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The whole gastrointestinal tract of monogastric animals is colonised by micro-organisms with highly variable metabolic potentials. Their metabolic activity and cell number is most pronounced in the hindgut, however significant bacterial nutrient conversion takes place in the small intestine, which is also the major site for host immune response and thus critical to the animals health status.
The actual knowledge on the biodiversity of intestinal microbiota is rather limited, due to various methodological problems. In addition to cultural techniques new techniques based on detection of bacterial ribosomal nucleic acids are available and will support our gain of knowledge in this field.
In this paper examples on the interaction of nutritional factors with intestinal bacteria are given. It was shown that elevated NSP concentrations in feed stimulate a specific functional group of bacteria which produce NSP-hydrolysing enzymes. Addition of a xylanase to a diet rich in arabinoxylans induced a shift of this specific microbial population towards proximal segments of the intestine in chickens. Furthermore, it was shown that studies on the response of bacteria to nutritional factors require techniques that are sensitive on the species level.
Furthermore, feed additives aimed to beneficially modify the intestinal microflora were studied. Probiotic bacteria do modify intestinal microbial populations, however, at present interpretation of underlying probiotic mechanisms including interactions with the epithelial tissue or the immune system are still of a hypothetical character.