Estimation of the genetic parameters for some of semen quality characteristics using animal models with combined phenotype and genotype data of Holstein bulls

This transversion enables the genotyping of this particular locus using the endonuclease AluI, since in the mutant bull, this enzyme does not recognize its target sequence. Several point mutations in the bovine growth hormone (GH) gene have been described, and as such, the Leu127Val polymorphism described by Lucy et al.(1993) has been extensively investigated based on production and reproduction traits. In addition, Lechniak et al.(1999) have reported the relationship between individual semen quality traitsand fertility. The purpose ofthe present study was to estimate the genetic parameters of some semen quality traits using animal models containing genotype of candidategene data on Holstein bulls.Material and methods: For this reason, 67bulls were selected from two breeding stations inthe Northwest of Iran(41 bulls) and the National Livestock Improvement Center (26 bulls), which were in the sperm production stage between 2003-2013. In this regard, four related traits of semen qualitywere considered, including:volume of ejaculation, sperm concentration, live sperm percentage before freezing,and live sperm percentage after thawing. The DNA extraction was done from semen according to commercial DNA kit and quality and quantity tests were done using spectrophotometry and gel monitoring. The nucleotide polymorphisms were evaluated in two loci of the leptin gene (Exon 2 and intron 2) by the PCR-RFLP method and in the growth promoter receptor gene (promoter region) using PCR-SSR technique. Finally, using combined phenotypic and molecular information, genetic parameters were estimated through Bayesian statistics and Gibbs sampling. POPGENE software was used for moleculardata and descriptive statistics (genotype frequencies, allele frequencies,and hetrozygosity index calculation).Univariate and multi variate analysis for semen characteristics was done using gibbs3f90 and renumf90 softwares. Results and discussion:According to the molecular outputs, in all investigate genes nucleotide variation and polymorphism wasobserved. The results of univariate analysis of animal model for estimating heritability for traits of semen volume, sperm count, live sperm percentage before freezing,and thawing point were 0.22, 0.14, 0.20,and0.10, respectively. Reproductive performance is controlled by the genetic make-up of dam, sire,and offspring, but it is largely affectedby environment. Thus, the reproductive efficiency of the breeding herd depends on the fertility of the bulls(Gredleret al.,2005). Bull's fertility is also essential,since bull's DNA is the primary mechanism through which genetic improvements can efficiently be accomplished. Implementation of artificial insemination (AI) in dairy cattle production allowed improving selection of bulls for production traits. Also, frequent freezing and thawing process of bull semens significantly affected quality index and consequent evaluation of fertilization potential of a semen sample for AI in Holstein breeding stations(Mathevonet al.,1998).However, the preselection of the samples, the high number of sperm per doses,and the high quality of the semen used in the AI programs can reduce the variability, thereby giving alow probability of detecting fertility differences associated with seminal parameters. Spermatogenesis is a complex process that involves stem-cell renewal, genome reorganization,and genome repackaging;so, it culminates in the production of motilegametes(Kealeyet al.,2006). The process of spermatogenesis is regulated by reproductive hormones in gonadotropinaxis and is controlled by a large number of genes(Sunet al., 2012). Therefore, hormone and their receptors are presumed to be good candidate genes for reproductive traits.Conclusion: The results of this study indicatedthat the range of heritability values for the different semen quality characteristics are low to moderate, whichmay indicate that improvement of environmental factors is more effective than genetics basis.