In the present study, 2 experiments were carried out. In experiment 1, mouse spermatozoa were frozen and stored in an ultra-low temperature freezer maintained at -79°C, from 1 week to 8 months. In vitro fertilization rates of the frozen-thawed sperm after 1 week and 4 months of storage were high at 71 and 71%, respectively. These values did not differ significantly from the value (73%) of the control stored at -196°C. In contrast, the 8-month storage rate was significantly lower at 51%. In experiment 2, frozen spermatozoa were transported in a Styrofoam box packed in dry ice from Hokkaido to Tokyo. In vitro fertilization rate of frozen-thawed sperm after transport at -79°C was high at 88%, which was not significantly different from that (84%) of the transported control at -190°C. After transferring two-cell embryos derived from frozen spermatozoa to recipients, 37-62% of the embryos developed into offspring in both experiments. These results indicate that mouse spermatozoa can survive cryopreservation in an ultra-low temperature freezer (-79 °C) for up to 4 months and transport at -79°C.
2001 Japanese Association for Laboratory Animal Science