Rethinking dietary fibers in poultry nutrition: physicochemical properties and their role in digestion processes

The increasing use of fiber-rich agricultural by-products in poultry diets requires a better understanding of how dietary fiber (DF) affects digestion. This thesis investigated the effects of DF physicochemical properties, including solubility, viscosity, particle size, and hydration capacity, on digesta passage, endogenous protein losses (EPL), and nutrient digestibility in chickens. Soluble arabinoxylans increased digesta retention time, EPL, and reduced nutrient digestibility, whereas the particle size of soybean hulls generally had limited effects. A minimally invasive 15N-isotope dilution method was developed and validated to quantify EPL under practical feeding conditions. Using this method, different fiber sources were shown to affect EPL and protein digestibility through distinct mechanisms. High-hydration fibers, such as sugar beet pulp and lignocellulose, increased EPL or reduced nutrient digestibility, while particle size effects remained small. Furthermore, genetic background influenced digestive physiology and nutrient utilization in laying hens. Overall, viscosity and hydration capacity were identified as key DF properties influencing digestion and should be considered in poultry feed formulation.