Evaluation of Sargassum cristaefolium, Sargassum crassifolium, and Enhalus acoroides as feed additives for improving rumen fermentation and mitigating enteric methane emissions in vitro

Background and Aim: Enteric methane emissions from ruminants contribute substantially to greenhouse gas accumulation and energy loss in livestock systems. In maritime regions such as Indonesia, macroalgae and seagrass represent abundant but underutilized bioresources with potential antimethanogenic properties. This study evaluated the effectiveness of Sargassum cristaefolium, Sargassum crassifolium, and Enhalus acoroides as feed additives for improving rumen fermentation characteristics and mitigating methane production in vitro. Materials and Methods: A completely randomized factorial design was employed using three marine plant species and four inclusion levels (0%, 5%, 10%, and 15%) with six replicates. Parameters assessed included dry matter degradation (DMD), organic matter degradation (OMD), pH, ammonia nitrogen (NH₃), volatile fatty acids (VFA), gas production, methane (CH₄), and microbial protein synthesis. Proximate, Van Soest, and phytochemical analyses were performed to determine nutritional composition and bioactive compounds. Data were analyzed using analysis of variance followed by Duncan’s multiple range test. Results: All three species exhibited favorable nutritional profiles and contained bioactive compounds, including tannins, flavonoids, and saponins. Supplementation at 10% significantly enhanced DMD, OMD, NH₃, VFA, gas production, and microbial protein synthesis (p < 0.05), with S. cristaefolium demonstrating the most pronounced effects. Rumen pH remained within the optimal physiological range (6.60–7.01) across treatments. Methane production decreased significantly at 10% inclusion, with reductions of 39.86%, 29.30%, and 23.92% for S. cristaefolium, S. crassifolium, and E. acoroides, respectively. Although 15% inclusion yielded greater methane suppression, it adversely affected fermentation efficiency and digestibility parameters. Projections indicated that adopting 10% supplementation could reduce methane emissions in North Sumatra Province from 5,286,097,238 kg to 3,645,821,265 kg by 2050. Conclusion: Supplementation with S. cristaefolium, S. crassifolium, and E. acoroides at 10% optimizes rumen fermentation while effectively mitigating methane emissions. These findings highlight the potential of marine biomass as a sustainable feed additive for improving livestock productivity and environmental performance. Further in vivo studies are warranted to validate long-term efficacy and practical applicability under field conditions. Keywords: enteric methane mitigation, in vitro fermentation, marine biomass, methane emissions, ruminant nutrition, Sargassum crassifolium, Sargassum cristaefolium, Enhalus acoroides.