**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PREGNANCY AND LACTATION IMPOSE SUBSTANTIAL ADDITIONAL NUTRIENT DEMANDS TO MODERN SHEEP AND DAIRY COWS.THESE HIGHLY PRODUCTIVE ANIMALS FACE THIS CHALLENGE BY BECOMING SOMEWHAT UNRESPONSIVE TO THE HORMONE INSULIN.ALTHOUGH THIS ADAPTATION IS GENERALLY BENEFICIAL, IT BECOMES EXCESSIVE IN SOME OF THESE ANIMALS LEADING TO DISEASES AND REDUCED PRODUCTIVITY.A MAJOR LIMITATION IN ADDRESSING THIS PROBLEM IS OUR INCOMPLETE UNDERSTANDING OF FACTORS REGULATING INSULIN ACTION IN SHEEP AND DAIRY COWS.THE OVERALL GOAL OF THIS PROJECT IS TO ASSESS THE ROLE OF NOVEL, TISSUE-DERIVED SIGNALS KNOWN AS EXOSOMES IN REGULATING INSULIN ACTION.THIS GOAL WILL BE ACHIEVED BY PURSUING 3 RELATED AIMS: FIRST, BY DESCRIBING CHANGES IN EXOSOMAL VARIABLES IN THE SHEEP DURING STATES OF REDUCED INSULIN RESPONSE, SUCH AS PREGNANCY AND OBESITY, SECOND, BY ASSESSING THE ABILITY OF THESE EXOSOMES TO ATTENUATE INSULIN ACTION IN ISOLATED CELLS AND FINALLY, BY ASSESSING THE ROLE OF BIOACTIVE CIRCULATING LIPIDS AS PRIMARY FACTORS DRIVING CHANGES IN EXOSOMAL VARIABLES.WE EXPECT TO SHOW THAT EXOSOMES INCREASE IN ABUNDANCE WHEN ANIMALS BECOME SOMEWHAT UNRESPONSIVE TO INSULIN AND THAT THEY REPRESS INSULIN ACTION BY ACTING DIRECTLY ON CELLS AND TISSUES. IDENTIFICATION OF EXOSOMES AS REGULATORS OF INSULIN RESPONSES WILL ALLOW DEPLOYMENT OF NEW APPROACHES TO COUNTER EXCESSIVE ATTENUATION OF INSULIN ACTION AND THEREFORE TO IMPROVE THE HEALTH AND WELL-BEING OF HIGHLY PRODUCTIVE ANIMALS AND THE OVERALL PROFITABILITY OF US SHEEP AND DAIRY FARMS.