Selenium
Selenium is an important component of enzymes involved in antioxidant defense. Selenium and vitamin E have closely related functions, but requirements are independent of one another. Feedstuffs grown in low-selenium soil, as is the case of many areas in the United States, are deficient in selenium. Selenium deficiency signs are similar to signs of vitamin E deficiency, which includes white muscle disease, mulberry heart disease, sudden death, and impaired reproduction. Selenium toxicity at levels of 5 to 10 ppm selenium is characterized as chronic selenosis, with signs of low growth rate and separation of the hoof at the coronary band. Selenium toxicity at levels above of 10 to 20 ppm selenium is characterized as acute selenosis, with signs of posterior paralysis and lesions in the central nervous system (NRC, 2012; Gomes et al., 2014). The amount of selenium inclusion is regulated in the United States and restricted to a maximum of 0.3 ppm added selenium in any swine diet.