The degree of polymerization influences the effects of pectic oligosaccharide on intestinal histomorphology, barrier function and microbial community structure in broilers.

This study aimed to investigate whether the degree of polymerization (DP) influences intestinal health benefits of pectic oligosaccharide (POS) in broilers. A total of 360 one-day-old female Huanghua yellow-feathered broilers were randomly allocated into 3 groups (10 replicates/group), which received a basal diet alone or supplemented with 600 mg/kg low‑DP (DP = 10) POS (LPOS) or 600 mg/kg high‑DP (DP = 17) POS (HPOS) over a 21‑day experimental period. The results showed that supplemental LPOS and HPOS tended to reduce (P = 0.081) average daily feed intake, but tended to increase (P < 0.10) relative duodenal weight and length along with relative ileal length. They also increased (P < 0.05) relative cecal weight and length, ileal villus height (VH), as well as duodenal and ileal VH to crypt depth ratio (VCR). LPOS showed a greater (P < 0.05) effect on ileal VCR, whilst HPOS additionally increased (P < 0.05) duodenal VH. Both LPOS and HPOS reduced (P < 0.05) serum endotoxin level, with HPOS also lowering (P < 0.05) serum D-lactic acid level. LPOS upregulated (P < 0.05) duodenal Zonula Occludens (ZO)-1 expression, while HPOS upregulated (P < 0.05) ileal Claudin-1 and ZO-1 expression. Cecal microbial analysis demonstrated that HPOS elevated (P < 0.05) most α‑diversity indices, including Simpson index, Shannon index, Chao1 index, and phylogenetic diversity, whereas LPOS only increased (P < 0.05) Simpson index. Notably, LPOS, rather than HPOS, reduced (P < 0.05) the within‑group β‑diversity index (heterogeneity) of cecal microbial communities, and caused greater microbial separation (P < 0.05) from control group. Further analysis indicated that HPOS enriched (P < 0.05) a greater variety of beneficial bacteria in the cecum than LPOS. Moreover, LPOS increased (P < 0.05) cecal isovaleric acid concentration, while HPOS elevated (P < 0.05) cecal concentrations of propionic, valeric, isobutyric, and isovaleric acids. In summary, LPOS and HPOS differentially promoted intestinal health in broilers, with HPOS being superior to LPOS in improving intestinal barrier and microbial community structure. These findings highlight an influence of the DP on the efficacy of POS, supporting the efficient application of POS in poultry production.