Genetic Diversity of the Beta-Casein Gene in Brown Swiss and Creole Cattle From the Peruvian Highlands.

Cattle's milk and derivatives are essential for human nutrition. However, up to 90% of people experience gastrointestinal discomfort after consumption. Milk digestibility depends on its protein composition. Casein, about 80% of milk proteins, includes beta-casein (CSN2) with two variants: A1 and A2. The A1 variant is linked to gastrointestinal issues, while A2 is easier to digest. Therefore, some dairy farms now market A2 milk from cattle homozygous for the A2 allele. This study aimed to evaluate the genetic diversity of the CSN2 gene in Brown Swiss and Creole cattle in the Andes of Peru (Junín, Huánuco, Pasco, Ayacucho and Puno). Blood from 445 Brown Swiss and 190 Creole was collected, DNA extracted with a commercial kit, and genotyped using the Axiom Bovine v3 SNP array. The distribution of A1 and A2 alleles and genotypes showed variation across breeds and regions, likely influenced by local breeding practices and selection programs. In Brown Swiss, the average A2 allele frequency was 0.66 (0.60 to 0.73) and the genotypic frequencies of A2A2 was 0.43 (0.35 to 0.52) and the A1A2 frequency was 0.45 (ranged from 0.41 to 0.50). In Creole, the A2 allele frequency was 0.60 (0.55 to 0.66), and the A1A2 genotypic frequency was 0.53 (0.49 to 0.56), being the most common. In conclusion, the frequency of the A2 allele was high in Creole but intermediate in Brown Swiss. These results suggest that the Brown Swiss and Creole have a favorable genetic potential for A2 milk production in the Highlands of Peru.