THIS STUDY AIMS TO DEFINE THE IMPACT OF DIFFERENT ROUTES OF CEFTIOFUR ADMINISTRATION ON THE INTESTINAL MICROBIOME AND RESISTANCE GENE POOL USING METAGENOMICS IN A POPULATION OF DAIRY CATTLE FOLLOWED LONGITUDINALLY. CEFTIOFUR IS COMMONLY USED IN DAIRY FARMS AND CEFTIOFUR RESIDUES HAVE BEEN FOUND IN THE FECES OF DAIRY COWS TREATED BOTH SUBCUTANEOUSLY AND VIA INTRAMAMMARY INFUSION. ALTHOUGH SEVERAL STUDIES HAVE BEEN CONDUCTED TO EXAMINE THE MILK MICROBIOME USING METAGENOMICS, NO PRIOR STUDIES HAVE EXAMINED INTESTINAL COMMUNITIES. OUR OVERARCHING HYPOTHESIS IS THAT SPECIFIC MICROBIAL COMMUNITIES ARE SELECTED FOR BY CEFTIOFUR, WHICH PROMOTES EXPANSION OF CERTAIN BACTERIAL POPULATIONS THAT MORE READILY HARBOR RESISTANCE GENES. WE AIM TO: 1) DETERMINE HOW SUBCUTANEOUS TREATMENT WITH CEFTIOFUR IMPACTS THE INTESTINAL MICROBIOME IN COWS WITH METRITIS RELATIVE TO HEALTHY, UNTREATED COWS SAMPLED FOR 4-WEEKS; AND 2) DETERMINE HOW DRY COW THERAPY USING INTRAMAMMARY CEFTIOFUR IMPACTS THE INTESTINALMICROBIOME COMPARED TO A NON-ANTIBIOTIC TEAT SEALANT OVER A 12-WEEK PERIOD. WE WILL ALSO DETERMINE HOW FREQUENTLY RESISTANCE DETERMINANTS ARE ACQUIRED BY UNTREATED CATTLE AND ARE SHED IN TO THE ENVIRONMENT AND WILL DETERMINE WHETHER TEAT SEALANT TO PREVENT MASTITIS AT DRY OFF CONTRIBUTES TO FEWER PERTURBATIONS IN THE MICROBIOME COMPARED TO SUBCUTANEOUS OR INTRAMAMMARY TREATMENTS. DATA GENERATED THROUGH THE PROPOSED WORK WILL AID IN THE DEVELOPMENT OF GUIDELINES FOR THE JUDICIOUS USE OF ANTIBIOTICS AS WELL AS NOVEL CONTROL METHODS THAT CAN BE USED TO LIMIT THE FLOW AND POOL OF RESISTANCE GENES AND RESISTANT BACTERIAL HOSTS IN DAIRY CATTLE AND THE FARM ENVIRONMENT.