Vitamin D
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 by 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).