Effect of polymorphic variants of GH, Pit-1, and beta-LG genes on milk production of Holstein cows.

Effect of polymorphic variants of growth hormone (GH), beta-lactoglobulin (beta-LG), and Pit-1 genes on milk yield was analyzed in a Holstein herd. Genotypes of the cows for these genes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Allele frequencies were 0.884 and 0.116 for L and V variants of GH, 0.170 and 0.830 for A and B variants of Pit-1, and 0.529 and 0.471 for A and B variants of beta-LG, respectively. GLM procedure of SAS software was used to test the effects of these genes on milk yield. Results indicated significant effects of these genes on milk yield (P < 0.05). Cows with LL genotype of GH produced more milk than cows with LVgenotype (P < 0.05). Also, for Pit-1 gene, animals with AB genotype produced more milk than BB genotype (P < 0.05). In the case of beta-LG gene, milk yield of animals with AA genotype was more than BB genotype (P < 0.01). Therefore, it might be concluded that homozygote genotypes of GH (LL) and beta-LG (AA) were superior compared to heterozygote genotypes, whereas, the heterozygote genotype of Pit-1 gene (AB) was desirable.