Fat-soluble vitamins can be stored in appreciable amounts in the body (liver and adipose tissue); whereas, the water-soluble vitamins cannot be stored in the body. Rumen microbes have the ability to synthesize vitamin K, vitamin C, and the B-complex vitamins. The main discussion of this article will focus on vitamins A, D, and E with short discussions of important features of the other vitamins as they relate to modern production practices.