**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** WITHIN PIG PREGNANCY, APPROPRIATE EMBRYO AND FETAL DEVELOPMENT HAVE A SIGNIFICANT IMPACT ON PREGNANCY SUCCESS AND THEREFORE THE EFFICIENCY OF SWINE PRODUCTION. THE PREIMPLANTATION PERIOD OF PIG PREGNANCY, PRIOR TO WHEN EMBRYOS HAVE IMPLANTED INTO THE UTERINE LINING, IS MARKED BY DRAMATIC CHANGES AS THESE EMBRYOS CHANGE AND ELONGATE FROM SPHERICAL TO FILAMENTOUS MORPHOLOGIES. SUCCESSFUL ELONGATION IS NECESSARY FOR MAINTENANCE OF PREGNANCY, ADEQUATE NUTRIENT EXCHANGE, CORRECT SPACING OF EMBRYOS IN THE UTERUS, PROPER PLACENTAL DEVELOPMENT, LITTER SIZE, BIRTHWEIGHT UNIFORMITY, AND POSTNATAL PIGLET SURVIVAL. UNFORTUNATELY, A SIGNIFICANT PORTION (~20%) OF EMBRYOS FAIL TO UNDERGO PROPER ELONGATION, RESULTING IN EMBRYONIC LOSS OR NON-UNIFORM EMBRYONIC DEVELOPMENT WITHIN LITTERS. DUE IN PART TO THE DIFFICULTY OF REPLICATING THIS PROCESS IN THE LABORATORY (IN A CULTURE DISH), LITTLE IS KNOWN ABOUT THE SPECIFIC FACTORS THAT CONTRIBUTE TO PROPER PIG EMBRYO ELONGATION, INCLUDING THE INFLUENCE OF EXTRACELLULAR VESICLES (EVS) PRESENT IN THE UTERINE ENVIRONMENT. EVS ARE SMALL, SPHERICAL MEMBRANE-BOUND PARTICLES THAT ARE SECRETED BY CELLS. THESE EVS CONTAIN A VARIETY OF BIOMOLECULES AND HAVE BEEN SHOWN TO INFLUENCE CELLULAR PROCESSES, INCLUDING DEVELOPMENT. HOWEVER, NO PREVIOUS STUDIES HAVE BEEN ABLE TO ISOLATE AND CHARACTERIZE EVS FROM PIG EMBRYOS ACTIVELY UNDERGOING ELONGATION OR INVESTIGATE THE EFFECTS OF EVS ISOLATED FROM THE PREIMPLANTATION UTERINE ENVIRONMENT ON EMBRYO SURVIVAL AND ELONGATION. OUR RESEARCH TEAM HAS DEVELOPED AND UTILIZED A NOVEL THREE-DIMENSIONAL (3-D) MATRIX TO ENCAPSULATE PIG EMBRYOS FOR STUDIES OF ELONGATION IN THE LAB. THEREFORE, THE GOAL OF THIS PROJECT IS TO CHARACTERIZE EVS ISOLATED FROM MATERNAL AND EMBRYONIC SECRETIONS DURING EMBRYO ELONGATION, AND THEN INVESTIGATE THE EFFECT OF DIFFERENT EV POPULATIONS ON EMBRYO ELONGATION USING OUR UNIQUE 3-D CULTURE SYSTEM. WE WILL ACHIEVE THIS GOAL WITH TWO OBJECTIVES: 1) STUDY EVS ISOLATED FROM MATERNAL AND EMBRYONIC SECRETIONS DURING PIG EMBRYO ELONGATION AT DIFFERENT TIME POINTS AND CHARACTERIZE WHAT PROTEINS AND MOLECULES ARE CONTAINED WITHIN THE EVS. 2) DETERMINE THE EFFECTS OF THESE EVS ON THE SURVIVAL AND INITIATION OF ELONGATION OF PIG EMBRYOS DURING CULTURE WITHIN THE 3D SYSTEM. THE MAJOR EXPECTED OUTCOME OF THIS RESEARCH IS THE UNDERSTANDING OF ROLES AND MECHANISMS OF MATERNAL AND EMBRYONIC EVS PRESENT IN THE PREIMPLANTATION UTERINE ENVIRONMENT ON THE INITIATION OF PIG EMBRYO ELONGATION. THIS NEW AND DEEPER UNDERSTANDING OF EMBRYO ELONGATION CAN ALLOW FOR THE DEVELOPMENT OF INTERVENTIONS TO IMPROVE PREGNANCY OUTCOMES IN THE PIG AND OTHER DOMESTIC AGRICULTURAL SPECIES, THUS CONTRIBUTING TO INCREASED ANIMAL PRODUCTION AND GLOBAL FOOD SECURITY.