Vitamins A, D, E, and K are fat-soluble vitamins and are mainly involved in tissue development, calcium and phosphorus metabolism, antioxidant defense, and blood clotting, respectively.
Vitamin A is essential for vision, reproduction, and tissue development. Grains and oilseeds commonly used in swine diets have a precursor of vitamin A, b-carotene, which is converted in vitamin A in the intestine of the pig. However, b-carotene is found in low concentration and is easily degraded. Vitamin A deficiency is characterized by blindness, incoordination, reproductive failures, and low growth rate. Vitamin A toxicity develops above 20,000 IU/kg for growing pigs and 40,000 IU/kg for sows, and signs include scaly skin, rough hair coat, and incoordination (NRC, 2012).
Vitamin D is essential for calcium and phosphorus absorption and thus, is important for bone mineralization. Grains and oilseeds commonly used in swine diets have a form of vitamin D which requires exposure of pigs to sunlight to become active. In enclosed swine facilities, the active form of vitamin D, vitamin D3, needs to be supplemented in the diet. Vitamin D deficiency is characterized by rickets in growing pigs and osteoporosis in sows, which are manifested as lameness and fractures. Vitamin D toxicity develops above 2,200 IU D3/kg for long-term feeding or 33,000 IU D3/kg for short-term feeding, and causes mineralization of soft tissues (NRC, 2012).
Vitamin E is important for antioxidant defense. Vitamin E and selenium have closely related functions, but requirements are independent of one another. Vitamin E content in grains and oilseeds commonly used in swine diets is mostly lost during storage and processing. Vitamin E deficiency signs are similar to signs of selenium deficiency, which includes white muscle disease, mulberry heart disease, sudden death, and impaired reproduction.
Vitamin K is essential for blood clotting. Vitamin K is available in feedstuffs of plant origin (K1), produced by the intestinal microbiota of pigs (K2), and added to the diet in synthetic form (K3). Vitamin K deficiency is characterized by prolonged blood clotting time and hemorrhages.