Polymorphisms Of Prolactin Gene, Growth Hormone Receptor Gene And Their Correlation With Milk Production Traits In Cows

Background Prolactin is a polypeptide hormone with multiple functions,secreted mainly by the anterior pituitary gland. Gene disruption experiments proved their mandatory role for mammary gland development, lactogenesis, and expression of milk protein genes. The growth hormone receptor (GHR) is a member of the prolactin and growth hormone receptor super family. GHR through binding to GH plays an important role in animal metabolic process like growth and development .Therefore the bovine prolactin gene (PRL) and GHR gene seem to be excellent candidates for linkage analysis with quantitative trait loci (QTS) affecting milk production traits. Allelic variation in the structural or regulatory sequences of the PRL gene and GHR gene would be of interest because of the possible direct or indirect effect on milk production. SNPs occurring within the prolactin gene may influence the chemical composition of milk.Objectives To evaluate whether PRL and GHR gene polymorphisms might be associated with the milk production traits in Chinese Holstein cows.Methods The study included 300 DNA sanmples of Chinese Holstein cows. All genotyping were identified by the methods of PCR-RFLP and CRS-RFLP. Software Primer Premier 5.0 and Oligo 5.0 were used to design all the primers.The associations between variants of the genes and milk performance traits were analyzed by the GLM procedure (SAS 9.0).Results About PRL 8398 site, the frequency of allele A and G is 0.257 and 0.743 respectively. The frequency of genotype AA,AG and GG is 0.010, 0.497 and 0.493 respectively. In lactationâ…¡,The least squares of protein percentage of this population was higher for genotype GG than for genotype AG (P<0.05) . The least squares of milk yield of this population was higher for genotype AG than for genotype GG (P<0.01). About PRL 8377 site, the frequency of allele C and G is 0.815 and 0.185 respectively. The frequency of genotype CC,GC and GG is 0.655, 0.320 and 0.025 respectively. The least squares of milk yield of this population was higher for genotype GG than for genotype CC and GC(P<0.05). The least squares of protein percentage of this population was higher for genotype GC than for genotype CC (P<0.05). About PRL 8510 site, the frequency of allele C and T is 0.204 and 0.796 respectively. The frequency of genotype CC,TC and TT is 0.204, 0.000 and 0.796 respectively. The least squares of milk yield of this population was higher for genotype CC than for genotype TT (P<0.05). About GHR 4962 site, the frequency of allele C and G is 0.628 and 0.272 respectively. The frequency of genotype AA,TA and TT is 0.469, 0.317 and 0.214 respectively. The least squares of fat percentage of this population was higher for genotype TT than for genotype AA (P<0.05).Conclusion About PRL 8398 site, allele G is a positive allele to inhance protein percentage, while allele A is a positive allele to inhance milk yield. About PRL 8377 site, allele G is a positive allele to inhance protein percentage and milk yield. About PRL 8510 site, allele C is a positive allele to inhance milk yield. About GHR 4962 site, allele T is a positive allele to inhance fat percentage. In conclusion, we established a quick and effective method to identify the 8398, 8377, 8510 locus of PRL and 4962 locus of GHR in Chinese Holstein cows. We further confirmed that these sites were significantly associated with dairy production traits. So we could take these genes as candidate molecular markers and apply them to dairy cattle breeding using maker assisted selection(MAS), which could increase the accuracy and efficiency of selection an improve the production of Chinese Holstein rapidly and effiectively.