Effects of dead spermatozoa on motion characteristics and membrane integrity of live spermatozoa in fresh and cooled-stored equine semen.

This research sought to understand if dead sperm in horse semen lessened the movement or compromised the health of living sperm in both fresh and cooled sperm samples. The findings revealed that while the presence of up to 75% dead sperm did not negatively impact total and progressive movement of live sperm, it did reduce velocity and overall membrane health, providing important insights for equine semen processing.

Methodology of the study

• The study focused on three ejaculates from each of three stallions.
• Almost all seminal plasma was removed through centrifugation and replaced by resuspending sperm in EZ-Mixin CST extender and 10% autologous seminal plasma.
• These sperm suspensions were then divided into five aliquots. Dead sperm, created by repeatedly freezing and thawing pooled ejaculates, were then added to four of them in varying percentages (10, 25, 50, 75%), leaving one as a control (0% dead sperm).
• All aliquots were then heated to 37 degrees Celsius and stored in an Equitainer for 24 hours.

Data collection

• Using a computerized spermatozoal motion analyzer, the motion characteristics (% total movement, % progressive movement, and average curvilinear velocity) for both the fresh and 24-hour cooled sperm samples were determined.
• The integrity of the sperm membranes in the samples was also assessed using carboxyfluorescein diacetate-propidium iodide staining. Membrane integrity was found to be highly correlated (r>0.8; P<0.001) with total and progressive movement in both fresh and cooled sperm samples.

Findings and implications

• The presence of up to 75% dead sperm did not reduce the total or progressive movement of live sperm in either fresh or cooled semen. However, comparisons with the control samples revealed reductions in average curvilinear velocity and percentage of membrane-intact sperm when 75% dead sperm was present.
• These findings suggest that dead sperm does not adversely affect the motility of live sperm, but may affect their speed and the integrity of their membranes.
• The results provide valuable insights that are applicable to the processing of equine semen, both cooled and frozen, potentially informing refinement of methods and ensuring the viability of equine sperm used in breeding programs.