Dietary fatty acids have been shown to affect the activity of the immune system in a variety of species (Calder, 1998) although the exact mechanism by which they influence the nature of the immune response is unclear. The effect of dietary fatty acids on the fatty acid composition of intestinal mucosa is important since this tissue has a rapid turn over and is a major site of antigenic exposure and immune defence. The speed with which changes in dietary fatty acid intake are reflected in the fatty acid composition of cells and tissue of the body varies. In ruminants the development of a functional rumen greatly influences the nature of the fatty acids available for absorption from the small intestine, however, in pre-ruminant animals, milk may be used as a medium to supplement the diet with specific dietary fatty acids. This work was carried out to establish the extent to which different oil supplements could change the fatty acid composition of intestinal mucosa in milk fed pre-ruminant calves.