Vitamin D has long been referred to as ‘the sunshine vitamin’, so as dark winter days are upon us and less turnout and more rugging becomes the norm, how can we be sure our horse’s requirements are being met?

1. Horses produce their own vitamin D! A form of cholesterol in the skin is converted to vitamin D in the presence of UV light. Consequently, it is sensible to supplement the diet of horses that are stabled or rugged for long periods.


2. Vitamin D is important for strong bones and teeth and is involved in the absorption of calcium and phosphorus. Although less common, vitamin D deficiency may lead to rickets in young horses or osteomalacia in adult horses – a condition in which reduced vitamin D intake results in calcium being drawn from the bones causing them to soften, weaken and become deformed.

3. Vitamin D requirements do not increase as result of work, pregnancy or lactation. However at 18 months of age, the requirements of growing horses are almost 90% higher than adult horses. Feeding the recommended ration of compound horse feed or balancer alongside suitable forage will ensure your horse’s requirements are met, regardless of their exposure to sunlight.


4. As excess vitamin D is stored in the liver, it can be harmful if oversupplied and toxicity may lead to the calcification of soft tissue. Although feeds produced by reputable manufacturers will not lead to toxicity if fed at the recommended ration, the feed with the highest level of vitamin D is not automatically better for your horse.

5. Vitamin D is also considered a hormone because it is produced it is produced in one area of the body and acts on another. Cholecalciferol (a form of cholesterol) is converted to vitamin D3 in the skin which is transported via the lymph-blood system to to the liver and then finally to the kidneys where it is converted to an ‘activated’ form that can be used by the body. This final product (dihydroxycholecalciferol) is then released back into the blood stream where it regulates the absorption calcium and phosphorus under hormonal control.

For more information on providing a balanced diet for your horse contact the SPILLERS Care-Line on 01908 226626.