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Vitamin D For Horses: Quick Facts - Horse Curator Skip to content
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Vitamin D For Horses: Quick Facts

Vitamin D is fat soluble.  Fat soluble vitamins are stored within the body’s fat and liver and can become toxic if certain levels are reached.

Why Vitamin D Is Important For Horses :

  • It maintains the levels of calcium in the blood.
  • It is required for the absorption of both calcium and phosphorous which are key minerals for bone health.
  • It has a role in cell growth and development.
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Vitamin D is vital for proper absorption of calcium and phosphorus. This two minerals are important for strong bones.

Signs Of Vitamin D Deficiency In The Horse:

  • Deficiency is known to cause rickets in others animals and contribute to weak bones. Rickets is rarely observed in horses.
  • Research suggests that deficiency may play a role in insulin resistance.
  • Research is now being conducted to determine if deficiency may contribute to gastric ulcers.

Signs Of Vitamin D Toxicity In Horses:

Signs of vitamin D toxicity are not visible but can be deadly. Excess levels cause calcium to deposit in the soft tissues and joints. Too much vitamin D is a known contributor to calcification of the blood vessels, heart, kidney and other organs. It is may also contribute to osselets, bone spavins and ringbone. It is important to note toxicity has not been found in horses that are out in the sun all day. The body only processes what is needed.

Vitamin D Sources For Horses:

Vitamin D is known as the sunshine vitamin. A few hours of daily exposure to sunshine usually maintains healthy levels. It is also found in sun cured hay, though levels start to deplete after 6 months of storage. Small quantities are also found in most fortified feeds.

Vitamin D Supplements For Horses:

Vitamin D and its’ role and its’ effects in the equine body is probably the second most researched vitamin after vitamin E. It is the most common overdosed vitamin due to over supplementation. Because so many horses are now kept in stalls or are covered with blankets or sheets while outside, vitamin D deficiency has become a concern. Most experts agree that horses turned out in pastures and paddocks each day without blankets or sheets do not need supplementation. Opinions vary about added supplements for horses that are stalled and do not receive several hours sun exposure each day. Because vitamin D toxicity can have dire consequences, vets and nutritionists advise checking levels through a blood test before increasing the dosage.

Recommended NCR Daily Requirements of Vitamin D For Horses (2007):

  • Requirements for all adult horses including mares pregnant or lactating, stallions and horses under a heavy work load
    • 1,000 pound (460 kg) adult horse – 3036 I. U.
    • 1,100 pound (500 kg) adult horse – 3300 I. U.
  • Foals
    • 6 months estimated weight 476 lbs. (216 kg) – 3972 I. U.
    • 7 months estimated weight 522 lbs. (237 kgs) – 4740 I. U.
    • 8 months estimated weight 567 lbs. (257 kgs) – 5131 I. U.
    • 9 months estimated weight 606 lbs. (275 kgs) – 5492 I. U.
    • 10 months estimated weight 641 lbs. (291 kgs) – 5827 I. U.
    • 11 months estimated weight 642 lbs. (307 kgs) – 6137 I. U.
    • 12 months estimated weight 708 lbs. (321 kgs) – 6424 I. U.
    • 13 months estimated weight 736 lbs. (334 kgs) – 6690 I. U.
    • 14 months estimated weight 765 lbs. (347 kgs) – 6936 I. U.
    • 15 months estimated weight 789 lbs. (358 kgs) – 7164 I. U.
    • 16 months estimated weight 814 lbs. (369 kgs) – 7374 I. U.
    • 17 months estimated weight 833 lbs. (378 kgs) – 7569 I. U.
    • 18 months estimated weight 853 lbs. (387 kgs) – 7750 I. U.
    • 19 months estimated weight 873 lbs. (396 kgs) – 7917 I. U.
    • 20 months estimated weight 891 lbs. (404 kgs) – 8072 I. U.
    • 21 months estimated weight 906 lbs. (411 kgs) – 8215 I. U.
    • 22 months estimated weight 919 lbs. (417 kgs) – 8348 I. U.
    • 23 months estimated weight 934 lbs. (424 kgs) – 8470 I. U.
    • 24 months estimated weight 946 lbs. (429 kgs) – 8584 I. U.

 It is important to remember when considering additional supplementation of vitamins, minerals, electrolytes or amino acids to consider all sources of hay, grain (nearly all grain is fortified) , grazing, and other supplements to ensure proper levels and avoid toxicity.