The effect of warming velocity on motility and acrosomal integrity of boar sperm as influenced by the rate of freezing and glycerol level.

The effect of thawing velocities ranging from 10 degrees C/min to 1,800 degrees C/min on the motility and acrosomal integrity of boar spermatozoa frozen at 1 degree C/min (suboptimal), 5 degrees C/min, and 30 degrees C/min (optimal) rate was studied with the sperm suspended for freezing in diluent containing 2, 4, or 6% of glycerol (v/v). The influence of thawing on sperm survival depends on the rate at which the sperm had been frozen. In semen frozen at a suboptimal rate of 1 degree C/min, the percentage of motile sperm (FMP) initially fell to 3.5-4.0% when the thawing rose to 200 degrees C/min, but, with further increases in thawing rate, increased and reached peak values (10.3-11.0% FMP) after thawing at 1,800 degrees C/min. The percentage of sperm with normal apical ridge (NAR) also increased moderately with thawing rate, but the degree of improvement decreased as the glycerol level was increased. In semen frozen at 1 degree C/min, acrosomal integrity (NAR) was best maintained in 2% glycerol, reaching 22.9% NAR after thawing at 1,800 degrees C/min. In semen frozen at the optimal rate of 30 degrees C/min, the increases in thawing rates above 200 degrees C/min substantially improved motility. Motility was generally higher in semen protected by 4 or 6% glycerol, with the peak values of 44 or 46% FMP, respectively, after thawing at 1,200 degrees C/min. The proportion of sperm with NAR also increased with thawing rate, but as in the case of suboptimally frozen sperm it was influenced negatively by the glycerol concentration.(ABSTRACT TRUNCATED AT 250 WORDS)