Fucoidan Derived from Saccharina japonica Modulates Intestinal Morphology and Gut Microbiota in Weaned Pigs

With global restrictions on in-feed antibiotics, sustainable alternatives are urgently needed to combat weaning-induced intestinal dysfunction in piglets. Fucoidan, a bioactive seaweed polysaccharide, exerts beneficial effects on gut health due to its immunomodulatory and prebiotic properties, but its mechanisms in the gastrointestinal tract of piglets remain unclear. This study investigated the effects of dietary fucoidan supplementation on growth performance, intestinal morphology, gut microbiota composition, and microbial metabolites in weaned piglets. The extracted fucoidan was characterized by a sulfate content of 23.7%, a molecular weight of 29.3 kDa, and fucose as the predominant monosaccharide. A total of 48 weaned piglets were randomly divided into two groups (n = 24 per group): a control group and a 500 mg/kg fucoidan treatment group. Growth performance was evaluated throughout the experiment. On day 28, jejunal and colonic tissues were collected to assess mucosal morphology (n = 6 per group), while cecal and colonic contents were collected for analysis of the gut microbiota and bacterial metabolites. Fucoidan supplementation significantly enhanced average daily gain (ADG, p < 0.05) and feed conversion ratio (FCR, p < 0.05) and mitigated diarrhea during the trial. Notably, piglets fed fucoidan exhibited increased villus height compared to controls (p < 0.05). Fucoidan modulated the gut microbiota by increasing cecal microbial diversity (p < 0.05) and shifting bacterial composition. These modifications involved an altered Bacteroidetes/Firmicutes ratio, as well as an enrichment of Prevotellaceae, Lactobacillus, and Lachnospiraceae (p < 0.05). Consistently, metabolite profiling analysis revealed increased cecal concentrations of lactate (p < 0.05) and butyrate (p < 0.05), which were positively associated with the growth of beneficial taxa. These findings demonstrate that fucoidan alleviates weaning-induced intestinal disorders by improving intestinal morphology and modulating gut microbiota and their metabolites. This study provides a strategy for utilizing marine-derived polysaccharides as functional feed additives to enhance animal health.