Abstract
Including additional dietary fibre fractions in broiler feed has gained renewed interest due to its potential for stimulating (gut) health and performance. The beneficial effects of fibre are mainly due to its fermentation in the caecal lobes, but the influx of digesta into these lobes seems restricted to small particles and solubles. To boost caecal fermentation via fibre inclusions, more knowledge on how fibre particle size in feed can affect the fibre particle size distribution along the gastrointestinal tract (GIT), and hence the caecal influx and the fermentation of fibre, is required. To this end, 78 one-day-old male broilers (Ross 308, average initial weight of 43.96 ± 2.97 g) were divided into 3 treatment groups (n = 26 birds per treatment group, 1 replicate pen per treatment), receiving a wheat-based diet with a 10% replacement of the wheat fraction by wheat bran with an average particle size of 1026 (coarse bran), 506 (medium bran) or 106 μm (fine bran), respectively, over a period of d 1 to 24. Digesta of the gizzard, duodenum-jejunum and ileum was collected at d 7 and 24 to determine the fibre particle size distribution in it. The overall ileal and caecal digesta particle size distribution and short-chain fatty acid (SCFA) content were also determined. An increase in the relative content of arabinoxylan along the GIT in the size fractions corresponding to the included bran particle size in the feed was observed for each dietary treatment (P < 0.05), indicating that the particle size differences induced by the bran incorporations were conserved along the GIT. Bran particle size did not affect the gizzard's development or grinding action. The coarse bran treatment resulted in the smallest caecal digesta average particle size (50th percentile, D50) (P = 0.088) and the highest caecal SCFA contents at d 7 (P < 0.001). At d 24, no differences in caecal digesta D50 were observed (P = 0.298), and the fine bran treatment resulted in the highest caecal SCFA contents (P = 0.026). The different effects of bran size on caecal fermentation as a function of broiler age can be ascribed to the limitations of caecal influx that also change with age. The fibre particle size distribution along the GIT can be steered by including the desired fibre particle size in the feed, and the effect of broiler age on caecal influx should be considered when aiming to improve caecal fibre fermentation through fibre inclusion.