Structurally distinct yeast-derived β-glucans modulate intestinal morphology and microbial metabolism in broiler chickens differentially

This study aimed to investigate the effects of yeast β-glucan structural properties on broiler growth performance, intestinal morphology, caecal metabolite profiles, and microbial composition. A total of 952 one-day-old Ross 308 broilers were allocated to a 38-day trial that included a maize-based basal diet (CON) and six basal diets supplemented with three structurally distinct, high-purity yeast β-glucans: SLG (water-soluble, low molecular weight [MW]), IMG (water-insoluble, medium MW), and IHG (water-insoluble, high MW). Each β-glucan was supplemented at two inclusion levels (0.02% [L] and 0.35% [H]). Compared with the CON group, IHG_L supplementation improved body-weight uniformity and enhanced ileal villus height (VH) and VH/crypt depth (CD) ratio ( p < 0.05), while SLG_L increased jejunal VH ( p < 0.05). SLG_H supplementation increased caecal propionate concentration on day 10 and elevated SCFA levels and the SCFA/BCFA ratio on day 38, accompanied by an increase in the Berger Parker index ( p < 0.05). Across β-glucan structures, IHG supplementation showed higher levels of ileal VH and VH/CD ratio relative to both SLG and IMG ( p < 0.05). Additionally, IHG reduced the Berger-Parker index compared with SLG, while enhancing the Shannon index relative to both SLG and IMG ( p < 0.01). Regarding dosage effects, the high dose significantly increased propionate production on day 10 and elevated butyrate, total SCFAs, and the SCFA/BCFA ratio while reducing BCFA concentrations compared with the low dose on day 38 ( p < 0.05). Distinct structure- and dose-dependent alterations in microbial community composition were also observed, and these compositional changes were closely linked to metabolite profiles and intestinal morphology. Overall, these findings underscore an integrated host-microbiota-metabolite response framework that is jointly modulated by β-glucan structural characteristics and dosage in broilers.