Determinants of sperm quality and fertility in domestic species

Abstract

Fertilization success cannot be attributed solely to the absolute number of vital, motile, morphologically normal spermatozoa inseminated into the female but more especially to their functional competence. A range of in vitro tests has therefore been developed to monitor crucial aspects of sperm function: their ability to adapt to changing osmotic conditions, to bind to the oviductal epithelium, and to undergo capacitation in an appropriate and timely manner. The tests employ flow cytometry in conjunction with fluorescent techniques, electronic cell counting, and computer-assisted image area analysis. The highly quantitative analysis provided by electronic sizing and flow cytometry enables assessment of representative cell numbers in a very short time with high reproducibility. More importantly, it allows the detection of physiological heterogeneity within an ejaculate in terms of the development of cell subpopulations and enables the kinetic analysis of changes in living cell suspensions. The tests offer a promising strategy for evaluating fertility in domestic animals. The capability for volume regulation ensures that sperm recover from the tonic shocks experienced at ejaculation and during cryopreservation. Assessment of capacitation in vitro provides valuable information on both the sperm's ability to respond to fertilizing conditions and the sequence and rates of ongoing capacitation/destabilization processes. The monitoring of response to capacitating conditions in kinetic terms allows the sensitive and adequate detection of sperm populations expressing fertilization attributes and their ability to respond to external stimuli in a timely manner. However, subfertility is likely to be associated with a suboptimal response (i.e. too high or too low) rather than a minimal response.

Sperm release from oviduct epithelial binding is controlled hormonally by peri‐ovulatory graafian follicles

“…Viewed at the molecular level, a remodelling of plasma membranes in different sub-populations of spermatozoa and in corresponding regions of the epithelium would be anticipated. Despite this emphasis on physiological control mechanisms, none of the preceding remarks is intended to deny that in-vitro binding assays using oviduct epithelial cells may offer a valuable new route towards sperm quality assessment, that is, a form of screening for potential fertility (De Pauw et al, 2002;Gualtieri and Talevi, 2003;Waberski et al, 2005Waberski et al, , 2006Petrunkina et al, 2007).…”

Cytometric solutions in veterinary andrology: Developments, advantages, and limitations

“…However, within the female tract, its life is much shorter, particularly around the time of ovulation, when capacitation takes place most efficiently. Both exocytosis of the acrosome and fusion with the egg require that the plasma membrane has been rendered markedly less stable, and development of hyperactivated motility requires increased permeability of the plasma membrane to calcium [see (5) and references therein]. Overall, therefore, capacitation can be considered as a destabilizing process (50).…”

“…Although a poor overall response to capacitating conditions (in terms of merocyanine binding, increased tyrosine phosphorylation, calcium uptake, or induced acrosome reaction) will probably indicate an inability to capacitate and therefore imply subfertility, an overrapid response may equally suggest inadequate sperm survival in the female reproductive tract (98). In fact, it seems that the ability to respond to capacitating conditions in terms of absolute values or percentages of responding cells is not of itself the crucial factor, but the occurrence of a certain response level within a certain interval of time (5,88). Slowly responding samples may in fact be indicative of optimal fertilizing ability as long as the response is not too slow to provide sufficient numbers of capacitated cells.…”

“…(89)]. We believe, therefore, that capacitational changes must be assessed on the basis of several parameters measured over a suitable period of time, within which several subpopulations may develop (5).…”

“…(5). Early stages could be characterized by monitoring functional changes in membrane permeability, lipid architecture, and mitochondrial potential by using a combination of merocyanine, Yo-Pro-1, Pacific Blue-Annexin V, Mitotracker Deep Red, and/or Propidium iodide (or compatible fixable viability dye).…”