Do Blanketed Horses Get Enough Vitamin D?

Horses derive vitamin D through the feedstuffs they ingest, but horses can also synthesize vitamin D when their skin is exposed to sunlight.

Under natural conditions, grazing horses are exposed to many hours of sunlight every day, theoretically producing enough vitamin D to meet their needs. However, some horses live indoors throughout the year, receiving very little sunlight, and others may be turned out only at night or when they are wearing rugs or blankets that leave little skin exposed to light.

Scientists at Massey University in New Zealand conducted a study* to check the vitamin D levels in the blood of 21 mature horses. During the six-month trial, the horses were pastured and also given supplemental hay. Five of the horses wore rugs and neck covers while the other 16 did not.  Blood samples and pasture samples were collected monthly and were analyzed for levels of vitamin D.

Horses that wore rugs showed a slightly lower serum vitamin D serum level than uncovered horses, but the difference was not significant. Dietary levels of vitamin D were high, indicating that the horses were able to get the necessary amount of this nutrient from fresh and harvested forage.

Vitamin D is important in skeletal growth and maturation. This trial was conducted with mature horses that were maintaining skeletal components rather than increasing bone mass. It is possible that younger horses spending a lot of their time in stalls might need supplemental vitamin D to meet their growth requirements. It is also possible that study periods of more than six months could have shown different results.

Owners who are concerned about vitamin levels for their horses should contact an equine nutritionist who can analyze the current diet and make recommendations for changes. Micro-Max, a low-calorie source of vitamins and minerals, is helpful for some horses and ponies that require supplementation but do not need the extra energy provided by grain meals. Micro-Max contains vitamin D as well as a number of other nutrients important to equine health. Horse owners in Australia can use Gold Pellet, a similar product.