Effect of Fiber Fermentation and Protein Digestion Kinetics on Mineral Digestion in Pigs

Simple Summary There is increasing interest in improving nutrient utilization in pigs and poultry and thereby reduce nutrient excretion into the environment. The present review aims to provide an overview on interactions between fermentable substrates (e.g., starch, fiber, and protein) and selected minerals on nutrient digestion and absorption to determine nutritional solutions to maximize animal performance, principally in the grower-finisher phase. Using in vitro models, the site and rate (kinetics) of nutrient digestion or fermentation of a feed ingredient or diet can be estimated. However, for minerals, no standardized methodology to assess in vitro mineral digestion exists. In vivo, the diet total tract digestibility of phosphorus might be underestimated in diets with fermentable ingredients because of increased diet-specific endogenous phosphorus losses and requires further clarification to better calculate the true total tract digestibility of phosphorus in pigs. The quantification of fiber type, composition of fiber fractions within individual raw materials, their influence on digestion kinetics, and effects on digesta pH and nutrient solubility related to fermentation should be considered. In conclusion, applications of nutrient kinetic data should be considered as part of an integrated approach to support nutrient digestion and absorption in the gastrointestinal tract of pigs, thereby helping to reduce nutrient excretion. Nutrient kinetic data and the timing of nutrient release along the gastrointestinal tract (GIT), are not yet widely used in current feed formulations for pigs and poultry. The present review focuses on interactions between fermentable substrates (e.g., starch, fiber, and protein) and selected minerals on nutrient digestion and absorption to determine nutritional solutions to maximize animal performance, principally in the grower-finisher phase, with the aim of minimizing environmental pollution. For phosphorus (P), myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate) (InsP(6)), copper (Cu), and zinc (Zn), no standardized methodologies to assess in vitro mineral digestion exist. The stepwise degradation of InsP(6) to lower inositol phosphate (InsP) forms in the GIT is rare, and inositol phosphate(4) (InsP(4)) might be the limiting isomer of InsP degradation in diets with exogenous phytase. Furthermore, dietary coefficients of standardized total tract digestibility (CSTTD) of P might be underestimated in diets with fermentable ingredients because of increased diet-specific endogenous P losses (EPL), and further clarification is required to better calculate the coefficients of true total tract digestibility (CTTTD) of P. The quantification of fiber type, composition of fiber fractions, their influence on digestion kinetics, effects on digesta pH, and nutrient solubility related to fermentation should be considered for formulating diets. In conclusion, applications of nutrient kinetic data should be considered to help enhance nutrient digestion and absorption in the GIT, thereby reducing nutrient excretion.