Vitamin D3

Vitamin D designates a group of closely related compounds that possess antirachitic activity. It may be supplied through the diet or by irradiation of the body. The two most prominent forms of vitamin D are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D facilitates calcium absorption from the intestine and reabsorption of calcium from the kidney, and influences both mobilization and accretion of calcium (and phosphorus) from bone. Vitamin D3 is the most common supplemental form of vitamin D for horses.

Vitamin D can be destroyed by over-treatment with ultraviolet (UV) light and by peroxidation in the presence of rancidifying polyunsaturated fatty acids (PUFA).