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Nutritional Requirements of Horses - Part 4

The Rusty Spur Tack, Feed & Pet

Reproduced with permission of Otter Co-op Feeds

In this multi-part series, we talk about the Nutritional Requirements of Horses including Energy, Proteins, Vitamins, Macro Minerals and Micro Minerals.

Part 4 – Vitamins

Vitamins are needed for all normal metabolic functions in a horse’s body and are divided into two classes.  Fat soluble and water soluble.  Horses are able to obtain most of the vitamins they require from their diet, their own body stores and from the bacteria that synthesize B-Complex vitamins in the digestive tract.  Exceptions would be horses under stress, brood mares, performance horses, young growing horses and senior horses who may all require supplemental vitamins.  Feeding a well fortified manufactured feed formulated in B.C. should fill any vitamin gaps that exist in a horse’s diet.  Remember to follow manufacturer’s feeding guidelines.


Fat soluble vitamins include vitamins A, D and E.  These are stored in the fat reserves of a horse’s body.  Green pasture is rich in fat soluble vitamins but forage that has been stored for some time will rapidly lose these vitamins.

-Vitamin A helps maintain health in cells that relate to skin, eyes and digestive tract as well as reproductive and immune systems as well as normal vision.  Green forage is an excellent source of vitamin A but additional supplementation is usually required.  Generally deficient in unfortified feeds and usually needs to be supplemented through fortified feeds and/or complete supplements.

-Vitamin D helps with growth and bone development.  Very rare to have a deficiency in horses as they produce their own Vitamin D when exposed to sunlight.  Stabled horses and horses during the winter when sunlight exposure is low can benefit from added Vitamin D.

-Vitamin E is very important for immune, nervous system and muscle functions, reproduction, muscle development, red blood cells and other chemical functions in a horse’s body.  Vitamin E is an antioxidant and is rapidly lost from stored forages and processed grains like COB.  Recent studies have shown that supplementation is essential for all horses.

Water soluble vitamins like vitamin C and B- Complex vitamins cannot be stored for long periods of time because of the lack of a place to store them in a horse’s body.

-Vitamin B-Complex vitamins are generally not deficient in horses as they are produced in large amounts by bacteria in the large intestine.  Freshness of forages and fortified feeds is critical to prevent oxidation of vitamins.  High quality fortified horse feeds are supplemented with b-complex vitamins including biotin to ensure horses that maybe getting marginal or reduced forage get enough to meet their requirements.

-Vitamin C  No deficiencies or toxicities has been reported in horses because they can manufacture what they require.