** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** BESIDES BEING A POTENT GLOBAL WARMING GAS, ENTERIC METHANE FROM RUMINANTS REPRESENTS ARELEVANT SOURCE OF FEED INEFFICIENCY BY SEQUESTERING 3-12% OF THE ENERGY INTAKE. HOWEVER, DIRECTINHIBITION OF RUMEN METHANOGENESIS HAS NOT CONSISTENTLY INCREASED ENERGY CAPTURE FROM THE DIET.NEVERTHELESS, TO TRANSLATE METHANE INHIBITION TO FEED EFFICIENCY IMPROVEMENTS, THE CONSERVEDENERGY NEEDS TO BE REROUTED TOWARDS THE SYNTHESIS OF NUTRITIONALLY RELEVANT METABOLITES FOR THEANIMAL LIKE RUMINAL PROPIONATE. THE INCONSISTENT IMPROVEMENTS IN PRODUCTION PARAMETERS AS ARESULT OF DIRECT INHIBITION OF METHANOGENESIS, SUGGESTS THAT SPARED ENERGY IS BEING ALTERNATIVELYREDIRECTED TOWARDS OTHER PATHWAYS.WE DEMONSTRATED THAT FEEDING CATTLE NOVEL PROBIOTICS COMPOSED OF COMPETITIVE KEYSTONERUMEN-NATIVE SUCCINOGENIC BACTERIA ISOLATED FROM THE RUMEN OF FEEDLOT STEERS, IMPROVED GROWTHPERFORMANCE PARAMETERS, DECREASED METHANE EMISSIONS YIELD, AND MODIFIED THE COMPOSITION OFTHE RUMEN MICROBIOME. THESE KEYSTONE PROBIOTICS, WHICH ALREADY SUCCESSFULLY COMPETED WITHMETHANOGENS IN VIVO, HOLD GREAT POTENTIAL TO THRIVE AND DIVERT THE CONSERVED ENERGY TOWARDSPROPIONATE PRODUCTION IN A METHANOGENESIS-INHIBITED RUMEN ENVIRONMENT. THEREFORE, WEHYPOTHESIZE THAT THE USE OF RUMEN-DERIVED SUCCINATE-PRODUCING BACTERIA, TOGETHER WITH A POTENTMETHANE INHIBITOR, CAN CONSTITUTE AN INNOVATIVE APPROACH TO REDUCE METHANE EMISSIONS WHILE ALSOFURTHER IMPROVING FEED EFFICIENCY IN BEEF CATTLE. THE OBJECTIVE OF OUR RESEARCH PROJECT IS TO TESTTHE ABOVE HYPOTHESIS USING A COMBINATION OF THE NEW PROBIOTICS (RUMEN-NATIVE SUCCINOGENICBACTERIA) AND RED ALGAE (ASPARAGOPSIS TAXIFORMIS). THE OUTCOMES OF THIS RESEARCH WILL NOT ONLYMITIGATE METHANE EMISSIONS AND SUPPORT A MORE SUSTAINABLE BEEF PRODUCTION, BUT WILL ALSO BENEFITPRODUCERS ECONOMICALLY DUE TO GROWTH PERFORMANCE IMPROVEMENTS.