Vitamin C, also known as ascorbic acid, is an important water-soluble vitamin for horses. It works together with vitamin E and selenium to provide antioxidant protection against cell damage. [1][2]

In addition to its antioxidant properties, Vitamin C plays other roles in the horse’s body including involvement in collagen production, hormone synthesis, and bone calcification. It also supports the absorption of iron from the gut. [3]

Horses do not have a nutritional requirement for vitamin C because they can typically synthesize enough of this vitamin in their liver. However, older horses, those with compromised liver function, or other health conditions such as chronic infections and respiratory illness may benefit from supplemental vitamin C. [3][4]

When choosing a Vitamin C product for your horse, keep in mind that ascorbic acid is relatively unstable and degrades quickly when mixed into a feed or supplement. Choose vitamin C supplements that provide this ingredient in a stable form.

Vitamin C for Horses

Vitamin C’s primary role in the horse’s body is as a powerful antioxidant that protect cells from oxidative stress and damage caused by harmful free radicals. By neutralizing these free radicals, vitamin C contributes to the overall health and function of cells, supporting various physiological processes. [1]

This essential nutrient also supports joint health, immune function and hormone synthesis in its role as an enzyme co-factor.

Roles of Vitamin C

Vitamin C is necessary for several physiological functions in horses, including: [6]

  • Antioxidant Protection: Free radicals, which are reactive molecules produced during metabolism, can cause oxidative damage to DNA, fats, and proteins. Antioxidants play a crucial role in neutralizing these free radicals, thereby providing protection against such oxidative damage.
  • Immune Function: Vitamin C accumulates in cells of the immune system and enhances their ability to kill microbes. [19]
  • Collagen Production: Vitamin C is a cofactor for enzymes involved in making collagen, which is an important protein found connective tissues such as cartilage, ligaments, and tendons.
  • Vitamin D Conversion: Vitamin C is needed for the conversion of vitamin D3 to its active form calcitriol.
  • Hormone Production: Vitamin C is involved in making norepinephrine (noradrenaline), an important stress hormone and neurotransmitter.

Sources of Vitamin C for Horses

Endogenous Production

Like most mammals, horses can make ascorbic acid from glucose in their liver. A healthy horse can produce an estimated 72 grams of ascorbic acid per day. [4]

Humans and guinea pigs are the only mammals that cannot synthesize vitamin C internally. Unlike humans and guinea pigs, horses have the enzyme L-gulonolactone oxidase in their liver, which enables endogenous Vitamin C production. [4]

The adrenal gland also stores a limited reserve of ascorbic acid. However, prolonged exposure to stressors can deplete vitamin C reserves. In this case, endogenous production may not be sufficient to maintain adequate levels of this vitamin in the body. [4]

Dietary Sources

Horses can also obtain vitamin C through dietary intake by consuming plants that produce vitamin C for their own antioxidant protection. While the vitamin C content has not been measured in forages typically consumed by horses, in other plants the levels range from 25 – 800 mg of ascorbate per 100 grams of fresh weight. [18]

It is hypothesized that vitamin C content is lower in hay compared to fresh pasture. This is because ascorbic acid is oxidized when exposed to heat and light, both of which are required to make hay.

Horses can also obtain vitamin C from certain commercial dietary supplements formulated to provide this nutrient either as part of a premix or on its own.

Veterinarians may also recommend subcutaneous, intramuscular, or intravenous injections of vitamin C for horses that require a higher dose due to a medical condition. [15]

Mad About Horses
Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.
Apple Podcasts Spotify Youtube
Mad Barn - Equine Nutrition Consultants | Mad Barn Canada

Vitamin C Requirements for Horses

The National Research Council (NRC) currently does not list a specific vitamin C requirement for horses. [7] Researchers believe that healthy horses can synthesize enough vitamin C in their liver to meet their needs.

Recommended Intake Level

Although there is currently no dietar