Three ejaculates from each of eight stallions were initially centrifuged in INRA 96 extender and spermatozoal pellets were resuspended in a milk/egg yolk-based freezing extender or an egg yolk-based freezing extender. Extended semen was exposed to a fast pre-freeze cooling rate (FAST -semen immediately subjected to cryopreservation) or a slow pre-freeze cooling rate (SLOW -semen pre-cooled at a controlled rate for 80 minutes prior to cryopreservation). After thawing, semen was diluted in initial freezing medium (FM) or INRA 96 prior to analysis of 9 experimental endpoints: total motility (MOT; %), progressive motility (PMOT; %), curvilinear velocity (VCL; µm/sec), average-path velocity (VAP; µm/sec), straight-line velocity (VSL; µm/sec), linearity (LIN; %), intact acrosomal and plasma membranes (AIVIAB; %), intact acrosomal membranes (AI; %), and intact plasma membranes (VIAB; %). Mean values for these endpoints were higher following spermatozoal exposure to a slow pre-freeze cooling period, regardless of freezing extender type (P<0.05). The effects of pre-freeze cooling rate on MOT, AIVIAB, AI, and VIAB were more pronounced in spermatozoa cryopreserved in MF extender, as compared to LE extender. Within treatment groups SLOW and FAST, mean MOT, AIVIAB, AI, and VIAB were higher (P<0.05) for spermatozoa cryopreserved in LE extender, as compared to MF extender.
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