Polymorphism has been studied and occurrence frequency of genotypes and alleles by genes of kappa-casein and diacylglycerol O-acyltransferase in first-calf heifers and highly productive black-and-white cows of different genealogical lines has been determined. The highest frequency of CSN3 AB genotype (34.7% and 38.9%) and CSN3 BB genotype (10.2 and 5.6%) has been registered in the first-calf heifers of M. Chiftein and R. Sowering line at the B allele frequency of CSN3 gene – 0.28 and 0.25.