** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** FOR DAIRY COWS, PROPER FUNCTION OF FAT TISSUE IS CRITICAL FOR SUPPORTING THE HEALTH AND PRODUCTIVITY OF THESE ANIMALS, ESPECIALLY AT THE ONSET OF LACTATION WHEN COWS MUST DEAL WITH SIGNIFICANT METABOLIC STRESS THAT CAN LEAD TO INFLAMMATION, DISEASE, AND ECONOMIC LOSSES. MACROPHAGES, THE MOST ABUNDANT IMMUNE CELLS IN FAT TISSUE, AND ENDOTHELIAL CELLS, WHICH SUPPORT BLOOD FLOW INTO AND OUT OF FAT TISSUE, ARE IMPORTANT CELLS THAT HELP GUIDE THE FUNCTIONS OF FAT TISSUE AND PLAY IMPORTANT ROLES IN METABOLISM AND INFLAMMATION. HOWEVER, THE CHANGES THAT OCCUR IN THESE CELL TYPES AND HOW THEY INTERACT WITH EACH OTHER AS DAIRY CATTLE GO FROM BEING PREGNANT TO LACTATING, AND WHEN DAIRY CATTLE EXPERIENCE METABOLIC STRESS, HAVE YET TO BE FULLY UNDERSTOOD. OUR HYPOTHESIS IS THAT CHANGES IN BOTH THE ABUNDANCE AND FUNCTIONS OF MACROPHAGES AND ENDOTHELIAL CELLS WITHIN FAT TISSUE OF DAIRY CATTLE ARE INVOLVED IN THE DEVELOPMENT OF METABOLIC STRESS AND THE ADAPTATION REQUIRED OF DAIRY CATTLE DURING THE TRANSITION FROM PREGNANCY TO LACTATION.TO INVESTIGATE THE MACROPHAGE AND ENDOTHELIAL CELLS IN FAT TISSUE, WE WILL COLLECT FAT TISSUE SAMPLES FROM DAIRY CATTLE BOTH BEFORE AND AFTER CALVING AS WELL AS FROM DAIRY COWS AT THE BEGINNING OF LACTATION THAT ARE EXPERIENCING METABOLIC STRESS. MACROPHAGES AND ENDOTHELIAL CELLS WILL BE ISOLATED FROM THESE FAT TISSUE SAMPLES AND EVALUATED FOR THEIR OVERALL ABUNDANCE AS WELL AS POTENTIAL CHANGES IN THEIR FUNCTION AND GENETICS AS COWS TRANSITION FROM PREGNANCY TO LACTATION. IN ADDITION, TECHNIQUES WILL BE USED TO UNDERSTAND HOW THE MACROPHAGES AND ENDOTHELIAL CELLS IN FAT TISSUE INTERACT AND HOW THESE INTERACTIONS MAY DIFFER DURING PREGNANCY AND EARLY LACTATION, AS WELL AS IN COWS THAT ARE EXPERIENCING METABOLIC STRESS. BY FURTHERING OUR UNDERSTANDING OF THE ROLE THAT MACROPHAGES AND ENDOTHELIAL CELLS PLAY IN THE FAT TISSUE OF DAIRY COWS, WE MAY IDENTIFY NEW TARGETS FOR POTENTIAL THERAPEUTICS FOR IMPROVING THE HEALTH AND PRODUCTIVITY OF DAIRY CATTLE DURING EARLY LACTATION.