Dietary fiber in poultry nutrition: impacts on physiology, digestive metabolism and on productive performance.

Dietary fiber (DF) consists of non-starch polysaccharides (NSPs) and lignin, and is categorized into soluble and insoluble DF. DF is often regarded as an antinutritional element; however, the intake of both soluble and insoluble fiber can induce physiological alterations in the gastrointestinal tract (GIT). These adaptations include increased synthesis and secretion of digestive enzymes, altered gastrointestinal motility and development, improved gizzard functionality, and the proliferation of intestinal and caecal microbiota. The induced adaptations interfere with the digestibility of energy and nutrients in diets, which can affect the productive performance of the birds. Insoluble DF exhibit more beneficial effects on the GIT than soluble fibers, potentially enhancing the secretion of hydrochloric acid, pepsinogen, and cholecystokinin. The soluble fraction causes detrimental effects by increasing digesta viscosity and bacterial fermentation in the small intestine, which are exacerbated with increased soluble PNAs. This can be mitigated using exogenous carbohydrase enzymes that hydrolyze the β-bonds of the polysaccharide chain. This review aims to clarify the effect of DF on poultry diets, describe the effects caused in the GIT and digestion physiology by the soluble and insoluble fractions, how the use of carbohydrases can be a very efficient tool in reducing the antinutritional effects of NSPs, and the impacts of using fiber-rich feedstuffs on the productive performance of poultry.