Genetic variation of PRLR gene and association with milk performance traits in dairy cattle

Prolactin plays an important regulatory function in mammary gland development, milk secretion, and expression of milk protein genes. Prolactin exerts diverse functions in its several target tissues through specific membrane receptors. Hence, prolactin receptor (PRLR) gene is a potential quantitative trait locus and genetic marker of milk performance traits in dairy cattle. In this study, the genetic polymorphisms of part of the PRLR gene were detected in a population of 385 cows of Chinese Holstein dairy cattle to determine the association between PRLR gene and milk performance traits. Using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and sequencing, two alleles in exon 3 and three alleles in exon 7 of PRLR gene were identified. Four of the detected SNPs lead to the amino acid substitution. Statistical results indicated that PRLRE3 and PRLRE7 loci were significantly associated with milk yield (P < 0.01), and fat percentage (P < 0.05). The cows with genotypes AB had significantly higher milk yield (P < 0.05), and cows with genotypes AA had significantly higher fat percentage (P < 0.05) in locus PRLRE3. The cows with genotypes BB had significantly higher milk yield (P < 0.05), and fat percentage (P < 0.05) in locus PRLRE7. In addition, based on the nine genotypes constructed from 13 combined genotypes, the association analysis between combined genotypes and milk performance traits was carried out. Results show that the cows with combined genotypes ABBB had significantly higher milk yield and fat percentage. Our finding implies that PRLRE3 and PRLRE7 loci of the PRLR gene would be useful genetic markers in selection program on milk performance traits in Holstein dairy cattle.