The influence of different levels and forms of selenium on the productivity and metabolic processes of lactating cows was studied. When feeding various concentrations of organic selenium – 4,9, 3,7 and 2,5 mg/head/day, the average daily milk yield with a fat mass fraction of 4 % was 22,48, 24,70 and 24,56 kg, respectively, which is 1,7, 11,7 and 11,2 % more than the control group, whose diet included sodium selenite. The amount of selenium in milk increased by 1,5, 26,1 and 24,6 %, the content of somatic cells decreased by 3,3, 13,0 and 11,5 %. The digestibility of dry matter, organic matter, protein, fat, fiber, BEV increased by 0,24–3,25, 0,41–4,43, 1,23–2,67, 0,06–2,47, 1,09–1,71 and 0,16–2,21 %. Bactericidal, lysozyme, phagocytic activity was high and amounted to 43,48–45,71 %, 0,62–0,65 µg/ml and 42,33–43,66 %, respectively, or by 0,62–2,85, 3,3–8,3 and 2,67–3,04 % more than the control. The content of TBA-active products in the blood serum of cows of the experimental groups compared with the control was 9,9–42,8 % less, the total amount of water-soluble antioxidants was 18,9–53,5 % more, while increasing the concentration of selenium in the blood serum. The insemination index decreased by 0,20, 0,55, 0,45 %, the service period – by 4, 19 and 10 days, respectively. The profit from the sale of milk obtained from cows fed with 3,7 mg/head/day of organic selenium was the largest and amounted to 10 980 rubles on the head.