Identification of κ-Casein Genotype in Holstein Sires: A Comparison Between Analysis of Milk Samples from Daughters and Direct Analysis of Semen Samples from Sires by Polymerase Chain Reaction

Abstract

Two different methods were used to determine κ-casein genotypes of Holstein sires. In the earlier procedure, genotypes of sires were deduced by analyzing frequency distribution data of κ-casein variants obtained through typing of milk samples from daughters by electrophoresis. The second method involved direct analysis of DNA obtained from semen samples of the sires. The polymerase chain reaction was used to amplify a 99-bp region from the κ-casein gene that contains nucleotide substitutions that are diagnostic of variants A and B. Identity of the amplified product was confirmed by sequencing. Results obtained by both methods of genotyping were similar. For the 42 sires that were analyzed by both methods, the distribution of κ-casein genotypes were 31 AA, 11 AB, and 0 BB. The frequency of B allele for κ-casein in the sire population studied was lower than in larger Holstein cow populations. Due to the high demand for κ-casein B milk by the dairy industry, it might be advantageous to increase this allele in the dairy cattle population by identifying sires with homozygous κ-casein B and using them more frequently as service sires.