‘Antioxidants’ is a mysterious category of supplements commonly fed to horses despite a general lack of understanding by the average horse person as to what they actually do. Most of us would suggest that antioxidants just make our exercising horses appear to ‘do better’ or ‘feel better’ without really being able to say with any certainty what aspect of health or performance is actually improved.
Essentially, you can think of antioxidants as a biological vacuum cleaner. During times of physiological stress, such as that created by exercise, the increased consumption of oxygen leads to production of reactive oxygen species (ROS) which can break down proteins and impair function of tissues. The body launches natural antioxidant defenses against ROS, but when lots are being produced (such as during exercise), consumption of oxygen and consequent production of ROS can ‒ and frequently does ‒ exceed the body’s ability to clean up the ROS mess, contributing to exercise intolerance and fatigue.
Dietary antioxidants help maintain a balance between oxygen consumption and persistence of ROS in exercising tissues. Part of the contribution of ROS to the development of fatigue during exercise is the ROS-caused ‘stiffening’ of red cell membranes. Red cells are the delivery wagon for oxygen to exercising tissue, and in order for them to effectively to their job, red cell membranes need to stay as flexible as possible so they can move through tiny capillary beds, deliver their oxygen cargo, and take away carbon dioxide waste.