Effects of sub-optimal glycerol concentration and cholesterol-loaded cyclodextrin in a Tris-based diluent on cryopreserved ram sperm longevity and acrosomal integrity

Cryopreservation Techniques for Ram Sperm

Germplasm storage and transportation in artificial insemination (AI) and other advanced technologies are facilitated by cryopreservation. In reproduction, the cryopreservation of sperm allows it to be transported across vast distances and used even after the sire's death. However, the technique of cryopreservation might damage sperm and limit their activity. Several cryobiological investigations have reported that the integrity of the sperm membrane is frequently involved in the physical and biological elements that affect sperm survival at low temperatures during the cryopreservation process. However, successful cryopreservation of ram sperm is still a work in progress because a considerable percentage of sperm do not survive the freezing and thawing process. Sperms are destroyed during cryopreservation of semen due to varying concentrations of cryoprotective chemicals and if semen is not cooled at optimal cooling rates. Hence, it is crucial to know the optimum cooling rates with freezing and thawing protocols for maximum recovery of viable and functional sperm cells for a successful cryo-freezing of ram spermatozoa. Therefore, the current study compiled and compared the research on the impact of different cryopreservation procedures, cooling rates, equilibration time, and thawing protocols on post-thaw ram semen quality.

Effect of different levels of glycerol and cholesterol-loaded cyclodextrin on cryosurvival of ram spermatozoa

This study was conducted to determine the optimum level of glycerol and cholesterol-loaded cyclodextrin (CLC) in a Tris-based diluent for cryopreservation of ram spermatozoa. Ram semen was treated with 0, 1.5, 3 or 4.5 mg CLC/120 × 10(6)  cells in Tris-based diluents containing 3, 5 or 7% glycerol in a factorial arrangement 3 × 4 and frozen in liquid nitrogen vapour. Sperm motility, viability (eosin-nigrosin staining) and functional membrane integrity (hypo-osmotic swelling test) were assessed immediately after thawing (0 h) and subsequently after 3 and 6 h at 37°C. There was an interaction between CLC and glycerol on the functional membrane integrity (p < 0.05). In the presence of 3% glycerol, the highest functional membrane integrity (32.2%) was found in the spermatozoa treated with 1.5 mg CLC/120 × 10(6)  sperm. Post-thaw sperm motility was highest in 1.5 mg CLC immediately after thawing (40.5%) and after 3-h (30.6%) incubation at 37°C (p < 0.05). Viability of spermatozoa was higher in all CLC treatments than in the untreated samples, and it was highest (33.9%) in the spermatozoa treated with 1.5 mg CLC (p < 0.05). These data indicate that the addition of cholesterol to sperm membranes by 1.5 mg CLC/120 × 10(6)  cells may allow the use of a lower concentration of glycerol (3%), which is sufficient to mitigate the detrimental effects of freezing and thawing.