Determination of temperature and cooling rate which induce cold shock in stallion spermatozoa.

Experiments were conducted to determine temperatures between 24 and 4 degrees C at which stallion spermatozoa are most susceptible to cold shock damage. Semen was diluted to 25x10(6) spermatozoa/ml in a milk-based extender. Aliquots of extended semen were then cooled in programmable semen coolers. Semen was evaluated by computerized semen analysis initially and after 6, 12, 24, 36 and 48 hours of cooling. In Experiment 1A, semen was cooled rapidly (-0.7 degrees C/minute) from 24 degrees C to either 22, 20, 18 or 16 degrees C; then it was cooled slowly (-0.05 degrees C/minute) to a storage temperature of 4 degrees C. In Experiment 1B, rapid cooling proceeded from 24 degrees C to either 22, 19, 16, or 13 degrees C, and then slow cooling occurred to 4 degrees C. Initiating slow cooling at 22 or 20 degrees C resulted in higher (P<0.05) total and progressive motility over the first 24 hours of cooling than initiating slow cooling at 16 degrees C. Initiation of slow cooling at 22 or 19 degrees C resulted in higher (P<0.05) total and progressive motility over 48 hours of cooled storage than initiation of slow cooling at 16 or 13 degrees C. In Experiment 2A, semen was cooled rapidly from 24 to 19 degrees C, and then cooled slowly to either 13, 10, 7 or 4 degrees C, at which point rapid cooling was resumed to 4 degrees C. Resuming the fast rate of cooling at 7 degrees C resulted in higher (P<0.05) total and progressive motility at 36 and 48 hours of cooled storage than resuming fast cooling at 10 or 13 degrees C. In Experiment 2B, slow cooling proceeded to either 10, 8, 6 or 4 degrees C before fast cooling resumed to 4 degrees C. There was no significant difference (P>0.05) at most storage times in total or progressive motility for spermatozoa when fast cooling was resumed at 8, 6 or 4 degrees C. In Experiment 3, cooling units were programmed to cool rapidly from 24 to 19 degrees C, then cool slowly from 19 to 8 degrees C, and then resume rapid cooling to storage temperatures of either 6, 4, 2 or 0 degrees C. Storage at 6 or 4 degrees C resulted in higher (P<0.05) total and progressive motility over 48 hours of storage than 0 or 2 degrees C.