The In Vitro Evaluation of Cecal and Colonic Fermentation Kinetics of Locally Sourced Feedstuffs from Shandong Province in China for Donkeys

Locally sourced roughages constitute the dietary foundation of donkey production in northern China, yet their fermentation behavior in the donkey hindgut remains poorly characterized. The present study employed in vitro batch cultures to compare the dry matter disappearance (IVDMD), gas production (GP) kinetics and short-chain volatile fatty acid (VFA) profiles of five locally available feedstuffs—peanut vine (PNV), soybean straw (SBS), wheat shell (WS), reed grass (RG) and bamboo leaf (BL)—when incubated separately with cecal or colonic microbial inocula obtained from Dezhou donkeys. After 40 h incubation, both IVDMD and total VFA concentrations ranked identically across the two hindgut segments: PNV > SBS > WS > RG > BL (p < 0.05), and all indices were consistently higher in the cecal than in the colonic fermentation system (p < 0.05). The asymptotic gas production (A) and the time required to reach half of A (T1/2) followed the same ranking as IVDMD (p < 0.01), indicating that feedstuffs with greater fermentable substrate availability sustained fermentation for longer periods. In contrast, the fractional gas production rate (c) and the average gas production rate (AGPR) in RG and BL exceeded those of PNV, SBS, and WS under cecal incubation (p < 0.05), reflecting rapid utilization of a small pool of readily fermentable components in these fibrous substrates. Regarding VFA stoichiometry, BL yielded the highest molar proportion of acetate and PNV the lowest in the colonic system (p < 0.05), whereas the propionate proportion followed the order PNV > SBS > WS > RG > BL (p < 0.01). Consequently, the acetate-to-propionate (A:P) ratio and the non-glucogenic-to-glucogenic (NGR) ratio were highest in BL (p < 0.05). The molar proportions of butyrate and branched-chain VFAs (BCVFAs) in WS, RG, and BL were greater than those in PNV (p < 0.05). Collectively, the five feedstuffs differed markedly in their fermentability, kinetic behavior, and VFA yield profiles, reflecting distinct energy-supply potentials for the donkey host. PNV and SBS exhibited superior overall in vitro fermentation performance and are therefore recommended as preferred roughage sources, whereas BL and RG may serve complementary roles by supporting hindgut epithelial health through elevated butyrate production. These findings provide a mechanistic basis for the rational selection and combination of locally sourced roughages to optimize feeding strategies and improve feed-use efficiency in donkey production.