Beef cattle have defined requirements for vitamins. In some instances, vitamin supplementation may be necessary to avoid deficiencies. Vitamins are classified into two categories: water-soluble and fat-soluble. Water-soluble vitamins include the B vitamins, such as riboflavin, thiamin, and niacin, as well as vitamin C. Fat-soluble vitamins include vitamins A, D, E, and K. Supplementation for beef cattle generally focuses on vitamins A and E. This is because the rumen microbes synthesize the water-soluble vitamins and vitamin K in sufficient quantities to avoid deficiencies. Vitamin D requirements can often be met by exposure to the sun and would therefore only be of concern for cattle in confinement housing.