Post-cooling semen processing and sperm re-suspension as an alternative method to circumvent poor semen cooling in stallions.

Abstract

BACKGROUND: Artificial insemination with cooled-shipped semen is the primary method used in the equine breeding industry; yet, sperm quality and fertility can be suboptimal for some stallions when standard techniques are used. Therefore, there is a critical need to develop alternative approaches for these stallions. OBJECTIVE: To assess sperm quality parameters and fertility of cooled-stored stallion semen processed by SpermFilter&#xae; or centrifugation and resuspended in three extenders. STUDY DESIGN: Controlled and field study. METHODS: In Experiment 1, semen was collected from 21 stallions classified as having good ('Good-coolers', n&#x2009;=&#x2009;8) or poor ('Bad-coolers', n&#x2009;=&#x2009;13) semen cooling. The semen was extended at 30 million spermatozoa/mL in a skimmed milk-based (SM) diluent, and refrigerated for 24&#x2009;h. Then, the cooled-stored semen was processed through SpermFilter&#xae; or centrifugation, and the resulting sperm pellets were resuspended in SM, SM containing pentoxifylline (SM-P), or an egg yolk-based (EY) extender. Unprocessed cooled-stored semen served as control. Sperm motility parameters, plasma membrane integrity (PMI), and mitochondrial membrane potential (HMMP) were assessed in cooled-semen pre- and post-processing. Experiment 2, cooled semen from 9 stallions classified as Bad-coolers was used to inseminate 18 embryo donor mares at 66&#x2009;cycles (Unprocessed, n&#x2009;=&#x2009;22; SpermFilter&#xae;/SM-P, n&#x2009;=&#x2009;16; or SpermFilter&#xae;/EY, n&#x2009;=&#x2009;28). Data were analysed with a mixed model and Tukey's as posthoc, and logistic regression. RESULTS: Processed semen resuspended in EY had superior sperm motility compared to unprocessed, SM and SM-P (p&#x2009;<&#x2009;0.0001). Semen processed by SpermFilter&#xae; resuspended in SM-P was similar to EY (p&#x2009;>&#x2009;0.05). Pellet resuspension with EY and SM-P improved the HMMP of Bad-cooler stallions (p&#x2009;=&#x2009;0.0010). Semen processed by SpermFilter&#xae; had superior PMI to centrifuged semen (p&#x2009;<&#x2009;0.0001). Mares inseminated with SpermFilter&#xae;/SM-P (50%, 8/16) or SpermFilter&#xae;/-EY (68%, 9/28) had higher pregnancy rates than mares bred with unprocessed semen (14%, 3/22) (p&#x2009;<&#x2009;0.001). MAIN LIMITATIONS: Low number of mares in the fertility trial. CONCLUSION: Sperm quality and fertility of Bad-cooler stallions can be enhanced by SpermFilter&#xae; and pellet resuspension with either EY or SM-P.