Comparison of cryoprotective effects of iodixanol, trehalose and cysteamine on ram semen.

This study was conducted to improve cryosurvival of electroejaculated (EE) ram semen in the presence of iodixanol (OptiPrep™), trehalose or cysteamine. A tris-based extender was used to prepare 12 extenders containing OptiPrep™ (Op), trehalose (Tr) or cysteamine (Cy) alone, or different combinations of these compounds. Extenders were designated as follows: Tris (control), Op1.25 (1.25% Op, v/v), Op2.5 (2.5% Op, v/v), Op5 (5% Op, v/v), Tr50 (50mM Tr), Tr100 (100mM Tr), Cy (5mM Cy), OpTr (2.5% Op and 100mM Tr), OpCy (2.5% Op and 5mM Cy), TrCy (100mM Tr and 5mM Cy), OpTrCy1 (2.5% Op, 100mM Tr and 5mM Cy) and OpTrCy2 (1.25% Op, 50mM Tr and 2.5mM Cy). A two-step dilution was used and glycerol was added at 5°C in the second step. Diluted samples were equilibrated for 1h, loaded in 0.25mL straws and frozen in a programmable freezing machine. Supplementation of 5% OptiPrep™ significantly protected post-thaw progressive motility, membrane integrity, acrosomal integrity and morphological damages. Trehalose supplementation protected membrane integrity of ram sperm; however, it did not help post-thaw motility and morphology. Supplementation of 5mM cysteamine had detrimental effect on cryosurvival of EE ram semen. These results demonstrate that the supplementation of iodixanol increases the cryosurvival of EE ram semen in a dose-dependent manner.