Cryopreservation of stallion semen: laboratory assessment of sperm injuries after cushioned centrifugation and freezing with conventional and alternative directional freezing methods.

This study investigates the effectiveness of different semen freezing methods on stallion sperm. It finds that cushioned centrifugation provides some benefits for sperm health, but that the use of flat straws in the freezing process may need refinement.

Introduction and Study Design

• The experiment involved the collection of 36 ejaculates from 13 stallions. These samples were divided into two volumes.
• Each volume was processed using cushioned and uncushioned centrifugation – a method used to separate components based on size and density – and frozen using three different techniques: the traditional method and two prototypes referred to as the Drum and Directional methods.
• The Conventional and Drum methods used 0.5 ml straws, while the Drum and Directional methods used larger, 2 ml flat straws.

Findings on Centrifugation

• In comparing cushioned and uncushioned centrifugation, researchers found that the cushioned method led to better sperm motility and velocity, measured after samples were cooled to 4 degrees Celsius for 90 minutes prior to freezing.
• Cushioned centrifugation also resulted in a greater percentage of spermatozoa with intact mitochondrial and acrosomal/plasmatic membranes after thawing, compared to uncushioned centrifugation.
• However, the researchers observed no significant differences in classical kinetic parameters – measures of sperm movement – based on the type of centrifugation.

Findings on Freezing Methods

• Researchers noted detrimental effects on most parameters measured at thawing and after 3 hours of incubation at 37 degrees Celsius for samples frozen with flat straws.
• Contrarily, the Drum method, using a different container known as a Paillette, did not have notable negative impacts.

Inter-Stallion Variability

• The disparities among stallions were prominent, with variance in kinetics and membrane status ranging from 5% to 69%.
• Meanwhile, variability among different ejaculates from the same stallion was lesser, ranging from 9% to 28%.

Conclusion

• The analysis identified three key factors with different impacts on sperm quality: membranes status, kinetics at T₀ (directly after thawing), and kinetics at T₁ (after 3 hours of incubation).
• The cushioned centrifugation technique showed some positive effects on sperm membrane status post-thawing, indicating that this method could improve the outcome of the freezing process.
• Meanwhile, the use of flat straws demonstrated poor results and researchers suggest this approach needs improvement.