Question
One of our foals was diagnosed with OCD in both knees and hocks. I’ve asked several veterinarians and professors about the influence of vitamin D in bone formation, but apparently the role of vitamin D is of little importance. I can hardly believe this, as I’ve seen products based on the plant Solanum glaucophyllum, which contains a metabolite of vitamin D called 1,25-dihydroxycholecalciferol, help youngsters of other species with growth problems, namely poultry and swine. Could I obtain the same effect in horses by adding some of this metabolite to the feed of foals? What experience do you have with this in horses? Would you try this to improve bone and cartilage formation in young horses?
Answer
True vitamin D deficiency is not seen in horses, except maybe in extreme abuse cases, and this is why experts might not have a lot to say on the subject. A horse only needs exposure to sunlight and sun-dried forage to meet the minimal requirement of vitamin D. That said, the importance of additional vitamin D in the development and maintenance of bone in horses is well understood. Vitamin D is an ingredient in most bone-building supplements for horses, as is calcium. Researchers at Kentucky Equine Research have included vitamin D in its bone supplements DuraPlex and Triacton. Look for Bone Food Plus in Australia.
A horse may benefit from vitamin D supplementation if it is kept stalled without exposure to sunlight, if it lives in the more northerly latitudes in the darker months of the year, or if it is only turned out with a blanket. In fact, these are reasons why feed manufacturers add vitamin D into their concentrate feeds. Supplemental vitamin D may be effective as a bone-builder in poultry and swine because of their housing situations and lack of exposure to direct sunlight.
Whether your growing horses may benefit from supplemental vitamin D would depend on many factors: (1) housing situation, e.g., kept inside for long periods of time without access to the sun; (2) type of forage fed, e.g., sun-dried hay; and (3) types of concentrates or supplements fed and their vitamin D content.
I have no experience with 1,25-dihydroxycholecalciferol glycoside or the plant Solanum glaucophyllum (commonly known as waxyleaf nightshade) as a source of vitamin D in horses, but there are reports of poisonings and deaths in horses from overconsumption of the plant. However, extracts of the plant appear to be equal in effectiveness to synthetic vitamin D as a supplement.
Vitamin D works in concert with calcium and phosphorus, so before supplementing with vitamin D, I would recommend a diet evaluation for your horses. A nutrition advisor at Kentucky Equine Research can provide you with a free consultation to ensure adequate amounts of calcium and phosphorus are present in the diets of your growing horses. This evaluation will also reveal the nutrient balance of the entire ration.
Other important aspects of the diet aside from vitamin D may have an influence on bone health. Nutrition is only one factor that can influence the development of osteochondritis dissecans (OCD).
