SUBOPTIMAL LEVELS OF PROGESTERONE MAY BE ATTRIBUTED TO PREMATURE LOSS OF CORPUS LUTEUM (CL) FUNCTION AND ARE ASSOCIATED WITH REDUCED EMBRYONIC SURVIVAL (LOSS OF PREGNANCY), WHICH IS A SIGNIFICANT COMPONENT OF IMPAIRED REPRODUCTIVE PERFORMANCE IN CATTLE. THIS PROPOSAL WILL TEST THE HYPOTHESIS THAT LIPID DROPLETS PROVIDE A METABOLIC OR HORMONE-SENSITIVE ORGANELLE WHICH CAN PROVIDE CELLULAR ENERGY AND/OR STORE AND MOBILIZE SUBSTRATE FOR PROGESTERONE SYNTHESIS. THE OBJECTIVES OF THIS PROPOSAL ARE 1) DETERMINE IF LIPID DROPLETS OF STEROIDOGENIC LUTEAL CELLS (BOTH LARGE AND SMALL) ARE A STORAGE DEPOT FOR CHOLESTEROL AND UTILIZED DURING STEROID BIOSYNTHESIS AND 2) DETERMINE THE METABOLIC EVENTS THAT REGULATE LIPID DROPLETS DURING STEROID BIOSYNTHESIS. SUCCESSFUL COMPLETION OF THIS PROJECT WILL REVEAL THE SEQUENCE OF EVENTS THAT REGULATE LIPID DROPLETS AND DETERMINE HOW THESE EVENTS AFFECT LIPID DROPLETS AND THEIR CONTRIBUTION TO LUTEAL PROGESTERONE SYNTHESIS. THE FINDINGS OF THIS WORK WILL BE PUBLISHED IN SCIENTIFIC JOURNALS AND PRESENTED AT LOCAL, REGIONAL AND NATIONAL RESEARCH CONFERENCES. THIS PROJECT WILL ALSO PROVIDE TRAINING FOR GRADUATE STUDENTS AND COMPLETION OF THESIS REQUIREMENTS. OUTCOMES FROM THIS PROJECT MAY ALLOW FOR MANAGERIAL METHODS TO REGULATE PROGESTERONE IN BREEDING FEMALES.