Effect of antioxidants on intracellular enzymes and the sperm membrane lipid peroxidation in bull semen freezing extender of Holstein and Simmental breeds

The sperm cell membrane is prone to oxidative stress and peroxidative damage due to an increase in reactive oxygen species (ROS) caused by the freezing process. The aim of present study was to determine the effect of different levels of reduced glutathione (GSH) and superoxide dismutase (SOD) antioxidants in freezing extender on the biochemical parameters of frozen–thawed bull semen. Thirty five ejaculates (5 ejaculate per bull) were collected from Holstein (n = 4) and Simmental (n = 3) breeds. Semen samples with appropriate conditions were pooled (separately for each replicate of each breed) and were diluted in Tris-egg yolk containing 5 and 7.5 mM GSH and 100 and 150 IU/ml SOD and an extender with no additives (control). Semen samples were cooled to 5°C during 2 h then they were filled and frozen in 0.5 ml French straws. Malonaldialdehyde (MDA) level, the intracellular activity of SOD and glutathione peroxides (GPx) enzymes were assayed after thawing samples. Results showed that, the addition of both levels of GSH to the semen freezing extender significantly decreased MDA level compared to the control group (P<0.05). However, the addition of 5 mM GSH improved GPx activity compared to the control group in Simmental breed (P <0.05). Generally, the results of this study showed that, the addition of 5 or 7.5 mM of GSH to the Tris-egg yolk extender has a positive effect on intracellular defense system and reduction of sperm membrane lipid peroxidation.