Comparative Susceptibility of Donkey and Horse Sperm to Liquid-Storage Temperature

Preservation protocols for donkey sperm are based on those developed for horses, despite potential interspecific differences in cooling tolerance. This study compared horse and donkey sperm during long-term storage at 5°C and 17°C. Ejaculates from four stallions and four jacks (n = 16) were centrifuged, resuspended in skimmed milk-based extender, and stored at both temperatures. Sperm motility, plasma and acrosome membrane integrity, and morphology were evaluated after 1, 2 and 7 days. Fresh semen parameters showed no interspecific differences (p > 0.05). At 5°C, donkey sperm showed reduced motility and membrane integrity from Day 1, whereas horse sperm parameters remained stable at both temperatures up to Day 2. After 7 days, horse doses stored at 5°C maintained significantly higher quality. In conclusion, donkey sperm was more sensitive to storage at 5°C than horse sperm, highlighting the need for species-specific preservation strategies.