WE WILL EXPLORE THE USE OF SENSOR-BASED, TIME-SERIES MONITORING OF RUMEN CONDITIONSTO ENHANCE UNDERSTANDING OF RUMEN FERMENTATION AND SUPPORT THE DESIGN OF INDIVIDUAL CATTLE FEEDING ALGORITHMS THAT OPTIMIZE USE OF HUMAN-INEDIBLE FEEDSTUFFS FOR MULTI-CRITERIA FEEDING GOALS. OUR PRELIMINARY WORK SHOWS CAPACITY TO ESTIMATE VOLATILE FATTY ACID (VFA) DYNAMICS FROM NEW EXPERIMENTAL APPROACHES AND FROM SENSOR SYSTEMS. IN THE PROPOSED PROJECT, WE BUILD ON THIS WORK THROUGH 3 SPECIFIC AIMS: 1) EVALUATE CAPACITY OF A TIME-SERIES SAMPLING METHODOLOGY IN CHARACTERIZING FERMENTATION CONDITIONS; 2) REFINE AN INDWELLING RUMINAL SENSOR SUITE FOR ESTIMATING VFA AND FLUID DYNAMICS; AND, 3) CHARACTERIZE PRODUCTIVITY RESPONSES ASSOCIATED WITH INCORPORATING RUMEN FERMENTATION CHARACTERISTICS INTO PRECISION FEEDING ALGORITHMS. THE AIMS WILL BE ACCOMPLISHED THROUGH EXPERIMENTS FOCUSING ON THE SUBSTITUTION OF HUMAN-INEDIBLE FEEDS FOR CORN AND SOY. THE FIRST EXPERIMENT WILL CHARACTERIZE HOW RUMEN FERMENTATION CONDITIONS IN LACTATING COWS RESPOND TO DIETS DIFFERING IN CP, NDF, AND STARCH PERCENT. THIS EXPERIMENT WILL BE USED TO EVALUATE THE UTILITY OF TIME-SERIES RUMEN SAMPLING AS A STRATEGY FOR REPRESENTING VFA PROFILES. THE EXPERIMENT WILL ALSO BE USED TO TEST THE EFFICACY OF INDWELLING RUMEN SENSORS IN ESTIMATING VFA AND FLUID DYNAMICS. A SECOND EXPERIMENT WILL TEST HOW RUMEN FERMENTATION METRICS CAN BE USED IN PRECISION FEEDING ALGORITHMS TO ACHIEVE SIMULTANEOUS IMPROVEMENTS IN PRODUCTIVITY, ECONOMIC, AND ENVIRONMENTAL OBJECTIVES. THESE EXPERIMENTS WILL GENERATE DATA, TOOLS, AND KNOWLEDGE CONTRIBUTING TO OUR UNDERSTANDING OF THE RUMEN ENVIRONMENT, RUMINANT NUTRITION, PRECISION FEEDING AND NOVEL FEEDSTUFF USE, THUS DIRECTLYSUPPORTING THE GOAL OF LEVERAGING NUTRITIONAL STRATEGIES TO SUPPORT SUSTAINABILITY AND PROFITABILITY OF RUMINANT PRODUCTION SYSTEMS.