MELATONIN IS A HORMONE THAT REGULATES CIRCADIAN RHYTHMS, BUT ALSO HAS BEEN IMPLICATED TO HAVE A ROLE AS A REPRODUCTIVE HORMONE. PREVIOUS WORK IDENTIFIED ROLES FOR MELATONIN IN OOCYTE QUALITY, EMBRYO DEVELOPMENT, PREGNANCY LOSS, AND OVERALL FERTILITY. OOCYTE QUALITY AND EMBRYO DEVELOPMENT ARE THE FOCUS OF THIS WORK GIVEN THAT POOR QUALITY OOCYTES GENERATE EMBRYOS WITH REDUCED GROWTH AND VIABILITY. THESE OBSERVATIONS WERE USED TO DEVELOP THIS CENTRAL HYPOTHESIS - MELATONIN FUNCTIONS AS A CRITICAL COMPONENT OF OOCYTE DEVELOPMENT IN CATTLE, SPECIFICALLY IN LOW ANTRAL FOLLICLE COUNT (AFC) CATTLE AND IS ESSENTIAL FOR OOCYTE PRODUCTION IN VIVO AND OOCYTE MATURATION IN VITRO. TWO AIMS WILL BE USED TO TEST THIS HYPOTHESIS; BY SUPPLEMENTING HIGH AND LOW AFC COWS WITH MELATONIN BEFORE PERFORMING OVUM PICK-UP TO EVALUATE OOCYTE QUALITY AND BY SUPPLEMENTING OOCYTES FROM HIGH AND LOW AFC ANIMALS WITH MELATONIN IN VITRO AND PERFORMING IN VITRO MATURATION TO EVALUATE EMBRYO DEVELOPMENT. THIS PROPOSED RESEARCH IS NOVEL AND IS ANTICIPATED TO PROVIDE VALUABLE INFORMATION INTO OOCYTE DEVELOPMENT AND MATURATION IN CATTLE. THE OVERALL GOAL OF THIS RESEARCH IS TO IDENTIFY METHODS TO IMPROVE OOCYTE QUALITY AND EMBRYO DEVELOPMENT IN CATTLE. EXTENSION PROGRAMMING WILL BE DEVELOPED TO BUILD UPON THIS WORK AND PROVIDE TEXAS DAIRY PRODUCERS WITH PUBLICATIONS TO DISSEMINATE RESEARCH FINDINGS, PROVIDE KNOWLEDGE, AND HANDS-ON SKILLS TO IMPROVE REPRODUCTIVE MANAGEMENT.