Effects of five cryoprotective agents on quality of sheep epididymal spermatozoa during pre-freezing

The objective of this study was to test five cryoprotective agents during ram epidydimal spermatozoa incubation (at 4 °C), of up to 3 h, typical equilibration time before the freezing step begins, in order to establish a starting point for future freezing and thawing protocols. The parameters analyzed were: progressive motility (PM), vitality, and the plasma membrane functional integrity by the hypoosmotic swelling (HOS) test. Testes and epididymides were collected immediately after death. The tail of both epididymides were isolated and spermatozoa were recovered constituting one sample (n=20). A Tes–Tris–Yolk extender was employed. The extender contained five alternative CPAs: Dimethylacetamide (DMA), Dimethyl sulfoxide (DMSO), Ethylene glycol (EG), Glycerol (GLY) and Propylene glycol (PG) at three final concentrations: 2.5%, 5.0% and 10.0%. Control groups consisted of samples mixed only with the extender, without any CPA. All sample groups were exposed to the CPAs for 1 h or 3 h at 4 °C. EG exposure yielded better responses in both PM and HOS test parameters compared to extender only and also the other CPAs. There was no difference among all the treatments regarding vitality. EG (with best results at 2.5%) is thus proposed as a good CPA (followed by DMA as an explorable alternative) for the implementation of forthcoming ram epididymal spermatozoa freezing protocols.