Particle size of insoluble fibres and gelation of soluble fibres influence digesta passage rate throughout the gastrointestinal tract of finishing pigs

Fibres, as abundant in agricultural by-products, exhibit a large range of physicochemical properties that can influence digestive processes such as digesta mean retention time (MRT), thereby affecting nutrient digestion kinetics. In this study, we investigated the effects of particle size of insoluble fibres, and gelation of soluble fibres on MRT of liquids, fine solids, and fibrous particles in the different segments of the gastrointestinal tract (GIT) of pigs. Twenty-four boars (51.6 ± 4.90 kg) were allocated to four diets; two diets contained 15% wheat straw, either coarsely chopped or finely ground (1-mm screen), two diets contained 27% wheat bran without or with the addition of 10% low-methylated pectin. After 14 days of adaptation to the diet, a total collection of faeces was performed to determine the total tract digestibility of nutrients. Thereafter, pigs were fed diets supplemented with tracers for at least 5 days and dissected following a frequent feeding procedure to approach steady-state passage of digesta. The MRT of liquids (Co-EDTA), fine solids (TiO2), and fibrous particles (Chromium-mordanted fibres) in the different segments of the GIT were quantified. In the stomach, particle size reduction of straw decreased the MRT of fine solids by 02:39 h, and fibrous particles by 07:21 h (P 0.10). The complete fermentation of pectin did not influence the degradation of wheat bran fibres (∼51%). In conclusion, the effects of particle size of insoluble fibres and gelling properties of soluble fibres on the passage of digesta phases were most pronounced in the stomach, but less prominent in distal segments of the GIT.