Viscosity of dietary fibre in relation to lipid digestibility in broiler chickens

The aim of the thesis was to identify the physicochemical properties of nonstarch polysaccharides (NSPs) that are most relevant to the nutrition of the broiler chicken. More specifically, the mechanisms by which fibre viscosity can affect lipid digestibility in broiler chickens have been investigated in a series of experiments. The effect of fibre viscosity per se was investigated by using carboxymethylcelluloses (CMC) with varying viscosity. The CMC types were non-fermentable in vitro . Fibre viscosity per se depressed the digestibility of lipids, protein and starch in broiler chickens fed diets containing CMC with varying viscosity. The effect of fibre viscosity on lipid digestibility was dependent on the type of fat. The digestibility of animal fat that was predominantly composed of saturated long chain fatty acids was depressed, whereas there was no effect on the digestibility of soyabean oil or coconut oil. The reduction in lipid digestibility coincided with a reduced bile salt concentration and raised microbial numbers in the small intestine. CMC did not affect the condition of the small intestinal mucosa. The morphological parameters indicated that the condition of the mucosa was even improved in CMC fed birds. A study with germfree rats and rats with a specific pathogen free intestinal flora revealed that the effect of CMC on lipid digestibility is mediated, at least partially, by the intestinal flora. it was concluded that the small intestinal microflora can mediate the antinutritive effect of fibre viscosity on lipid digestibility in broiler chickens. Moreover, it was proposed that a reduction in bile salt concentration and bacterial transformation of bile salts reduces their efficacy to solubilise lipids. The results show that fibre viscosity is an important antinutritive property which should be taken into account in diet formulation for broiler chickens.