Recent Developments in Stallion Semen Preservation

• Review of stallion semen storage techniques.
• Discusses membrane-stabilizing compounds, antioxidants, and energy substrates.
• Advantages of ambient temperature storage over cryopreservation and chilling.
• Compares the recent developments using various storage strategies.

Since the commercialization of artificial insemination in the early 20th century, there has been a need reduce the logistical difficulties associated with the coordination of semen collection and insemination. This need has been met through the development of various approaches to extend the longevity of spermatozoa through semen dilution and temperature-induced metabolic restriction, and these strategies have provided livestock breeders with a valuable tool for the genetic improvement of many species. As the horse is not a production animal, the resources available for the research of stallion semen preservation have been scarce. Despite this, significant progress in semen processing and preservation techniques has been made in the areas of chilled storage, cryopreservation, and more recently ambient temperature storage. While the major focus for research in the areas of chilled and cryopreserved spermatozoa has been the stabilization of membranes during the deleterious phase changes that occur throughout cooling, ambient temperature storage presents a completely different set of problems associated with the rapid metabolic rate of stallion spermatozoa which use oxidative phosphorylation and produce vast quantities of reactive oxygen species. This article reviews the tactics that have been used to overcome the damaging effects of semen preservation which are unique to each strategy, while touching on the fundamental discoveries which have brought the field to the position it is in today.