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 conditions of the Republic of Belarus the seasonal derangements of metabolic processes at high-producing cows usually take place in the period from March till May. Analysis of efficiency of application of national preparation CMP (complex-mineral preparation -iron (15 mg/ml); iodine (6,8 mg/ml); magnesium (6,0 mg/ml); selenium (0,32 mg/ml) and vitamin preparation Trivitim (vitamin A – 30000 IU; , vitamin D – 40000 IU; vitamin E – 20 mg) for the preserving of high milking yielding capacity and prevention of metabolic processes disorders was realized. Four groups of high productive cows were formed. First group was entered 10 ml of CMP intramuscular; cows of the second group were entered 10 ml of Trivitim intramuscular; cows of the third group were entered CMP and Trivitim in the same doses; and the fourth group was a controlled one. On the 1-st, 7-th and 15-th days there was realized evaluation animal clinical state, hematologic and biochemical blood indexes (leukocytes; erythrocytes; hemoglobin; thrombocytes; ESR; total protein; albumins; urea; creatinine; glucose; calcium; phosphorous; magnesium; iron), and average daily milk yield. There was also analyzed the phagocytic activity of neutrophilic leukocytes. Research results showed that content of leukocytes and ESR in blood in all experimental groups was within the standard limits. In the first experimental group there was state the increasing of hemoglobin (from 91,4 +/- 4,38 up to 111,83 +/- 4,3 g/l (P less than0,05) ) and erythrocytes (from 4,48 +/- 0,21 up to 5,97 +/- 0,45 10E12/l) content. The same changes were stated in cows of the 2-d and 3-d experimental groups. Content of hemoglobin and erythrocyte in blood of cows which were administrated with CMP and Trivitim increased from 90,6 +/- 0,06 to 99,83 +/- 3,61 g/l and from 4,51 +/- 0,27 to 5,55 +/- 0,28 10E12/l, respectively. Analyze of biochemical indexes of cow blood showed that content of total protein, calcium, phosphorus, magnesium and iron increased. On the 15-th day there was stated the decrease of urea. Research results proved that the combined application of CMP and Trivitim was efficient and prevented subclinical disorders of metabolic processes

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.

Factors which increased milk productivity (age and continuance of service period) were studied in the conditions of an educational establishment of the Republic of Belarus by an example of cows of black-and-white breed. Dynamics of growth of milk productivity in course of 8 research years was presented. Analysis of interrelation between cow productivity and cow age was given. Mathematical calculation of relations between cow productivity indexes (milk yield, fat content, butter fat) and service period duration was given. Research results showed that increasing of an average term of economic use of cows and decreasing of duration of service period up to 90 days made it possible to increase dairy effiiemcy and herd reproduction, as well as obtain higher economic efficiency

Determination of influence of polymorphic variants of genes of kappa casein, beta-lactoglodulin and alpha-lactoalbumin on indexes of milk producing ability (milk yield, fat and protein content) of brood cows of Belarusian white-and-black breed was studied in the conditions of the Republic of Belarus. In course of analysis of polymorphism of kappa casein gene there was revealed the exceeding of frequency index of allel CSN3**a over the index of allel CSN3**b (0,795 and 0,205 respectively). Studying of polymorphism of beta-lactoglodulin gene showed that the frequency indexes of allel variants formed in the following way: BLG**a - 0,489 and BLG**b - 0,511. There were revealed three genotype variants of alpha-lactoalbumin among which the highest frequency indexes were stated for heterozygous genotype LALBA**aa *(32%) and LALBA**bb (14%). There was calculated the genetic equilibrium for loci of studied genes: x2 value for all studied loci was 0,008 – 1,96. Analysis of milk producing ability data in groups with different genotypes by locus of CSN3 gene showed that the highest indexes of milk yield were stated for group of cows with genotype CSN3**aa. Animals with genotype CSN3**bb had the highest fat percent, animals with genotype CSN3**aa - the lowest. Analysis of milk yield indexes showed that animals with homozygous genotypes BLG**aa and BLG**bb showed lower average milk yield than animals with genotype BLG**ab on 130 and 570 kg, respectively

An effort to demonstrate the mechanism of homeostatic alteration of high-producing cows at the period of increasing milking capacity and peculiar features of its changing in the conditions of introduction into cattle diets of carbohydrate containing and carbohydrate compensative additives was realized in the conditions of the Republic of Belarus. In course of the experiment there were used white-and-black breed cows of 3-4 lactations with body weight of 700 kg and milk yield over the last lactation of 7000-8000 kg of milk. Experimental cows in two weeks before the supposed calving were administrated with 50 ml of propylene glycol, 6 g of niacin and 50 ml of glycerin; and in course of 60 days after calving the administration of the additives was realized in doses of 125 ml; 6 g; 50 ml, respectively. Research results showed that application of mentioned above additives rendered the positive effect on cow liver that was proved by the improved hemic function of experimental cows: increasing of quantity of erythrocytes, hemoglobin, and hematocrit