In the conditions of the Republic of Belarus there was realized the evaluation of genetic inheritance indexes of producing bulls at a cattle breeding enterprise in Belarus depending on a selection source (in accordance with an average productivity of female ancestors) in order to use them properly for the increasing of genetic potential of black-and-white Belarusian cows in Gomel region. The carried out analysis allowed to draw a conclusion, that bulls of national breeding lines according to the indexes of cow milk yields concede foreign bulls, i.e. delivered of Sweden on 2744 kg of milk or on 27,5% and from Russia and Hungary - on 1272-2906 kg of milk or 12,7-29,1% (Р less than 0,001). In accordance with butter-fat yielding capacity of bull mothers obtained at breeding farms of Belarus and in accordance with groups delivered from the other countries there were stated no essential distinctions (0,05). Butter-fat yielding capacity percentage of bull mothers varied within 3,99-4,10%. However, the yield of dairy fat per lactation the difference was in favour of bull mothers delivered from Sweden (114 kg or 27,9%) at P less than 0,001. Distinctions on milk producing ability of bull mothers from various cattle breeding enterprises of Belarus were revealed. It was established, that at mothers of bulls delivered from Hungary the variability of milk yield was the highest (3032 kg or 23%). Low variability indexes of milk yield and butter-fat yielding capacity percentage was typical for bull mothers of the Belarusian selection. The standard deviation at them made 872 kg of milk yield with 9% variability coefficient, and 0,03% - for butter-fat yield and 7% respectively. Variability on all indicators of dairy efficiency of bull mothers from various cattle breeding enterprises of Belarus in most of the cases was low - from 2,3 to 13%.

In the conditions of the Republic of Belarus there were analyzed indices of impregnating ability and efficiency of stud bull mothers of various genotypes on a kappa-casein gene (CSN3). As a result of genotyping of kappa-casein gene by DNA-diagnostics method it is revealed three genotypes - CSN3АА, CSN3AB, CSN3BB. Frequency of occurrence of homozygous genotype CSN3AA at stud bulls - 87,3%; heterozygotic CSN3AB - 20,5%; homozygous CSN3BB - 1,2%. Statistically authentic difference between these indices depending on a genotype it is not established. Thus, authentic connection between indices of impregnating ability and efficiency of stud bull mothers and their genotype on a locus of a kappa-casein gene that specifies in absence of influence of the last on the given indices is not established and gives the chance to conduct selection on gene CSN3 without decrease in breeding value of stud bulls on reproductive qualities.

In the conditions of the Republic of Belarus there was analyzed the influence of the following paratypical factors on cow productive longevity: age of the first calving; milk yield at the first lactation; and a birth season. At the experimental animals there studied the indices of dairy efficiency: a lifelong milk yield (kg); a lifelong yield of dairy fat (kg); the total duration of the lactation period (days); duration of practical use (lactations). There was noted a tendency of increasing of a term of productive use and lifelong productive efficiency at the animals the practical economic use of which was begun in later terms. The insemination of these animals was approximately realized at the age older than 21 months. Also it was stated that in accordance with all investigated indices (except for a milk yield per one day of lactation) the highest indexes were typical for cows which had the least milk yield at the first lactation.

The study has stated that heifer replacements, from the date of birth to 18 months, got through transplantation of frozen-defrosted embryos were not inferior to and in many cases superior to the heifers of their age but got through traditional reproduction. Transplant first-calf heifers have a high level of milk productivity which amounts to 7536,10 kilos, with 3,62% of fat and 3,23% of protein. Thus they provide a good selection material for new generation champions to be chosen among them and for being used as mothers of bulls for service

In the conditions of the Republic of Belarus there was studied a therapeutic effectiveness and influence on milk productivity of 22% Timbendazole after spontaneous infestation of cows with fascioliasis (Fasciola hepatica). As a result of studies the Timbendazole 22% proved to be highly efficient against Fasciola hepatica in cattle – from 92,9% up to 100% (in comparison with Albendatimum-100 granulated material the efficiency of which was 88-90%). As a result of cows treatment by anthelmintics – Timbendazole 22% and Albendatimum-100 against Fasciola hepatica there was stated the substantial increasing of milk productivity of animals (on 23,4 and 11,0%, respectively) in comparison with animals which were not administratec with mentioned above preparations.

Investigation of peculiar features of productive and reproductive qualities (milk producing ability; reproductive qualities; live weight at different ages) of milking cows of white-and-black breed was realized in the conditions of CJSC Lipovtsy of Vitebsk region of the Republic of Belarus. On the basis of obtained results there was calculated the selective differential of milk yield and butter-fat yielding capacity which were increased by means of maternal and father's cattle; genetic progress through selection in reliance on generation and target standard for the analyzed herd, as well as the minimal requirements to first-calf heifer productivity.Research results showed that average milk yield in the analyzed herd was 5204 kg with average butterfat percentage 3,59%; for first-calf heifers – 4838 kg with butter-fat yield of 3,47%. Productivity of first-calf heifers and cows was higher than the standard valuation requirements to milk yield on 1350-1588 kg

In the research the genetic structure of populations of bulls Vitebsk of cattle breeding state farm and cows of Belarusian Black-and-White breed of Joint-Stock Company Olgovskij of Vitebsk region (Republic of Belarus) on a locus of a gene of kappa-casein was analyzed. As a result of genotyping a gene of kappa-casein by DNA-diagnostics method there were revealed three genotypes CSN3**AA, CSN3**AB, CSN3**BB. Frequency of occurrence of homozygous genotype CSN3**AA at cows has made 69,5%, at bulls of Vitebsk cattle breeding state farm - 78,3%; heterozygotic genotype CSN3**AB - 26,3% and 20,5%; homozygous genotype CSN3**BB - 4,2% and 1,2%, respectively. Frequency of CSN3**A allele in population of cows and bulls has made 0,83 and 0,88; CSN3**B - 0,17 and 0,11%, respectively. The presence of authentic influence of polymorphic variants of a gene of kappa-casein on level of milk yield and fat and protein content in cow milk was stated. The highest milk productivity in course of 305 days of lactation was observed at cows with homozygous genotype CSN3**BB (5984 kg), that was on 890 kg higher than in animals with genotype CSN3**AB (5094 kg), and on 1406 kg higher (Р less than 0,05), than at animals with CSN3**AA genotype (4578 kg). Cows with B kappa-casein allele in genome were characterized by higher fat content in milk (CSN3**AB - 3,61%, CSN3**BB - 3,72%) than animals with a CSN3**AA genotype - 3,60%. Cows with genotype CSN3**BB had higher level of protein in milk (3,28%) in comparison with the animals with CSN3**AA genotype (3,18%). In animals with CSN3**AB genotype the mentioned above index 3,19%. Research results showed that genetic variants of the gene of kappa-casein are important for selection practice as they could be used as breeding-genetic markers which could raise milk yields and protein content in milk

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).

In the conditions of the Republic of Belarus there was studied the efficiency of application of national mineral additives (mineral feed additive produced on the basis of dolomitic meal) in rations of milking cows. In course of the study there were analyzed physical and chemical blood indexes; hematological indexes of cows; biochemical blood indexes; mineral composition of blood; natural resistance of cows. As a result of the realized study it was established, that an optimum dose of a dolomitic meal for milking cows during the winter period was 0,3% per dry matter of a diet. There was proved the possibility of increasing of a daily average milk yield of cows on 11,7%, fat and protein content in milk - on 0,04 - 0,06%, as well as lowering of quantity of somatic cells on 13,6%. Application of a national mineral additive rendered the positive influence on blood indices to what that was proved by increasing of erythrocytes (on 10,9%), thrombocytes (on 5,4%), haemoglobin (on 6,5%), crude protein (on 10,6%), and also macro- and trace elements. Introduction of a dolomitic meal into cow diets made it possible to increase the indices of natural resistance of cows on 0,5 - 4,0%.

In the conditions of the Republic of Belarus there was analyzed the interrelation between the main indexes of cattle milk performance of dairy cattle of Large Red Belarusian breed and Belarusian Black-and-White breed with different genotypes of kappa casein gene. In course of the study there was determined the frequency of occurrence of genotypes and alleles by kappa-casein gene in population of cows of mentioned above breeds. Values of correlation coefficients between some indexes of milk performance of the studied breeds were analyzed. Correlation factors between the basic indexes of milk performance of cows with different genotypes of kappa casein. Research results showed that milk protein content and butter-fat yielding capacity were in negative association with the main breeding trait of dairy cattle – amount of milk yield. Butter-fat yielding capacity and milk protein content correlated positively. Thus, selection breeding in accordance with one of this traits will promote increasing of the other. Besides, it is necessary to realize DNA-diagnostics of cattle according to kappa casein gene and to select animals having in their genomes allele CSN3**B connected with higher milk protein content.