Examining the quality and fertilization competence of bovine ejaculate with low progressive motility – should we give it a chance?

Spermatozoa progressive motility is positively correlated with fertilization competence. Bulls’ ejaculates with progressive motility lower than 50% are routinely rejected through the process of straw preparation, designated for artificial insemination of dairy cows. We examined the quality and fertility competence of ejaculates with relative low progressive motility (55–60%, n = 5; control) with those of very low progressive motility i.e. below the lower threshold, (20-45%, n = 5; rejected). Analysis revealed a lower volume for the control vs. rejected samples. Dip-Quick staining revealed a higher proportion of spermatozoa with abnormal morphology in the rejected group, in particular those with detached heads. Activation of spermatozoa with calcium ionophore, resulted by a lower proportion of activated spermatozoa in the rejected group. In addition, a higher proportion of spermatozoa with DNA damage were recorded in the rejected vs. the control samples. Following in-vitro fertilization, the proportion of oocytes that developed to the 2- and 4-cell stage embryos did not differ between groups. However, the proportion of embryos that further developed to blastocysts, was higher in the control group. Transcript abundance of selected genes in the blastocysts and the apoptotic index did not differ between groups, suggesting that the forming blastocysts were of the same quality. It is suggested that in specific cases, for example genetically superior bulls, ejaculates with very low progressive motility can be used for in vitro production of embryo. Further in vivo examinations, i.e. artificial insemination or transferring of embryos derived from these inferior ejaculates, might clarified this point.