METRITIS, AN ACUTE INFLAMMATORY DISEASE OF MULTIPLE LAYERS OF THE UTERINE LINING WITH SYSTEMIC IMPLICATIONS. IT AFFECTS ~ 20% OF POSTPARTUM DAIRY COWS AND IT HAS MARKED WELFARE, HEALTH, PRODUCTION, REPRODUCTION, AND ECONOMIC CONSEQUENCES TO THE INDIVIDUAL ANIMAL AND THE HERD. THE DAIRY COW IS UNIQUE IN THE SENSE THAT VIRTUALLY ALL COWS ARE INFECTED WITH BACTERIA IN THE FIRST DAYS AFTER CALVING, AND FAILURE TO ELIMINATE PATHOGENIC BACTERIA LEADS TO THE ESTABLISHMENT OF DISEASE. OUR PREVIOUS WORK SHOWED THAT THE MICROBIOTA IS IDENTICAL BETWEEN COWS THAT DEVELOP METRITIS AND HEALTHY COWS UP UNTIL 2 DAYS POSTPARTUM, AFTER WHICH THE BACTERIAL NUMBER AND STRUCTURE DEVIATE IN FAVOR OF GREATER ABUNDANCE OF PATHOGENIC GRAM-NEGATIVE ANAEROBIC BACTERIA IN METRITIC COWS. THE TUG OF WAR BETWEEN THE PATHOGENS AND THE IMMUNE SYSTEM DETERMINES WHETHER OR NOT BACTERIA THRIVE AND CAUSE DISEASE IN THE UTERUS. HOWEVER, DURING TRANSITION INTO LACTATION, FEED INTAKE CANNOT MEET THE NUTRIENT DEMANDS OF HIGH-PRODUCING DAIRY COWS, RESULTING IN A SHARP DECREASE IN GLUCOSE AND MINERALS, PARTICULARLY CALCIUM, LEADING TO BODY FAT MOBILIZATION IN THE FORM OF NON-ESTERIFIED FATTY ACIDS (NEFA), AND ACCUMULATION OF PRODUCTS OF INCOMPLETE OXIDATION OF NEFA SUCH AS BETA-HYDROXYBUTYRATE (BHB). BOTH THE DECREASE IN GLUCOSE AND CALCIUM CONCENTRATIONS AND THE INCREASE IN NEFA AND BHB CONCENTRATIONS ARE ASSOCIATED WITH IMMUNOSUPPRESSION AND INCREASED RISK OF METRITIS. IN ADDITION, BYPRODUCTS OF BACTERIAL METABOLISM SUCH AS PROTEINS, SHORT-CHAIN FATTY ACIDS AND OTHER METABOLITES ALSO AFFECT IMMUNE FUNCTION. IN COWS, VASCULAR DEGENERATION THAT OCCURS SHORTLY AFTER CALVING ALLOWS BLOOD TO SEEP INTO THE UTERINE LUMEN, WHICH ALLOWS FOR EXCHANGE OF METABOLITES BETWEEN BLOOD AND UTERUS. THIS EXCHANGE MEANS THAT BLOOD METABOLITES CAN AFFECT THE UTERINE MICROBIOTA, WHEREAS MICROBIAL-DERIVED METABOLITES AFFECT LEUKOCYTES IN BLOOD AND TISSUES, BOTH OF THESE PROCESSES CAN AFFECT BACTERIAL PROLIFERATION IN THE UTERUS. ALTHOUGH THE ASSOCIATIONS OF INDIVIDUAL MINERALS OR BLOOD AND MICROBIAL METABOLITES WITH IMMUNE FUNCTION AND RISK OF METRITIS HAVE BEEN STUDIED, THE IMPORTANT QUESTION OF HOW THE BLOOD AND MICROBIAL/UTERINE WHOLE METABOLOME AFFECTS THE MUCOSAL IMMUNE SYSTEM OF THE UTERUS AND THE RISK OF METRITIS HAS NOT BEEN ADDRESSED. THIS KNOWLEDGE IS CRITICAL FOR UNDERSTANDING WHY SOME COWS DEVELOP METRITIS AND OTHERS DO NOT. OUR LONG-TERM GOAL IS TO DEVELOP SOLUTIONS FOR IMPROVING ANIMAL HEALTH AND WELFARE. HEREIN, WE WILL INVESTIGATE THE METABOLOME FROM PLASMA AND UTERINE FLUID TO DETERMINE WHAT METABOLITES ARE ASSOCIATED WITH IMMUNE FUNCTION AND PATHOGENIC BACTERIAL PROLIFERATION IN THE UTERUS WITH THE OVERALL GOAL OF IDENTIFYING BIOMARKERS ASSOCIATED WITH IMPROVED IMMUNE FUNCTION, REDUCED PATHOGENIC BACTERIAL GROWTH IN THE UTERUS, AND REDUCED INCIDENCE OF METRITIS. OUR CENTRAL HYPOTHESIS IS THAT METABOLITES PRESENT IN PLASMA THAT SEEP INTO THE UTERUS, METABOLITES PRESENT IN THE UTERUS AFTER CALVING, OR METABOLITES PRODUCED IN THE UTERUS BY THE INVADING MICROBIOTA CAN MODULATE THE HOST IMMUNE RESPONSE AND THE GROWTH OF BACTERIA IN THE UTERUS, AND INFLUENCE THE DEVELOPMENT OF METRITIS. OUR RATIONALE FOR THIS PROPOSAL IS THAT IDENTIFYING BIOMARKERS FOR IMPROVED IMMUNE FUNCTION AND REDUCED PATHOGENIC BACTERIAL GROWTH IN THE UTERUS WILL ALLOW FOR THE DEVELOPMENT OF IMMUNE MODULATORS, PREBIOTICS, PROBIOTICS OR ALTERNATIVE ANTIBIOTICS FOR THE PREVENTION OR TREATMENT OF METRITIS. THIS IS EXPECTED TO IMPROVE ANIMAL HEALTH, WELFARE, AND FERTILITY WHICH WILL ENHANCE FARM PROFITABILITY AND SUSTAINABILITY. FURTHERMORE, REDUCING DEPENDENCE ON TRADITIONAL ANTIBIOTICS IS EXPECTED TO DELAY DEVELOPMENT OF BACTERIAL RESISTANCE TO ANTIBIOTICS USED IN HUMAN MEDICINE, WHICH WILL IMPROVE PUBLIC SENTIMENT TOWARDS ANIMAL AGRICULTURE WHICH WILL ULTIMATELY IMPROVE THE SUSTAINABILITY OF THE DAIRY INDUSTRY.