PROPER FETAL NUTRITION THROUGH ADEQUATE BLOOD FLOW TO THE UTERUS AND PLACENTA IS CRITICAL TO MAXIMIZE OFFSPRING PRODUCTION POTENTIAL WHILE MINIMIZING PREGNANCY WASTAGE AND CALF MORBIDITY AND MORTALITY, WHICH ARE ESTIMATED TO COST CATTLE PRODUCERS OVER $1 BILLION ANNUALLY. RECENTLY OUR TEAM OBSERVED DAILY RHYTHMS IN UTERINE AND PLACENTAL BLOOD FLOW, WHICH INCREASED FOLLOWING MELATONIN SUPPLEMENTATION. OUR RATIONALE FOR THE PROPOSED STUDIES IS THAT ONCE THE IMPACT OF MELATONIN ON CONTROLLING DAILY RHYTHMS IN PLACENTAL FUNCTION ARE IDENTIFIED IN THE CONTEXT OF A COMPROMISED PREGNANCY (SUCH AS MATERNAL NUTRIENT RESTRICTION), STRATEGIES FOR IMPROVING AND MAXIMIZING OFFSPRING HEALTH AND VIGOR CAN BE OPTIMIZED. THE HYPOTHESIS FOR THE PROPOSED RESEARCH IS THAT SUPPLEMENTAL MELATONIN DURING THE DAYTIME WILL AMELIORATE INADEQUATE PLACENTAL FUNCTION DURING MATERNAL NUTRIENT RESTRICTION. OUR OBJECTIVES ARE TO EXAMINE DAILY RHYTHMS IN UTERINE AND PLACENTAL BLOOD FLOW IN ADEQUATELY FED AND NUTRIENT-RESTRICTED CATTLE SUPPLEMENTED WITH OR WITHOUT DIETARY MELATONIN. MOREOVER, WE WILL EXAMINE DAILY RHYTHMS IN PLACENTAL GENE EXPRESSION ASSOCIATED WITH BLOOD FLOW AND NUTRIENT TRANSFER. FOR OUR RESULTS, WE EXPECT THAT DIETARY MELATONIN SUPPLEMENTATION DURING THE DAYTIME WILL COUNTERACT THE MATERNAL NUTRIENT RESTRICTION-INDUCED DECREASE IN DAYTIME UTERINE AND PLACENTAL BLOOD FLOW. MOREOVER, PLACENTAL GENE EXPRESSION RELATED TO DAILY RHYTHMS WILL BE INCREASED IN DIETARY MELATONIN SUPPLEMENTED HEIFERS, THEREBY REVERSING THE NEGATIVE CONSEQUENCES OF A COMPROMISED PREGNANCY BROUGHT ABOUT BY NUTRIENT RESTRICTION. THESE OUTCOMES ARE EXPECTED TO HAVE SIGNIFICANT POSITIVE IMPACTS ON MAXIMIZING CATTLE PLACENTAL EFFICIENCY AND DIRECTLY INFORMING THE DEVELOPMENT OF SUPERIOR STRATEGIES TO MITIGATE WASTAGE OF PLACENTAL FUNCTION DURING PREGNANCY. IN ADDITION, THE NEW KNOWLEDGE GAINED FROM THESE STUDIES WILL CHANGE FUTURE PLACENTAL RESEARCH BY EXPANDING OUR UNDERSTANDING OF DAILY PLACENTAL RHYTHMS, WHICH HAVE NOT BEEN PREVIOUSLY STUDIED.