Relationship of GHRL Gene Polymorphism with Milk Production and Components in Holstein Cows

Abstract

Abstract The current study was conducted in private station located in the middle of Iraq by using 100 samples of blood to determine the effect of GHRL gene polymorphism on milk traits in Holstein cows. Results showed two alleles with co-dominance and three genotypes was detected in the site -97, the allele frequency was 0.72 and 0.28 for G and A allele respectively. Results showed a significant effect of SNP on lactation period length (P<0.01). The cows with mutant genotype (AA) were the longest lactation period (241 day) while the cows with wild genotype were the shortest lactation period. Total milk yield affected significantly (P<0.01) by allele type, the highest quantity of milk yield was in cows with mutant genotype namely, 3366.77 Kg. High significant differences in daily milk yield were reported in cows according the alleles type, AA cows genotypes achieved 13.97 Kg /day compared with the cows with GG genotype which achieved 8.82 kg/day. Milk components such as lactose and protein were affected significantly (P<0.01) by GHRL gene SNP, the highest rate of lactose and protein were noticed in cows with wild genotype namely, 5.45 and 3.60% respectively. Milk fat differed significantly (P<0.05) in cows depending on its genotype, the highest rate was recorded in cows with wild genotype (GG) namely 3.90%.