** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** MILK IS AN IMPORTANT SOURCE OF NUTRIENTS IN AMERICANS' DIETS AND REPRESENTS OVER 10% OF US FARM CASH RECEIPTS. MILK FAT IS A MAIN CONTRIBUTOR TO THE VALUE OF MILK, BUT IT IS ALSO THE MOST VARIABLE COMPONENT AS IT IS VERY RESPONSIVE TO DIET AND MANAGEMENT. FAT IS AN EXPENSIVE NUTRIENT TO FEED TO DAIRY COWS AND OPTIMAL FEEDING LEVELS ARE NOT ESTABLISHED.OUR OVERARCHING HYPOTHESIS IS THAT THERE IS AN OPTIMAL FEEDING LEVEL FOR DIETARY FAT THAT WILL MAXIMIZE MILK FAT AND THAT LIPOGENESIS INCREASES IN ADIPOSE TISSUES WHEN FEEDING LOW FAT LEVELS.OUR SPECIFIC OBJECTIVES ARE:1. QUANTIFY HOMEORHETIC ADAPTATIONS IN TRANSFER OF DIETARY FATTY ACIDS TO MILK FAT.2. DETERMINE DYNAMICS OF THE CONTRIBUTION OF PREFORMED FATTY ACIDS SYNTHESIZED IN ADIPOSE TISSUE TO MILK FAT SYNTHESIS.3. CHARACTERIZE ELONGASE ENZYME ACTIVITY IN ADIPOSE TISSUE AND ITS REGULATION BY SHORT-TERM ENDOCRINE SIGNALS KNOWN TO IMPACT LIPOGENESIS AND LIPOLYSIS.THE PROPOSAL WILL PROVIDE FUNDAMENTAL INSIGHT INTO THE SUPPLY OF PREFORMED FATTY ACIDS TO THE MAMMARY GLAND FOR MILK FAT SYNTHESIS AND IDENTIFICATION OF KEY INTERACTING NUTRITIONAL AND COW PHYSIOLOGICAL FACTORS THAT IMPACT MILK FAT YIELD. THIS INFORMATION WILL ALLOW ESTABLISHMENT OF RECOMMENDED FEEDING LEVELS FOR DIETARY FAT AND IDENTIFICATION OF LIMITATION IN FAT SYNTHESIS DUE TO NUTRIENT SUPPLY THUS SUPPORTING OPTIMAL FAT YIELD AND EFFICIENCY.