Sargassum mcclurei as a feed additive: mitigating methane emissions and affecting rumen microbial community in ruminants

Methane emissions from ruminants contribute significantly to greenhouse gases, and seaweed supplementation has emerged as a potential mitigation strategy. However, the efficacy of methane reduction varies across seaweed species, supplementation levels, and treatment methods. This study investigated the effects of different treatment methods and supplementation levels of Sargassum mcclurei (S. mcclurei) on nutrient degradation, ruminal fermentation, methane inhibition, and the intricate microbial community structure in vitro. Using two distinct treatments (freeze-dried and drying) and three supplement levels (2%, 5%, and 10% of dry matter), the experimental design aims to reveal relevant issues. Particularly noteworthy was the freeze-dried treatment at a 2% supplementation level of S. mcclurei, showcasing a significant 18.85% reduction in CH4 emissions (P<0.05) coupled with a significant enhancement in crude protein degradability (P<0.01). However, analyses of total volatile fatty acids and acetate concentrations indicated reductions in both freeze-dried (P=0.02, P<0.01) and drying treatments (P<0.01, P<0.01) compared to the control (CON). Based on the previous results, we initially recommend using the supplementation level of 2%. The microbial community at the 2% supplementation level demonstrated notable alterations in bacterial abundance. A decrease in Lachnospiraceae_NK3A20_group and Ruminococcus was observed, concomitant with an increase in Selenomonas, Succinivibrio, and Saccharofermentans. These shifts in microbial communities promote propionate production and explain an indirect mechanism for methane inhibition. Intriguingly, the freeze-dried group exhibited a significant reduction in the relative abundance of Methanomicrobium, indicative of a direct mitigation of methane production. These findings indicate the potential of S. mcclurei as a feed additive to mitigate CH4 emissions from ruminants. In conclusion, this study reveals the potential of freeze-dried S. mcclurei, particularly at a 2% supplementation level, as an effective methane mitigation strategy with minimal impact on rumen fermentation. The detailed insight into microbial communities and fermentation pathways provides valuable knowledge, making S. mcclurei a promising feed additive for sustainable methane reduction in ruminant systems.