Unlike many vitamins that are produced by ruminal bacteria, vitamin A is a requirement in the diet of cattle. Cattle convert carotene from leaves of plants to vitamin A in the wall of the small intestine. Vitamin A is necessary for vision, maintenance of epithelial tissue and mucous membranes, bone development, and immune function. Since vitamin A is a fat soluble vitamin, cattle can store it in their liver when their daily intake is 3 to 5 times greater than their requirements. Mature cows can store up to 4 months of vitamin A in their livers under plentiful conditions. Therefore under ideal conditions cattle fed good quality hay during the winter will have adequate vitamin A levels from carotene in hay and accumulated liver stores. However, under less than ideal situations vitamin A supplementation may be required to maintain proper health and reproductive performance of the cow and normal development and health of calves.