The identification of the kappa-casein genotype in Holstein dairy cattle using the polymerase chain reaction.

The polymerase chain reaction (PCR) was used to amplify a 99-bp region from the kappa-casein gene of Holstein dairy cattle which contains nucleotide substitutions that are diagnostic of the two major protein variants of kappa-casein. Identity of the amplified product was confirmed by direct sequencing. Digestion of the PCR product with MboII (A-variant specific) or TaqI (B-variant specific) allowed direct determination of the genotype of the animal (homozygous or heterozygous). A total of 58 lactating cows with known kappa-casein phenotype were tested using PCR. In all cases, the measured genotype confirmed the phenotype. We have also tested the genotype of 42 sires that were top ranked for milk yield by the CIAQ (Centre d'insemination artificielle du Quebec). The B-allele of kappa-casein which occurred at a frequency of 0.13 among the proven bulls is associated with superior milk for industrial applications. Identification of the kappa-casein genotype by PCR in bulls and calves would provide a means for rapidly changing the frequency of the B-allele in the breeding population by selection.