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Recent aspects in stallion sperm preservation for Artificial Insemination
Equine industry needs more and more to improve long-term sperm storage (chilled or frozen) to optimize artificial insemination (AI) and fertility rates and consequently genetic exchanges. In most domestic animal species, sperm extenders are composed of animal products as milk and/or egg yolk (EY). However, these products are potential sources of bacterial contaminations and have a variable composition. In equine species, milk and egg yolk have been used for years in the composition of extenders. In our laboratory, we have decided to focus our research on the composition of extenders and our objective was to adapt extenders free of milk and or egg yolk for both chilled and frozen sperm. For chilled transported sperm, milk or milk based extenders have been used to dilute and store stallion sperm for AI. However, all milk components are not optimal for sperm protection. So milk fractions were tested and finally we developed an extender named INRA96®, containing the purified fraction of native milk caseins, for long-term sperm storage at 4°C or 15°C. INRA96® is a ready to use extender and it can maintain fertility potential for up to 24- 72 hours. INRA96® has proved itself and lot of breeders use it nowadays in many countries. Since the first insemination with frozen semen, the low or fluctuating fertility results have limited the use of this technology. Our objective was to develop a new freezing extender, easy to use and able to improve the success of artificial insemination with equine frozen semen. We first demonstrated that INRA96® extender, used previously for chilled transported sperm, supplemented with EY and glycerol improved significantly the fertility rates of equine frozen sperm. More sterilized EY-plasma afforded the same protection as EY. These results lead to the commercialization of an extender available ready to use and called INRA Freeze®. Our next objective was to identify the cryoprotective molecule(s) in egg yolk plasma. EY and more precisely LDL, composed mainly of phospholipids, are considered since a long time as cryoprotective agents. In our analytical approach to develop a new freezing extender, we have tested the effect of EY-phospholipids instead of EY or EY-plasma. Our results demonstrate that EY-phospholipids as cryoprotective agents are a promising approach that we have to finalize.
Keywords: Equine, INRA 96, Sperm Storage