**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** TO FEED THE GROWING HUMAN POPULATION, GLOBAL FOOD PRODUCTION NEEDS TO INCREASE. HOWEVER, THIS AGRICULTURAL INTENSIFICATION MUST BE SUSTAINABLE AND PROTECT BOTH FOOD SECURITY AND ENVIRONMENTAL HEALTH, AS AGRICULTURE IS A MAJOR DRIVER OF CLIMATE CHANGE THROUGH ENTERIC FERMENTATION. ENTERIC FERMENTATION IS THE PROCESS BY WHICH FEED IS BROKEN DOWN BY MICROBES IN THE RUMEN (SPECIALIZED STOMACH COMPARTMENT OF COWS), WHICH ALLOWS CATTLE TO UTILIZE FIBROUS PLANTS AS ENERGY SOURCES, UNLIKE MANY OTHER ANIMALS. HOWEVER, ENTERIC FERMENTATION ALSO RESULTS IN THE PRODUCTION OF METHANE, A POWERFUL GREENHOUSE GAS. RECENT ADVANCES IN OUR UNDERSTANDING OF HOW THIS METHANE IS PRODUCED HAVE LED TO THE DEVELOPMENT OF SUBSTANCES ADDED TO AN ANIMAL'S FEED, OR ANIMAL FEED ADDITIVES (AFA), THAT CAN REDUCE ENTERIC METHANE EMISSIONS. HOWEVER, MANY INTERACTING FACTORS IMPACT METHANE PRODUCTION, SUCH AS CATTLE TYPE, WEIGHT, FEED INTAKE, AND THE COMPOSITION OF THE COW'S DIET. IN ADDITION, AFA CAN HAVE INDIRECT EFFECTS THAT MAY INCREASE THE EXCRETION OF OTHER ENVIRONMENTAL POLLUTANTS BY COWS. TO REDUCE METHANE AS MUCH AS POSSIBLE WITH AFA, WE NEED TO KNOW HOW THE EFFECTIVENESS OF AFA DEPENDS ON ALL THESE INTERACTING FACTORS. HOWEVER, THIS CAN BE VERY CHALLENGING TO ASSESS IN EXPERIMENTS WITH REAL ANIMALS, WHERE IT IS DIFFICULT OR IMPOSSIBLE TO MEASURE ALL THE POSSIBLE INTERACTING VARIABLES. TO COMPLEMENT STUDIES IN REAL ANIMALS, ANIMAL SCIENTISTS ALSO USE MATHEMATICAL MODELS, OR A SERIES OF EQUATIONS THAT DESCRIBE HOW THE COW'S FEED IS TURNED INTO METHANE, TO ANSWER QUESTIONS ABOUT ENTERIC FERMENTATION AND HOW IT MAY BE AFFECTED BY AFA.I HAVE PREVIOUSLY DEVELOPED A COMPREHENSIVE MATHEMATICAL MODEL OF ENTERIC FERMENTATION IN DAIRY COWS THAT IS DESIGNED TO ANSWER THESE QUESTIONS. MY MODEL PREDICTS HOW MUCH METHANE A COW WILL PRODUCE, AS WELL AS MANY OTHER VARIABLES, DEPENDING ON WHAT SHE IS EATING AND WHICH AND HOW MUCH AFA SHE IS FED. HOWEVER, I HAVE NOT YET ASSESSED HOW ACCURATE THE MODEL'S PREDICTIONS ARE, WHAT PARTS OF THE MODEL ARE MOST IMPORTANT TO MAKING ITS PREDICTIONS BETTER, OR HOW CERTAIN OR UNCERTAIN THE MODEL'S PREDICTIONS ARE. IN THIS PROJECT, MY OBJECTIVES ARE TO: 1) EVALUATE THE ACCURACY OF THE MODEL'S PREDICTIONS IN SEVERAL DIFFERENT SCENARIOS AND TO COMPARE THIS ACCURACY TO THAT OF SIMILAR MODELS; 2) CONDUCT ANALYSES THAT WILL TELL ME WHICH PARTS OF THE MODEL ARE THE MOST IMPORTANT TO ITS PREDICTIONS, AND 3) ASSESS HOW CONFIDENT WE ARE IN THE MODEL'S PREDICTIONS, GIVEN UNCERTAINTIES IN INPUTS TO THE MODEL. AFTER I EVALUATE THE MODEL WITH THESE ANALYSES, MY LAST OBJECTIVE IS TO USE THE MODEL TO FIND A DIET AND AFA COMBINATION THAT MOST EFFECTIVELY DECREASES METHANE EMISSIONS FROM DAIRY COWS.ACHIEVING THESE GOALS WILL CONFIRM THAT THE MODEL IS A USEFUL, ACCURATE TOOL THAT ANIMAL SCIENTISTS AND POLICY MAKERS FEEL CONFIDENT USING TO ANSWER QUESTIONS ABOUT THE INTERACTIONS BETWEEN AFA USE AND METHANE PRODUCTION. WE CAN THEN USE THIS TOOL,TO FIND WAYS TO MAXIMIZE AFA EFFICIENCY, MINIMIZE GREENHOUSE GAS EMISSIONS FROM DAIRY COWS, OR ASK MORE BASIC QUESTIONS ABOUT ENTERIC FERMENTATION, ULTIMATELY HELPING US REDUCE THE ENVIRONMENTAL IMPACTS OF ANIMAL AGRICULTURE.