Methane concentration, ruminal fermentation, digestibility, and microbial protein synthesis of beef cattle with the addition of various types of seaweed from West Java-Banten with different levels in the ration <em>(in vitro)</em>

The environmental health of the rumen plays a crucial role in ruminant livestock productivity. One of the byproducts of rumen fermentation is methane gas, which is a significant contributor to greenhouse emissions. The global warming potential of methane is approximately 23 times higher than that of CO2. Seaweed is recognized as a potential feed additive that can support microbial growth and suppress methane production. This study aimed to investigate the effects of seaweed supplementation on fermentability, digestibility, and methane production in beef cattle through an in vitro approach. A completely randomized factorial design was used, incorporating four different seaweed species at varying supplementation levels, with five replications. The findings demonstrated that the level of seaweed supplementation significantly influenced (p<0.05) fermentability, digestibility, and methane gas concentration. Additionally, the type of seaweed had a notable effect (p<0.05) on digestibility, ammonia concentration, and methane levels. Different compounds were identified among the seaweed types via metabolomic analysis. Supplementation with Gracilaria spp., Gelidium spp., and Sargassum spp. improved dry matter digestibility while reducing the ammonia concentration. However, variations in seaweed species did not significantly alter total volatile fatty acid production. Supplementation with Eucheuma spp., Gracilarian spp., and Sargassum spp. lowered the methane concentration. The supplementation level of 15% for Sargassum spp., is suitable for methane mitigation.