Dietary fiber source-dependent modulation of pregnant sow fecal microbiota, gas profiles, and short-chain fatty acids in vitro

BACKGROUND: Growing evidence indicates that dietary fiber (DF) modulates gut microbiota and microbial fermentation metabolites, but the dynamic fermentation outcomes of different DF sources remain difficult to monitor directly under physiological conditions. This study used an in vitro batch fermentation model inoculated with pregnant sow fecal microbiota to compare the effects of a fiber-free control (CON), commercial concentrated fiber (CCF), beet pulp (BP), and alfalfa meal (AM) on microbial composition, gas concentration profiles, and short-chain fatty acid (SCFA) concentrations at 8, 12, 24, and 36 h. RESULTS: Different fiber substrates generated distinct fermentation profiles. CO₂ was the predominant gas throughout fermentation, whereas H₂ showed clearer substrate-dependent differences. AM generally resulted in higher total measured gas concentration, H₂ concentration, and total SCFA concentration than the other treatments. 16 S rRNA sequencing showed that different fiber substrates shaped the overall fecal microbial community structure, with selected genus-level taxa, including Lactobacillus, norank_f__Muribaculaceae, Prevotellaceae_NK3B31_group, Holdemanella, and Fusobacterium, exhibiting substrate-associated variation patterns. Correlation analysis further linked H₂ with SCFAs and selected fermentation-associated taxa. PICRUSt2 prediction suggested that AM fermentation was associated with differences in predicted microbial functional potential. CONCLUSIONS: These findings indicate that different DF sources generate substrate-specific fecal microbial fermentation patterns in vitro. Among the tested substrates, AM produced a stronger SCFA- and H₂-associated fermentation response and was linked with selected microbial response patterns. Integrated correlation analysis suggested microbiota-associated co-variation between H₂ and SCFAs during DF fermentation, which requires further validation.