Keto Acids/metabolism; Valerates/metabolism; Valine/metabolism; Animals; Bacitracin/pharmacology; Body Weight/drug effects; Butyrates/metabolism; Carbon Dioxide/biosynthesis; Carbon Radioisotopes; Chromatography, Thin Layer; Decarboxylation; Diet; Growth/drug effects; Intestinal Absorption; Intestine, Small/drug effects; Keto Acids/chemical synthesis; Keto Acids/pharmacology; Magnetic Resonance Spectroscopy; Malabsorption Syndromes/metabolism; Male; Neomycin/pharmacology; Pentanols/chemical synthesis; Pentanols/metabolism; Pentanols/pharmacology; Polymyxins/pharmacology; Rats; Valerates/chemical synthesis; Valerates/pharmacology; Valine/analysis; Valine/pharmacology