Effect of thawing rate and cold post-thaw temperatures on bovine semen packaged in glass ampules.

Experiment I was designed to test the effect of thaw rate on semen packaged in glass ampules. One ejaculate from each of 10 Holstein bulls was diluted in egg yolk-citrate-glycerol, packaged in 1.0 ml glass ampules and frozen in liquid nitrogen vapor. Water bath thaws of 5 C for 10 rain, 20 C for 4 rain, 35 C f o r 4 min, 50 C for 75 sec, 65 C f o r 4 8 sec, 80 C for 37 sec and 100 C for 20 sec were compared. Comparisons were based on percentage of motile spermatozoa and percentage intact acrosomes. Initial estimates of moti l i ty and percentage intact acrosomes were made immediately following thaw (0 hr) and again at 4 and 8 hr of incubation at 37 C. Overall means (averages of O, 4 and 8 hr for all ejaculates) for percentage intact acrosomes were 34.5, 24.2, 32.4, 46.3, 47.6, 50.3 and 52.2 for the 5 C, 20 C, 35 C, 50 C, 65 C, 80 C and 100 C thaws, respectively. Significant damage to spermatozoa (P<.O1) resulted following thaws of 20 C while thaws of 35 C did not differ from 5 C thaws. For moti l i ty and percentage intact acrosomes there was a significant (P<.O1) ejaculate x thaw rate interaction. However, all ejaculates responded favorably to thaws above 35 C. Overall means for percentage of motile spermatozoa (all ejaculates at O, 4 and 8 hr) were greater (P<.O1) following thaws above 35 C when compared to the 5 C and 20 C thaws. Experiment II was designed to compare the effect of sudden post-thaw temperature reduction on semen thawed at various rates. Thaws