INFLUENCE OF DIET COMPOSITION ON THE MICROBIAL ACTIVITY IN THE GASTROINTESTINAL-TRACT OF DOGS .3. IN-VITRO STUDIES ON THE METABOLIC-ACTIVITIES OF THE SMALL-INTESTINAL MICROFLORA

Investigations were performed in vitro with ileum chyme collected from one fistulated dog. The chyme was incubated anaerobically with several feedstuffs (carbohydrates or proteins, and combinations of a protein source with glucose or soya oil). In four consecutive experimental periods, the nutrition of the donor dog was varied (dry food, canned food, lung, dry food and lactose) to test potential influences on the microbial metabolic activities in vitro. The composition of the fermentation gas (hydrogen, hydrogen sulphide, methyl mercaptan) and the pH and production rates of volatile fatty acids were measured. In vitro fermentation intensity varied depending on the nutrition of the donor dog, lower gas formation was observed if the dog was fed on a dry food, while higher values were found after ingestion of lung or the addition of lactose to the dry food. H-2-formation was high after the incubation of ileum chyme with protein-rich feedstuffs, especially if animal proteins were used as substrates (meat meal, greaves, fish meal, casein). plant products (corn or wheat gluten, soya meal and isolated soya protein) induced considerably lower 2(H)-production, and isolated carbohydrates (mono-, di-, oligosaccharides, starch) were fermented with low gas production only. Hydrogen sulphide and methyl mercaptan were found at high concentrations in the fermentation gas after incubation of ileum chyme with animal proteins. The production rates of volatile fatty acids increased under these conditions, with a significant rise in butyrate concentrations compared with incubations of carbohydrates. Interactions between feedstuffs could be demonstrated in vitro: the cofermentation of a protein source (casein) with glucose changed the fermentation pattern significantly (enhanced H-2-production, reduced levels of sulphur gases). Soya oil as an additive did not influence either gas production or the other parameters. In conclusion, the in vitro investigations show that the microflora of the canine ileum has considerable proteolytic activity, especially if animal proteins are available as substrates. In vitro investigations into the metabolic activities of small intestinal bacteria can be a useful alternative to in vivo investigations, but, for the interpretation of test results, additional in vivo data are required.