Evidence of oxidativestress in horses has been described in reports dealing with intense and enduranceexercise. Oxidative stress occurs when antioxidant systems are insufficientcausing oxidation to potentially damage DNA, proteins, and lipids, and contributeto degenerative changes. Vitamin E is the most commonly supplemented antioxidantin horses and has been shown that horses in exercise conditioning may requirehigher intakes of vitamin E than recommended. Also in various species vitaminC potentiates the effects of vitamin E; however, under maintenance conditionshorses have the ability to synthesize sufficient ascorbate, the demand increasesas stress on the body is increased. Competitive endurance horses were estimatedto consume 1.2 to 5-times higher levels of vitamin E than recommended intakes.In these horses a negative correlation was found between the vitamin E intakeand creatine kinase, and aspartate aminotransferase. Similarly, three-day eventhorses have vitamin E average intakes about 50% over recommended levels, andit was also found that intake of vitamin E negatively correlated with inflammatorymarkers. However, large doses of vitamin E at about 10-times the recommendedlevels could potentially interfere with beta-carotene absorption. While somestudies have shown benefits of lipoic acid supplementation in endurance trainedhorses similar to that of vitamin E, other studies failed to show any benefitof supplemental superoxide dismutase in intensely exercising horses. The implicationsfrom this broad scope of work show potential benefits for supplementing variousantioxidants however, before assuming efficacy from other species horse specificstudies should be performed.
