Genetic potential of Sindhi cattle for A2 milk production

Context. Cow milk is consumed in many countries. However, its consumption can be associated with gastrointestinal disorders in humans. The genetic profile of beta-casein is one of the factors responsible for these disorders and the A1 variant is a causal agent. The beta-casein A1 leads to the formation of bioactive peptides, which trigger intestinal reactions. The same is not observed for the A2 allele. A2 milk is obtained from cows with the A2A2 genotype. The identification of breeds and selection of animals for A2 milk production is important for public health and animal production. The Sindhi cattle (Bos taurus indicus) possesses characteristics such as adaptation to hot climate, resistance to parasites and utilisation of low-quality forage that are important for rearing in the tropics. Aims. The objective of the present study was to genotype the single-nucleotide polymorphism (SNP) that forms A1 and A2 alleles of the beta-casein in Sindhi cattle. Methods. In total, 348 Sindhi animals were used. DNA was extracted from hair follicles and submitted to PCR-sequencing for genotyping. Key results. Allele frequency for A2 was 0.94 and for A1 it was 0.06. Genotype frequencies were 0.90 (A2A2), 0.09 (A1A2) and 0.01 (A1A1). The frequency of the A2A2 genotype in Sindhi cattle was similar to or higher than those found in zebu breeds and higher than those reported for specialised taurine breeds. Conclusions. This high frequency of the A2A2 genotype indicates a genetic potential of the breed for A2 milk production and easy, assisted selection (if that is the intention).