Relations between genetic variants of kappa-casein and beta-lactoglobulin and performance of Black and White and Polish Red cattle

Performance of 184 cows from 4 herds of Black and White (SR) and 178 cows f rom 4 herds of Polish Red breed (RP) was compared due to genotype encoding milk proteins: kappa -casein and beta -lactoglobulin. Frequence of inividua l genotypes differend significantly both between herds within the breed. St atistically significant influence of genotype was found in relation to milk fat content in SR cattle (kappa -CNAA > kappa -CNBB and beta -LG(BB) >beta - LG(AB) > beta -LG(AA)) and in RP cattle milk protein yield (kappa -CNBB > kappa -CNAA) and fat content (beta -LG(AA) > beta -LG(AB) and beta -LG(BB) ). The highest protein content and protein yield in milk was found in cows of both breeds carrying kappa -CNBB genotype (P>0.05). Significant relation with the age of first calving was stated in SR cows: kappa -CNAA > kappa - CNAB, in RP cows kappa -CNBB > kappa -CNAB and in SR cows beta -LG(BB) >bet a -LG(AB). Other traits such as longevity, life-time number of calvings and lactations, life-time yield were not found significantly related to search ed genotypes although some trends were observed.