Combined Single-Straw Packaging of Cryopreserved Stallion Epididymal Sperm and Separated Homologous Seminal Plasma

Abstract

The aim of the present study was the investigation of stallion epididymal sperm frozen with seminal plasma within the same straw separated by an air bubble before freezing. We hypothesized that mixing both components after thawing improves the sperm quality compared with conventionally frozen-thawed epididymal sperm. Cryopreservation of epididymal sperm allows the preservation of spermatozoa in case of death or termination of the breeding carrier. However, these sperm lack contact with the seminal plasma, which plays an important role in the development of sperm functionality and the regulation of uterine inflammatory response after insemination. Motion characteristics, morphology, and viability were assessed in epididymal sperm mixed with seminal plasma after thawing (group SP) and compared with conventionally packed cryopreserved epididymal sperm that had no contact with seminal plasma (group FT). Total and progressive motility, curvilinear velocity (VCL), and average lateral head displacement were significantly higher in group SP (P < .05). During post-thaw incubation, VCL decreased in group FT but not in group SP (P < .05), and beat cross-frequency was significantly lower in group FT than in group SP after post-thaw incubation (P < .05). Straightness did not differ between the groups (P > .05). Although the percentage of tail abnormalities and isolated sperm heads increased significantly only in group SP after cryopreservation (P < .05), the proportion of morphologically abnormal and nonviable sperm was not affected by seminal plasma (P > .05). Mixing both components after thawing increased sperm motility and velocity but did not negatively affect morphology or viability. This packaging system is promising for routine artificial insemination of stallion epididymal sperm.