AGRICULTURE IS UNDER INCREASING SCRUTINY REGARDING ITS ROLE IN GLOBAL GREENHOUSE GAS EMISSIONS. IN THE UNITED STATES, ENTERIC FERMENTATION BY RUMINANTS IS THE LARGEST SOURCE OF ANTHROPOGENIC METHANE EMISSIONS. FORAGE-BASED DAIRY SYSTEMS HAVE BEEN PARTICULARLY TARGETED DUE TO GREATER METHANE EMISSIONS THAN CONFINEMENT DAIRIES. HOWEVER, THE GROWING SEASON IN THE NORTHEAST UNITED STATES IS RELATIVELY SHORT AND CHARACTERIZED BY PERIODS OF LOW FORAGE BIOMASS PRODUCTION DURING EARLY SPRING, MID-SUMMER, AND LATE FALL. BRASSICAS, WHICH INCLUDE TURNIP, SWEDE, RAPE, KALE, AND CANOLA AMONG OTHER SPECIES HAVE EMERGED AS PROMISING ANNUAL CROPS FOR FALL GRAZING BECAUSE OF THEIR HIGH PRODUCTIVITY AND DIGESTIBILITY AND DECREASED ENTERIC METHANE EMISSIONS IN VITRO AND IN VIVO. WE ARE PROPOSING TO LINK RUMINANT NUTRITION AND RUMEN MICROBIOLOGY TO FILL KNOWLEDGE GAPS CONCERNING ANIMAL AND MICROBIAL FACTORS UNDERLINING THE METHANE MITIGATION POTENTIAL OF CANOLA AS A GRAZING FORAGE FOR LACTATING DAIRY COWS THROUGH THE FOLLOWING OBJECTIVES: (1) MEASURE MILK PRODUCTION, METHANE EMISSIONS, AND NUTRIENT UTILIZATION CHANGES, AND (2) QUANTIFY CHANGES IN THE COMMUNITY COMPOSITION AND FUNCTION OF THE RUMEN MICROBIOTA. WE EXPECT A 10% INCREASE IN MILK PRODUCTION IN COWS GRAZING CANOLA DUE TO DIETARY ENERGY PARTITIONED TO MILK SYNTHESIS RATHER THAN METHANOGENESIS. WE ALSO EXPECT AN INCREASE OF APPROXIMATELY 15% IN THE NUMBER OF ACRES USED FOR CANOLA AND OTHER BRASSICAS AS FALL GRAZING SPECIES DUE TO PROJECT RESEARCH AND ACTIVITIES. WE FURTHER EXPECT AN INCREASED UNDERSTANDING OF THE DYNAMICS (I.E., DIVERSITY AND FUNCTION) OF RUMEN MICROBIOTA IN RELATION TO DIET. ADDIITONAL OUTCOMES OF OUR PROJECT CONSIST OF PRODUCERS' ADOPTION OF PRACTICES TO EXTEND THE GRAZING SEASON WHILE MAXIMIZING FORAGE PRODUCTION AND UTILIZATION.