This project will mechanistically quantify the metabolic re- partitioning of hydrogen ([H]) in the rumen following methanogen inhibition, testing the hypothesis that the microbiota activates compensatory hydrogenotrophic pathways to maintain redox balance. The study employs a robust randomized block design, conducting four independent 11-day runs in a dual-flow continuous culture system. Each run comprises two control fermenters (basal diet) and two treatment fermenters (basal diet + the specific methanogen inhibitor 3- NOP), ensuring statistical power (n=8 per treatment). To capture microbial community dynamics, time-series sampling for 16S rRNA sequencing will be performed at critical points: pre- inhibition (baseline), initial shock (24h post-inhibition), adaptation (day 7), and new steady state (day 11). This temporal data will be integrated with daily gas emissions (CH4, H2, CO2) and detailed stoichiometric analysis of fermentation end- products (VFAs, lactate, ethanol) to quantitatively track the redirection of electron flow from methane towards sinks like propionogenesis and lactate production. The budget is allocated to core activities: consumables for fermentation and 3-NOP (€1,800), gas and metabolite analysis (€500), 16S sequencing of time-series samples analysis (€1,000), conference dissemination (€1,000), and open-access publication (€700). Total: €5,000. This research is critically important because simply inhibiting methanes is insufficient; understanding the rumen's adaptive metabolic network is key to developing stable, long-term mitigation strategies. The practical application lies in using these findings to design next-generation feed additives or microbial consortia that actively steer the rumen towards efficient, non-methane electron sinks, ensuring both reduced environmental impact and maintained animal productivity.