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%.

In the physiological experience spent on male pigs-manufacturers, we had been studied influence of various doses of selenium (10 mg, 20 and 30 mg) in structure premix on nutrients. It is established, that increase of level of selenium in mixed fodders for male pigs-manufacturers to 30 mg/kg especially promotes increase in degree of use in their organism of fat to 58,7%; (P less than 0,05), the digested nitrogen to 62,1%, calcium – to 78,3% and phosphorus – to 72,5%

Determination of chronic toxicity of a new selenium-containing preparation Aesel was realized in the conditions of the Republic of Belarus. There was realized endermatic administration of the experimental preparation to laboratory white mice. Studying of sensitivity of some organs and systems of mice and revelation of a degree of reversibility of processes caused by active substances of the drug was realized. The main clinical, pathomorphologic, biochemical, hematological changes in the organism of laboratory animals with induced chronic toxicity were determined.

Application in diets of breeding bull calves of an optimum dose of selenium (0,4 mg on 1 kg of a solid of a diet) renders positive influence on formation of reproductive ability of bull-calves: promotes increase daily average gains live weight on 7,1%, indicators of natural resistance – on 0,6-6,7% and to improvement of quality sperm production – on 16,4% during the winter period. During the summer period daily average gains live weight on 6,8%, indicators of natural resistance – on 0,5-13,9% and to improvement of quality sperm production – on 15,7% accordingly

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).

This article is devoted to a problem of biochemical interaction of selenium and antioxidational system of animals and people organism. The problem we have touched is about the efficiency of influence of organic and inorganic taking place on subcellular level. The advantages of organic selenium are proved, the degree of its bjochemical influence on an antioxidationi status of health are indicated.

Determination of the optimal doses of selenium inclusion into premix structure for breeding boars for the maintenance of their higher producing capacity was realized in the conditions of the Republic of Belarus. Selenium lack in boar rations caused the degenerative changes in seminal glands, low male germ cells concentration and lowering of spermatozoon motility, which subsequently decreased their producing efficiency. Research showed, that selenium inclusion in premix KS-1 structure in quantity of 30 mg per 1 kg in comparison with premix in 20 mg dose have improved the yielding productivity of mature boars: the average quantity of male germ cells per one ejaculate increased on 17,2%, the average quantity of born pigs from per one sow increased on 4,8%. The additional profit per one boar was on 6,06% higher than in control experiment

Studying of influence of various levels of selenium on growth, protein structure of blood serum, natural resistance, and reproductive performance of pedigree bull-calves was realized in the conditions of the Republic of Belarus. It was established, that feeding with an optimum dose of selenium (0,4 mg per 1 kg of dry matter) in rations of replacement bull-calves during the raising period promoted the increasing of daily average weight gain on 6,8%, indexes of natural resistance - on 0,5-13,9%, and sperm production quality - on 4,5-27,3%. In the conditions of optimization of selenium level of in diets the protein structure of blood serum of replacement bull-calves exceeded the similar index at control animals by the crude protein index - on 8,3 (Р less than 0,05), by albumine and alpha globulin -on 2,2% and 1,6%, respectively. Application of selenium in dose of 0,4 mg per 1 kg of dry matter made it possible to increase the indexes of natural resistance on 0,5-13,9%. Increase of selenium dose up to 0,4 mg per 1 kg of dry matter in made it possible to increase the quantity and quality of sperm of bull-calves, that was proved by the increasing of ejaculate volume on 4,5%, concentration of male germ cells in ejaculate – on 15,7% (Р less than 0,05) and male germ cells activity - on 7,3% (Р less than 0,001)

Development of new selenium preparations in a complex with vitamins for the purpose of decrease of trace element toxicity and increase of its bioavailability is the topical problem of veterinary science. A new antioxidant water-soluble complex Aesel, which includes selenium as the activated product of interaction of methionine and sodium selenite, vitamins A and E, is researched. Lethal doses of the preparation for mice and rats were identified through intragastric and subcutaneous introduction. Due to the results of the research it was determined that Aesel is rated among the forth class of danger, so it is dangerous to a very little degree. Lethal doses of the preparation on the pure selenium, calculated on Pershin method, for rats at parenteral introduction is equal 5,48, at enteral introduction - 39, for mice at parenteral introduction - 7,72 mg/kg. Lethal doses of the preparation calculated on all making components equal to 39000 mg/kg.

Belarus is among regions, where the selenium content in soil, hence, in cereal and other cultures considerably below requirements that leads to insufficiency of this microelements in a diet as the person, and animals. Synthesized in the All-Russian Scientific Research Institute of Physiology, Biochemistry and Feeding of Agricultural Animals new organic compound of selenium - selenopyran on variety of criteria has no analogues in the world among considerable quantity selenium of containing preparations and favourably differs from all known forms of microelements. Selenopyran, brought in fats and forages, shows antioxidatic the properties which are not conceding traditionally applied in veterinary science and medicine to antioxidants. Arriving in animal body with forage or in the form of injections, selenopyran is capable to play a role of a metabolic regulator. It activates enzymes of antioxidatic body protection, reduces formation new and will neutralize of earlier formed activeproducts of peroxide lipids oxidations, improves functioning of cellular membranes, normalizes metabolism, makes active cellular, humoral and phagocytal immunity links, raises nonspecific resistance and efficiency of animals. Toxicity of selenopyran more low, than at all known organic connections of selenium, and more than in 100 times is less, than at sodium selenit. The data allow to expand possibilities of application of organic selenium and to use it as a preparation raising resistance and body viability at the expense of the patronage of cellular structures from influence of oxidizers and free radicals, to normalize metabolism and to stimulate thus the big additional body weight at animals. The influence of medicine organic selenium on piglet bodies what are behind a growth and development is shown. The results showing the dynamical changes of haematologicals, physiologicals and biochemicals indices under the influence of selenopyran was given.