Alginate oligosaccharides derived from tropical brown seaweeds as sustainable alternatives to antibiotic growth promoters in poultry nutrition: Functional mechanisms and production perspectives

The global restriction and withdrawal of antibiotic growth promoters (AGPs) in poultry production have accelerated the search for natural, safe, and sustainable feed additives that maintain bird health and productivity. Alginate oligosaccharides (AOS), derived from the depolymerization of alginate present in brown seaweeds, have gained increasing attention due to their multifunctional biological properties, including prebiotic, immunomodulatory, antioxidant, and antimicrobial activities. Although most available research has focused on alginate sources from temperate seaweeds, tropical brown seaweeds such as <i>Sargassum</i> and <i>Turbinaria</i> are abundant, renewable, and rich in alginate, particularly in Southeast Asia, making them attractive and underutilized resources for the development of functional feed additives. This review summarizes current knowledge on the biodiversity of tropical brown seaweeds, alginate extraction and depolymerization techniques suitable for feed-grade AOS production, and the physicochemical properties that influence their functionality in poultry nutrition. Emphasis is placed on AOS behavior in the poultry gastrointestinal tract, including resistance to enzymatic digestion, fermentation by beneficial microbiota, and stimulation of short-chain fatty acid production. Evidence from experimental studies indicates that dietary AOS supplementation improves gut morphology, enhances microbial balance, strengthens intestinal barrier function, and modulates immune responses. These effects are consistently associated with improved growth performance, feed efficiency, egg production, and antioxidant status, with outcomes comparable to or exceeding those achieved using AGPs. The review also highlights emerging processing strategies, such as low-energy extraction and encapsulation technologies, that enhance AOS stability and bioavailability during feed manufacturing. Overall, tropical seaweed-derived AOS represent a promising, sustainable alternative to AGPs in poultry systems, supporting productivity while addressing antimicrobial resistance and environmental sustainability concerns. Further large-scale field studies and optimization of dosage and formulation strategies are recommended to facilitate commercial adoption.