Therapeutic and anti-oxidant potential of vitamin E and selenium was evaluated in mastitic cows. The CMT point score and milk somatic cell count (SCC) was significantly (P0.05) higher in mastitic cows prior to treatment. Reduced activity of enzymatic anti-oxidant catalase was observed in mastitic animals. The parameters studied in mastitic cows treated amoxicillin sulbactum (group II) and with amoxicillin sulbactum, vitamin E and selenium (group III) were compared with that of group I healthy cows. Significant reduction (P0.05) in CMT and SCC was observed in both the treated groups. However, reduction in CMT point score and SCC was more pronounced in group III than group II cows. Synergistic action of antibiotic and vitamin E selenium significantly (P0.05) enhanced the activity of catalase in group III mastitic animals on day 8 time period. Therefore, vitamin E and selenium supplementation could be advised in the therapy of mastitis.

In the conditions of the Republic of Belarus there was analyzed the efficiency of application of organic form of selenium Sel-plex in feeding of producer bulls. In course of the study there was showed the dynamics of live weight and average daily weight gain of producer bulls; blood indexes of analimals by the end of the experiment; sperm quality of experimental bulls. As a result of research it was established, that application of organic form of selenium Sel-plex in feeding of breeding bulls during the summer and winter periods in a dose of 0,4 mg/kg of dry matter of a ration promoted the increasing of daily average live weight gain on 6,4-8,1%, improvement of morphological and biochemical blood structure, increasing of indices of natural resistance on 0,5-6,1% and sperm production quality - on 7,3-28,0%.

Influence of various levels of the organic form of selenium of Sel-Pleks on the formation of reproductive function of breeding bull-calves is studied in the conditions of the Republic of Belarus. Feeding of organic selenium to bull-calves promoted volume increase of ejaculate on 5,0%, quantities of male germ cells in ejaculate - on 9,1% and concentration of male germ cells in ejaculate - on 7,5% in comparison with animals in which rations sodium selenit was used. Application in winter period of the premix with inclusion of selenium in a dose of 0,4 mg per 1 kg of a dry matter of a ration allows to increase the quantity and quality of sperm of bull-calves: volume ejaculate - on 9,5%, concentration of male germ cells in ejaculate - on 16,4% (Р less than 0,05) and activity of male germ cells - on 8,9% (Р less than 0,001). Increasing of a dose of selenium up to 0,4 mg per 1 kg of a dry matter in rations of bull-calves in summer period allows to increase quantity and quality of sperm. At bull-calves of the third experimental group the ejaculate volume has increased on 4,5%, concentration of male germ cells in ejaculate - on 15,7% (Р0,05) and activity of male germ cells - on 7,3% (Р less than 0,001).