Consequences for immune function of metabolic adaptations to load

Abstract

AbstractProlonged periods of stress have been associated with impaired immune function; the experiment reported here investigates a potential link between level of metabolic load and immune function in lactating dairy cattle. A group of 111 Holstein-Friesian dairy cows was used. The cows belonged to one of two genetic lines: a selection line (S) with high genetic merit for fat plus protein yield and an unselected control line (C). The cows were offered one of two silage-based total mixed diets containing either 200 g (LC) or 450 g (HC) of concentrate per kg dry matter. Combination of genetic selection and food gave four groups: S-LC, S-HC, C-LC and C-HC. All cows were inoculated with a live attenuated BHV-1 vaccine soon after parturition and the primary antibody response in whey monitored. The number of BHV-1 antibody positive cows was not significantly different between the four groups; but, the initial antibody response was lower in cows of high genetic merit which were given a low concentrate diet. Statistical analysis demonstrated that the contribution of diet to this effect was highly significant. One year later, again after parturition, the experiment was repeated, this time using serum as the test sample. The average antibody response of the BHV-1 antibody positive cows was not significantly different between the four groups but the number of antibody positive cows was group-dependent. In conclusion, diet type but not genetic merit for high fat plus protein yield made a highly significant contribution to the antibody response of dairy cows to BHV-1 vaccination, both initially and a year later.