L-carnitine and acetyl-L-carnitine enhance stallion sperm quality during semen storage at 5°C

Carnitine, a powerful antioxidant, has an essential role in sperm energy metabolism. Among carnitines, only L-carnitine’s effect on stallion semen has been tested and not acetyl-L-Carnitine. Therefore, we aimed to determine the ideal concentrations of L-carnitine (LC) and acetyl-L-carnitine (AC) and their effects on stallion semen cooled at 5℃ for up to 48 hours. Semen was extended to 50 x 106 sperm/ml in commercial extender (Control), and concentrations of 5, 10, and 15 mmol/l of LC and AC were evaluated in Experiment 1. Sperm motility and plasma membrane integrity were assessed by CASA and epifluorescence microscopy, respectively. In Experiment 2, the combination of the intermediate doses of LC (10 mmol/l) and AC (10 mmol/l) was tested. Sperm parameters were evaluated as in Experiment 1 and in addition, DNA fragmentation index (DFI), production of reactive oxygen species (ROS), and lipid peroxidation (PEROX) were evaluated by flow cytometry. All analyses were performed at 0, 24, and 48 hours after semen collection, processing, and cooled-stored at 5°C. In Experiments 1 and 2, the groups supplemented with LC and AC or LC+AC had higher plasma membrane integrity and motility parameters compared to Control group (p < 0.05). The LC and AC combination did not change sperm parameters compared to LC or AC alone (p > 0.05). No differences (p > 0.05) were observed for DFI, ROS, and PEROX. In conclusion, LC and AC’s addition, alone or in combination, enhanced sperm motility and plasma membrane integrity of stallion sperm after cooled-storage at 5℃ for up to 48 hours.