Status of β-casein (CSN2) Polymorphism in Frieswal (HF X Sahiwal Crossbred) Cattle

Cow milk is a rich source of protein and selected micronutrients such as calcium. Recently, a relationship between disease risk and consumption of a specific bovine β-casein fraction either A1 or A2 genetic variants has been identified. Polymorphism at codon 67 of the beta-casein gene: CCT→CAT causes a substitution of amino acid proline (in A2 variant) by histidine (in A1 variant). The presence of histidine residue at codon 67 makes A1 variants exclusively vulnerable to gastrointestinal proteolysis digestion to release bioactive peptide, beta-casomorphin-7 (BCM-7) which has been implicated in potential risk of human cardiovascular disease, type 1 diabetes, atherosclerosis and sudden infant death syndrome. Furthermore, consumption of milk with A2 variant may be associated with less severe symptoms of autism and schizophrenia. Besides, A2 variant has also been reported to have positive relationship with milk production traits especially protein and milk yield. Considering the importance of CSN2 polymorphism with health promoting properties and milk production traits, the present investigation was undertaken to explore A1/A2 polymorphism in crossbred, Frieswal (HF X Sahiwal; N=172) cattle population using allele-specific PCR. All the three possible genotypes (viz., A1A1, A1A2, and A2A2) were identified in Frieswal population. The sequences, specific to A1 and A2 allele, were submitted to GenBank (JQ408387 and JQ408386). The distribution of three genotypes was in Hardy-Weinberg equilibrium [χ test (P>0.05)]. 250 Indrajit Ganguly et al Overall frequency of A2 allele in the population observed to be 0.65. Gene heterozygosity, gene homozygosity, fixation index, polymorphism information content (PIC) were calculated. The observed heterozygosity (0.41) and PIC value (0.351) pointed towards the existence of medium genetic variability in the tested population. Present value of fixation index (0.110) revealed that random mating is being practiced in the population. In view of healthfulness of A2 milk as well as positive relationship of A2 allelic variant with milk performance traits in different cattle breeds, the existing variability of β-casein (A1/A2) locus in Frieswal population may be exploited near future for genetic selection once detail associations study of A1/A2 polymorphism with milk production traits in large number of Frieswal cattle is available.