**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THERE IS SPECULATION THAT SELECTION FOR 'ECONOMIC' TRAITS (GROWTH, MILK, AND CARCASS TRAITS) RESULTS IN REDUCED IMMUNE FUNCTION AND INCREASED SUSCEPTIBILITY TO DISEASE, WITH MORBIDITY OCCURRING LATER IN THE FINISHING PERIOD THAN TYPICAL MORBIDITY PATTERNS.HYPOTHESIS:FOCUSED SELECTION OF BEEF CATTLE FOR ECONOMIC TRAITS IN ELITE HERDS HAS REDUCED ROBUSTNESS AND RESILIENCE TO STRESSORS IN THE BEEF PRODUCTION CHAIN.OBJECTIVES:1. DETERMINE THE EFFECTS OF SELECTION FOCUSED ON ECONOMIC TRAITS ON PHENOTYPIC EXPRESSION OF IMMUNE COMPETENCE AND STRESS RESPONSIVENESS OF GROWING STEERS.2. EXAMINE THE IMPACTS OF SEASONAL CHANGES IN CLIMATE AND DIETARY RESOURCES PROVIDED TO THE DAM ON PHENOTYPIC EXPRESSION OF IMMUNE COMPETENCE AND STRESS RESPONSIVENESS OF THEIR OFFSPRING.WE AIM TO DETERMINE THE EFFECTS OF SELECTION OF MODERATE OR EXTREME GENETICS FOR WEANING AND YEARLING WEIGHT, AND MILK YIELD IN THE COW/CALF SECTOR ON THE FEED INTAKE, FEED EFFICIENCY, GROWTH PERFORMANCE, AND CARCASS CHARACTERISTICS OF STEERS; AND CHARACTERIZE THE STRESS AND IMMUNE RESPONSIVENESS, BEHAVIOR, AND TEMPERAMENT AND THUS SUBSEQUENT ROBUSTNESS TO STRESSORS AND HEALTH CHALLENGES.THE RESULTS OF THIS PROJECT WILL PROVIDE A FOUNDATION FOR FURTHER INVESTIGATIONS INTO THE EFFECTS OF GENETIC SELECTION ON ANIMAL HEALTH AND WELLBEING AND OFFER A BIOLOGICAL BASIS FOR ALTERNATE SELECTION CRITERIA AND GENETIC-BASED TOOLS FOR HEALTH AND WELFARE-BASED SELECTION.