**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** REPRODUCTIVE EFFICIENCY IS A MAJOR CONCERN OF BEEF PRODUCERS ACROSS THE UNITED STATES. THE MAJOR GOALS OF THIS STUDY ARE TO INCREASE THE UNDERSTANDING OF THE CHANGES IN THE IMMUNE SYSTEM OF THE UTERUS THAT OCCUR IN RESPONSE TO MATING. WE WILL ALSO BEGIN TO ESTABLISH HOW THE UTERINE IMMUNE SYSTEM CONTRIBUTES TO VARIATIONS IN PREGNANCY RATES AND HOW MUCH OF THAT RESPONSE IS CONNECTED TO THE PATERNAL CONTRIBUTION. OUR HYPOTHESIS IS THAT DIFFERENT LEVELS OF BULL NUTRITION WILL ALTER CYTOKINE PROFILES OF SEMINAL PLASMA AND THE SUBSEQUENT UTERINE RESPONSE AND EMBRYONIC DEVELOPMENT. TO TEST THIS HYPOTHESIS, WE WILL COMPLETE FOUR SPECIFIC OBJECTIVES: 1) EVALUATE UTERINE RESPONSE, 2) DETERMINE THE IMPACTS OF THESE UTERINE ENVIRONMENTS ON EMBRYONIC DEVELOPMENT, 3) DEFINE THE EFFECTS OF DIFFERENT EJACULATE COMPONENTS ON THE UTERINE RESPONSE, AND 4) ESTABLISH THE EFFECT OF PATERNAL NUTRITION ON GENE EXPRESSION. WE EXPECT PATERNAL NUTRITION TO ALTER THE IMMUNE RESPONSE OF THE UTERUS AND SUBSEQUENTEMBRYO DEVELOPMENT BASED ON THE DIET OF THE BULL. THE COMPLETION OF THIS PROPOSAL WILL CONTRIBUTE TO AN UNDERSTUDIED AREA THAT COULD HAVE MAJOR INFLUENCES ON PREGNANCY ATTAINMENT AND MAINTENANCE AS WELL AS OFFSPRING PRODUCED. THIS COULD LEAD TO FEEDING STRATEGIES, FOR BOTH MALE AND FEMALE DIETS, TO MAXIMIZE REPRODUCTIVE EFFICIENCY IN BEEF CATTLE. OUR FINDINGS COULD ALSO UNCOVER AN AREA OF NEED FOR FUTURE RESEARCH TO HELP EXPLAIN VARIATIONS IN PREGNANCY RATES THAT CURRENT MEASURES OF SPERM QUALITY ARE UNABLE TO ACCOUNT FOR. ADDITIONALLY, THIS PROPOSAL WILL PROVIDE FOUNDATIONAL DATA FOR THE FUNDING OF FUTURE RESEARCH INTO THE CONTRIBUTION OF THE SIRE TO PREGNANCY ESTABLISHMENT, EMBRYONIC DEVELOPMENT, AND OFFSPRING PRODUCTIVITY.