A note on the evaluation of a beta-casein variant in bovine breeds by allele-specific PCR and relevance to beta-casomorphin

Two genetic variants of the bovine beta-casein gene (A(1) and B) encode a histidine residue at codon 67, resulting in potential liberation of a bioactive peptide, beta-casomorphin, upon digestion. An allele-specific PCR (AS-PCR) was evaluated to distinguish between the beta-casomorphin-releasing variants (A(1) and B) and the non-releasing variants. AS-PCR successfully distinguished P-casein variants in 41 of 42 animals as confirmed by sequence analysis. Overall, while the incidence of the homozygous A, and B animals (i.e., homozygous for the histidine residue; 21.4%) was lower than that for animals without the histidine residue (30.9% respectively), 69% of animals carried at least one allele for the histidine residue at codon 67.