Vitamin D Cholecalciferol

Vitamin D2 (ergocalciferol) is found in some plants. Vitamin D3 (cholecalciferol) is the form found in animals and is synthesized in the skin when exposed to sunlight from a form of cholesterol derivative. As dietary sources are low (Lucerne is better than most other forages) it is commonly supplemented as Vitamin D3 in manufactured feeds.

Vitamin D acts as a steroid hormone controlling the homeostasis of Calcium & Phosphate partly by influencing absorbtion of Calcium from the intestine and partly by mobilization of bone minerals. Deficiency of Vitamin D causes Osteomalacia in adults or Ricketts in young animals due to decalcification and weakening of bones. Classical Ricketts is not seen in foals though alterations to bone density and growth plate morphology can be caused experimentally by low Vitamin D diets and avoidance of sunlight. Deficiency disease is not reported under normal situations and the requirements are presumed to be met through exposure to sunlight. Supplementation may be of use for horses kept mostly indoors for long periods.

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