摘要Intra-flock body weight(BW)variability in broilers increases production costs,as underperforming chicks often show suboptimal gut development and performance.Increasing grain particle size and dietary fiber content has been shown to improve digestive efficiency and intestinal health.This study investigated whether dietary inclusion of coarse corn(CC)and oat hulls(OH)could improve gut health and reduce the performance gap between low-and high-BW(LBW and HBW)broilers.On d 7,1400 Ross 308 male broilers were categorized as LBW or HBW,with 504 LBW chicks assigned to 4 isocaloric and isonitrogenous diets with 10％fine corn(LBWC),7％CC with 3％fine corn(LBW+CC),3％OH with 10％fine corn(LBW+OH),or 7％CC and 3％OH(LBW+CO).High BW chicks received a 10％fine corn diet(HBWC).Each group had 6 replicates with 21 chicks per pen.The HBWC group showed the highest BW at each timepoint(P＜0.05).By d 38,LBW+OH chicks had significantly reduced the weight difference with HBWC chicks and significantly outperformed LBWC chicks(P＜0.001),whereas other groups showed intermediate values.Coarse corn and OH,individually or combined,reduced the relative plasma FITC-dextrann concentration d 14(P=0.014)and increased gizzard weights on d 21 and 38(P＜0.05)as compared with LBWC group.The LBW+OH group showed increased pancreas relative weight on d 21(P=0.005,vs.HBWC)and villus height(P=0.042,vs.LBWC)on d 38.Additionally,LBW+OH group reduced isobutyrate and isovalerate levels in cecum(P＜0.05,vs.HBWC and LBWC)on d 21,and upregulated ileal genes related to gut barrier function(CLDN1,vs.HBWC and LBWC;CLDN4,vs.HBWC;CLDN5,vs.LBWC),amino acid and glucose transporters(SLC15A1 and SLC1A4,vs.HBWC and LBWC),and immune function(NOS2,vs.HBWC and LBWC;TLR4,vs.HBWC)on d 14(P＜0.05),and sodium-phosphate transporter SLC34A2(P=0.049,vs.HBWC)on d 38.LBW+CC birds upregulated SLC15A1(vs.HBWC and LBWC)on d 38(P＜0.001).Lactobacillus was enriched in the cecum of HBWC birds,while Escherichia-Shigella was abundant in LBWC birds on d 14,with CC and OH promoting beneficial bacterial shifts in LBW groups.Overall,incorporating structural components into diets,particularly 3％OH,enhanced gastrointestinal development,intestinal integrity,and growth performance in LBW broilers.These improvements reduced disparities in BW between LBW and HBW birds,thereby contributing to more uniform flock performance at slaughter age.