| Summary: | ABSTRACT: The aim of this study was to evaluate the effect fiber type, particle size, and inclusion level on the performance parameters, intestinal development and gene expression in broiler chickens. A total of 648 one-day old Cobb male broilers were randomly assigned to a control diet and 8 other dietary treatments divided in 2 fiber types (cellulose vs. soyhulls), 2 particle sizes (100 and 600 µm), and 2 inclusion levels (4 and 8% crude fiber). Birds were reared to 21 days of age in battery cages (n = 6 replicates). Growth performance parameters and intestinal viscosity were measured on da 7, 14, and 21. On d 14 and 21, digestive organ weights were recorded for analyses of organ growth. On d 21, intestinal samples were taken for analyses of histology, and jejunal mucosas were collected for analyses of nutrient transporters. Data were analyzed as a 2 × 2 × 2 factorial design using JMP 2021. Treatments were compared against the control group using one-way analysis of variance, whereas the main effect interactions were evaluated as a factorial excluding the control group to be able to assess the effect of the independent variables without the variability introduced by the control group. The groups fed 8% crude fiber from cellulose (8% CL) had the lowest weight gain regardless of the particle size (P < 0.01). The control group had the highest feed intake among the treatments (P < 0.01). The groups fed 8% crude fiber from soyhulls (8% SH) with a coarse particle size had the heaviest relative gizzard weight among the treatments (P = 0.045). The groups fed 8% SH had the heaviest small intestine weights regardless of the particle size (P = 0.009). No differences were observed in the relative weights of the ceca. The highest viscosity was observed in the group fed 8% SH with a fine particle size (P < 0.001). The group fed 4% SH with a coarse particle size had the longest duodenal villus (P < 0.001). The shortest jejunal villus height was observed in the group fed 8% CL with a fine particle size (P < 0.001). Ileal villus was highest in the groups fed high CL levels regardless of the particle size (P < 0.001). The highest digestibility of dry matter was observed in the group 4% SH with fine particle (P = 0.017). The group 4% CL with fine particle had the highest digestibility of crude protein (P = 0.033). The highest expression of peptide transporter 1 was observed in the group fed 8% CL with a coarse particle size (P = 0.008). In conclusion, fiber type, particle size, and inclusion levels are important factors in the regulation of intestinal morphology, viscosity, nutrient transporters, and growth performance.
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