Nutritional composition, bioactive potential, and <i>in vitro</i> rumen fermentation of tropical brown <i>(Sargassum binderi)</i> and green <i>(Kappaphycus striatum)</i> seaweeds as functional feed additives for ruminants.

Abstract

<h4>Background and aim</h4>Mitigating enteric methane emissions in ruminants remains a global challenge in achieving sustainable livestock production. Although seaweed supplementation has shown promising results, most research has focused on temperate species, leaving tropical species underexplored. This study investigated the nutritional composition, bioactive compounds, and <i>in vitro</i> rumen fermentation characteristics of two tropical seaweeds, brown seaweed (<i>Sargassum binderi</i>) and green seaweed (<i>Kappaphycus striatum</i>), as potential functional feed additives for ruminants.<h4>Materials and methods</h4>The proximate composition, macro- and micro-minerals were determined using Association of Official Analytical Chemists and Inductively Coupled Plasma-Optical Emission Spectrometry methods. <i>In vitro</i> digestibility of dry matter digestibility (DMD) and organic matter digestibility (OMD) was evaluated using the Tilley and Terry two-stage technique. Rumen fermentation characteristics, pH, ammonia (NH₃), and total volatile fatty acids (VFA), were analyzed after 48 h of incubation. Amino acids and fatty acids were profiled using high-performance liquid chromatography and gas chromatography-flame ionization detection, respectively, while bioactive metabolites were identified through liquid chromatography-high-resolution mass spectrometry metabolomics.<h4>Results</h4>Green seaweed exhibited a higher crude protein content (7.52%) and digestibility (DMD = 73.56%; OMD = 72.71%) than brown seaweed (6.84%; 46.38%; 44.99%). VFA production (136.75-151.75 mM) and NH₃ concentrations (22.21-26.78 mM) differed significantly (p < 0.01) between species, while pH remained within the optimal range (7.00-7.21). Both seaweeds contained balanced essential and non-essential amino acid profiles and abundant polyunsaturated fatty acids, notably linoleic, α-linolenic, eicosapentaenoic acid, docosahexaenoic acid, and conjugated linoleic acid. Metabolomic screening identified ~85 bioactive compounds, including lipid-derived metabolites, amino alcohols, vitamins, and osmolytes such as betaine and cholecalciferol, indicating their potential to modulate rumen fermentation and enhance animal resilience.<h4>Conclusion</h4>Both <i>S. binderi</i> and <i>K. striatum</i> demonstrated promising nutritional and bioactive potential as ruminant feed additives. Their compositional diversity suggests species-specific applications - <i>S. binderi</i> as an energy-dense supplement and <i>K. striatum</i> as a functional additive for stress adaptation. However, further <i>in vivo</i> trials are necessary to determine optimal inclusion levels, long-term safety, and methane mitigation efficacy under production conditions.