MILK PROTEIN POLYMORPHISM IN DANISH DAIRY-CATTLE AND THE INFLUENCE OF GENETIC-VARIANTS ON MILK-YIELD

In milk samples from 549 cows of the breeds Danish Jersey, Red Danish Dairy Cattle (RDM), and Black and White Danish Dairy Cattle (SDM) the genetic polymorphisms of the αs1, β and k-casein and β-lactoglobulin (β-Lg) loci were determined by isoelectric focusing in agarose gels. The results of the screening were compared with results obtained by Larsen & Thymann (1966). In addition, the genetic linkage of the three casein loci was studied, and the association between milk protein genotypes and yields in first and second lactations of milk, fat and protein were investigated. The distribution of genotypes of all four milk protein systems was different from breed to breed. For Jersey cows, significant differences in the gene frequencies from the results of the 1966 investigation were found for αsl and K-casein and β-Lg. For SDM cows a change in the k-case in frequency had occurred whereas for RDM cows no changes were found. Linkage between some of the casein loci was found within all three breeds. For the R DM breed the possible linkage between as1-casein and the other caseins could not be tested because nearly all the cows were homozygous for the αs1-cascin-B genotypes. β-Casein genotypes were associated with yield parameters in all breeds. The A2 A2 genotype of this protein gave higher yields of milk, fat, and protein in the second lactation than the A1A1 genotype. © 1990, Proprietors of Journal of Dairy Research. All rights reserved.