Cryosurvival of dog spermatozoa at different glycerol concentrations and freezing/thawing rates

Techniques for canine semen freezing need to be optimized in order to maxim ize pregnancy rates and to increase the number of AI-doses obtainable from a single ejaculate. To improve these techniques, simultaneous investigation of different aspects of the cryopreservation process must be performed, to find the best combination of extender and freezing and thawing rate. Four ejaculates were obtained from each of five dogs, and split-samples were dil uted in a Tris citrate glucose extender containing 0.5% Equex STM Paste and either 3 or 5% glycerol. Two ejaculates from each dog were frozen at a slo w freezing rate (10 degrees C/min in the range -6 degrees to -40 degrees C) and two at a fast freezing rate (50 degrees C/min in the range -6 degrees to -40 degrees C), in 0.5 mi straws using a programmable freezer. Prior to evaluation, the straws from each freezing rate and glycerol concentration w ere thawed in a water-bath, either at 38 degrees C for 1 min or at 70 degre es C for 8 s. Samples of cryopreserved semen were evaluated for motility an d for the proportion of spermatozoa having an intact plasma membrane, immed iately after thawing and during 5 h of incubation at 38 degrees C. The high er glycerol concentration and the faster thawing rate tested favoured the r ecovery of living and motile spermatozoa and their survival during incubati on, while the tested freezing rates had no influence on sperm post-thaw lon gevity.