**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** INFERTILITY IS A LONG-STANDING LIMITATION FOR DEVELOPING A SUSTAINABLE CATTLE PRODUCTION SYSTEM THAT HAS AN ECONOMIC IMPACT ON PRODUCERS. IN BEEF CATTLE, A FERTILE HEIFER WILL OPTIMIZE HER CONTRIBUTION TO THE CONTINUED GROWTH OF THE BEEF CATTLE INDUSTRY, WHICH ACCOUNTS FOR THE SECOND MOST CONSUMED PROTEIN IN THE USA. BY CONTRAST, HEIFERS THAT BECOME PREGNANT LATE IN THE BREEDING SEASON, OR DO NOT BECOME PREGNANT, REPRESENT A DEFICIENCY IN FOOD PRODUCTION, AS THOSE HEIFERS DO NOT EXPRESS THEIR FULL POTENTIAL FOR PROTEIN OUTPUT. OUR OVERARCHING HYPOTHESIS IS THAT MOLECULAR FEATURES IN THE BLOODSTREAM ARE INDICATORS OF HEIFER FERTILITY. OUR SPECIFIC OBJECTIVES ARE TO: 1- IDENTIFY QUANTITATIVE RELATIONSHIPS OF GENE EXPRESSION BETWEEN STRUCTURES IN THE BRAIN AND CIRCULATING WHITE BLOOD CELLS; 2- IDENTIFY GENES EXPRESSED IN THE CIRCULATING WHITE BLOOD CELLS THAT CAN PREDICT PREGNANCY IN BEEF HEIFERS. WE EXPECT TO IDENTIFY GENES WHOSE EXPRESSION IN WHITE BLOOD CELLS ARE FUNCTIONALLY LINKED TO REPRODUCTIVE PHYSIOLOGY AND FUNCTIONS. WE ANTICIPATE THE IDENTIFICATION OF GENES THAT CAN BE USED FOR THE EARLY DETECTION OF INFERTILE HEIFERS, AND THE DEVELOPMENT OF MEANS FOR PRODUCERS TO MAKE EARLY DECISIONS ON THE HEIFER MANAGEMENTS TO REDUCE THE UNNECESSARY USE OF CRITICAL FARM RESOURCES.