Ability of donkey sperm to tolerate cooling: Effect of extender base and removal of seminal plasma on sperm parameters and fertility rates in mares.
Authors: Gobato Mariana L M, Segabinazzi Lorenzo G T M, Scheeren Verônica F C, Bandeira Rafael S, Freitas-Dell'Aqua Camila P, Dell'Aqua José A, Papa Frederico O
Journal: Frontiers in veterinary science
Summary
# Editorial Summary Donkey semen has historically performed poorly when cooled for transport using standard equine extenders, limiting access to genetic material from valuable jack donkeys in mule breeding programmes. Researchers evaluated six treatment protocols on ejaculates from seven donkeys cooled at 5°C for 48 hours: three extender bases (milk-based, sodium caseinate-based, and egg yolk-based) either with or without seminal plasma removal by centrifugation, measuring motility, membrane integrity, mitochondrial function, and oxidative stress markers at intervals before assessing fertility outcomes in 163 inseminated mare cycles. Both egg yolk and sodium caseinate-based extenders substantially outperformed milk-based extenders across all sperm parameters at 24 and 48 hours post-cooling, with conception rates of 89% (egg yolk) and 67–89% (sodium caseinate with or without centrifugation) compared to only 33% for milk-based extenders alone. Centrifugation to remove seminal plasma proved particularly beneficial when used with milk or sodium caseinate extenders, suggesting it reduces oxidative stress and stabilises membrane function during the cooling process. For practitioners involved in donkey breeding and mule production, switching to egg yolk or sodium caseinate-based extenders—and considering seminal plasma removal when using less optimal base formulations—offers a practical, evidence-based route to substantially improve conception rates with cooled donkey semen.
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Practical Takeaways
- •When transporting cooled donkey semen for breeding mules, use egg yolk or sodium caseinate-based extenders rather than milk-based formulations—these improved conception rates from 33% to 67–89% in this study.
- •Consider removing seminal plasma (centrifugation) before cooling donkey semen in milk or sodium caseinate extenders to further enhance sperm survival and fertility potential.
- •Donkey semen is fundamentally different from horse semen in its cooling physiology; standard equine extenders will not produce optimal results for donkey breeding programs.
Key Findings
- •Egg yolk-based (EY) and sodium caseinate-based (SC) extenders significantly improved donkey sperm motility, membrane integrity, and mitochondrial function during 48-hour cooling at 5°C compared to milk-based (SM) extenders (P < 0.05).
- •Conception rates in mares were highest with SC-C (89%), EY (89%), and EY-C (74%) treatments, compared to SM alone (33%, P < 0.05).
- •Centrifugation to remove seminal plasma positively affected sperm quality parameters in SM and SC extenders but had variable effects on fertility outcomes.
- •Donkey semen demonstrates poor cooling tolerance in standard equine extenders, but SC and EY formulations substantially improve both analytical parameters and reproductive success in recipient mares.