Inc., Scituate, MA, USA) and 4% cryoprotectant. Therefore, 2% acetamide (w/v) and glycerol (v/v) were compared for sperm cryopreserving. The spermatozoa in the mixed cryopreservation medium cooled to 5°C was loaded into 0.5- ml plastic straws (Fujihira Inc., Tokyo, Ja-pan) and exposed to liquid nitrogen (LN) vapor at –160°C, 4 cm above the LN level for 15 min. The straws were kept on 0.2-mm wire mesh on a perfo-rated Styrofoam float. The straws were then plunged into LN and stored for at least one week. Thereafter, straws were thawed in a 37°C water bath for 10 s. Thawed semen in the straw was transferred into a 1.0-ml centrifuge tube and then incubated at 37°C. The
rate of forward progressive motile spermatozoa was then evaluated microscopically.