The studies were carried out on Black-and-White cows with various contribution of Holstein-Friesian genes in their genotype. The aim of the study was (1) to analyse the milk performance of the cows with various milk protein genotypes and (2) to relate the obtained results to the milk, fat, and protein yield levels, and the percentage of fat and protein during 305-day lactation. Polymorphic character of the proteins was examined for kappa-casein, beta-casein, alpha-S1-casein, and beta-lactoglobulin. The milk samples for laboratory analyses were collected during a test day between 60 and 120 days of lactation. A positive effect of some genotypes on milk performance traits was found. Consequently, an increase in dairy cow productivity and improvement of technological value of the milk may be achieved through increasing the frequency of desired genotypes in the herd during the selection of the animals for the herd.

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