Dietary crude fiber (CF) is an intrinsic component in plant feedstuffs that have been associated with physiological and functional changes in the gastrointestinal tract. Therefore, the objective of this study was to evaluate the effect of dietary fibers in the form of purified cellulose (solka floc®, SF) or soybean-hulls (SH) on growth performance, nutrient digestibility, gut morphology, and intestinal transporter gene expression of broiler chickens. A total of 420 one-day old Cobb® male broilers were randomly assigned to seven dietary treatments and reared to 20 days of age in battery cages (n=6 replicates per treatment). The control group consisted of a simple corn and soybean-meal based diet. The six fiber treatments had increasing amounts of SF or SH to achieve 4, 6, and 8% crude fiber. Chromium oxide was added as an indigestible marker at 0.3% in all treatment diets from 14 to 20 d for nutrient digestibility analyses. Intestinal samples from the duodenum, jejunum, and ileum were taken on d20 for morphology analyses. Growth performance was measured weekly. At 20 d, six birds per cage were euthanized, and ileal digesta samples were collected from five birds for nutrient digestibility analyses and ileal samples from one bird for gene expression. Data were analyzed by one-way ANOVA using JMP® 2019. Birds fed the 4% SH diet had a higher d20 body weight gain compared to those fed 8% CF regardless of fiber sources (P=0.0118). Control and 4% SH groups had the best feed conversion ratio among treatments at 7, 14, and 20 d (P<0.05). Birds fed 8% SH diets had the highest duodenal villi height among all treatments (P<0.001). Birds fed the control and 4% SH had the highest jejunal villi height among treatments (P<0.001). Birds fed the 4% SF and 4% SH had the highest ileal villi height among treatments (P<0.001). No statistical differences in GLUT2 (glucose transporter), SLC7A9 and SLC7AL (amino acid transporters) were observed among treatments (P>0.05). No differences in energy and crude protein digestibility were observed among treatments (P>0.05). Dry matter digestibility was higher in 6% SF compared to 8% SH (P=0.0105). Birds fed 8% SH had the highest methionine digestibility among treatments (P<0.001). Birds fed 6 and 8% SH had the highest threonine digestibility among treatments (P<0.001).
In conclusion, fiber type is a crucial factor regulating intestinal development, nutrient digestion, and growth performance.