Bull and Line Differences in the Survival of Spermatozoa after Freezing and Thawing

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Abstract
A study of the differences among bulls, among different inbred lines, and among different periods in the survivability of spermatozoa was made before and after freezing to -79[degree] C with 12 Holstein-Friesian bulls representing 6 different inbred lines. Before freezing the diluted semen contained a final concentration of 7.5% glycerol and each milliliter of diluted semen contained about 20 million spermatozoa. Spermatozoa were allowed to equilibrate at a temperature of 5[degree] C for 18 hours before freezing. Semen was observed for per cent survival and type of motility of the spermatozoa at 0, 1, 3, 7, 14, 28, 56 and 84 days post-freezing. A marked difference was found among bulls in the ability of their spermatozoa to withstand freezing, although there were no significant differences prior to freezing. No line differences were seen at any of the pre- or post-freezing periods, and as such this study does not indicate any evidence of genetic difference in the survival of spermatozoa before or after freezing. A highly significant decline in ther per cent survival of spermatozoa was seen from period to period. The rate of decline was the highest during the first two weeks after freezing. Although the rate of decrease in motility of spermatozoa with time in storage in a mechanical freezer at -89[degree] C differed among bulls, the per cent of motile spermatozoa after 12 weeks storage generally could be predicted immediately after freezing.