bull fertility and its relation with density gradient selected sperm

background: sperm selection is generally used to describe methods for separation of spermatozoa for in-vitro-assisted reproduction. few studies reported relation in vivo fertility and semen parameters after selection of fertile spermatozoa; hence, our research attempt to assess different semen parameters after post-thaw (pt) or after selecting sperm sample (ssp), using density gradient separation bovipure®, to predict in vivo fertility. materials and methods: frozen semen quality of four montbeliard bulls after post-thaw (pt) or selected sperm (ssp), using density gradient separation bovipure®, to predict fertility in vivo. pt or ssp semen were examined for concentration, motility, morphology abnormalities, viability, acrosome and plasma membrane integrities. fertility is measured as non return rates within 56 days after first insemination (nrr) or as corrected nrr (cnrr). nonparametric kruskal-wallis test was performed to compare semen parameter variables. fertilities were compared using chi-square. linear mixed model was conducted to correct nrr, expressed as cnrr, to the factors influencing fertility. pearson correlation analysis was used to test the relationship between cnrr and semen parameters. statistical analyses were performed using spss package program, version 21.0. results: most of proven bulls exhibit a high fertility (3/4 bulls, 62.1-81.8% for nrr or 67.2-98.5% for cnrr). fertility expressed as cnrr was related to ssp parameters and not to those pt. thus, cnrr increases with decrease of ssp total motility, progressive spermatozoa and abaxial implantation frequencies (r= - 0.999, p<0.001; r= - 0.990, p=0.010; r= - 0.988, p<0.012); while cnrr decreases as ssp immotile spermatozoa decrease (r= +0.995, p<0.005), underlying that maximal limit of immotile spermatozoa observed is 47%. conclusion: high frequencies of total and progressive motility spermatozoa, and abaxial implantation in gradient selected sperm appear to be not favorable for in vivo fertility.