Centrifugation and addition of glycerol at 22 degrees C instead of 4 degrees C improve post-thaw motility and fertility of stallion spermatozoa

The aims of this study were to evaluate the effects of cooling rate to 4 de greesC and temperature at the time of centrifugation/glycerol-addition (fre ezing extender: INRA82 + 2% egg yolk + 2.5% glycerol) on postcentrifugation recovery rate, post-thaw motility and per-cycle fertility. When centrifuga tion/glycerol-addition was performed at 4 degreesC (14 ejaculates), a moder ate cooling rate (37 degreesC to 4 degreesC in 1 h) resulted in higher post -thaw motility (45%) than when using a slow cooling rate (37 degreesC to 4 degreesC in 4 h) (39%; P<0.05). When centrifugation/glycerol addition was p erformed at 22<degrees>C (37 degreesC to 22 degreesC in 10 min) (10 ejacula tes), post-thaw motility was lower when spermatozoa were frozen directly fr om 22 degreesC (23%) than when spermatozoa were cooled to 4 degreesC (22 de greesC to 4 degreesC in 1 h) before freezing (47%; P<0.0001). When centrifu gation/glycerol-addition was performed at 22<degrees>C (before cooling at a moderate rate), as opposed to 4 degreesC (after cooling at a moderate rate ), a significant improvement of 1) recovery of spermatozoa after centrifuga tion (P<0,0001), 2) postthaw motility of spermatozoa at thawing (40% vs 36% (n<less than or equal to>291 ejaculates/group), P<0.0001) and 3) per-cycle fertility (56% vs 42% (n<greater than or equal to>190 cycles/group), P<0.0 1) was observed. In conclusion, centrifugation/glycerol-addition at 22<degr ees>C followed by cooling to 4 degreesC at a moderate rate results in an im provement of post-thaw motility, spermatozoa recovery rate and per cycle fe rtility. (C) 2000 by Elsevier Science inc.