Semen Quality Factors Associated with Fertility

Introduction: Since the early 60s, in our lab we sought useful correlations of seminal traits and fertility in order to ultimately predict the reproductive outcome of bovine semen used in artificial breeding or the fertility of a specific male under natural service. Despite these efforts, to this day we can only account for approximately 50-60% of the variation in fertility among males by measuring seminal traits, leaving the goal of predictability quite unachieved. In our frustration and need to progress in this endeavor, shared by many other reproduction laboratories throughout the world, the fate of sperm in the female reproductive tract, both quantitatively and qualitatively, has become an important consideration needing to be addressed. Quantitatively, the question asked centers on how few sperm from a male are necessary for optimal fertility? This question has been important toward maximizing influence of genetically sound males and has gained considerable importance with recent advancements in the x-y sorting of sperm, still a rather inefficient process requiring low sperm dosages for acceptable economic returns. Seminal traits addressing sperm number per dose are considered compensable. Qualitatively, we also know that seminal deficiencies exist that result in subfertility at any sperm dosage, suggesting incompetence in the fertilizing sperm. Such deficiencies are considered uncompensable. In this review, I would like to address some of the insights that have been derived from our growing understanding of the fate of sperm in the female tract and the interaction of seminal traits with that fate. Hopefully, they may at least explain some of the frustrations encountered or perhaps offer solutions to the critical eye as new tools become available in control of semen production as well as in the control of ovulation in the female. To do this, I would like to consider data from a variety of species.