To study the polymorphism of β-casein gene and its effecton the quality of cow's milk the research was conducted in the breeding herds of Ukrainian Black-and-White Dairy, Lebedynand Simmental breeds. Genotyping of 200 head of cattle wascarried out. Determination of β-casein gene polymorphismwas performed in the genetic laboratory of Bohomolets Institute of Physiology. The TagMan@Genotyping system and aset of primers and probes were used for allelic discrimination.It was found that the frequencies of alleles A1 (0.294-0.380) and A2 in the locus of β-casein gene differed in animals of different breeds. The highest frequency of the desiredallele A2 had the population of Lebedyn breed cows (0.706),while the lowest was in Simmental ones (0.620). The frequency of A1 allele was the lowest in the cows of Lebedyn breed(0.294), and the highest in Ukrainian Black-and-White Dairybreed (0.380). Accordingly, the frequencies of genotypesA1A1, A1A2 and A2A2 differed depending on the origin. Thedesired genotype was more common in animals of UkrainianBlack-and-White Dairy and Lebedyn breeds (53-52%, respectively). Heterozygous genotype occurred more frequently in animals of Lebedyn and Simmental breeds (37%). Thehighest frequency of A1A1 genotype was characteristic ofanimals of Ukrainian Black-and-White Dairy and Simmentalbreeds (20%). According to the genetic and statistical analysis, there was an excess of homozygous variants of A1A1 andA2A2 in β-casein locus, and a lack of heterozygous A1A2.At the same time in animals of Ukrainian Black-and-WhiteDairy breed, the difference between the actual and expecteddistribution of genotypes was statistically significant.There was a difference in the quality characteristics ofmilk between animals of different genotypes. In animals ofdifferent breeds, the content of certain components of milkdid not vary equally depending on theβ-casein genotype, butthis difference was statistically insignificant.Cows of Ukrainian Black-and-White Dairy breed withhomozygous A1A1 genotype exceeded others in terms offat content, those with heterozygous A1A2 genotype had anadvantage in terms of protein, lactose and dried skimmedmilk remainder (DSMR). Animals of Lebedyn breed with theA2A2 genotype predominated animals of other genotypes inall investigated indicators of milk quality. Animals of Simmental breed with the desired A2A2 genotype had a lower fatcontent in milk compared to animals of other genotypes andthe average values in the sample. These animal together withA1A1 homozygotes had higher protein content in milk thanheterozygous animals and average values in the sample. Inour opinion the small number of experimental animals wasone of the reasons for the lack of a definite difference betweenthe average values of the milk components of cows of different β-casein genotypes.

Key words: breed, fatcontent, proteincontent, kappacasein, genotype, allele, sire.