Effects of green tea extract on sperm quality, reactive oxygen species and lipid peroxidation in long-term liquid preservation of boar spermatozoa

During storage, boar spermatozoa undergo several changes including diminished motility and viability and accumulated reactive oxygen species (ROS). In this study, we investigated the effects of green tea extract (GTE) supplementation in the Sui Dil extender on the sperm motility, viability, ROS and lipid peroxidation (LPO) of long-term preserved boar semen at 17°C. A total number of eight boars were used for this experiment. Pooled ejaculates were diluted to 20 × 10⁶ sperm/ml in the Sui Dil extender containing 0 (control), 1, 10, 100 or 500 mg/l GTE and were preserved at 17°C for 24, 72, 120 and 168 h, respectively. At each storage time, sperm motility and viability were estimated by microscopic examination and the fluorescent double stain Fertilight®, respectively. Sperm ROS level and LPO were assessed using the 2’, 7’-dichlorodihydrofluorescein diacetate (H₂DCFDA)/propidium iodide (PI) and C11-BODIPY581/591/PI with flow cytometry, respectively. Compared to that of the 500 mg group, there were higher sperm motility and viability in the 1, 10 and 100 mg GTE groups during the preservation from 24 to 168 h (p < 0.05). The ROS levels of the 10 and 100 mg groups during the 168 h preservation were lower than those of the 0, 1 and 500 mg groups (p < 0.05). There were no significant differences in LPO regardless of the preservation period or the GTE concentration. In conclusion, the optimal concentrations (10 and 100 mg/l) of GTE that led to lower ROS levels may be useful for liquid boar sperm preservation at 17°C for a period of 168 h.