Effects of selection practiced on the frequencies of κ-casein and β-lactoglobulin genotypes in Canadian artificial insemination bulls

The gene and genotypic frequencies at Kappa -casein and beta -lactoglobulin loci of Canadian AI bulls were investigated to determine the effect of selection of bulls for extensive AI service on the frequency of the two common allelic variants A and B of Kappa -casein and beta -lactoglobulin genes. A total of 641 Holstein, 132 Ayrshire, and 20 Jersey bulls were genotyped for Kappa -casein A and B alleles. Of these bulls, 600 Holstein, and all of the Ayrshire and Jersey bulls were also typed for beta -lactoglobulin A and B alleles. In addition, 88 Holstein embryo donor cows that had been selected for yield and conformation were genotyped for the two loci. The respective frequencies of B allele for Kappa -casein and beta -lactoglobulin were .14 and .55 in Holstein bulls, .11 and .58 in Holstein embryo donor cows, .22 and .59 in Ayrshire bulls, and .92 and .32 in Jersey bulls.