Dietary Supplementation with Algal-Derived Oligosaccharides: Impacts on the Growth Potential, Systemic Immunity, and Cecal Microbiota of Weaned Piglets

Sustainable piglet farming faces challenges from weaning stress, which necessitates the exploration of effective, natural antimicrobial alternatives to enhance growth and gut health. So, this study evaluated the effects of algal oligosaccharide (OSA) supplementation (0, 200, 400, 600, 800 mg/kg) as a natural antimicrobial alternative. Results showed that OSA significantly (p < 0.05) improved slaughter performance and the apparent digestibility of nutrients (OM, CP, amino acids) and energy. OSA increasing serum glucose while decreasing urea nitrogen and cholesterol, suggesting a shift in energy substrate mobilization. Enhanced antioxidant capacity was evidenced by increased T-SOD and GSH-Px activities and reduced MDA content. Immunologically, OSA elevated serum IgA, IgM, and IL-10, while inhibiting pro-inflammatory cytokines (IL-1β, IL-6). In the jejunum, OSA obviously increased disaccharidase activities and sIgA levels. Microbial analysis revealed that OSA favorably modulated cecal microbiota by increasing the abundance of Firmicutes and beneficial genera while decreasing Proteobacteria and potential pathogens (e.g., Escherichia). In conclusion, dietary OSA improved antioxidant capacity, and immunity while optimizing nutrient utilization and gut microbiota. The optimal dosage was determined to be 600–800 mg/kg. These findings suggest that OSA serves as a promising antimicrobial alternative in piglet farming.