Study On Genetic Polymorphism Of GnRH, LHR And PRL Genes And Their Relationship With Semen Quality In Chinese Holstein Bulls

According to the regulation mechanism by reproductive endocrine of spermatogenesis and sperm quality, the genes of reproductive hormones and their receptors, as well as other reproductiion related genes were selected as the candidates in the present study. The polymorphisms and therir associations with the semen quality were studied. The purposes of the present study are to analyse the polymorphisms of the candidate genes and their relationship with semen quality, so as to establish methods for moleculte marker-assisted selection of dairy bulls.The candidate genes for polymorphism analysis included Gonadotropin-releasing hormone (GnRH), Luteinizing hormone receptor (LHR) and prolactin (PRL). The parameters of semen quality traits involved in average ejaculate volume, sperm density, sperm motility, frozen sperm motility, acrosome intact rate and deformity rate of the dairy bovine semen. A total of 209 Holstein bulls from four breeding stations were blooded and analysed for gene polymorphism by PCR-RFLP, sequencing and PCR-SSCP. The main results are shown as follows:1. A new mutation locating at exon 2 (A883G) of GnRH gene was found by endonuclease Hinfl resulting in three genotypes named AA, AB and BB in four breeding stations. The allele A was dominant in the sample groups. Association analysis showed that the bulls with AB genotype had better fresh sperm motility than the animals with BB genotype (P<0.05). It can be indicated that the AB genotype of GnRH gene locus had a positive effect on fresh sperm motility, and the allele A was dominant.2. A mutation locating at intron 9 (A51703G) of LHR gene was found by endonuclease Bfal resulting in three genotypes named AA, AB and BB in four breeding stations. The genotype frequency of the gene ranked in AB> AA>BB, which indicated the allele A was dominant. Association analysis showed that the bulls with AB genotype had better fresh sperm motility than the animals with AA genotype (P<0.05). It can be indicated that the AB genotype of LHR gene locus had a positive effect on fresh sperm motility.3. A mutation locating at intron 9 (G51656T) of LHR gene was found by endonuclease Hinfl resulting in three genotypes named AA, AB and BB in three breeding stations. The AA genotype absences in Zhengzhou breeding station. The genotype frequency of the gene ranked in BB>AB> AA, which indicated the allele B was dominant. Association analysis showed that the bulls with BB genotype had better fresh sperm density than the animals with AA genotype (P<0.05), had better fresh sperm motility than AB genotype (P<0.05). The bulls with AA genotype had the lowest acrosome intact rate. It can be indicated that the BB genotype of LHR gene locus had a positive effect.4. A new mutation locating at extron 4 (G7550A) of PRL gene was found by endonuclease Rsal resulting in three genotypes named AA, AB and BB in four breeding stations. The BB genotype absence in Zhengzhou and Tianjin breeding stations. the genotype frequency AA was higher than AB, and the lowest in BB, which indicated the allele A was dominant. Association analysis showed that the bulls with these differences genotype were no siginificant (P>0.05). It can be indicated that the polymorphism of PRL gene locus had no siginificant effect on the Holstein bull semen quality traits.5. A new mutation locating at intron 4 (C7661T) of PRL gene was found by endonuclease Alul resulting in three genotypes named AA,AB and BB in four breeding stations. The BB genotype absence in Zhengzhou and Shanghai breeding stations. the genotype frequency AA was higher than AB, and the lowest in BB, which indicated the allele A was dominant. Association analysis showed that the bulls with these differences genotype were no siginificant (P>0.05). It can be indicated that the polymorphism of PRL gene locus had no siginificant effect on the Holstein bull semen quality traits.6. A new mutation locating at extron 5 (T8370C) of PRL gene was found by endonuclease Acil resulting in three genotypes named AA, AB and BB in four breeding stations. The genotype frequency was the highest in BB, and the lowest in AA, which indicated the allele B was dominant. Association analysis showed that the bulls with these differences genotype were no siginificant (P>0.05). It can be indicated that the polymorphism of PRL gene locus had no siginificant effect on the Holstein bull semen quality traits.