** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** DIVERSE AND DYNAMIC MICROBIAL COMMUNITIES (KNOWN AS MICROBIOTA) RESIDE WITHIN THE GASTROINTESTINAL, RESPIRATORY, AND REPRODUCTIVE TRACTS OF CATTLE AND ARE VITAL TO CATTLE HEALTH AND PRODUCTION. EMERGING EVIDENCE INDICATES THAT MICROBIAL COLONIZATION OF CALF INTESTINE MAY OCCUR BEFORE BIRTH AND EVEN DURING EARLY PREGNANCY, HIGHLIGHTING THE POTENTIAL AND EXTENDED ROLE OF THE MATERNAL MICROBIOTA IN CALF GASTROINTESTINAL MICROBIOME DEVELOPMENT. RECENT EVIDENCE OBTAINED FROM MOUSE STUDIES DEMONSTRATED THAT THE MATERNAL MICROBIOTA DURING PREGNANCY MODULATES PROGRAMMING OF FETAL METABOLIC AND NERVE SYSTEM DEVELOPMENT. ACCORDINGLY, OUR HYPOTHESIS IS THAT THE MATERNAL MICROBIOTA IS PARAMOUNT IN FETAL PROGRAMMING (CERTAIN MATERNAL STIMULUS OR INSULT OCCURRING DURING PREGNANCY MAY HAVE A LONG TERM EFFECTS ON THE OFFSPRING) AND OFFSPRING MICROBIOTA DEVELOPMENT IN CATTLE. THE LONG-TERM GOAL OF THIS PROJECT IS TO DEVELOP MATERNAL MICROBIOME-TARGETED APPROACHES TO IMPROVE OFFSPRING HEALTH AND PRODUCTIVITY, AND THEREBY ENHANCE THE EFFICIENCY OF BEEF PRODUCTION. THE SHORT-TERM GOAL OF THIS PROJECT IS TO EVALUATE THE IMPACT OF ALTERING MATERNAL MICROBIOTA VIA HIGH FORAGE OR HIGH CONCENTRATE DIETS ON OFFSPRING MICROBIOME DEVELOPMENT, ENERGY BALANCE, METHANE EMISSIONS AND FEEDLOT PERFORMANCE IN BEEF CATTLE. TO ACHIEVE THIS GOAL, THE FOLLOWING THREE SPECIFIC AIMS WILL BE ASSESSED: 1) CHARACTERIZE THE MATERNAL GUT, NASOPHARYNGEAL AND VAGINAL MICROBIOTA IN RESPONSE TO PREGNANCY; 2) INVESTIGATE PRENATAL MICROBIAL COLONIZATION (IN UTERO MICROBIAL TRANSFER) WITH A FOCUS ON METHANOGENIC ARCHAEA (A GROUP OF MICROORGANISMS RESPONSIBLE FOR PRODUCING METHANE GAS IN THE RUMEN); 3) EVALUATE THE INFLUENCE OF ALTERING MATERNAL MICROBIOTA VIA FEEDING HIGH FORAGE OR HIGH CONCENTRATE DIETS ON OFFSPRING MICROBIOME DEVELOPMENT, ENERGY BALANCE, METHANE EMISSIONS, AND FEEDLOT PERFORMANCE. THIS PROJECT IS ANTICIPATED TO PROVIDE NOVEL AND IMPORTANT INFORMATION FOR CONSIDERATION OF DEVELOPING STRATEGIES TO IMPROVE FEED EFFICIENCY AND DISEASE RESILIENCE IN CALVES BY HARNESSING THE MATERNAL MICROBIOME AND FETO-MATERNAL MICROBIAL CROSSTALK.