Knud Erik Bach Knudsen, PhD
Professor & Section Manager - Molecular Nutrition & Reproduction
Department of Animal Science
Aarhus University, Denmark
Fiber is not a well-defined chemical entity, but a term that in both human and animal nutritional literature has been defined by the method applied for its analysis; crude fiber, neutral detergent fiber, acid detergent fiber and dietary fiber. Because the fiber methods are based on different analytical principles the values reported for the same feedstuff can vary by a factor of 4 to 6. Nevertheless, the fiber fraction represents the part of the feed that cannot be digested by endogenous enzymes but requires microbial enzymes for its degradation. Consequently, the fiber fraction is the least digestible part of the feed and with physicochemical properties that can influence the digestion and absorption processes in all parts of the gastrointestinal tract. For instance, in the small intestine rate and extent of glucose absorption can be influenced by soluble dietary fiber and type of starch and in the large intestine the composition of short-chain fatty acids can be influenced by the composition of the substrate available for fermentation. As a result, the profile of assimilation products is directly linked to the dietary carbohydrate composition with consequences for the whole-body metabolism and for the utilization of nutrients. Results from the author’s research projects on sows and pigs and the literature will be used to illustrate these aspects.