THE TURKEY PRODUCTION INDUSTRY CONSISTS OF AT LEAST THREE DISTINCT ENTITIES: 1) HATCHERIES THAT INCUBATE FERTILIZED EGGS UNTIL THE EGGS HATCH; 2) GROW-OUT FARMS THAT RAISE THE NEWLY HATCHED POULTS TO THE POINT OF HARVEST; AND 3) FACILITIES THAT SLAUGHTER AND PROCESS THE BIRDS INTO PRODUCTS. THE LOCATION OF EACH OF THESE FACILITIES MAY BE SEPARATED BY LONG DISTANCES, SOMETIMES HUNDREDS OF MILES. TRANSPORTATION OF BIRDS AMONG THESE FACILITIES IMPOSES STRESS THAT MAY AFFECT QUALITY OF THE MEAT PRODUCTS.THIS PROJECT FOCUSES ON THE EFFECTS OF ENVIRONMENTAL EXPOSURE OF HATCHLINGS DURING TRANSPORTATION FROM HATCHERIES TO GROW-OUT FARMS. DURING SHIPPING, THE HATCHLINGS ARE FREQUENTLY EXPOSED TO HOT OR COLD TEMPERATURES THAT MAY HAVE SERIOUS PHYSIOLOGICAL CONSEQUENCES FOR MUSCLE GROWTH AND DEVELOPMENT. THESE INCLUDE REDUCED GROWTH, ALTERED FAT DEPOSITION, AND MUSCLE FIBER DISORGANIZATION, ALL OF WHICH HAVE SERIOUS IMPACTS ON MEAT QUALITY. POULTS HAVE POORLY DEVELOPED PHYSIOLOGICAL SYSTEMS FORMAINTAINING THEIR BODY TEMPERATURES, MAKING THEM VULNERABLE TO THE EFFECTS OF EXTREME HEAT OR COLD. AS TEMPERATURE EXTREMES GROW IN FREQUENCY AND INTENSITY, MEAT QUALITY PROBLEMS ARISING FROM THE EFFECTS OF TEMPERATURE ON MUSCLE GROWTH AND DEVELOPMENT ARE ALSO EXPECTED TO INCREASE.IN THE HATCHLING, A GROUP OF STEM CELLS CALLED SATELLITE CELLS ARE RESPONSIBLE FOR NEW MUSCLE GROWTH BEFORE AND IMMEDIATELY AFTER HATCH. THESE CELLS ARE HIGHLY RESPONSIVE TO HEAT AND COLD STRESS, AND TO MANIPULATION BY MANAGEMENT. SATELLITE CELLS MAY SERVE AS THE TARGET OF THERMAL STRESS IN THE POULT, AND RESPOND BY PRODUCING MORE FAT AND POORLY STRUCTURED MUSCLE IN THE MARKET-AGE BIRD, THEREBY LEADING TO MEAT QUALITY PROBLEMS. THE OVERARCHING HYPOTHESIS FOR THIS RESEARCH IS THAT THERMAL CHALLENGE (HEAT STRESS OR COLD STRESS) RESULTS IN CHANGES IN EXPRESSION OF VERY SPECIFIC GENES OF THE SATELLITE CELL THAT LEAD TO CHANGES IN MUSCLE STRUCTURE AND MUSCLE METABOLISM. OUR FIRST SPECIFIC AIM IS TO ANALYZE THE EFFECTS OF THERMAL CHALLENGE ON TURKEY SATELLITE CELL FUNCTION BY MEASURING CHANGES IN: SATELLITE CELL DEVELOPMENT, GENE EXPRESSION, A NEWLY DISCOVERED GROUP OF MOLECULES CIRCULAR RNAS, AND MUSCLE METABOLITES. OUR SECOND SPECIFIC AIM EXTENDS THIS STUDY TO THE LIVE BIRD. WE WILL SUBJECT TURKEY HATCHLINGS TO HOT OR COLD TEMPERATURES TO ANALYZE THE EFFECTS OF THERMAL CHALLENGE ON MUSCLE STRUCTURE, GENE EXPRESSION, AND MUSCLE METABOLISM. THE RESULTS FROM THESE EXPERIMENTS WILL PROVIDE US WITH A MORE DETAILED UNDERSTANDING OF THE MECHANISMS AT THE MOLECULAR LEVEL OF THE PHYSIOLOGICAL RESPONSE OF THE TURKEY HATCHLING TO THE EFFECTS OF THERMAL STRESS. WE WILL ALSO UNCOVER NEW DISCOVERIES ON HOW THIS NOVEL CLASS OF REGULATORY MOLECULES CALLED CIRCULAR RNA RESPOND TO THERMAL CHALLENGE AND AFFECT MUSCLE GROWTH AND MEAT QUALITY. OUR RESULTS WILL ENABLE THE POULTRY INDUSTRY TO IMPLEMENT NEW BREEDING AND MANAGEMENT PRACTICES THAT EFFICIENTLY INCREASE BREAST MUSCLE MASS WHILE MAINTAINING A HIGH QUALITY PRODUCT.