** 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 COSTLY DISEASE AFFECTING NORTH AMERICAN BEEF CATTLE, AND IS RESPONSIBLE FOR 40-50% OF THE MORTALITY AND 70-80% OF THE MORBIDITY IN THESE ANIMALS, RESULTING IN OVER $3 BILLION/YEAR IN LOSSES TO THE CATTLE INDUSTRY. DECREASED WEIGHT GAIN AND PERFORMANCE AFFECTS AN ADDITIONAL 10% OF THESE ANIMALS. BRD IN PRE-WEANED CALVES ALONE COSTS THE US BEEF COW-CALF INDUSTRY ~$165 MILLION ANNUALLY. BRD IS THE LEADING CAUSE OF MORBIDITY AND MORTALITY IN U.S. FEEDLOT AND STOCKER CATTLE AND THE SECOND LEADING CAUSE OF LOSS IN DAIRY CALVES. THE PRIMARY BACTERIAL AGENTS RESPONSIBLE FOR BRD ARE H. SOMNI, MANNHEIMIA HAEMOLYTICA, PASTEURELLA MULTOCIDA, AND MYCOPLASMA BOVIS. HOWEVER, H. SOMNI CAN ALSO CAUSE A WIDE RANGE OF INFECTIONS OTHER THAN BRD, AND IS THEREFORE THE TARGET BACTERIUM FOR THIS INVESTIGATION. CURRENT COMMERICAL VACCINES CONSISTING OF KILLED BACTERIA THAT HAVE BEEN GROWN IN VITRO ARE NOT ADEQUATELY EFFECTIVE AT PREVENTING BRD AND SOME OTHER SYSTEMIC INFECTIONS. WE AND OTHERS HAVE SHOWN THAT OPPORTUNISTIC BACTERIA EXPRESS NOVEL PROTEINS IN THEHOST IN ORDER TO SEQUESTER IRON THAT IS BOUND TO HOST PROTEINS, SUCH AS TRANSFERRIN AND HEMIN. THESE PROTEINS ARE NOT PRODUCED IN VITRO WHERE ADEQUTE IRON IS AVAILABLE. FURTHERMORE, DURING CHRONIC INFECTIONS BACTERIA PERSIST IN THE HOST IN THEFORM OF A BIOFILM. WE HAVE SHOWN THAT HALF OF THE BACTERIAL GENOME IS DIFFERENTIALLY EXPRESSED WHEN THE BACTERIA ARE IN A BIOFILM, COMPARED TO WHEN GROWN SHAKING OR IN A FERMENTOR, AND THAT MANY NOVEL PROTEINS ARE PRESENT WHEN THE BACTERIA ARE IN A BIOFILM. IN ADDITIION, H. SOMNIAND OTHER BACTERIA MAY BE ABLE TO PRESIST IN PHAGOCYTIC OR OTHER CELLS AND AVOID RECOGNITION BY ANTIBODIES. THEREFORE, MANY POTENTIALLY PROTECTIVE ANTIBODIES ARE NOT PRODUCEDOR ABLE TO REACH THE BACTERIA, AND AN IMPORTANT CELLULAR IMMUNE RESPONSE IS LACKING.H. SOMNIAND OTHER GRAM-NEGATIVE PATHOGENS ALSO PRODUCE ENDOTOXIN, WHICH RESULTS IN SERIOUS SIDE-EFFECTS IN SOME IMMUNIZED ANIMALS. AS A RESULT OF THE DEFICIENCIES IN CURRENT VACCINES, WE WILL PRODUCE A VACCINE THAT INCLUDES THE COMPONENTS OF THE BACTERIA THAT ARE EXPRESSED IN THE HOST (IRON BINDING PROTEINS AND BIOFILM MATRIX COMPONENTS) IN THE FORM OF OUTER MEMBRANE VESSICLES (OMV), WHICH ARE RELATIVELY SIMPLE TO PREPARE, COMBINED WITHTHE BIOFILM MATRIX ANDA NOVEL VACCINE THAT HAS BEEN SHOWN TO GREATLY STIMULATE BOTH THE HUMORAL AND CELLULAR IMMUNE RESPONSES OF THE HOST TO DESIRED ANTIGENIC COMPONENTS. TO PRODUCE A SAFE VACCINE WE WILL GENERATE A MUTANT THAT LACKS ONLY ENDOTOXIC ACTIVITY THROUGH THE MUTATION OF ONE GENE BY AN ESTABLISHED ALLELIC EXCHANGE METHOD. OMV FROM THE MUTANT BACTERIA WILL BE GROWN TO PRODUCE IRON-BINDING PROTEINS AND OTHER OURTER MEMBRANE PROTEINS, WHICH ARE COMBINED WITH BIOFILM MATRIX AND THE ADJUVANT. THOROUGH GENETIC AND BIOCHEMICAL CHARACTERIZATION OF THE MUTANT WILL BE CARRIED OUT. THE OPTIMAL CONCENTRATIONOF ALL COMPONENTS WILL FIRST BE DETERMINED IN HOLSTEIN CALVES FOR IMMU,NE EFFICACY AND SAFETY, AND COMPARED TO COMMERCIAL BACTERINS. ONCE OPTIMIZED, ADDITIONAL SAFETY DATA WILL BE COLLECTED ON A LARGE NUMBER OF COMMERCIAL BEEF CALVES IN COMPARISON TO COMMERCIAL VACCINES. APPROVED STATISTICAL ANALYSES WILL BE USED FOR ALL DATA ANALYSIS.