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 article showed results of the researches of the influence on productive longevity of cows of such factors, as a linear belonging, a genotype of the father, type of selection are stated. The lead researches have shown, that more longer duration of use characterized the animals belonging to line Siling Trajdzhun Rockit 252803 - 4,5 lactations. Among daughters of various bulls the greatest term of productive use daughters of the bulls the Silach 158 - 5,0 lactations differed. At the maximal deviation in efficiency of ancestors (6001-7000 kg of milk) longevity of their daughters was the greatest and has made 4,18 lactations. The greatest influence on duration of economic use of cows was rendered by specific features of bulls (32,2%) and a linear accessory -12,0%. While the selection variant practically does not influence longevity of animals - a share of influence of 3,7%

The efficiency of influence of iodon on the reproductive function of fullmouthed sire bulls of white-and-black breed was studied in the conditions of the Republic of Belarus. There were formed two groups of sire bulls: experimental group with low indices of sperm quality; control one – with high indices. In course of studying the interrelation of thyroid and sexual glands there was established the presence of parallelism in their development and function. In a period of sexual arousal the thyroid gland came into hyperactivity condition. At the same time, the quantity of triiodothyronine increased from 2,23 +/-0,02 to 3,05 +/-0,02 ng/ml, thyroxine - from 38,7 +/-1,02 to 59,8 +/-1,07 ng/ml. For the increasing of the reproductive qualities of sire bulls there was developed a iodine-containing preparation Iodon which should be spread with a medical syringe over a skin along the spine column. Iodon preparation applied in such a way made it possible to reduce the stressful influence more efficiently in comparison with an injection; it was well acquired and promoted the increasing of the reproductive function of sire bulls. The Iodon was developed on a basis of dimethylsulfoxide that promoted the efficient absorption through a skin. The preparation is a homogeneous hyaloid russet liquid with a specific smell, it is produced in bottles of 200 and 400 cm cubic. Iodon preparation realizes medical and preventive action in cases of impairment of sexual glands function against the background of iodine hunger. The preparation does not possess any allergenic properties, shows weak cumulative properties, and is harmless. The sperm quality improvement has been marked in all parameters, sexual reflexes become more stable and vigorous, animal fertility increased

Determination of the influence of new premixes on sperm quality and natural resistance of sire bulls during winter and summer periods was realized in the conditions of the republic of Belarus. Application of the developed vitamin and mineral additive in rations of sire bulls in course of winter and summer periods made it possible to increase their natural resistance, that was proved by the 7,2-8,8% increasing of the bactericidal activity of blood serum indicators, 0,6% increasing of lysozymic activity of blood serum, and 3,3-5,1% increasing of the phagocytic ability of leukocytes. There was determined the possibility to increase sire bull sperm quality during different year periods by means of application of the enhanced doses of vitamins and trace elements. As a result, the ejaculate volume increased on 7,4-2,4%, concentration of male germ cells in ejaculate on - 6,3-7,8%, sperm activity - on 6,7-7,3%, and also there was stated the decrease of spoilage percent of sperm production. Results of the industrial testing have confirmed efficiency of use of the recommended vitamin and mineral additive and calculated on its basis premixes. Its application made it possible to increase the quality of bull of sperm production on 3,6-10,8%