Effect of Oat Hull as a Source of Insoluble Dietary Fibre on Changes in the Microbial Status of Gastrointestinal Tract in Broiler Chickens

Simple Summary The aim of this study was to determine the effect of the addition of oat hull (0–3%) and high amounts of cereal grains to the diets of broiler chickens in terms of the development of the upper gastrointestinal tract, and individual microbial counts in the crop and ileum, and the effect of dietary fibre fractions on microbial changes from the beak to the ileum. The addition of 3% oat hull increased the weights of the proventriculus and gizzard, thereby improving the gizzard barrier function. The presence of dietary fibre and hemicelluloses in diets increased the total aerobic microbial count and Lactobacillus spp. bulk in the crop. The presence of insoluble dietary fibre in the diet decreased the total aerobic microbial count and increased the E. coli count in the crop. In the ileum, insoluble dietary fibre decreased the E. coli count and soluble dietary fibre decreased the total combined yeast and mould count. Abstract This study aimed to determine the effect of the addition of oat hull (0–3%) and high amounts of cereal grains to the diet of broiler chickens in terms of the development of the upper gastrointestinal tract, individual microbial counts in the crop and ileum, and the effect of dietary fibre fractions on microbial changes from the beak to the ileum. In the 28 d trial, 162 one-day-old Hubbard Flex male chickens with an average body weight of 44.5 g were randomly allocated to 27 metabolic cages. The experiment consisted of a randomised, one factorial ANCOVA design composed of a covariate with two ANOVA factorial designs containing nine treatments (3 × 3): three sources of cereal grains (maize, wheat, and barley, with a minimum amount of 500 g · kg−1, each with nine replications) and three levels of oat hull (0, 1, and 3%, each with nine replications). At the end of the study, 81 chickens (9 in each treatment) were slaughtered to determine the weight of the individual organs and characterise the intestinal microbiota. The application of 3% oat hull to the cereal diets increased the weight of the proventriculus and the gizzard (6.3 and 27.3 g, respectively) in comparison to diets without the addition of this structural component (6.0 and 23.7 g). Higher crop counts of total aerobic microbes (6.29 log CFU · g−1) and Lactobacillus spp. (4.05 log CFU · g−1) were observed in diets containing wheat grain compared with maize (4.62 and 3.55 log CFU · g−1, respectively). The main reason for the microorganism’s growth (p < 0.05) was the amount of soluble dietary fibre and hemicelluloses present in the diet: total aerobic microbial count (respectively r = 0.918 and r = 0.816) and Lactobacillus spp. (respectively r = 0.416 and r = 0.442). Barley diets decreased (p < 0.05) E. coli counts in the ileum (2.69 log CFU · g−1) vs. maize and wheat diets (3.41 and 3.45 log CFU · g−1, respectively), mainly due to the increase in the amount of insoluble dietary fibre in the diet (r = −0.462). Reduced total yeast and mould counts in the ileum were also observed (p < 0.05) in connection with the presence of soluble dietary fibre and hemicelluloses in diets (r = −0.397 and −0.398, respectively).