The influence of selenium and zinc addition in food on concentration of these elements in blood and milk, on somatic cells number and histological characteristics of cows udders

The experiment included 30 cows of Holstein-Friesian breed, out of which 15 were receiving selenium and zinc in optimal doses before calving, while the others had never been supplemented with these micronutrients. There was analysed the concentration of selenium and zinc in blood and milk serum as well as the average number of somatic cells in corresponding lactation. After the cows exclusion from production, histological characteristics of cows udders were examined. The results of the investigation have shown that addition of selenium and zinc before calving has a positive effect on the values of these microelements in the blood and milk during the period of early lactation, that is, the concentration of these elements was significantly higher in the blood and milk of the cows that obtained selenium and zinc supplements. Also, in these cows there was significantly lower number of somatic cells during the following lacation period. In the parenchyma of the udder there was found less pronounced infiltration of leukocytes, notably thicker keratin layer of ductus papillaris and less expressed repairing processes that indicate a chronic inflammation of the udder in the samples after exclusion of the cows from production. There was a significant positive correlation between selenium in blood and milk, while there was not observed such a correlation for zinc. On the other hand, there was a significant negative correlation between the concentration of selenium in the blood and milk with the average number of somatic cells and the degree of infiltration of leukocytes, while its influence on the keratin layer of ductus papillarus was not shown. Zinc from blood and udder had a negative correlation with the number of somatic cells, had a positive correlation with the thickness of ductus papillaris keratin layer and had no influence on the level of leukocyte infiltration of udder parenchyma. Zinc demonstrates a positive influence on the formation of ductus papillaris keratin layer and protects the udder from pathogens penetration, while selenium stimulates the immunological response of the udder. Their positive impact can be defined as additive, because athough they have effect on two morphologically separate udder parts, adding both of them significantly decreases the number of somatic cells in milk. [Projekat Ministarstva nauke Republike Srbije, br. TR31062]