Effects of Selection Practiced on the Frequencies of κ-Casein and β-Lactoglobulin Genotypes in Canadian Artificial Insemination Bulls

Abstract

The gene and genotypic frequencies at κ-casein and β-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 κ-casein and β-lactoglobulin genes. A total of 641 Holstein, 132 Ayrshire, and 20 Jersey bulls were genotyped for κ-casein A and B alleles. Of these bulls, 600 Holstein, and all of the Ayrshire and Jersey bulls were also typed for β-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 κ-casein and β-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. No significant difference in genotypic frequencies existed among the bulls returned for service and those not returned regardless of breed and milk protein type. No adverse effects of milk protein genotypes on fitness were found. This result implies that the methods used for selection of young bulls to return to service had no significant effect on the frequency of the genes and distribution of the milk protein genotypes studied.