**4. Effect of vitamins and minerals**

The glutathione peroxidase is main intracellular antioxidant enzyme that catalyses to reduce the hydrogen peroxide and organic hydroperoxides to nontoxic metabolized compounds. The essential component of this enzyme is selenium. Vitamin E or alpha-tocopherol is the dominant antioxidant in cell plasma membranes. Many researches have shown a synergism of antioxidant activity between selenium in glutathione peroxidase and vitamin E. The ef‐ fects of selenium supplementation on semen quality were more reported than the effects of vitamin E supplementation, and selenium supplementation improved in higher conception rates when gilts were serviced with extended semen from the boars [33]. However, feed ad‐ ditive on boar diet with high levels of vitamin C had no effects on semen quality or libido characteristics in healthy boars. U.S. Food and Drug Administration (FDA) regulations al‐ low up to 136 g of selenium add on/pound of feed for pigs.

Vitamin C or ascorbic acids are a dominant water-soluble antioxidant. Their action is scav‐ enger to disable the function of any type ROS. Vitamin C is a powerful source of electron donor which reacts with hydroxyl radicals, peroxide and superoxide to form de-hydroxyl ascorbic acid. The level of ascorbic acid in seminal plasma is approximately 10-fold higher concentration comparing with blood plasma in human [30,34]. The level of ascorbic acid in seminal plasma has a positively correlation with the percentage of normal [35].
