Nutrition and immune response in periparturient dairy cows

The general aim of the thesis was to increase the knowledge about the complex changes in, and interactions between, nutrition and immune system in dairy cows during the period around calving with emphasis on micronutrients. The specific aims were to study changes in blood concentrations of selected micronutrients and leukocytes, evaluate the effects of feeding intensity during the dry period on blood leukocyte numbers and functions, evaluate if a mid dry period blood sample can predict the micronutrient concentration at calving, and to compare the a-tocopherol concentration and stereoisomer composition in blood and milk after supplementation of synthetic or natural vitamin E, in periparturient dairy cows. Blood samples were taken around calving from 10 dairy cows fed according to Swedish recommendations to evaluate the blood concentrations of vitamins, minerals and trace elements. At calving, leukocytosis due to neutrophilia and monocytosis was detected, as well as a decreased proportion of neutrophils with adhesion molecules. Moreover, reduced concentrations of vitamins A and E, and zinc (Zn) were observed at calving. Twenty-three dairy cows were fed three different levels (low (L), medium (M) and high (H)) of a total mixed ration during the dry period. Blood samples were taken from 8 weeks before to 8 weeks after calving. Dry period diet had small effects on leukocyte numbers, and had no effects on neutrophil functions and disease incidence. However, an increase in the proportion of B-cells and a decrease in WC1+ T-cells were observed after calving in H and L cows, but not in M cows. The weeks around calving were characterised by neutrophilia, eosinopenia, lymphopenia and monocytosis, and the proportions of certain lymphocyte sub-populations increased in early lactation. The concentrations of vitamins A and E, selenium (Se) and Zn in blood was measured at several time points from one month before to one month after calving in 23 dairy cows fed three different feeding regimens during the dry period. The concentrations of vitamin A and E, and Zn decreased at calving, and Se was lower during the dry period than in early lactation. The concentrations of vitamin E and Se in the mid dry period sample predicted the occurrence of values considered marginal or deficient at calving. The effect of supplementation of 36 dairy cows with natural or synthetic vitamin around calving on the a-tocopherol concentration and stereoisomer composition in blood and milk was compared. The a-tocopherol concentration in blood was higher in the group fed RRR-a-tocopheryl acetate than in the groups fed all-rac-a-tocopheryl acetate, RRR-a-tocopherol or no supplement. A significant effect of time was also observed with lowest values at calving. The a-tocopherol concentration in milk was not affected by treatments, but was higher in colostrum than in milk. The proportion of the RRR-isomer was lower in the group fed synthetic vitamin E than in the other groups both in plasma and milk. In conclusion, substantial changes occur in blood contents of vitamin A and E, and Zn at calving, over- or under-feeding of dairy cows during the dry period may affect proliferation of lymphocytes during early lactation, analyses of mid dry period blood samples can predict the vitamin E and Se status at calving, and RRR-a-tocopheryl acetate is the preferential source of vitamin E when supplementing dairy cows in the periparturient period.