Antioxidant Effects of Thyme (Thymus vulgaris) Extract on Ram Sperm Quality during Cryopreservation

Oxidative stress during freezing-thawing reduces sperm motility, viability, membrane functions and anti-oxidant capacity. Thymus vulgaris has antioxidant properties due to phenolic compounds. The purpose of current study was to evaluate the effect of Thymus vulgaris extract as a natural antioxidant on post-thawed Moghani ram sperm quality. Semen samples were collected twice a week from four rams. Samples were then pooled and diluted with Tris based extender supplemented with different concentrations of Thymus vulgaris (0, 2, 4, 8, 12 and 16 mL per dL diluent solutions). Following the cooling and equilibration stages for semen samples, the samples were frozen and stored in liquid nitrogen until evaluation. Following this freezing procedure, samples were thawed, and the sperm motility and velocity parameters, viability and plasma membrane integrity were evaluated. Our results showed that the addition of 2 and 4 mL/dL extracts at the extender stage increased the total motility percentages (P<0.05). Addition of 4 mL/dL extract im-proved progressive motility and percentages of viability compared to the control group and high levels of extract groups (P<0.05). Plasma membrane integrity of sperm in 4 and 8 mL/dL extract groups were greater (P<0.05) than the control and 12 and 16 mL/dL extract groups. Also, addition, 16 mL/dL extract had a sig-nificantly negative effect on all evaluated traits (P<0.05). In conclusion, supplementation of extender with intermediate amounts of Thymus vulgaris extract improves the quality of ram sperm after freezing and thawing in a dose-dependent manner.