Genotyping of Indigenous Cattle Breeds and their Exotic Crosses for beta -casein Milk Type using PCR-RFLP and Sequencing

The role of A1 and A2 AŸ casein milk variants and human health is a subject of concern for scientific investigations. The status of A1/A2 AŸ-casein variants in Bos taurus cattle breeds from several countries have shown presence of A1 variant in European cattle, which has been linked to range of illness. However, information on A1/A2 AŸ-casein variants in Bos indicus and their crosses is limited. Bulls can influence the population structure more profoundly. Hence, the intend of the study was to know the prevalence of variants of AŸ-casein (β-CSN2) in Gir and Kankrej, prominent Bos indicus breeds of the country and crossbred bulls (HF crossbreds) used for artificial insemination. Semen/ blood samples of 226 Gir, 88 Kankrej and 263 crossbred bulls and cows were collected from three semen stations and three non-government breeding farm, in Gujarat. PCR–RFLP and allele specific PCR analysis of the AŸ casein region revealed all three genotypes suggesting prevalence of A1 variant in Gir and Kankrej also. Frequency of A1 allele in the indigenous breeds was much higher than believed earlier. We also report the first case of A1A1 Gir bull. This is probably the first report of prevalence of A1A1 genotype in any of the zebu Bos indius breeds. Crossbred cattle showed prevalence of both variants, A1 and A2 with higher frequency of A2. Further, allelic frequencies confirmed deviation from H-W equilibrium in HF crossbreds but not in Gir and Kankrej. The sequence analysis confirmed SNP ‘C’ to ‘A’ causing replacement of proline by histidine between A1 and A2 AŸ casein. The present study confirmed the earlier theory that A2 allele of AŸ casein is predominant in Bos indicus.