1. An experiment of 21-d duration was conducted to examine the effects of diluting wheat-based diets with insoluble fibre sources and whole wheat inclusion on the performance, nutrient utilisation, digestive tract development and ileal microbiota profile of broiler chickens. The treatments
were as follows: Treatment 1, control diet based on ground wheat; Treatment 2, where 200 g/kg whole wheat replaced the ground wheat pre-pelleting; and Treatments 3 and 4 where the control diet was diluted with fine cellulose and wood shavings, respectively, at a ratio of 6 : 100 (w/w). 2.
Weight gains and apparent metabolisable energy were unaffected by dietary treatment. Gain : feed ratio was not influenced by the inclusion of whole wheat or wood shavings, but decreased with cellulose inclusion. However, when gain:feed of birds was corrected by subtracting the amount of cellulose
and wood shavings from the total feed consumption, it was found that the inclusion of wood shavings increased gain : feed, while cellulose inclusion had no effect. Similarly, AMEN was unaffected by dietary treatment. However, when AMEN was corrected for energy contribution from cellulose or
wood shavings, improvements in AMEN were observed in these two treatments. 3. Wood shavings increased the relative gizzard weights and improved ileal starch digestibility compared to other dietary treatments. All gut components were shorter in birds given diets containing cellulose and wood
shavings compared to those receiving the control and whole wheat diets. 4. Ileal microbiota profiling, using denaturing gradient gel electrophoresis, showed that microbial composition was affected by dietary treatment and that the treatments were grouped into two main clusters. The two groupings
showed similarity between birds receiving the control and cellulose diets and similarity between birds fed on the whole wheat and wood shavings diets. 5. The findings suggest that the effects of insoluble fibre on broiler performance differed depending on the fibre particle size.