The effect of selenium on the health of dairy cows, the milk composition and blood biochemical parameters

The effects of selenium on the health and on the milk content of fat, protein, lactose, fat-free dry matter, cell count and urea, the blood concentrations of glucose, urea, bilirubin and AST of dairy cows was investigated. A total of one hundred and four dairy cows were supplied with different quantities of selenium for 15 months. The control cows received 150 g of minerals daily which contained 19 mg selenium per kg and the experimental group received 150 kg of minerals daily containing 0.5 mg selenium per kg. Milk samples were taken over a period of twelve months, and serum and whole blood samples were taken for examination from thirty cows in each group. At the end of the experiment whole blood samples were examined for selenium. The incidences of mastitis and fertility problems were less in the controll group compared to the experimental group. However, in the first quarter of the experiment no significant differences between the groups were found. In the second quarter, the control group had significantly lower cell counts and significantly higher proportion of fat-free dry matter. In the third quarter, the control group had significantly greater blood phosphate concentrations, and, in the fourth quarter significantly lower milk lactose concentrations were observed in the control animals. During the whole study period, significantly greater blood selenium concentrations were observed in the control group. The results clearly demonstrate the importance of selenium supplementation of feed for dairy cattle.