Stalled Horses May Need Extra Vitamin D

Like humans, horses derive vitamin D from ultraviolet light, primarily sunshine. Horses kept outdoors and exposed to sunlight generally do not need vitamin D supplementation. However, those deprived of sunlight, such as show horses that are kept indoors, may benefit from dietary supplementation with vitamin D. A concentrate fortified with vitamin D would satisfy the requirement for this vitamin, as would eating a diet consisting of 50% fresh, sun-cured alfalfa (lucerne) hay.

Supplementation of vitamin D in the concentrate portion of the diet seems to be warranted due to the important role of the vitamin in bone growth and the variability young show horses may have to sunlight exposure. In addition, losses in vitamin content of forage that has been stored for long periods make prediction of dietary vitamin D content difficult.

Vitamin D should not be given in an effort to treat developmental orthopedic disease (DOD) by increasing calcium and phosphorus absorption and bone mineralization. DOD has not been shown to be caused by vitamin D deficiency, and supplementation with vitamin D will not make up for diets that are not properly fortified with calcium and phosphorus. Oversupplementation of vitamin D to horses causes toxicity and results in extensive mineralization of cardiovascular and other soft tissues.