Vitamin D for horses in the Northwest


“I am currently supplementing all of my horses (10) with Mega Dose which supplies 8000 IU of Vitamin D3.  I live on the coast of Oregon where our horses are blanketed a lot due to weather and sunlight is in short supply this time of year.  Should I consider a Vitamin D supplement during the winter?  (Requirements call for 22000 IU of D.)”

Vitamin D in horses in the Northwest


Answer by Ph.D. Equine Nutritionist, Kelsey Johnson-Nonella:

Thank you for the question. When feeding your horses a 4 ounce scoop of Mega Dose your horses are receiving 2,000 IUs of vitamin D. Your horses are also receiving 2000-10,000 IUs of vitamin D from your hay. An average 1,100 lb horse requires 3,300 IUs of vitamin D daily per the National Research Council. So your horses are receiving enough vitamin D from Mega-Dose and hay to meet their vitamin D requirement even with the limited exposure to sunlight. No need to supplement your horses with extra vitamin D. Below I have included a table showing the requirement of vitamin D for each stage of horse.

Table 5: Comparisons of Daily Vitamin D Requirements for a Horse with Mature weight of 1100 pounds.
State of Production or GrowthD (IU)
12 months of age5,600
Early pregnancy3,300
Lactation (3 months)3,300
Moderate exercise3,300
  1. Nutrient requirements are estimated from the National Research Council’s Recommendations for Nutrient Requirements of Horses (2007). b) These levels take into account all sources of vitamins in the diet including hay, grains and supplements. b) Different sources of vitamins will have differing concentrations of vitamins so accounting for ingredients and reading labels is important.

Front Image of Digestive, Hoof and Hair and Vitamin 10lb Mineral Supplement for horse health.


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