An improved vitrification protocol for equine immature oocytes, resulting in a first live foal.
Authors: Ortiz-Escribano N, Bogado Pascottini O, Woelders H, Vandenberghe L, De Schauwer C, Govaere J, Van den Abbeel E, Vullers T, Ververs C, Roels K, Van De Velde M, Van Soom A, Smits K
Journal: Equine veterinary journal
Summary
# Editorial Summary: Improved Vitrification Protocol for Equine Immature Oocytes Vitrification of immature equine oocytes has historically yielded poor success rates, with matured oocytes frequently failing to progress through normal embryonic development. Researchers compared two cryopreservation approaches—one using high concentrations of cryoprotective agents (CPAs) with brief exposure versus lower CPA concentrations with prolonged exposure—whilst investigating whether surrounding cumulus cell layers affected outcomes. Corona radiata oocytes (those with minimal cumulus investment) vitrified under the short-exposure, high-concentration protocol achieved nuclear maturation rates comparable to non-vitrified controls, whereas cumulus-rich oocytes showed significantly reduced maturation (P = 0.001). Both protocols produced aberrant spindle configurations at higher rates than controls, yet only the short-exposure protocol yielded blastocyst development, albeit substantially lower than controls (P <0.001); encouragingly, embryo transfer of five blastocysts produced one healthy live foal. These findings indicate that selecting oocytes with minimal cumulus investment and employing high CPA concentrations with short exposure times may be the critical parameters for preserving developmental competence through the vitrification process, offering a more promising foundation for equine reproductive biotechnology in clinical practice.
Read the full abstract on PubMed
Practical Takeaways
- •For equine oocyte vitrification, removing excess cumulus cells (retaining only corona radiata) improves developmental competence and viability outcomes
- •High concentration cryoprotectants with short exposure times optimize blastocyst development rates compared to prolonged low-concentration protocols
- •This technique now enables viable foal production from vitrified immature oocytes, expanding breeding options for mares with limited breeding windows or poor natural fertility
Key Findings
- •Corona radiata oocytes vitrified with long exposure to low CPA concentrations achieved similar nuclear maturation rates to non-vitrified controls
- •Short vitrification protocol with high CPA concentrations resulted in blastocyst development only in corona radiata oocytes, producing one live foal after embryo transfer
- •Both vitrification protocols caused significantly higher rates of aberrant spindle configuration compared to controls (P<0.05)
- •Cumulus cell layer presence during vitrification reduced maturation success, particularly with short exposure protocol (P=0.001)