Oat hulls and sugar beet pulp in diets for broilers. 2. Effects on the development of the gastrointestinal tract and on the structure of the jejunal mucosa

The effects of inclusion of oat hulls (OH) and sugar beet pulp (SBP) in the diet on the development of the gastrointestinal tract (GIT) were studied in broilers from 1 to 18 days (d) of age. A control diet based on rice that contained 16 g crude fibre (69 g dietary fibre)/kg was diluted with 25, 50 and 75 g of either OH or SBP/kg. Each of the seven treatments was replicated six times (a cage with 12 chicks). The weight of the digestive organs and the pH of the digesta contents were recorded at d 6, 12 and 18, and the jejunal morphology at d 12 and 18. The inclusion of a fibre source in the diet affected in different ways the development of the organs of the GIT. The relative weight of the GIT with digesta contents (g/kg body weight, BW) increased linearly (L; P≤0.001) as the level of fibre in the diet increased. The weight of the pancreas increased (L; P≤0.01 at d 6 and 12, and P<0.05 at d 18) with SBP inclusion but little effect was observed with OH. The relative weight of the gizzard (P≤0.001) and its DM content was increased (P≤0.001), and gizzard pH was reduced (P≤0.001) with fibre inclusion at all ages. Broilers fed OH had heavier gizzards (P≤0.001) that had higher DM content (P≤0.001) and gizzard pH (P<0.05 at d 12 and 18) than broilers fed SBP. The pH of the digesta of the duodenum increased with OH or SBP inclusion at d 6 (L; P≤0.01) and with SBP inclusion (L; P≤0.01) at d 12. Villus height at d 12 was reduced with SBP inclusion (L; P<0.05) but no effects were detected with OH. We conclude that the inclusion of up to 75 g OH or SBP/kg in low fibre diets increased the relative weight of the GIT and reduced digesta pH of the gizzard. The inclusion of high levels of SBP (75 g/kg) might have detrimental effects on the structure of the jejunal mucosa. Dietary fibre stimulates the development of the GIT in young birds but an excess might hinder intestinal mucosa structure.