Using real-time polymerase chain reaction methods, we have researched the CSN2 polymorphism gene in 2 populations of cows in the North-East of Ukraine. The observed distributions of genotype frequencies А1А1, А1А2, А2А2 and A1 or A2 alleles varies considerably in different cattle populations of cows: population of brown cattle – 1.7%, 38.5, 59.8% (0.209 and 0.791); black and spotted population – 18.3%, 44.7%, 37.0% (0.406 and 0.594). The ratio of genotypes were found significant differences when comparing genotypes A1A1 (p<0.001) and A2A2 (p<0.001). The results of DNA testing of the beta-casein locus for A1 and A2-allelic variants in stud bulls of the studied populations have shown that the highest frequency of the A2A2 desired homozygous genotype is characteristic of the breeders of brown cattle (46%). The obtained results indicate the prospects of breeding work to create herds with genotype A2A2 animals - specifically with the brown cattle.