Epididymal Spermatozoa Show Higher Cryoresistance to Vitrification Process Than Ejaculated Spermatozoa in Dogs

The aim of this study was to investigate differences in the sperm response to a vitrification-warming process between ejaculated and epididymal dog spermatozoa, and to evaluate the efficacy of an animal protein-free extender for vitrification of both types of sperm cells. Vitrified-warmed spermatozoa from the epididymis showed greater (p < 0.001) progressive motility and total motility values than ejaculated spermatozoa, regardless of the diluent. The vitrification procedure returned better results for viability and intact acrosome when human tubal fluid (HTF^®) was used (25.10 ± 7.90 and 56.50 ± 6.7, respectively) compared with Tris-Citric acid-Glucose (TCG) (15.20 ± 4.70 and 43.70 ± 7.9, respectively) in ejaculated samples. Similarly, higher total motility (34.5 ± 4.5) was observed in HTF postwarmed samples compared with TCG-treated samples (19.52 ± 5.1). The interaction source (epididymis, ejaculated) × extender had a significant effect (p < 0.001) on the values of total motile spermatozoa after warming. HTF-based extender improved (p < 0.001) total motility values in epididymal samples, but not in ejaculated samples. In conclusion, epididymal spermatozoa show higher cryoresistance to the vitrification process than ejaculated spermatozoa in dogs. The use of HTF is adequate for both ejaculated and epididymal canine sperm vitrification.