Survival Rates of Rapidly Frozen Bovine Spermatozoa

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Abstract
Sub-samples of semen from each of 2 ejaculates from each of 12 bulls were extended with a yolk-citrate-glycerol extender, equilibrated 5 to 6 hours at 5[degree]C, and placed directly in a freezing bath at temperatures of +5, 0, -5, -10, -15, -20, -25, -30, -35, and -40[degree]C. The freezing bath was cooled at the rate of 0.8[degree]C per minute from +5 to -15[degree]C, at a rate of 5[degree]C per minute from -15 to -40[degree]C, and at the rate of 10[degree]C per minute from -40 to -75[degree]C. Percentage of motile spermatozoa in ampules subsequently stored in a mechanical freezer at -85[degree]C for 60 days were, in order of decreasing temperature of the freezing bath at the time of transfer, 29, 21, 24, 27, 33, 36, 35, 35, 35, and 35. From these data it is concluded that time can be saved and a higher percentage of motile spermatozoa recovered by transferring the semen abruptly from +5[degree]C to a freezing bath ranging from -20 to -40[degree]C, and subsequently cooling as indicated to -75[degree]C.