Relationship between polymorphisms of growth hormone gene with milk yield and its components in Iraqi cattle bred of Janoubi, Cross and Holstein

This study aimed to identify the polymorphic SNPs of the growth hormone gene and their association with milk yield and its chemical components. A total of 24 cows were collected from local cattle belonging to Janoubi, cross, and Holstein breeds (8 cows each). Blood and milk samples were taken from each cow. The chemical composition of milk included moisture, protein, fat, solid not fat, and casein. PCR and sequencing of the growth hormone gene were performed to determine the polymorphic SNP. The results indicated that there is a polymorphic SNP at 172 bp (C A), as it changed from the genetic code (AGG) to the genetic code (CGG), both of which encode the amino acid Arginine. Two genotypes were observed for Janoubi and three for the cross. AA genotype exceeded other genotypes in daily milk yield, total milk yield, adjusted milk yield, and fat%.