Effects of Different Freezing Protocols on Motility, Viability, Mitochondrial Membrane Potential, Intracellular Calcium Level, and DNA Integrity of Cryopreserved Equine Epididymal Sperm.
Authors: Neuhauser Stefanie, Bollwein Heiner, Siuda Mathias, Handler Johannes
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Cryopreservation of equine epididymal sperm—harvested post-castration—offers valuable genetic preservation, but the freezing protocol substantially influences post-thaw viability and function. Neuhauser and colleagues compared four freezing protocols on ejaculated sperm from 10 stallions, using both programmable freezers and floating racks with slow or fast cooling rates, then assessed motility parameters, membrane integrity, mitochondrial function (via membrane potential), intracellular calcium regulation, and DNA damage across multiple time points. Slow cooling protocols (processes 1 and 2) consistently outperformed fast cooling (process 4), with significantly higher total and progressive motility both immediately post-thaw and after one hour of incubation, alongside superior viability and mitochondrial membrane potential in viable sperm populations. Intriguingly, the subpopulation of sperm demonstrating the optimal combination of viability, high mitochondrial potential, and low intracellular calcium—critical markers of fertilisation capacity—performed best with process 3 (fast cooling via floating rack), suggesting that this accessible alternative to programmable freezers may be viable, particularly when equilibration occurs in a cooled environment. These findings have direct implications for practitioners managing stallion reproduction: programmable freezers with controlled slow cooling remain the gold standard for epididymal sperm preservation, yet floating rack systems warrant consideration as a practical, cost-effective alternative when proper equilibration protocols are followed, whilst DNA integrity remained unaffected across all methods, indicating cryodamage primarily affects functional rather than genetic parameters.
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Practical Takeaways
- •Use slow cooling rates with programmable freezers for optimal post-thaw stallion sperm quality; if using floating rack methods, ensure equilibration occurs in a cooled environment rather than at room temperature
- •Slow cooling protocols preserve sperm motility and mitochondrial function better than rapid freezing, which is critical for breeding soundness and fertilization potential
- •All tested freezing methods preserve DNA integrity, so choice of protocol should prioritize motility and viability outcomes rather than genetic safety concerns
Key Findings
- •Slow cooling rates (processes 1 and 2) resulted in significantly higher post-thaw total motility, progressive motility, and viable sperm compared to fast cooling (process 4)
- •Process 1 (slow cooling with programmable freezer) produced the highest percentage of rapid sperm immediately after thawing and after 1 hour incubation
- •Viable sperm with high mitochondrial membrane potential were significantly more abundant in slow cooling protocols (processes 1 and 2) versus fast cooling (process 4) after 1 hour incubation
- •DNA integrity remained similar across all four freezing protocols, indicating freezing method does not compromise genetic material