DAIRY COWS IN THE U.S., ON AVERAGE, EXCRETE THREE QUARTERSOF DIETARY NITROGEN IN MANURE, POSING AN ECONOMIC BURDENFOR THE DAIRY INDUSTRY AND AN ENVIRONMENTAL THREAT FOR THE SOCIETY AS A WHOLE.THE LONG-TERM GOAL OF THIS PROPOSAL IS TO DEVELOP INNOVATIVE DIETARY STRATEGIES TOREDUCING MANURE NITROGEN EXCRETION IN DAIRY COWS. WE HYPOTHESIZE THAT SUPPLEMENTATION WITH AMINO ACIDS COULD INCREASE NITROGEN EFFICIENCY IF THE ADEQUATE ENERGY SOURCE IS PROVIDED. OUR OBJECTIVE IS TO COMPARE THE RESPONSE IN NITROGEN EFFICIENCY, MILK PRODUCTION, AND NITROGEN EXCRETION TOAMINO ACID SUPPLEMENTATION UNDER GLUCOGENIC AND KETOGENIC DIETS. WE EXPECT THAT SUPPLEMENTATION WITH THE AMINO ACIDS ISOLEUCINE, LEUCINE, AND METHIONINE WILL INCREASE PRODUCTION AND REDUCE WASTE NITROGEN ONLY UNDER A GLUCOGENIC DIET. THE KNOWLEDGE GENERATED FROM THIS PROJECT COULD POTENTIALLY CHANGE THE WAY THAT DIETS FOR LACTATING COWS ARE FORMULATED. FUTURE DAIRY COW DIETS COULD HAVELESS NITROGEN AND BE BASED ON ENERGY SOURCES THATPOTENTIATE THE RESPONSE TO AMINO ACID SUPPLEMENTATION.AS A RESULT OF A MORE TARGETED FORMULATION STRATEGY, NITROGEN EFFICIENCY FOR MILK PRODUCTION COULD INCREASED FROM 25% TO40%, MANURE NITROGEN EXCRETION FROM DAIRY COWS IN THE U.S. COULD BE REDUCED BY 100 TONS PER YEAR, AND MORE THAN ONE MILLION ACRES OF LAND CURRENTLY USED FOR DIETARY PROTEIN PRODUCTION, LIKE SOYBEANS, COULD BE RELEASED FOR OTHER PURPOSES. FURTHERMORE, A REDUCTION IN DIETARY PROTEIN CONTENT COULD REDUCE FEEDING COSTS AND INCREASE PROFITABILITY FOR DAIRY PRODUCERS.