CSN1S1 Gene: Allele Frequency, and the Relationship with Milk Production Traits in Three Indigenous Cattle Breeds and Holstein

CSN1S1 is one of the major genes encoding milk proteins of mammals. In this study we determined allele frequencies of CSN1S1-5` flanking region as well as exon 17 variants and their effects on milk traits in three indigenous cattle breeds Mazandarani, Golpaygani (Bos indicus) and Sarabi (Bos taurus) and Holstein cattle in Iran. CSN1S1*B variant was nearly fixed in Holstein but ranged from 0.40 to 0.66 in indigenous breeds. CSN1S1*C allele had higher frequency in indigenous breeds, especially in Bos indicus. Four genetic variants of the promoter were found in all breeds in different frequencies with allele 2 being the prevalent in all breeds (frequency 0.359 to 0.711) and allele 4 the least frequent (0.074 to 0.011). Allele B of the coding region was found in combination with all four promoter alleles. Allele 4 of the promoter was not found in any cow having the exon 17 allele C in all breeds except Mazandarani. BC / 23 genotype yielded the highest fat percentage (P<0.05) in Holstein but it had no significant effect in Golpaygani. There was not any homozygous CSN1S1*CC cow, to investigate the influence of C variant for fat content. None of the genetic combinations had significant effect on fat yield, although variant '2' of promoter indicated a negative effect. No significant effect among various combined genotypes on milk yield was found, but CSN1S1*B tended to higher milk production. Differences of allelic frequencies and milk production traits found among these breeds might be due to differences in origin of breeds or selection breeding programs.