The bioavailability and stability of natural and crystalline vitamins is affected by exposure to heat, ultraviolet (UV) light, moisture, pH (acids or bases), and trace min-erals.[3,4,11,12] Crystalline vitamin A stability has been improved with technology in the production process by incorporating the vitamin into a small beadlet of stable fat or gelatin. For vitamins A and E, esters are more stable than the alcohol forms. Vitamin stability in premixes and complete feeds may also be enhanced by adding natural antioxidants or synthetic antioxidants such as ethoxyquin, butylated hydroxytoluene (BHT), or butyl-ated hydroxyanisole (BHA).[4,12] Pelleting, a processing method commonly used in the swine industry, is destructive to most vitamins because it produces friction (abrasion), pressure, heat, and moisture. Pelleting may increase the bioavailability of niacin and biotin.[3,4] Extrusion is more destructive than pelleting because it produces higher moisture, pressure, heat, and redox reactions.[11,12] Extrusion is widely used in the pet food industry. Higher concentrations of vitamins are normally added to pelleted or extruded diets to compensate for the increased losses in vitamin activity.
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