damage to muscles.

Antioxidants are added to many horse feeds and supplements as they are widely perceived to benefit competing and exercising horses. How do antioxidants supplements work in the horse’s body and how does their function benefit horses in training?

What are Antioixdants?

The term “Antioxidants” refers to a group of chemicals that stop oxidation. They are “anti” “oxidation”. Oxidation occurs when a charged molecule (electron) is taken from one atom by another. The atom which lost its electron is now charged. Charging an atom, is like goading a bull, they are going to react! Charged atoms roam around trying to retrieve their lost electron, by stealing an electron from other atoms. This is the process of “Reactive Oxygen Species” (ROS) generation. Where one charged atom interacting with other atoms, sets off a self-perpetuating chain reaction of more and more charged atoms – also termed “reactive oxygen species”.

Reactive oxygen species include the well-known damaging molecules “free radicals” and also fat derived peroxides. These ROS are destined to attempt to interact with and steal electrons from any molecule they come into contact with. Often they interact with and damage:

  • DNA
  • Cell walls (lipids)
  • Proteins (such as muscle fibres)
  • Joints

Types of Antioxidants for Exercising Horses

When exercising, as the horse’s respiratory rate increases, so does their oxygen consumption and cellular metabolism. This leads to a rise in ROS production throughout the body, and in the muscles in particular.

Muscles naturally contain a variety of antioxidant mechanisms that reduce the impact of oxidative damage, during times of increased ROS production. The array of antioxidant mechanisms employed by the muscles includes;

  • Muscle cell produced antioxidants
    • Superoxide dismutase (SOD) – copper, manganese or zinc dependant
    • Glutathione peroxidase (GPX) – selenium dependant
    • Glutathione (GSH)
    • Co-enzyme Q10
  • Dietary derived antioxidants
    • Vitamin E
    • Vitamin C
    • Carotenoids

It is clear from the list above, that particular nutrients are required for optimum functioning of the muscles antioxidant mechanisms for exercising horses.

Copper, Manganese & Zinc

Horses have an absolute requirement for these trace elements, and they have many functions in the body among which is the proper functioning of Superoxide dismutase. This enzyme is present within the muscle cells and acts to defuse the superoxide free radical.

Exercise training for horses increases the muscle’s content of superoxide dismutase, meaning as training progresses the horse is better able to defuse free radicals. Typically the requirement for copper, manganese and zinc in exercising horses is met by their increased dietary intake.


Glutathione peroxidase is considered the main antioxidant of horses. It neutralises highly reactive peroxide radicals. The proper functioning of this enzyme is completely dependant on selenium availability. Most of a horse’s dietary intake of selenium is used in the functioning of glutathione peroxidase. Exercise training increases glutathione peroxidase concentration in the muscles, resulting in more efficient neutralisation of peroxide free radicals. Selenium is often supplemented to horses in training or competition to ensure adequate supply.

Vitamin E

Vitamin E is one of the most widely distributed natural antioxidants. Its main function is to stop free radical damage to cell walls.

It is well recognised that exercising horses have a greater intake requirement for Vitamin E than horses at rest. The recommended intake of vitamin E is approximately 2500mg Vitamin E for an adult race horse daily. Studies have shown improved racing performance in horses supplemented with Vitamin E. Furthermore studies have also shown supplementation with both vitamin E and selenium improves immune system in horses.

Vitamin C

Vitamin C has two functions as an antioxidant for horses. Vitamin C scavenges and eliminates harmful free radicals itself. Vitamin C also recycles Vitamin E, allowing it to continue to function as a free radical inhibitor.

Vitamin C is often included in horse supplements for its antioxidant role and also for the benefits it imparts to respiratory immunity. Exercise in horses increases the production of reactive oxygen species, which damage muscle cells and DNA.

Antioxidants, whether created by the body or supplied by the diet are a crucial defence in limiting the damage of reactive oxygen species. Increased training and competition, increases the need for antioxidant provision in the body. Dietary supplementation with Selenium, Vitamin E and Vitamin C can help meet this need.

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