The role of dietary fibre in the digestive physiology of the pig

Dietary fibre (DF) is usually defined as the sum of plant polysaccharides and lignin that are not hydrolysed by endogenous enzymes of the mammalian digestive system (non-starch polysaccharides and lignin). The amount and composition of DF varies over a wide range between and within feedstuffs. Furthermore, a precise distinction between dietary fibre and starch is far from easy. Therefore, the analysis as well as the physiological function of DF in the digestive tract of the pig can vary considerably. The age or body mass of the pig also interacts with the digestive processes and there is an adaptation developing in the animal over the time of exposure to fibrous diets. DF is generally considered as a fraction with a low energy content. This diluting effect of the diet is used to increase the feed intake during low performance of animals. DF influences transit time with a reduction in the upper and increase in the lower digestive tract and, therefore, decreases the digestibility of almost all nutrients and energy. On the other hand, it increases the microbial growth in the gastrointestinal tract. This can lead to an increased excretion of nutrients in faeces. Finally, DF beneficially influences well-being and health. Fibrous feedstuffs give pigs the opportunity to chew the feed over a longer time. More short chain fatty acids are produced and eventually undesired micro-organisms are excluded. A regular peristaltic action avoids the possibility of constipation. (C) 2001 Elsevier Science B.V. All rights reserved.