Vitamins A

Vitamin A was the first fat-soluble vitamin to be discovered and characterized. It has essential roles in vision, bone and muscle growth, reproduction, and maintenance of healthy epithelial tissue. Either vitamin A or a precursor must be provided in the diet. However, it is among the most highly variable nutrients in feeds. Plants do not contain vitamin A, and most grains other than yellow corn are almost devoid of the carotenoid precursors that provide plant sources of vitamin A activity. Consequently, vitamin A is a frequent nutritional concern, which has been extensively reviewed, most workers rank vitamin A deficiency next to protein and calorie deficiency as a worldwide health problem. It is the most important vitamin in ruminant animal diets and is almost universally added to commercial diets for nonruminant animals. Inadequate vitamin A intake may result in reduced feed intake, edema, lacrimation, xeropthalmia, nyctalopia (night blindness), slow growth, low conception rates, abortion, stillbirths, blindness at birth, abnormal semen, reduced libido, susceptibility to respiratory and other infections, and death. When several of these other signs are present, vitamin A deficiency should be suspected.