Vitamins are biological compounds, which are active in extremely small amounts.
Vitamins of concern in beef cattle nutrition include: Vitamin A, Vitamin D and Vitamin E. They are usually reported in international units (IU's). Fresh forage is a good source of Vitamins A,D and E. Vitamin content of well preserved hay is initially high, but declines over time. Silages usually contain low amounts since the fermentation process destroys most of the vitamins. Grains usually contain relatively low amounts of these vitamins.
Vitamin A is essential for normal growth, reproduction and maintenance. Insufficient Vitamin A is associated with lowered fertility in both bulls and cows. Vitamin D is required for proper development of bone. Vitamin D deficiency in calves results in bowing of the leg bones (rickets). In older animals bones become weak and easily fractured. Vitamin E and /or selenium causes nutritional muscular dystrophy, commonly called white muscle disease. This may be prevented by proper dry cow management and adequate levels of Vitamin E and Selenium.