocyte immune parameters.