Melatonin Has a Beneficial Effect on Stallion Sperm Quality in Cool Condition

• Evaluation of melatonin as an antioxidant on quality of cooled stallion spermatozoa.
• The level of 1.5-mM melatonin can improve sperm motility, viability, and malondialdehyde level.
• Melatonin has a potent inhibitor of lipid peroxidation on stallion spermatozoa.
• High concentration of melatonin could not improve stallion semen quality parameters.

The objective of this study was to evaluate the effects of melatonin on quality of Caspian stallion spermatozoa during cooling preservation. Semen of stallions were collected and diluted with Kenney's extender that was supplemented with different antioxidant concentrations: no melatonin and dimethyl sulfoxide (DMSO) (negative control [NC]); 0.9% (vol/vol) DMSO (vehicle control [VC]); 1-mM melatonin (M-1); 1.5-mM melatonin (M-1.5); and 2-mM melatonin (M-2). Total and progressive motility, viability, plasma membrane integrity, and lipid peroxidation (LPO) were determined at 0 (fresh), 6, 24, and 48 hours after the start of cooling. Total motility was greater in M-1.5 extender (63.6 ± 3.12%) than in M-2, NC, and VC extenders (P < .05) during 48 hours of storage. Progressive motility was greater in M-1.5 extender (35.97 ± 2.79%) than in M-2 extender (P < .05) during 48 hours of storage. The percentage of plasma membrane integrity was greater in M-1.5 (57.58 ± 3%) than in M-2, NC, and VC during the 48-hour storage (P < .05). The percentage of sperm viability during the 48-hour storage was greater in M-1, M-1.5, and M-2 than in NC and VC extenders. The results showed that malondialdehyde concentration was lower in M-1.5 and M-2 (1.34 ± 0.2 and 1.36 ± 0.2 nm/mL, respectively) than in other extenders during 48 hours of storage. Also, all sperm parameters with exception of LPO were decreased with increasing storage time. In conclusion, the results showed that semen extender containing M-1.5 improved sperm quality of Caspian stallion during 48 hours of storage in cool condition.