Effects of dietary fiber on the gut microbiota, intestinal barrier, and inflammatory factors in Xinjiang black pigs

Alfalfa meal is rich in insoluble dietary fiber and bioactive compounds, which undergo fermentation in the hindgut of pigs. Its metabolites are closely associated with intestinal barrier function and immune responses. In this study, we investigated the effects of varying dietary fiber levels on the gut microbiota, Gut metabolites, the intestinal barrier, and inflammatory cytokines in Xinjiang black pigs. A total of 36 experimental pigs (21.55 ± 4.22 kg) were randomly assigned to three groups, with six replicates per group and two pigs per replicate. They were fed a basal diet (CON), a low-fiber diet (LF), or a high-fiber diet (HF), with the dietary fiber levels adjusted using alfalfa meal. The experimental results were as follows: In the LF group, the beneficial bacterium Lactobacillus was significantly upregulated (P < 0.05), whereas the pathogenic bacteria Streptococcus and Opportunistic pathogen Clostridium_sensu_stricto_1 were significantly downregulated (P < 0.05). Metabolic pathway analysis revealed significant enrichment in Choline metabolism in cancer, Biosynthesis of various antibiotics, and ‘Prodigiosin biosynthesis (P < 0.05). The levels of IL-10, MUC1, MUC2, SOD, and CAT were significantly increased (P < 0.05), while the levels of IL-1β, IL-6, and TNF-α were significantly decreased (P < 0.05), with no significant difference in D-LA levels (P > 0.05). In the HF group, the abundance of the phylum Actinobacteria increased (P < 0.05), leading to a significant decrease in the abundance of the phylum Firmicutes (P < 0.05). The abundances of Clostridium_sensu_stricto_1 and Corynebacterium were significantly elevated (P < 0.05). Metabolic pathways were enriched in histamine-related pathways such as Asthma, Fc epsilon RI signaling pathway, Synaptic vesicle cycle, and Histidine metabolism (P < 0.05). The gene expression of tight junction proteins was significantly downregulated (P < 0.05). The serum D-LA concentration significantly increased (P < 0.05), whereas the SOD and CAT activities significantly decreased (P < 0.05). Furthermore, the gene expression of IL-6 and TNF-α was significantly upregulated (P < 0.05). In summary, a moderate-fiber diet enhances beneficial bacterial abundance, suppresses pathogenic bacteria, strengthens intestinal barrier function, improves antioxidant capacity, and maintains intestinal homeostasis. In contrast, an excessive-fiber diet reduces the abundance of Firmicutes, promotes the colonization of pathogenic bacteria, leads to gut microbiota dysbiosis, and triggers the release of inflammatory cytokines. This is accompanied by reduced antioxidant capacity and increased intestinal permeability, thereby exacerbating intestinal inflammation.