Dietary Laminaria japonica Polysaccharide Alleviates Aged-Maize-Associated Intestinal Oxidative Stress and Systemic Inflammation in Hu Sheep: Associations with Cecal Microbiome–Metabolome Remodeling

Long-term maize storage causes oxidative deterioration, but its effects on intestinal redox status, systemic inflammation, and liver-related responses in ruminants remain unclear. Laminaria japonica polysaccharide (LJP) has antioxidant, immunomodulatory, and microbiota-regulating properties, but its efficacy during aged-maize feeding is unknown. This study evaluated whether LJP mitigates oxidative and inflammatory responses in Hu sheep fed aged maize and characterized cecal microbiome and metabolome alterations. Twenty-one Hu sheep (39.05 ± 3.55 kg) were assigned to three diets (n = 7) and fed for 10 weeks (a 14-day adaptation period followed by 8 weeks of treatment): normal maize (CK), aged maize (AM), or aged maize with 0.5% LJP (AML). Compared with CK, AM increased plasma lipopolysaccharide (0.428 vs. 0.379 EU/mL), TNF-α, and IL-1β, and raised ileal reactive oxygen species (248.79 vs. 166.23 fluorescence intensity/mg; p < 0.001) and malondialdehyde (1.87 vs. 1.63 nmol/L; p = 0.006), consistent with systemic inflammation and intestinal oxidative stress. AML lowered these inflammatory and oxidative indices and increased hepatic T-AOC (p = 0.009) and catalase activity (p = 0.013). Integrated 16S rRNA and untargeted metabolomic analysis revealed treatment-associated cecal microbe–metabolite associations. These findings indicate that aged-maize feeding was associated with intestinal and systemic redox–inflammatory changes in Hu sheep, whereas dietary LJP was associated with partial mitigation, potentially involving microbial and metabolic remodeling.