** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** COMMERCIAL LAYING HENS FACE NUMEROUS WELFARE CHALLENGES DURING PRODUCTION CYCLE. WHILE THERE ARE NUMBERS OF WAYS ENVIRONMENT, GENETICS, AND BEHAVIOR CAN INTERACT TO LEAD TO POOR WELFARE, THEY ARE ALL ROOTED IN STRESS. RECENT RESEARCH BY OUR TEAM, AND OTHERS, HAVE DEMONSTRATED THE EXISTENCE OF A GUT MICROBIOME-IMMUNE-BRAIN AXIS. CHANGES IN GUT MICROBIOTA CAN AFFECT THE STRESS RESPONSE AND CENTRAL REGULATION OF BEHAVIOR AND COGNITION. UNDERSTANDING THIS COMMUNICATION AXIS CAN HELP DEVELOP NOVEL APPLICATIONS OF GUT MICROBIOTA TO ENSURE THE WELFARE AND WELL-BEING OF BIRDS. THE MAIN GOAL OF THIS PROJECT IS TO EXAMINE THE ROLE OF GUT MICROBIOTA AS THE DRIVER OF BEHAVIORAL AND WELFARE CHANGES IN LAYING HENS DURING STRESSFUL SCENARIOS. THE SPECIFIC OBJECTIVES ARE TO (1) DETERMINE THE EFFECTS OF STRESS EXPOSURE DURING EARLY-LIFE AND TOWARDS THE END OF PULLET PHASE ON HENS' INTESTINAL MICROBIOTA, AND BEHAVIOR (2) EVALUATE BEHAVIOR AND COGNITIVE ABILITIES OF CHICKEN AS INFLUENCED BY EXPERIMENTALLY ALTERED MICROBIOTA STATUS. THE PROPOSED PROJECT ADDRESSES THE PROGRAM AREA OF WELFARE AND WELL-BEING OF AGRICULTURAL ANIMALS (A1251), AND SPECIFICALLY UNDERSTANDING THE EFFECT OF THE MICROBIOME ON ANIMAL WELFARE AND WELL-BEING. THIS PROJECT WILL DETERMINE THE IMPACT OF STRESS ON GUT MICROBIOTA SHIFT, IMMUNE RESPONSE, AND NEUROTRANSMITTER FUNCTION IN THE BRAIN IN LAYING HEN MODEL. ADDITIONALLY, THIS PROJECT WILL DETERMINE IF GUT MICROBIOTA TRANSPLANTATION CAN ALTER COGNITIVE AND BEHAVIORAL PHENOTYPE IN LAYING HENS. IN THE LONG-TERM, THE RESULTS WILL LEAD TO THE APPLICATION OF GUT MICROBIOTA FOR PREDICTION AND PREVENTION OF WELFARE PROBLEMS IN POULTRY.