Effects of Alfalfa Fiber Meal on the In Vitro Fermentation Characteristics and Community Structure of the Colonic Microbiota of Sows

The gut microbiota plays a critical role in hindgut health and nutrient utilization in monogastric animals. Alfalfa fiber meal (AFM) was rich in essential vitamins and minerals as a valuable nutritional supplement. In this study, an in vitro fermentation model was established using fecal microbiota from pregnant sows as the inoculum to evaluate the effects of different supplementation levels of alfalfa fiber powder (AFM) on fermentation metabolites and microbial community composition, with particular attention to interactions between the microbiota and metabolites. Fecal inocula from healthy sows were fermented with AFM at three inclusion levels: low (LAFM: 50 mg), medium (MAFM: 100 mg), and high (HAFM: 200 mg). Fermentation samples were collected at 8, 12, 24, and 36 h for analysis of gas production and short-chain fatty acid (SCFAs) concentrations. Microbial community composition was characterized at 36 h, followed by correlation analysis between dominant genera and fermentation parameters. The results showed that total gas and hydrogen production increased significantly with both AFM level and time, while hydrogen sulfide decreased across all treatments. Methane production rose in the early stages and remained elevated only in the high-AFM group. AFM supplementation promoted the production of total and individual short-chain fatty acids in a dose- and time-dependent manner. Microbial analysis revealed reduced Fusobacterium and increased Lactobacillus, Bacteroides, and Collinsella, with high AFM further enriching Prevotella and Megasphaera. Positive correlations were observed between SCFA production and Collinsella, Prevotella, and Olsenella, whereas hydrogen sulfide correlated negatively with Prevotella and Sharpea. AFM effectively improved gut microbial composition and fermentation efficiency, with 100 mg identified as a more balanced level of fermentation additive supplementation for pregnant sows under in vitro conditions.