**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** DAIRY COWS ARE IMPORTANT IN THE USA, WITH MILK PRODUCTION VALUED AT NEARLY $32 BILLION. IT IS IN OUR BEST INTEREST TO IMPROVE THE QUALITY AND OUTPUT OF DAIRY HERDS. RECENT ADVANCES IN OUR ABILITY TO CHARACTERIZE MICROBIAL COMMUNITIES HAVE INCREASED OUR AWARENESS OF THE ROLE THAT RUMINAL MICROBES PLAY IN PROMOTING THE GROWTH AND NUTRITION OF COWS. THE RUMEN MICROBIOTA IS THUS AN ATTRACTIVE TRAIT FOR THE SELECTION AND IMPROVEMENT OF DAIRY COW PERFORMANCE. A SIGNIFICANT BARRIER TO THIS IS THE LACK OF PAIRED HOST GENOTYPE-RUMINAL MICROBIOTA DATA FROM A LARGE COHORT OF COWS, PRIMARILY DUE TO OUR INABILITY TO EFFECTIVELY SAMPLE TO RUMEN MICROBIOME IN A NON-INVASIVE AND HIGH-THROUGHPUT METHOD. TO ADDRESS THIS, WE HAVE PIONEERED A BUCCAL SWABBING APPROACH AND DEMONSTRATED THAT IT IS AN EFFECTIVE PROXY FOR THE RUMINAL MICROBIOME. WE WILLLEVERAGETHIS METHODTO GENERATE RUMINAL MICROBIOME DATA FOR A COHORT OF 800 GENOTYPED DAIRY COWS ACROSS TWO USDA RESEARCH FARMS. EACH ANIMAL WILL ALSO BE SUBJECTED TO TARGETED GENOTYPING TO DETERMINE HOST VARIANTS IN GENETIC MARKERS ASSOCIATED WITH MILK PRODUCTION EFFICIENCY. BOTH HOST GENOTYPE AND RUMINAL MICROBIOME DATA WILL BE CORRELATED IN A GENOME-WIDE ASSOCIATION STUDY TO DETERMINE THEIR RELATIVE CONTRIBUTIONS TO MILK PRODUCTION EFFICIENCY. FINALLY, THESE DATA WILL BE INCORPORATED INTO BOVINEMINE TO ALLOW FOR PUBLIC ACCESS AND DISSEMINATION. THIS IMPORTANT RESOURCE AND TOOL WILL EXPEDITE THE DISCOVERY OF POTENTIAL MICROBIAL TRAITS ASSOCIATED WITH HOST GENETIC MARKERS USABLE FOR SELECTION AND IMPROVEMENT OF DAIRY COW PRODUCTION.