Kappa-casein (CSN3) and beta-lactoglobulin (LGB) loci affect milk yield traits and the quality of milk protein. Their polymorphisms explain the role of genetic variance and facilitate estimation of breeding value. Our research was aimed at estimating the effect of beta-lactoglobulin and kappa-casein genotypes on milk yield and the chemical composition of milk, for cows bred in three herds in the kujawsko-pomorskie province. We divided the cows into three groups depending on their beta- lactoglobulin and kappa-casein polymorphisms: AA, AB and BB. The percentage of AB LGB heterozygotes in the examined population was the highest, at 44%; whereas the frequency of both gene alleles was at a similar level. In the kappa-casein gene, we found that there was a predominance of AA CSN3 genes (0.69), and a small percentage of BB CSN3 genotypes (0.07). We also observed a higher frequency of the A allele (0.81) as compared to the B allele (0.19), which is desired in breeding. Analysing the influence of the examined factors, we established a statistically significant influence of the barn as well as interactions between the barn and the LGB and CSN3 genotype on the percentage of fat and protein in milk from all examined lactations. Milk yield is influenced by the interaction between examined genotypes and the LGB genotype. The highest fat and protein content in the first lactation was found in animals with the AB LGB genotype: 4.53% of fat and 3.41% of protein. In lactations 2 and 3, the highest values for these parameters were noted for cows with the AA LGB genotype. As to the kappa-casein gene, we observed that cows with the AA CSN3 genotype constituted the largest group. Heterozygous animals produced the highest amount of milk with higher fat and protein yield as compared to the other groups.
