Anti-Methanogenic Potential of Seaweeds and Impact on Feed Fermentation and Rumen Microbiome In Vitro.

A series of in vitro studies were conducted to explore the anti-methanogenic potential of five seaweeds collected from the Indian sea and to optimize the level(s) of incorporation of the most promising seaweed(s) into a straw and concentrate diet to achieve a significant reduction in methane (CH) production without disturbing rumen fermentation characteristics. A chemical composition analysis revealed a notable ash content varying between 55 and 70% in seaweeds. The crude protein content was highly variable and ranged between 3.25 and 15.3% of dry matter. Seaweeds contained appreciable concentrations of tannins and saponins. Among the seaweeds, exhibited significantly higher CH production, whereas the percentage of CH in total gas was significantly lower in the cases of and . The ranking of seaweeds in terms of CH production (mL/g OM) is as follows: < < < < . A remarkable decrease of 31-42% in CH production was recorded with the incremental inclusion of at levels of 3-5% of the dry matter in the diet. The addition of led to a significant decrease of 36-48% in CH emissions when incorporated at levels of 4-5% of dry matter, respectively. The findings of this study revealed a significant decrease in the numbers of total protozoa and , coupled with increasing abundances of sulfate-reducing microbes and minor methanogens. Metagenome data revealed that irrespective of the seaweed and treatment, the predominant microbial phyla included Bacteroidota, Bacillota, Pseudomonadota, Actinomycetota, Fibrobacterota, and Euryarchaeota. The prevalence of was similar across treatments, constituting the majority (~79%) of the archaeal community. The results also demonstrated that the supplementation of and did not alter the feed fermentation pattern, and therefore, the reduction in CH production in the present study could not be attributed to it. Animal studies are warranted to validate the extent of reduction in CH production and the key processes involved by supplementation with and at the recommended levels.