Comparison of an extender containing defined milk protein fractions with a skim milk-based extender for storage of equine semen at 5 degrees C.

The research paper examines the effectiveness of a semen extender containing only defined caseinates and whey proteins (EquiPro) in preserving equine spermatozoa during cooled storage, compared to a traditional skim milk-based extender.

Objective of Research

• The study primarily focuses on assessing the viability of an extender, EquiPro, constituted solely of defined milk protein fractions, caseinates, and whey proteins, in storing equine semen at 5 degrees Celsius. This is done against the backdrop of traditional extenders composed of various substances invariably found in milk or egg yolk, with the view that an extender of specific components with clearly sperm-protective characteristics would be beneficial.

Research Design and Method

• Two experiments were conducted with semen obtained from eight stallions. EquiPro was tested with and without an antioxidant, N-acetyl cysteine (NAC).
• The first experiment involved diluting semen with either PBS (Phosphate-Buffered Saline) or EquiPro. In the second, 90% of the seminal plasma was removed via centrifugation and replaced with EquiPro.
• Motility, velocity and membrane integrity of the spermatozoa were determined through Computer-Assisted Sperm Analysis (CASA) immediately after semen processing, as well as after 24, 48, and 72 hours of storage at 5 degrees Celsius.

Results of the Research

• The findings revealed that total motility after 24 hours of storage was lowest for PBS-diluted semen.
• For durations of 48 and 72 hours, semen stored in EquiPro exhibited higher motility rates than those in PBS or skim milk extender. The velocity of spermatozoa post-storage was also highest in the defined milk protein extender.
• Comparatively, membrane integrity was significantly lower in semen diluted with PBS than those diluted with both extenders.
• Contrary to what might be expected, the addition of NAC had no observable effect on any studied parameters. However, using centrifugation helped increase the percentage of motile and membrane-intact spermatozoa in the semen stored with EquiPro.

Implications of the Research

• Overall, the results suggest that the purpose-specific extender, EquiPro, performed better than traditional extenders in preserving equine semen during cooled storage, thereby addressing a longstanding issue regarding the complex, multi-substance composition of traditional extenders.
• Improvement was noted in sperm motility, velocity, and membrane integrity, particularly when centrifugation was applied. This highlights the potential of defined milk protein extenders to reliably and effectively maintain the viability of spermatozoa for artificial insemination in horses.