It is difficult to maintain sperm in liquid storage for a long time, compared with permanent frozen storage in liquid nitrogen. Antioxidants have been reported to improve the quality and fertility of liquid-stored semen. In this study, we investigated whether antioxidants can extend the motility and fertility of frozen-thawed sperm in liquid storage. Frozen-thawed semen from one Japanese black bull (one ejaculate) was diluted in Tris-citrate-fructose (TCF) diluent with 10% (v/v) egg yolk to a sperm concentration of 1×107 spermmL−1. The antioxidants β-mercaptoethanol (βMe) and glutathione (GSH) were added independently, at various concentrations (0.1, 0.5, 1, and 5mM) to sperm suspensions, and these preparations were compared with Control (no added antioxidant). Sperm suspensions were packaged in centrifuge tubes and placed at 17°C in air and monitored daily until sperm motility had stopped (up to 14 days). Sperm motility was analysed by the Sperm Motility Analysis System (SMAS; Ditect Co. Ltd), and the percentage of progressively motile sperm (straight-line velocity (VSL) of >25μm s−1; Grade A classified by WHO manual), compared with that recorded on Day 0 (100%), was determined each day. For evaluation of fertilizing ability, after incubation in liquid storage for 0, 3, 5, and 7 days, sperm were used for IVF with invitro-matured oocytes (30 oocytes per treatment, three replicates). Embryo development was recorded as the proportion of embryos that reached blastocyst by 8 days after IVF. Data for motility were analysed using one-way ANOVA with Tukey test, and embryo development using chi-squared test. A P-value<0.05 was considered statistically significant. At 7 days, the percentage of progressively motile sperm was significantly higher for 0.5, 1, and 5mM βMe than for Control (30.8%, 48.1%, and 50.3%, vs. 0%, respectively). Treatments with 1 and 5mM βMe maintained some sperm progressive motility for 14 days (9.5% and 14.5%). Treatment with GSH showed the same trend at 7 days (32.2%, 36.3%, and 13.7% for 0.5, 1, and 5mM, vs. 0% for Control); 1 and 5mM GSH maintained sperm progressive motility over 10 days (24.8% and 4.4%). In both antioxidant treatments, embryo development was achieved with sperm stored for up to 5 days (Day 0 vs. Day 5 for 0.1mM βMe: 17.6% vs. 13.8%; for 1.0mM GSH: 26.0% vs. 6.7%; for Control: 17.6% vs. 0%). In this study, antioxidants extended both motility and fertility of frozen-thawed bovine sperm in liquid storage. This result suggests the possibility of application to AI using liquid-stored bovine semen.
Study of bovine sperm motility in shear-thinning viscoelastic fluids