Physicochemical properties of fibres can strongly impact gastric processes such as emptying and sieving. This study evaluated the influence of particle size of insoluble fibres, and gelation of soluble fibres when added to insoluble fibres, on gastric emptying of digesta phases from the proximal and distal stomach of pigs. Twenty-four boars (51.6 ± 4.90 kg) were assigned to one of four diets, containing either 150 g/kg coarse or finely milled wheat straw (median particle area of 5.4 vs 0.3 mm