Assessment of Sperm Quality

During spermatogenesis, spermatozoa lose many of the organelles that most somatic cells possess (such as endoplasmic reticulum, lysosomes, and most of the cytoplasm) reducing the “baggage” they need to carry en route to the oocyte. The primary function of a spermatozoon, fertilizing an oocyte, is an integrated set of processes, which require multiple cell attributes. Therefore, although the spermatozoon contains few organelles, it remains a complicated cell, having multiple cell compartments, membrane compositions, and subcellular structures, all of which must be functioning properly for the spermatozoon to fertilize an oocyte. To complicate matters further, and of particular interest to the practitioner, during spermatogenesis the DNA of the cell is condensed in such a manner that genes cannot be expressed, hence no proteins can be made by the spermatozoon. This means the cell cannot repair itself from any cellular damage that occurs naturally or due to human interventions (semen handling, cooling, or cryopreservation). Improper handling of spermatozoa can permanently damage spermatozoa, making them infertile. The stallion spermatozoon consists of 3 major anatomical regions, the head, the middle piece, and the principle piece or tail, all of which are surrounded by a plasma membrane (for a detailed discussion of spermatozoal anatomy and function see Amann and Graham). The head contains the cell nucleus consisting of the cell’s chromosomes tightly packaged by protamine proteins which replace histones during spermatogenesis; and the acrosome, a membrane bound bag of enzymes at the anterior portion of the head which are necessary for the sperm to penetrate the zona pellucida of the oocyte. Disruption of the acrosome prior to the sperm being already bound to the zona pellucida renders a spermatozoon incapable of penetrating the zona pellucida and subsequently fertilizing the oocyte. The middle piece of the spermatozoa contains the mitochondria of the cell and provides the means of converting sugars, glucose primarily, into ATP which is utilized by the fibers of the principle piece to cause the movement of the sperm. Destruction of the mitochondria, either by physical damage (from improper cooling or freezing) or chemical damage (improper pH or osmolality) can render the spermatozoa incapable of producing the ATP necessary to fertilize an oocyte. Likewise, damage to the principle piece, will alter the ability of the spermatozoa to swim to the oocyte, penetrate the zona pellucida and fertilize the oocyte. In light of the complex nature of the stallion spermatozoa, analysis of sperm function is also more complicated than we generally acknowledge. In this article, I will discuss what analyses can be used