NUTRIENT METABOLISM BY GUT TISSUES

The gut uses a disproportionate amount of energy (about 25% of total o xygen consumption) for the size of the tissue (about 6% of body weight ). Therefore, knowledge of metabolites used in gut tissues is importan t to assess nutrient needs. The VFA produced intraruminally are used t o varying degrees by rumen epithelial tissue. A review of net portal a bsorption data essentially confirms earlier studies that show acetate, propionate, and butyrate metabolism by stomach tissue to be 30, 50, a nd 90%, respectively, of ruminant production. Glucose also is used by rumen epithelial tissue; however, glutamine appears to be a poor subst rate for energy production. Tissue of the small intestine uses glutami ne, glucose, and ketones but does not use VFA very well for energy. Ce cal and colonic tissues can use glucose and glutamine for energy, but butyrate is the preferred substrate in both tissues.