Equex STM paste improves post-thawed epididymal sperm motility and acrosome integrity in rhesus monkey (Macaca mulatta).

Equex STM paste, a water-soluble detergent, exerts the protective effect of egg-yolk during sperm cryopreservation. This study aims to evaluate the post-thaw quality of rhesus monkeys' epididymal spermatozoa in the Tris-citric-glucose egg-yolk extender, supplemented with or without Equex STM paste (0.5%, v/v) (n = 6). Sperm motility, progressive motility, motion characteristics, viability, acrosome integrity and mitochondrial activity were compared immediately post-thaw. Equex STM paste supplementation significantly improved sperm motility (35.0 ± 4.5 vs. 23.7 ± 5.0%), progressive motility (15.4 ± 2.1 vs. 9.8 ± 2.7%) and percentage of sperm with intact acrosome (30.4 ± 4.5 vs. 26.3 ± 4.6%) compared to the controls, respectively. This is the first report applying Equex STM paste for monkey epididymal sperm cryopreservation and is expected to be beneficial as a model for endangered non-human primates.