The research article investigates the impact of low sperm concentration and repeated freeze-thawing on the quality of the equine sperm. The researchers found that cryopreserving the sperm at concentrations as low as 50 million/ml maintains their quality, confirming that it is possible to efficiently store and use genetically valuable equine sperm.

Introduction and Aim

• The study was initiated as a response to the wasteful practice of freezing horse sperms at high concentrations and then only using a few, due to technological advances such as Intracytoplasmic Sperm Injection (ICSI), which only require one spermatozoon.
• The researchers, therefore, aimed to identify if reducing the sperm concentration for the cryopreservation process would affect the quality of sperm post-thaw, and if refreezing thawed spermatozoa could help reduce waste and maximize the benefits from genetically valuable horses.

Methodology

• Nine ejaculates were collected from stallions known to freeze well marking them as “good freezer” stallions.
• Each ejaculate was divided into eight parts differing in their sperm concentrations: five, 10, 20, 50, 100, 200, 300, 400 million sperm per millilitre, and then cryopreserved.
• Post-thawing, the researchers assessed the sperm’s motility, viability, acrosome integrity, and oxidative stress.
• In a second experiment, straws from the first experiment that contained 300 million sperm per millilitre were thawed, diluted to 20 million sperm per millilitre or left undiluted, and then refrozen. Again, post-thaw motility and viability were assessed.

Findings and Conclusion

• Results from the first experiment revealed that the sperm concentration did not significantly affect total motility, progressive motility or viability at 50 to 400 million sperm/ml.
• However, sperm concentrations within the range of five to 20 million/ml did show a difference in post-thaw total motility and progressive motility.
• Both refreezing and reducing the concentration of spermatozoa resulted in decreased total motility, progressive motility and viability after two freeze-thaw cycles.
• The study concluded that it is possible to cryopreserve sperm at concentrations as low as 50 million/ml, which should maintain the sperm’s quality in good freezer stallions.
• The researchers suggest that further studies should investigate the optimal condition for cryopreserving sperm initially at 20 million sperm/ml and after two freeze-thaw cycles.