STUDY OF β-CASEIN GENE POLYMORPHISM AND ITS RELATIONSHIP WITH MILK COMPOSITION OF UKRAINIAN BLACK-AND-WHITE DAIRY COWS

Abstract

In the breeding herds of the Ukrainian Black-and-White Dairy breed, the research was conducted to study the polymorphism of β-casein gene and its effect on the qualitative composition of cow's milk. Genotyping of 146 heads of cattle was carried out. Determination of β-casein gene polymorphism was performed in the genetic laboratory of Bohomolets Institute of Physiology. The TagMan@Genotyping system and a set of primers and probes were used for allelic discrimination. It was found that the frequencies of alleles A1 (0.421) and A2 (0.579) in the locus of β-casein gene were different, the latter being higher. Consequently, the frequencies of genotypes A1A1, A1A2 and A2A2 were different, 25%, 35% and 40% respectively. According to genetic and statistical analysis, there was an excess of homozygous variants of A1A1 and A2A2 in the β-casein locus, and a lack of heterozygous A1A2. There was a difference in the quality characteristics of milk between animals of different genotypes. The content of individual milk constituents did not vary equally depending on the β-casein genotype, but this difference was statistically insignificant. The average content of constituents in the milk of cows corresponded to the breed standards in terms of fat content and was slightly inferior to it in terms of protein content. Cows of Ukrainian Black-and-White Dairy breed with heterozygous A1A2 genotype exceeded others in terms of protein, lactose and dried skimmed milk remainder. Homozygous genotypes A1A1 and A2A2 had higher fat content in milk than heterozygotes. As there is no statistically significant difference in the main milk constituents (fat, protein) between animals of different genotypes for β-casein, the formation of herds with A2A2 genotype for β-casein will not adversely affect the productive traits of cows and thus ensure sufficient quality indicators of milk of new herd types. Livestock breeders need to pay some attention to selection and technological measures to increase the protein content in milk.