Casein (CSN) gene variants and parity affect the milk protein traits in crossbred (Bos taurus x Bos indicus) cows in sub-tropical climate

Genotypes at four casein (CSN) loci-A26181G of CSN1S1, C6227T of CSN1S2, A8101C of CSN2, and A13104C of CSN3-along with non-genetic factors were studied for their effects on various milk protein traits in 100 crossbred cows with major inheritance of Holstein Frisian (Bos taurus) and Tharparkar (Bos indicus). Results demonstrated the presence of all CSN genotypes with a predominance of heterozygotes. At CSN2 (A8101C; His67Pro) locus, the A2 allele, desirable for human health, was present in 62% as heterozygous and 29% in homozygous condition. Among non-genetic factors, parity of the cows had a significant influence on the milk protein traits in these crossbreds. The genotypes at CSN1S1, CSN2, and CSN3 loci were found to influence (p<0.05 to 0.01) the casein and whey protein yields and composition traits. The casein index and total milk yield were most influenced by the CSN1S2 locus. The AA (A1 milk) genotype of CSN2 had significantly higher yields and percentages of casein and whey proteins. Positive influence of CC genotype of CSNS3 on milk proteins of was observed similar to Bos taurus cows; however, such influence of AA genotype of CSN2 locus may be distinctive to the crossbred cows maintained in subtropical condition. Overall, the results revealed the diverse effects of CSN genotypes on milk proteins in crossbred cattle.