**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** HEAT STRESS (HS)-RELATED LOSSES CONTINUE TO ERODE THE U.S. SWINE INDUSTRY'S PROFITABILITY AT AN ACCELERATING RATE. DEVELOPING INTERVENTIONS THAT TARGET UNDERLYING TISSUE AND CELLULAR DAMAGE HAS BEEN LIMITED BY A RUDIMENTARY UNDERSTANDING OF HS-MEDIATED CELLULAR DYSFUNCTIONS AS WELL AS HOW SEX MAY INFLUENCE THESE DYSFUNCTIONS, BOTH IN SCOPE AND MAGNITUDE, AND THEREFORE THE NEED AND TYPE OF INTERVENTION. CONSEQUENTLY, THERE IS A CRITICAL NEED TO DETERMINE THE EXTENT TO WHICH HS DIFFERENTIALLY IMPACTS MUSCLE AND GROWTH EFFICIENCY IN GILTS AND BARROWS. OUR PRELIMINARY DATA INDICATE BARROWS ARE RESISTANT TO MUSCLE DYSFUNCTION OBSERVED IN GILTS; FINDINGS RECAPITULATED AT THE PRODUCTION SYSTEM LEVEL. THIS INDICATES LARGER NEGATIVE ECONOMIC AND ENVIRONMENTAL IMPACTS IN HEAT-STRESSED GILTS THAN BARROWS DUE TO INCREASED INPUTS AND OUTPUTS. OUR CENTRAL HYPOTHESIS IS THAT GILTS ARE MORE SUSCEPTIBLE TO THE NEGATIVE EFFECTS OF HS THAN BARROWS AND THEREFORE DISPROPORTIONATELY IMPACT AGRICULTURAL ECONOMICS AND THE ENVIRONMENT DURING HS. IN AIMS 1 AND 2 WE WILL PERFORM AN IN-DEPTH PHENOTYPIC, METABOLIC, BIOCHEMICAL, AND HISTOLOGICAL EVALUATION OF HEAT-STRESSED GILTS AND BARROWS OVER TIME IN A CONTROLLED SETTING AND AT THE COMMERCIAL LEVEL. IN EXTENSION AIMS 1 AND 2 WE WILL PERFORM DETAILED ECONOMIC AND ENVIRONMENTAL IMPACT ANALYSES OF PRODUCER DATA AS WELL AS OPTIMIZE ENGINEERED COOLING SOLUTIONS FOR BARROWS AND GILTS. ALL DATA WILL FEED INTO OUR MULTIDIMENSIONAL EXTENSION PLAN IN ORDER TO POSITIVELY AFFECT SWINE PRODUCTION. OUR FINDINGS MAY FUNDAMENTALLY ALTER HOUSING STRATEGIES, PIG ASSIGNMENT TO BARN LOCATION, AND APPLICATION OF COOLING STRATEGIES DURING HS IN ORDER TO OPTIMIZE ANIMAL MANAGEMENT FOR ENVIRONMENTAL HEALTH.