** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** BOVINE RESPIRATORY DISEASE (BRD) IS THE MOST DEVASTATING DISEASE AFFECTING U.S. CATTLE PRODUCERS. ALTHOUGH MANY ETIOLOGICAL AGENTS HAVE BEEN IMPLICATED IN BRD, A BACTERIAL INFECTION WITH THE OPPORTUNISTIC PATHOGEN MANNHEIMIA HAEMOLYTICA IS MOST OFTEN OBSERVED. ALTHOUGH MUCH RESEARCH HAS FOCUSED ON BRD, MORBIDITY AND MORTALITY HAVE NOT DECLINED IN THE PAST 45 YEARS, AND ANTIMICROBIAL RESISTANCE, ESPECIALLY IN M. HAEMOLYTICA, HAS BEEN OBSERVED. AS A RESULT, THERE IS A PRESSING NEED FOR NOVEL PREVENTATIVES. AS IT IS KNOWN THAT THE RESPIRATORY MICROBIOTA OF CALVES WITH BRD DIFFERS FROM THAT OF HEALTHY CALVES, IT IS POSSIBLE THAT PROBIOTICS FROM THE BOVINE RESPIRATORY MICROBIOTA MAY BE THE ANSWER. OUR PRELIMINARY DATA INDICATE THAT COMMENSAL CORYNEBACTERIUM FROM THE BOVINE RESPIRATORY TRACT CAN INHIBIT M. HAEMOLYTICA GROWTH IN VITRO, POTENTIALLY DUE TO THEIR ABILITY TO PRODUCE SECONDARY METABOLITES. HOWEVER, THE METABOLITES, THE MANNER OF INHIBITION, AND OTHER PROBIOTIC PROPERTIES POSSESSED BY THESE ISOLATES ARE UNKNOWN. AS A RESULT, THE OVERALL OBJECTIVE OF THIS PROJECT IS TO FURTHER CHARACTERIZE THE PROBIOTIC CAPABILITIES OF OUR COMMENSAL CORYNEBACTERIUM ISOLATES, PROVIDING VALUABLE DATA REGARDING THE ROLE WITHIN THE BOVINE RESPIRATORY MICROBIOTA, AS WELL AS THEIR POTENTIAL TO SERVE AS EFFECTIVE PROBIOTICS FOR BRD PREVENTION. THE DEVELOPMENT OF A PROBIOTIC FOR BRD PREVENTION WOULD BE HIGHLY VALUABLE AS IT WILL IMPROVE CATTLE HEALTH WHILE REDUCING ANTIMICROBIAL USAGE, INCREASING PRODUCER PROFITABILITY, AND ENSURING A SUSTAINABLE AND SAFE FOOD SUPPLY.