Biotin, a water soluble B vitamin, is essential for post- absorptive metabolism in animals. A deficiency of the vitamin is frequently associated with lesions of the skin and poor hair growth. Biotin may be supplied from the diet or by microorganisms in the digestive tract. The importance of dietary supply in pre-ruminant animals and the contribution of microorganisms from the rumen and elsewhere in the digestive tract following rumen development has not been adequately characterised.