Slow and ultra-rapid freezing protocols for cryopreserving mouflon (Ovis musimon) and fallow deer (Dama dama) epididymal sperm

This study examines the effectiveness of two methods for cryopreserving post-mortem epididymal sperm - conventional slow freezing employing a short equilibration time with glycerol, and ultra-rapid freezing - from the wild ruminant species Ovis musimon (mouflon) and Dama dama (fallow deer). A Tris-citric acid-glucose (TCG) + 12% egg yolk-based medium was used for the conventional slow freezing of the fallow deer sperm, whereas a Tes-Tris-glucose (TEST) + 6% egg yolk-based medium was used for the mouflon sperm. Glycerol was added to a final concentration of 5% to both media. The same diluents were used for ultra-rapid freezing but replacing the glycerol with 100 mM of sucrose. Sperm variables (motility, viability, acrosome integrity, membrane integrity, and morphological abnormalities) were analyzed before and after cryopreservation. Although values were generally better after the thawing of the conventionally cryopreserved sperm, total sperm motility (38.40 ± 4.44% in mouflon and 31.25 ± 3.37% in fallow deer) and total live sperm (47.19 ± 5.18% in mouflon and 43.13 ± 2.43% in fallow deer) were acceptable for the ultra-rapidly cooled sperm. Independent of the cryopreservation method, membrane integrity, acrosome integrity and the percentages of dead sperm and sperms with a damaged acrosome were better for the cryopreserved mouflon sperm than the fallow deer sperm (P < 0.05). Despite exerting a more harmful effect on sperm variables than conventional freezing, ultra-rapid freezing may be a useful alternative for the cryopreservation of these species' epididymal sperm in the field, as this simple technique does not require sophisticated equipment and expertise.