Frequência gênica e genotípica da β-caseína a1 e a2 nas diferentes raças bovinas leiteiras de Uberlândia – Minas Gerais

Abstract

β-casein is a major protein in bovine milk and exists in two predominant genetic variants: A1 and A2. During the digestion of A1 β-casein, β-casomorphin-7 is released—a peptide associated with gastrointestinal discomfort and other potential adverse effects on human health—whereas the A2 variant does not produce this compound. Therefore, this study aimed to determine the gene and genotype frequencies of A1 and A2 β-casein in various dairy cattle breeds from the Triângulo Mineiro region. Hair follicle samples were analyzed from 113 cows belonging to the Holstein, Girolando, and Jersolando breeds, as well as half-blood animals. DNA was extracted and subjected to allele-specific PCR (AS-PCR) to identify A1A1, A1A2, and A2A2 genotypes, followed by agarose gel electrophoresis to visualize the amplified products. The results showed a predominance of the A2 allele across all evaluated categories, with an overall frequency of 69.91%, while the A1 allele showed a frequency of 30.09%. Regarding genotypes, frequencies of 5.31% for A1A1, 49.56% for A1A2, and 45.13% for A2A2 were observed. The Girolando breed exhibited the highest frequency of the A2 allele (83.3%). Furthermore, the high proportion of heterozygotes suggests that the herds are undergoing a genetic transition, likely influenced by selection aimed at A2 milk production. These results highlight the importance of genotyping as a tool for genetic improvement programs, contributing to the selection of A2A2 animals and the development of herds that are more competitive and aligned with consumer market demands.