The influence of the gut microflora and of dietary fibre on epithelial cell migration in the chick intestine.

1. The renewal of the intestinal mucosal epithelium has been investigated in germ-free and conventional chicks given a practical chick diet and a low- and high-fibre diet, using tritiated thymidine to label the nuclei of mucosal cells undergoing division. 2. Villus height, crypt depth and number of mitoses in the crypt were generally, although not always significantly, greater for conventional chicks than for germ-free chicks at all sites investigated in the intestine, and all became progressively lower from the upper intestine to the lower intestine. 3. There was a linear relationship between the height of the radioactively labelled mucosal cells on the villus and the period after injection, and the rates of epithelial cell migration were higher for conventional than for germ-free chicks, the relative differences being greater in the lower intestine than the upper intestine. 4. The inclusion of wheat bran as a source of dietary fibre had no effect on the rate of epithelial renewal, either in germ-free or conventional birds.