Japanese Society for Animal Reproduction: award for outstanding research 2002. Cryopreservation of follicular oocytes and preimplantation embryos in cattle and horses.

The research paper explores the influences on the survival rates of cryopreserved (frozen and stored for future use) horse and cow eggs and embryos. The study finds that particular cryoprotectant agents and their applications can improve post-thaw viability. It also identifies some of the challenges inherent in the process, particularly with in-vitro produced bovine embryos and the cellular injuries occurring in immature equine eggs.

Vitrification of Equine Blastocysts

• The research showed that the survival of horse blastocysts (early stage embryos) when frozen in two stages depended greatly on the development of the embryonic capsule.
• Through the use of certain cryoprotective agents (CPAs), namely ethylene glycol and sucrose, the survival rate of these embryos post-thaw significantly improved.
• The added benefit of this approach is that the horse embryos could be transferred to recipient mares without needing to remove the cryoprotectants.
• Even early-stage blastocysts, if treated with vitrification solution in stages, could develop in vitro (in a controlled environment outside of an organism) or in vivo (inside the organism).

Cryopreservation of Bovine Embryos

• Bovine embryos produced in vitro have been known to be highly sensitive to cryopreservation.
• The study attempted to get around this issue by cooling Day-7 blastocysts produced without serum more slowly before transferring them to liquid nitrogen.
• This cooling speed alteration resulted in maintaining post-thaw viability.
• The research also found that adding LAA (likely an antioxidant) to the media used for maturing and fertilizing the eggs, or to the media where embryos grow, resulted in zygotes or morula-stage embryos that were more tolerant to freezing.

Challenges with Immature Equine Oocytes

• This research found that some level of cell damage occurred in immature horse eggs, particularly near the gap-junctions or the areas of close cell connection in the cumulus-oocyte complex.
• Meanwhile, for cattle, better fertilization rates were noted when oocytes were frozen at a particular point during in vitro maturation.
• Extreme rapid cooling (vitrification) of a certain stage of bovine oocytes, carried out in glass capillaries, was found to avoid potentially detrimental effects of the vitrification and thawing process.