We have already spoken in previous articles about oxygen reactive species and their harmful potential. These molecules can cause damage to DNA, proteins and lipids, and can affect the most different cells and tissues of the horse.
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Antioxidant substances play a protective role, preventing oxidation and reducing the risks associated with it.
Among the main antioxidants, the following stand out:
VITAMIN E
Vitamin E is possibly the best known and most studied antioxidant in horses. By vitamin E we mean several molecules (tocopherols and tocotrienols), the most potent and the one with the highest bioavailability being ?-tocopherol.
Vitamin E is a fat-soluble molecule capable of being incorporated into the lipid membrane of cells, protecting them from damage associated with oxidation. Not being produced by the horse, it must be supplied through the diet.
The requirements for this vitamin are 1 to 2 International Units (IU) per kilogram (kg) of live weight (bw) (NRC, 2007), which corresponds to 500 to 1000 IU in a 500 kg horse. Some investigators consider that vitamin E requirements may be higher, particularly in horses submitted to intense physical activity and on diets with a high lipid content. In case of doubt, the serum level of vitamin E should be evaluated and a supplementation protocol established accordingly.
Since vitamin E is naturally present in grass, permanent access to good quality pasture should in itself ensure that these needs are met.
In stabled horses, however, it is necessary to meet vitamin E needs in the form of compound feed, because plant processing and storage cause significant losses in this vitamin, with its content considered negligible.
Although excesses of this vitamin are well tolerated, they should be avoided considering that they can be harmful to the absorption of other substances (such as beta-carotene).
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VITAMIN C OR ASCORBIC ACID
Vitamin C, also known as ascorbic acid, contributes to the prevention of oxidative damage by capturing free radicals. This molecule works together with vitamin E, however, since the horse is capable of endogenous synthesis (that is, being able to produce this molecule), there are no defined requirements for the inclusion of this vitamin in the diet (NRC, 2007).
Additionally, there is no consensus regarding the hypothesis that oral supplementation translates into an increase in serum levels of this vitamin (some authors consider that its absorption after oral administration is poor, others question that it causes a decrease in its endogenous synthesis).
Supplementation may make sense in senior or immunocompromised horses.
BETA-CAROTENE
Beta-carotene is a precursor of vitamin A, a fat-soluble vitamin that prevents oxidative damage at the membrane level. Like vitamin E, it is an abundant vitamin in the pasture that suffers from the processing and storage of the plant, which is why it is normally added to compound feeds.
SELENIUM
Selenium works synergistically with vitamin E, which is why most vitamin E supplements include it. This mineral is also essential to the antioxidant activity of the enzyme glutathione peroxidase. Insufficient amounts of selenium affect the antioxidant activity of this enzyme. Excess should, however, be avoided as this substance presents a significant risk of toxicity.
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OTHER SUBSTANCES
In addition to vitamins and minerals with antioxidant properties, there are enzymes that perform the same function. These enzymes also depend on the presence of certain nutrients, such as iron (in the case of catalase), or copper, zinc and manganese (in the case of superoxide dismutase). The supply of these minerals through a properly balanced diet contributes to adequate antioxidant activity.
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