A male factor is responsible for about half of the cases of equine infertility: this fact highlights the need for a better understanding of the molecular basis of male equine infertility both at the genetic as well as at the biochemical level.This project is relevant for the study of male infertility from several perspectives: 1) results of the experiments will provide a significant advance in understanding at the molecular level the mechanisms of the causes of male infertility. 2) The methods to be developed during ths project could easily be translated to standardized tests in the clinical laboratory. 3) Understanding of male infertility at the molecular level could provide rational strategies to treat infertile stallions and/or improve the assisted reproductive technology (e.g. in cases that do not succeed in ICSI treatments). Reports of fertility with cooled transported semen in commercial breeding programs indicate seasonal pregnancy rates ranging from 60 to 90-percent. In comparison, semen-freezing techniques are not yet fully optimized, and pregnancy rates for some stallions have been 8 to 61-percent of those obtained with cooled semen. There is substantial difference in post-thaw sperm viability among individual stallions and between ejaculates of the same stallion (Amann, 1984). The decreased pregnancy rate with frozen-thawed equine semen may be attributed to a decline in the post-thaw motility and/or a reduction in the longevity of sperm after thawing.
Stallion semen is generally centrifuged prior to freezing or cryopreservation so it may be placed in small packages for freezing. The objective of centrifugation is to allow the recovering of sperm while minimizing physical damage. Centrifugation force and time, and composition of media vary considerably between laboratories which process stallion semen for freezing. Frozen stallion sperm is most dramatically affected by intrinsic stallion variation, but processing dictates the final outcome. For example, milk base extenders may be more advantageous for centrifugation than commercial extenders based on sperm motility parameters. A greater understanding of the damage associated with semen freezing is required.
The hypothesis and experiments detailed in this proposal concern a relatively new way of thinking about semen freezing. Because the poor fertility of frozen semen and the differences between stallions in their intrinsic fertility, it is important to understand the characteristic that sets apart sperm that freezes well versus poor freezers. The ultimate goal would be to understand the mechanism of cryoinjury so a standard protocol could be optimized and used on a large percent of the population of breeding stallions. Improved methodologies to freeze semen might offer insight into problems associated with the cryopreservation of equine sperm. These techniques are of increased importance for the success of assisted techniques in equine reproduction. Providing a first class service to the Northeast equine industry is only possible if there is a sound scientific background of equine sperm cryobiology.
