Abstract. Title of the paper: Relations between genetic variants of κ-casein and ß-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 from 4 herds of Polish Red breed (RP) was compared due to genotype encoding milk proteins: κ-casein and ß-lactoglobulin. Frequence of inividual genotypes differend significantly both between herds within the breed. Statistically significant influence of genotype was found in relation to milk fat content in SR cattle (κ-CN^AA> κ-CN^BB and ß-LG^BB >ß- LG^AB > ß-LG^AA) and in RP cattle milk protein yield (κ-CN^BB > κ-CN^AA) and fat content (ß-LG^AA > ß-LG^AB and ß-LG ). The highest protein content and protein yield in milk was found in cows of both breeds carrying KCN^BB genotype (P>0.05). Significant relation with the age of first calving was stated in SR cows: κ-CN^AA > KCN^AB, in RP cows κ-CN^BB > κ-CN^AB and in SR cows ß-LG^BB >ß-LG^AB. Other traits such as longevity, life-time number of calvings and lactations, life-time yield were not found significantly related to searched genotypes although some trends were observed.