Abstract
The nutritional property of milk depends on its chemical composition and a high degree of digestibility (95-98%) of all organic substances. The composition of milk includes more than 200 components that are complex in chemical structure, many of which nature has not repeated in any other products. Milk protein, fat and lactose are the main components that directly affect the taste and technological properties of milk. The actual content of the main components in commercial milk can vary in wide ranges: protein from 2.8 to 3.6%, fat from 2.8 to 6%, lactose from 4.5 to 4.8%. To determine the polymorphism of kappa-casein genes and evaluate economically useful traits in animals with different genotypes of kappa-casein, only 60 cows were selected, including 20 Holstein cows, 20 Alatau cows and 20 black-and-white cows. The polymorphism of kappa-casein genes was evaluated by PCR analysis. For further research, 3 subgroups of cows were formed in each group according to the principle of analogues, the results of genotyping and kappa-casein gene. The first group included cows with the AA kappa-casein genotype, the second – the AB genotype, and the third – the BB genotype.