**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE PREDOMINANT COOL-SEASON FORAGE IN THE SOUTHEASTERN U.S., ENDOPHYTE-INFECTED TALL FESCUE (TOXIC FESCUE), NEGATIVELY IMPACTS HEALTH AND PERFORMANCE OF LIVESTOCK, CONTRIBUTING TO OVER $1 BILLION IN ANNUAL AGRICULTURAL LOSES. THE ENDOPHYTE IN TOXIC FESCUE PRODUCES ERGOT ALKALOIDS THAT LEAD TO PERIPHERAL VASOCONSTRICTION AND FESCUE TOXICOSIS. WHILE NEGATIVE EFFECTS OF TOXIC FESCUE ON LIVESTOCK HAVE BEEN LONG-ESTABLISHED, AN EFFECTIVE AND COST-EFFICIENT THERAPEUTIC HAS NOT YET BEEN IDENTIFIED AND INTRODUCED INTO PRACTICE. FURTHERMORE, LIMITED RESEARCH HAS EVALUATED THE EFFECTS OF ERGOT ALKALOIDS CONSUMED BY PREGNANT DAMS ON OFFSPRING HEALTH AND PERFORMANCE. IN AGREEMENT WITH OUR PRELIMINARY RESULTS, CALVES BORN TO DAMS EXPOSED TO TOXIC FESCUE DURING MID TO LATE GESTATION HAD DECREASED BIRTH AND WEANING WEIGHTS. ADDITIONALLY, TOXIC FESCUE CONSUMPTION REDUCED UTERINE ARTERY AND VEIN CROSS-SECTION AREAS IN PREGNANT HEIFERS, CONSISTENT WITH OUR RECENT FINDINGS DEMONSTRATING DECREASED UTERINE ARTERY BLOOD FLOW IN PREGNANT HEIFERS CONSUMING TOXIC RELATIVE TO ENDOPHYTE-FREE FESCUE SEED. MELATONIN IMPLANTS HAVE BEEN ASSOCIATED WITH INCREASED UTERINE ARTERY BLOOD FLOW AND SUBSEQUENT WEANING WEIGHT OF CALVES BORN TO MELATONIN-TREATED DAMS. OUR PRELIMINARY RESULTS SHOWED THAT SUPPLEMENTING PREGNANT HEIFERS CONSUMING TOXIC FESCUE SEED WITH MELATONIN DURING LATE GESTATION RESULTED IN INCREASED BIRTH, WEANING, AND POSTWEANING BODY WEIGHTS OF OFFSPRING. OUR OVERARCHING GOAL IS TO IDENTIFY NOVEL METHODS TO IMPROVE POSTNATAL HEALTH AND PERFORMANCE PHENOTYPES OF OFFSPRING BORN TO DAMS GRAZING TOXIC FESCUE DURING GESTATION. SPECIFIC OBJECTIVES ARE TO 1) DETERMINE THE EFFECTS OF MELATONIN SUPPLEMENTATION ON UTERINE AND COCCYGEAL ARTERY HEMODYNAMICS IN PREGNANT CATTLE GRAZING TOXIC FESCUE, AND 2)ASSESS GROWTH PERFORMANCE-RELATED PHENOTYPES OF CALVES BORN TO DAMS GRAZING TOXIC FESCUE AND SUPPLEMENTED WITH OR WITHOUT MELATONIN DURING GESTATION.SUPPLEMENTING DAMS GRAZING TOXIC FESCUE WITH MELATONIN IS EXPECTED TO IMPROVE UTERINE AND COCCYGEAL ARTERY HEMODYNAMICS, AND THEREBY DECREASE TOXIC FESCUE-ASSOCIATED REDUCTIONS IN GROWTH PERFORMANCE OF OFFSPRING. ACCOMPLISHING OUR SPECIFIC OBJECTIVES IS EXPECTED TO NOT ONLY PROVIDE AN ESSENTIAL START TO FILLING A PROFOUND GAP IN THE CURRENT LITERATURE, BUT IT ALSO HAS THE POTENTIAL TO PROVIDE A COST-EFFECTIVE THERAPEUTIC THAT COULD BE QUICKLY INCORPORATED INTO PRACTICE. FOR EXAMPLE, POWDERED MELATONIN, 50 MG, CAN BE PURCHASED AND PACKED INTO IMPLANT SHELLS FOR APPROXIMATELY$1.20/IMPLANT. THEREFORE, MELATONIN SUPPLEMENTATION IN PREGNANT CATTLE GRAZING TOXIC FESCUE HAS THE POTENTIAL TO NOT ONLY IMPROVE OFFSPRING GROWTH PERFORMANCE BUT INCREASE PRODUCER RETURN ON INVESTMENT.