A strategy for improvement of postthaw quality of bison sperm.

The objective was to improve the postthaw quality of bison semen using zwitterion (ZI)-based extenders, glycerol addition at a lower temperature (4 °C), adding reduced glutathione (GSH) in extender, or treating bison sperm with cholesterol-loaded cyclodextrin (CLC) before freezing. Postthaw sperm motility and structural characteristics were analyzed using a computer-assisted sperm analyzer and flow cytometer respectively, at 0 and 3 hours postthaw incubation at 37 °C. In experiment 1, each ejaculate (N = 11) was diluted in Triladyl extender (control) or in ZI extenders (Tes-Tris or HEPES-Tris). In addition, glycerol in semen was added either at 37 °C or 4 °C before cryopreservation. Extenders had no significant effect on postthaw sperm motilities at 0 hour. However, sperm velocity parameters were higher (P < 0.05) in ZI extenders than in Triladyl. Sperm population with intact plasma membrane (IPM) and acrosomes (IACR) were higher in Triladyl than in ZI extenders (P < 0.05). Postthaw sperm total and progressive motilities, average path velocity, straight-line velocity, IPM, and IPM-IACR did not improve with the addition of glycerol at 4 °C. In experiment 2, semen was diluted (50 × 106 sperm per mL) in Triladyl extender containing 0 (control), 0.5, 1.0, or 2.0 mM GSH (an antioxidant) at 37 °C. Postthaw sperm motility and structural characteristics at 0 hour and percentage declined after 3 hour incubation, but did not differ because of GSH in the extender (P > 0.05). In experiment 3, fresh bison sperm (100 × 106 sperm in 1 mL) were pretreated with 0, 1, 2, or 3 mg/mL of CLC at 22 °C for 15 minutes and diluted to 50 × 106 sperm per mL in Tris-citric acid–egg yolk–glycerol extender before cryopreservation. The CLC pretreated sperm had higher (P < 0.05) postthaw total and progressive motilities, IPM, and IACR at 0 hour and less percentage of decline in these characteristics after 3 hour postthaw incubation. In conclusion, zwitterion extenders (Tes-Tris and HEPES-Tris), temperatures of glycerol addition, and GSH in extender did not significantly improve postthaw quality of bison sperm. However, pretreatment with CLC significantly improved postthaw quality of bison sperm, which should enhance its use in assisted reproductive technologies.