Sperm cryopreservation in the Burmese python Python bivittatus as a model for endangered snakes

Burmese pythons Python bivittatus captured in the Florida Everglades as part of an invasive species monitoring program served as a model for the development of sperm cryopreservation protocols for endangered snakes. Spermatozoa were collected from the vas deferens and initial motility, plasma membrane integrity and acrosome integrity were recorded before cryopreservation. Spermatozoa were extended in TES and Tris (TEST) yolk buffer with glycerol (GLY) or dimethyl sulfoxide (DMSO) concentrations of 8%, 12% or 16%, or combinations of GLY and DMSO with final concentrations of 4%:4%, 6%:6% or 8%:8%, and frozen at a rate of 0.3 degrees C min(-1). Sperm frozen in combinations of GLY and DMSO exhibited greater post-thaw motility and plasma membrane integrity than those frozen in GLY or DMSO alone. All DMSO and GLY:DMSO treatments preserved a greater proportion of intact acrosomes than GLY alone. To determine the best overall cryopreservation protocol for this species, a sperm quality index was calculated, giving equal weight to each of the three measured indicators of cryosurvival. This analysis revealed that Burmese python spermatozoa frozen in 6% GLY:6% DMSO or 4% GLY:4% DMSO exhibited the highest post-thaw viability. This study represents the first comparative, comprehensive attempt to develop a sperm cryopreservation protocol for any snake species.