Evaluation of Three Different Extenders for Use in Emergency Salvaging of Epididymal Spermatozoa from a Cantabric Brown Bear

Contents The Cantabrian brown bear (Ursus arctos) constitutes an endangered subpopulation of the European brown bear in the north of Spain. We have carried out a post-mortem recovery of epididymal spermatozoa from a Cantabrian brown bear (7 years old, 170 kg; 30 min post-mortem), cryopreserving those recovered from the cauda epididymis (929 x 106 spermatozoa, 54% motile, 82% cytoplasmic droplets). For freezing, three extenders based on Test-Tris-Fructose + 4% glycerol were used: (1) 325 mOsm/kg and 10% egg yolk; (2) 430 mOsm/kg and 15% egg yolk; (3) 300 mOsm/kg, Equex-EDTA and 20% egg yolk. After thawing, we obtained higher motility for extender 3 (31%), but extender 2 yielded the highest viability (66.9%) and mitochondrial activity (67.1%). Caffeine stimulation showed that extender two rendered the highest recovery values of post-thawing motility with respect to the fresh sample. In conclusion, epididymal spermatozoa of brown bear can be frozen applying an extender with osmolality similar to epididymal environment.