Screening of taurine and crossbred breeding bulls for A1/A2 variants of β-casein gene

Abstract

Amongst the 13 known allelic variants of b-casein gene, A1 and A2 are reported to be the most common forms in dairy cattle. A1 allele of β-casein has been implicated as a risk factor to several health disorders in human beings whereas milk with A2 allele, β-casein is considered safe for human consumption. Different studies in recent past have shown widespread presence of β-casein A1 allele in European Bos taurus cattle. In our country, extensive use of taurine germplasm under genetic improvement program could disseminate such undesirable allele in Indian native cattle breeds. The present study targeted several exotic (51 Holstein Friesian, 40 Jersey) and crossbred (89) bulls approved for genetic improvement programmes in India so as to determine their existing status of A1/A2. The frequency data indicated predominance of the desirable A2 allele across all cattle types studied with a mean frequency of 0.645. Among the genotypes, A1A2 was more common in Holstein Friesian and Jersey while A2A2 was at higher frequency in the crossbreds. The study suggested that screening of all breeding bulls for their A1/A2 variant status would be a promising way to check the flow of undesirable alleles in our native breeds. The study also revealed that moderate to high frequency of A2 allele among the crossbred bulls further favours the current belief that milk being marketed in India is safe for human consumption.