Sperm vitrification in horses and donkeys.
Authors: Hidalgo M
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Sperm Vitrification in Horses and Donkeys Hidalgo's 2025 investigation into sperm vitrification offers equine practitioners a potentially valuable alternative to conventional semen freezing, a technique that employs rapid cooling rates and non-permeable cryoprotectants to preserve sperm at ultralow temperatures. The research traced the technical development from early spheres-based approaches through to optimised 0.25 mL straws with outer covers, comparing post-thaw progressive motility outcomes against standard freezing protocols in both species. Using this refined methodology, vitrified donkey sperm maintained equivalent motility (44.3% versus 44.7%), whilst horse sperm demonstrated notably superior results (48.2% versus 37.3%)—a clinically meaningful improvement for breeding programmes relying on frozen genetics. Fertility validation proved encouraging: in vitro heterologous fertilisation confirmed vitrified equine sperm retained penetrative capacity, and a preliminary in vivo donkey trial showed comparable pregnancy rates to conventional frozen semen (22% versus 10%) alongside the additional advantage of reduced uterine inflammation post-insemination. For breeding operations and equine veterinarians managing valuable genetics, vitrification using 0.25 mL straws presents a pragmatic option that may enhance semen survival and reduce post-insemination complications, though larger-scale fertility studies in horses would strengthen clinical confidence in the technique's reliability.
Read the full abstract on PubMed
Practical Takeaways
- •Sperm vitrification using 0.25 mL straws is a viable alternative to conventional freezing for equine breeding programs, offering equivalent or superior post-thaw motility
- •Vitrified semen shows promise for improving pregnancy rates in donkeys with the added benefit of reduced uterine inflammatory response
- •Practitioners should avoid using larger 0.5 mL straws for vitrification due to poor post-thaw sperm quality; standardize on 0.25 mL format
Key Findings
- •Vitrification using 0.25 mL straws with outer covers achieved progressive motility of 48.2 ± 2.3% in horses versus 37.3 ± 2.2% for conventional freezing
- •Vitrified equine sperm demonstrated fertilizing capacity in heterologous IVF, achieving pronuclear formation and hybrid embryo cleavage with cattle oocytes
- •In vivo donkey fertility trials showed 22% pregnancy rate with vitrified semen versus 10% with frozen semen, with faster resolution of uterine inflammation after AI with vitrified semen
- •Vitrification of larger volumes in 0.5 mL straws resulted in poor sperm quality regardless of warming procedure