Predicting digesta retention times from dietary physicochemical properties in pigs

Dietary physicochemical properties (PP) partially modulate digesta passage along the gastrointestinal tract (GIT). Understanding which dietary PP influence digesta passage is relevant for predicting nutrient absorption kinetics. This study assessed the potential of dietary PP for predicting mean retention time (MRT) and phase segregation of digesta, combining data from four experiments (21 diets, n = 166 pigs, and body weight = 42 ± 14.0 kg) including diets broadly ranging in PP. The MRT of digesta in various GIT segments, measured using similar methodology, was related to dietary PP: rheological parameters (extract viscosity and solid phase moduli plus linear viscoelastic range) and water-binding capacity (WBC). For each GIT segment and digesta phase, PP were selected as independent variables to include in prediction models after a correlation and multicollinearity analysis, followed by MaxR and stepwise variable selection methods. Subsequently, multiple and single regression analyses were performed, including selected PP as predictor variables. The MRT of solid (MRT solids ) and liquid (MRT liquids ) digesta, and digesta phase segregation were predicted using model equations with (1) selected PP (full model), (2) WBC only, and (3) extract viscosity only; and calculated vs. observed values were compared. Coefficients of determination (R 2 ) were used to select the best model to predict digesta MRT by GIT segment. Dietary PP were capable of predicting digesta phase segregation in the stomach (R 2 = 0.56), largely explained by WBC (R 2 = 0.51), and MRT liquids (R 2 = 0.26), explained by WBC and rheological parameters. Dietary PP were less effective at predicting MRT in the small and large intestines (R 2 = 0.07–0.17), though phase segregation in the cecum was better predicted (R 2 = 0.26). Full PP-models, predicted MRT solids and MRT liquids in all segments more accurately than dietary WBC or extract viscosity alone, whereas WBC was the most important predictor of phase segregation in the stomach. Extract viscosity explained negligible variation in digesta passage. This information can be used in feed formulation to better anticipate how dietary PP influence digestion kinetics. • In pigs, dietary properties better predict stomach vs. lower gut digesta transit. • In pigs, stomach solids stay about twice as long as stomach liquids. • Dietary water-binding capacity explains digesta phase segregation in the stomach. • Dietary extract viscosity poorly predicts digesta retention time in the GIT of pigs. • Studying how feed properties affect digesta transit aids nutrient uptake strategies.