84 COMPUTER-ASSISTED SPERM ANALYSIS OF FROZEN SPERM MOTILITY AFTER REPEATED EXPOSURES TO ROOM TEMPERATURE

Abstract

The key factorin long-term cryopreservation is the very low temperature of liquid nitrogen. Several studies suggest temperatures should be maintained at -130°C or less to avoid cell damage. Damage due to initial exposure may not be overt; however, after repeated exposures a reduction in postthaw viability may become evident (Barth A 1991 Proc. 10th Annu. Conv. Am. ET Assoc, 20-26). The CASA system provides an opportunity to assess multiple motility characteristics on a semen sample objectively and with high repeatability. An experiment was designed to evaluate the effect that repeated exposure of frozen semen in 0.5-mL straws during 15 s to room temperature produces on motility characteristics assessed by CASA system. Groups were formed according to the number of exposures per straw; groups were as follows: 0, 3, 5, and 10 times of exposure during 15 s. Thirty-two ejaculates from different bulls (15 Angus, 3 Hereford, 8 Brangus, 3 others) were diluted using a chemically semi-defined media (Andromed, Minitub, Germany) and frozen in an automatic freezer (Digicool, IMV, Paillette Crista, France). Four frozen straws per bull were used, one for each group. Straws were exposed to a room temperature (15°C ± 1.28) and then placed back into liquid nitrogen. Semen thawing was conduced in a water bath at 37°C during 1 min. Motility characteristics were evaluated by the IVOS Sperm Analyzer (Hamilton Thorne Research). Two chambers of 20 μm depth and 5 fields per chamber were analyzed (30 frames/0.5 s for each field). Seven motility parameters were evaluated: % of motile sperm; % of progressive sperm; VAP (path velocity, μms^-1); VCL (track speed, μm/s); ALH (lateral amplitude, μm); BCF (beat frequency, Hz); and LIN (linearity, %). The Kruskal Wallis test was used to compare variables among groups, and results are shown in Table 1. The average temperature inside the straw after 15 s of exposure was of -122.6°C. No difference (P > 0.05) was found among the groups for any of the 7 motility parameters. In conclusion, sperm motility seems not to be affected if straws are exposed up to 10 times during 15 s to room temperature. More research should be done to test higher room temperatures and pregnancy rates after AI.

Table 1.  CASA parameters of frozen sperm after different numbers of exposures at 15°C