The objective of the research was to analyse the influence of selected genetic groups on the daily milk yield and its chemical composition in black and white Holstein-Friesian cows. The genotyping of beta-lactoglobulin and kappa-casein genes was conducted by means of the PCR-RFLP technique. The collected numeric data were analysed statistically with the covariance analysis. The joint effects of beta-lactoglobulin and kappa-casein genotypes were estimated. The greatest amount of milk was obtained from the genotype combination AAAB, whereas the milk of the genotype combination AABB was characterized with the greatest fat content. The smallest number of samples was collected from cows with genes that are preferred in terms of technological processing, combination BBBB. During test milking, the BBBB genotype combination was characterised by high milk yield and protein content, but also the highest content of somatic cells in milk samples under analysis.
