Preliminary study on effects of bovine frozen semen storage using a liquid nitrogen-independent method on the quality of post-thaw spermatozoa.

Frozen semen of eight bulls was used to assess effects of storage temperature and length of storage time on frozen-thawed bovine sperm quality. In experiment 1, 25 straws of frozen semen of each bull were allocated to 3 groups. The control was still maintained in liquid nitrogen (LN2). The rest were abruptly moved from LN2 to -80°C and -30°C mechanical freezers, respectively. After thawing, it was found that the sperm motility, vitality and membrane integrity were comparable (P>0.05) between the control and the -80°C samples and were significantly inferior (P<0.001) in the -30°C samples, irrespective of storage time (1-day, 1-week and 1-month). In experiment 2, two out of the three parts (16-18 straws) of frozen semen of each bull were rapidly removed from LN2 and further kept in the freezer (-80°C). One day before being thawed, half of the samples in the freezer were promptly put back to LN2. The results showed that the frozen-thawed sperm quality was not significantly affected (P>0.05) both by storage temperature (-196°C, -80°C and -80 & -196°C) and storage time [day-2, day-8 (1-week) and day-31 (1-month)]. At the same storage times, the quality measures at different temperatures were not significantly different from one another (P>0.05). In conclusion, a -80°C mechanical freezer was as effective as LN2 in preserving in vitro quality of frozen-thawed bovine spermatozoa throughout 1-month of storage. When required for use, frozen semen stored in the freezer could be thawed immediately or transferred to the LN2 tank for thawing elsewhere.