Vitamin D

The term ''vitamin D'' is appropriate for all steroids having cholecalciferol biological activity. Cholecalciferol itself is synonymous with vitamin D3, as distinguished from ergocalciferol, which is also called vitamin D2. Commercially, vitamin D3 is available as a spray-dried product or (frequently in combination with vitamin A) as gelatin-coated beadlets; one international unit is equal to 0.025 mg of cholecalciferol.[3] These products are quite stable if stored as the vitamin itself at room temperature. In complete feeds and mineral-vitamin premixes, 4 to 6 mo. of storage may cause activity losses of up to 30%.[2] Vitamin D precursors are present in plant (ergosterol) and animal (7-dehydrocholesterol) feedstuffs, but they require ultraviolet irradiation for conversion into active D2 and D3, respectively. Vitamin D3 has more biological activity than D2. Hydroxylated forms of cholecalciferol [25-OH D3, 1a-OH D3, 1,25(OH)2 D3] contain more D3 bioactivity than D3 itself.

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