Extender osmolality, glycerol and egg yolk on the cryopreservation of epididymal spermatozoa for gamete banking of the Cantabric Chamois (Rupicapra pyrenaica parva)

Abstract

Germplasm banking is a key technology enabling the ex-situ conservation of wild species. However, cryopreservation protocols must be tested to assure the applicability of the banked material. The objective of this study was defining a range of parameters for the composition of a semen extender for Cantabrian chamois epididymal spermatozoa (post-mortem collection). The freezing extender was based in a TES-Tris-fructose buffer, modifying its composition in three experiments: Osmolality of the buffer (320, 380 or 430 mOsm/kg, 8% glycerol, 15% egg yolk), glycerol (4 or 8%, 430 mOsm/kg, 15% egg yolk), egg yolk (10 or 15%, 430 mOsm/kg, 4% glycerol). Sperm was extended at 100 mill. spermatozoa/ml, cooled at 5 °C and frozen at −20 °C/min. Sperm quality was assessed pre and post-thawing (CASA, HOS test, abnormal forms, cytoplasmic droplets, and viability and acrosomal damage by flow cytometry). Freezability was good overall, with total motility of 65.5% ± 2.4 initial and 55.8% ± 2.4 post-thawing. The extenders affected the post-thaw sperm quality marginally. Whereas osmolalities and glycerol concentrations seemed not to differ, 430 mOsm/kg and 4% glycerol might be preferred. Egg yolk concentrations only differed on sperm velocity (VCL: 84.0 ± 6.7 μm/s in 10% vs. 70.7 ± 6.2 μm/s in 15%, P < 0.05). Our results suggest a good cryotolerance of chamois epididymal spermatozoa, with a preferred extender composition of hyperosmotic buffer, glycerol in the 4% range and lower egg yolk (10% range) than other ruminants.