Previously, we have shown that survival of cat sperm is maintained in both non-egg yolk, semi-defined extenders and in extenders with greatly reduced levels of egg yolk (2%). Usually, cryoprotectant is added to extended samples after gradual cooling to 4°C, but recent reports have shown that satisfactory sperm survival can be obtained after addition at 22°C. Here, our objectives were to examine sperm survival after (1) cryopreservation from 22°C vs after gradually cooling to 4°C or (2) cryopreservation in a completely defined extender without animal or plant proteins vs extender + 2% egg yolk. Epididymides from local veterinary clinics were dissected in HEPES 199 medium (He199). The sperm suspension was filtered (40 μ), layered onto a density gradient column and centrifuged at 650 × g for 20 min. Then, the sperm pellet was resuspended in 1 mL of He199 and centrifuged for 5 min at 800 × g and the subsequent pellet was extended in TEST Buffer with either 0% (0% EY) or 2% egg yolk (2% EY). Next, 0% EY samples were further split into 2 groups—either gradually cooled to 4°C before 12% glycerol (1:1) was added (4C-0%EY) or 12% glycerol (1:1) was added at 22°C without cooling (22C-0%EY). Control samples extended in 2% EY were cooled to 4°C before addition of 12% glycerol (1:1) (4C-2%EY). Samples were loaded into 0.25-mL straws and placed in a –80°C freezer for 20 min before storage in LN2. Sperm samples were thawed in air (22°C) for 5 s and immersed in a 60°C water bath for 5 s. After a 7-step addition of He199, samples were centrifuged at 800 × g for 5 min and pellets resuspended in He199. Sperm samples were evaluated for motility (Mot; computer-assisted semen analysis, 37°C) at 0 h (initial assessment), after cooling to 4°C (PC) and at 0-h (0-PT) and 3-h post-thaw (3-PT) incubation at 37°C. Membrane integrity (MI; SYBR 14-PI) and acrosomal status (AS; FITC-PNA) were analysed at the initial assessment, 0-PT and 3-PT. Results are shown in Table 1. At 4°C (PC), sperm extended in 0% EY and 2% EY maintained 92 and 91%, respectively, of their initial motility (66%). At 0-PT and 3-PT, motility in the 3 groups had decreased by >50% and >70%, respectively. Motility at 3-PT in the 22C-0%EY treatment was less than the other 2 treatments (P < 0.05; 1-way ANOVA). At 0-PT, samples in the 4C-2%EY group had a higher membrane integrity value (P < 0.05) than did the 22C-0%EY group, whereas that of the 4C-0%EY group was not different from the other 2 groups. However, at 3-PT, both groups cooled to 4°C before cryopreservation had higher membrane integrity values (P < 0.05) than the group cryopreserved at 22°C. At 0-PT and 3-PT, the percentage of sperm with intact acrosomes ranged from 69% (4C-2%EY) to 59% (22C-0%EY) and from 55% (4C-2%EY) to 43% (22C-0%EY) of the initial value (89%), respectively. In summary, we demonstrated that cat epididymal sperm could be frozen successfully in a completely defined TEST-buffered extender. Furthermore, we confirmed that addition of cryoprotectant (i.e. glycerol) after gradual cooling to 4°C is beneficial to post-thaw survival.
Table 1.Motility (Mot), membrane integrity (MI) and acrosomal status (AS) of cat epididymal sperm before and after cryostorage
DNA and lipid susceptibility of rat epididymal sperm cells exposed to chronic and intermittent hypobaric hypoxia