For production of milk the breeds of highly productive dairy cows of domestic and foreign selection are used. These breeds include the Black-and-white mottled breed, which makes up more than 51% of the total cattle herd in Russian Federation, and the Holstein breed, which share is more than 15% and is constantly increasing. It has been established that cows with different kappa-casein genotypes differ in usability of their milk for cheese production. The research of influence of kappa-casein genotype on milk yield capabilities of cows and the reasons for culling of cows is relevant and of interest nowadays. The biggest share of the herd consists of cows with AA genotype, and the least share, 3.8%, consists of the most favorable BB genotype cows. These cows feature higher milk yield. Though there was no significant difference between the milk yield of cows with genotype BB and genotypes AA and AB, but a tendency for BB genotype superiority was clearly observed. The higher milk yield determines a higher yield of nutrients with milk. The group with the AB kappa-casein genotype accounted for a greater share of culled cows in the first lactation period. The lower rejection rate was recorded in the group of BB genotype cows.

In Sverdlovsk region Holstein black-and-white cattle of the Ural type are bred, which are represented by highly productive animals with a high genetic potential for productivity. The aim of the work was to study the effect of genotypes of the kappa-casein gene on milk productivity and quality indicators of milk from Holstein black-and-white cattle of the Ural type. Most of the cows had the AA kappa-casein genotype, and they had the worst indicators of technological properties in terms of cheese suitability. The best technological properties of milk are possessed by cows with the BB kappa-casein genotype. There were only 4.2% of such animals among those examined. The highest milk yield in 305 days of lactation was observed in cows with the genotype for BB kappa casein (9595 ± 314.3 kg), which is 373 kg and 537 kg more, or 3.9 and 5.6% more than in animals with AA and AB genotypes, respectively. The indicators for the mass fraction of fat and mass fraction of protein in the milk of cows of different genotypes for kappa-casein were the same. There was a tendency to an increase in the protein content in the milk of cows with the BB genotype and a decrease in the mass fraction of fat in the milk of cows with the AB genotype. Thus, more nutrients, namely milk fat with the same content in milk, were obtained in the group of first-calf heifers with the BB genotype (380 ± 13.19 kg). They also had a higher yield of milk protein (311 kg), which is more than in other groups by 13 and 19 kg.