**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** MASTITIS IS TYPICALLY THE RESULT OF A BACTERIAL INFECTION WITHIN THE UDDER OF THE DAIRY COW AND REMAINS A COMMON AND EXPENSIVE DISEASE FOR THE DAIRY INDUSTRY. MASTITIS IS HIGHLY PREVALENT IN NOT ONLY MILKING COWS BUT IN NON-MILKING HEIFERS AND IS EXPECTED TO DAMAGE THE RAPIDLY GROWING AND DEVELOPING UDDER THAT IS PREPARING FOR FIRST LACTATION, BUT THIS HAS NEVER BEEN INVESTIGATED. THE CONSEQUENCES OF IMPAIRED GROWTH AND DEVELOPMENT OF THE UDDER ARE SUBSTANTIAL AND REDUCE LIFETIME MILK PRODUCTION AND PRODUCER PROFITABILITY. THE CENTRAL GOAL OF THIS RESEARCH IS TO INVESTIGATE HOW MAMMARY TISSUES IN HEIFERS ARE DAMAGED BY THESE INFECTIONS AND THE RESULTING IMMUNE RESPONSE. OUR OBJECTIVES ARE TO MICROSCOPICALLY EVALUATE TISSUES FROM HEIFER UDDERS DURING ACTIVE INFECTIONS TO UNDERSTAND HOW GROWTH OF THE MAMMARY TISSUE IS ALTERED AND IDENTIFY THE KEY CHANGES IN THE NORMAL BACTERIAL POPULATION DURING THESE TIMES. OVERALL, WE EXPECT TO OBSERVE SCARRING OF MASTITIS AFFECTED MAMMARY GLANDS ANDSTARK CHANGES IN THE BACTERIAL COMMUNITY WITHIN THE UDDER THAT WILL BE ASSOCIATED WITH THESE CHANGES IN TISSUE STRUCTURE AND GROWTH PATTERNS. THE RESULTS OF THIS WORK WILL GUIDE THE DEVELOPMENT OF MANAGEMENT PRACTICES FOR PRODUCERS TO LIMIT THE IMPACTS OF THESE INFECTIONS ON MAMMARY GROWTH AND DEVELOPMENT AND IDENTIFY KEY GROWTH AND DEVELOPMENT MECHANISMS THAT ARE CHANGED DURING THESE CASES OF MASTITIS WHICH WILL DIRECT THE DEVELOPMENT OF POTENTIAL THERAPEUTICS THAT LIMIT THESE INFECTIONS IMPACTS ON MAMMARY GROWTH AND DEVELOPMENT.