Abstract

Lycopene (LYC) is a plant-derived antioxidant that ameliorates oxidative and other stress-related damage in spermatozoa yet its inclusion in ovine freezing medium remains largely unexplored. In this study semen was collected from eight Oura-type Tibetan sheep with three ejaculates per male and cryopreserved in freezing medium supplemented with 0, 1, 2, 4, 8 and 16 μM LYC to identify the optimal concentration and evaluate its effects on structural integrity antioxidant status and fertilizing capacity. A dose of 2 μM LYC proved optimal markedly improving post-thaw survival and motion kinetics relative to the control ( P  < 0.01). At both 25 °C and 4 °C this concentration prolonged survival and increased the proportion of live cells at each observation point. It also enhanced acrosome ( P  < 0.01), head membrane ( P  < 0.05) and tail membrane ( P  < 0.01) integrity and elevated mitochondrial membrane potential (MMP) ( P  < 0.05). Compared with the control the 2 μM LYC group showed lower reactive oxygen species (ROS) and malondialdehyde (MDA) levels ( P  < 0.01) and higher superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) ( P  < 0.05 and P  < 0.01 respectively). In vitro fertilization (IVF) trials revealed that 2 μM LYC increased cleavage ( P  < 0.05) and blastocyst formation rates ( P  < 0.01) without affecting blastocyst cell number ( P  > 0.05). In a cervical artificial insemination (AI) programme pregnancy rates were 44 % for the 2 μM LYC group versus 28 % for the control. We conclude that adding 2 μM LYC to the freezing medium improves post-thaw quality counters oxidative stress and enhances the fertilizing capacity of Oura-type Tibetan sheep spermatozoa.