Ten ejaculates were used to test effects of slow (37.0 min), moderate (7.8 min) or fast (4.2 min) freezing from +5 to −120 C on post-thaw survival of sperm. Semen was extended at 37 C in Tris-yolk-glycerol, packaged in . 3-ml Continental straws at ambient temperature, frozen at one of the three rates and thawed in 95 C water for 7 seconds. For combined post-thaw incubations of 0, 3 and 6 hr at 37 C, acrosomal retention and progressive spermatozoal motility were not significantly different among straws frozen at the three rates. In a second experiment, 10 ejaculates were used to study effects of cooling time from 25 to 5 C (.5 or 3.5 hr), equilibration time (0, 3 or 9 hr) and thawing method (water at 35 C for 10.0 sec, 65 C for 7.5 sec or 95 C for 6.0 sec). Semen was extended in Tris-yolk-glycerol, packaged in straws at room temperature and frozen at the moderate rate. For combined incubation periods of 0, 3, 6 and 9 hr, acrosomal retention and spermatozoal motility were higher (P<.01) after cooling in 3.5 hr rather than .5 hr if semen was not equilibrated. Also 3 or 9 hr of equilibration was superior (P<.01) to 0 hr of equilibration, and thawing at 65 or 95 C was superior (P<.01) to thawing at 35 C. Interactions of equilibration time with cooling time and thawing method were significant (P<.01). Acrosomal retention and motility of sperm were maximal (P<.01) after 9 hr of equilibration when straws were thawed at 35 C; or after 3 or 9 hr when thawed at 65 or 95 C.
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Gilbert et al. (1978) studied this question.