Comparison of donkey and stallion semen preservation: effects of egg yolk plasma, seminal plasma and extenders on sperm motility, MALDI profiles and fertility.

The conservation of endangered donkey breeds relies on maintaining genetic diversity and improving reproductive success, particularly in populations with a limited number of breeding animals. This study aimed to optimise the preservation of donkey semen by evaluating different commercial extenders, as well as the effects of seminal plasma removal and egg yolk plasma supplementation during cooling, building on previous findings in the stallion. The results showed that supplementation of a milk-based extender with 5% egg yolk plasma improved sperm motility and viability after 24 hours of storage at 4 °C and partially limited alterations in protein profiles associated with cellular ageing. This improvement translated into a conception rate of 35%, compared with only 5% without egg yolk plasma, approaching that achieved with fresh semen (45%). The birth of four Grand Noir du Berry foals from semen stored for 24 hours provides in vivo validation of this approach and open new opportunities for assisted reproduction programmes.