** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** MAXIMIZING THE EFFICIENCY OF LIVESTOCK GROWTH IS VITAL TO MEETING THE WORLD'S SURGING DEMAND FOR ANIMAL PROTEIN. THE BEEF CATTLE RESEARCH COUNCIL ESTIMATES AN INCREASE IN FEED EFFICIENCY OF ONLY 1% WOULD SAVE THE FEEDLOT SECTOR ALONE OVER $11 MILLION EACH YEAR. A MORE EFFICIENT ANIMAL IS NOT ONLY DESIRABLE TO PRODUCERS BUT CAN IMPROVE THE AFFORDABILITY AND AVAILABILITY OF BEEF TO CONSUMERS AND REDUCE DEMAND FOR ENVIRONMENTAL RESOURCES. NEARLY 90% OF CELLULAR ENERGY, CRITICAL FOR GROWTH, IS PRODUCED BY MITOCHONDRIA - ORGANELLES FOUND WITHIN NEARLY ALL CELLS OF AN ANIMAL. MITOCHONDRIA HAVE A SMALL GENOME THAT INCLUDES GENES VITAL TO ENERGY PRODUCTION. UNLIKE NUCLEAR DNA WHICH IS INHERITED IN EQUAL PARTS FROM EACH PARENT, THE MITOCHONDRIAL GENOME IS INHERITED MATERNALLY; EACH CALF HAS MITOCHONDRIAL DNA IDENTICAL TO THAT OF ITS MOTHER. DESPITE ITS IMPORTANCE TO ENERGY PRODUCTION, GENETIC VARIATION OF THIS CRITICAL COMPONENT OF ENERGY PRODUCTION IS NOT CONSIDERED IN THE SELECTION OF BREEDING STOCK. FURTHER, THE IMPACT OF VARIATION IN MITOCHONDRIAL DNA ON ENERGY PRODUCTION IS NOT UNDERSTOOD. THE GOAL OF THIS PROJECT IS TO ADDRESS THIS GAP IN KNOWLEDGE AND DETERMINE HOW VARIATION IN MITOCHONDRIAL DNA IMPACTS ITS FUNCTION AND OVERALL ANIMAL EFFICIENCY. TO ADDRESS THIS GOAL WE WILL: 1) UTILIZE INDIVIDUAL GROWTH AND FEED INTAKE DATA TO ASSOCIATE ANIMAL EFFICIENCY WITH VARIATION IN THEIR MITOCHONDRIAL DNA, AND 2) COLLECT PHYSIOLOGICAL DATA TO UNDERSTAND HOW VARIATION IN THE MITOCHONDRIAL DNA IMPACTS CELLULAR METABOLISM. AS A RESULT, WE WILL CONNECT MITOCHONDRIAL GENOTYPE TO GROWTH EFFICIENCY. INFORMATION ONMITOCHONDRIAL GENOTYPE WILL THEN SERVE AS A NEW TOOL FOR THE SELECTION OF THE MOST ENERGY-EFFICIENT COWS THAT WILL IN TURN PRODUCE CALVES WITH THE SAME, DESIRABLEMITOCHONDRIAL GENOTYPE. THIS PROJECTBENEFITS THE FEEDLOT SECTOR WHERE EFFICIENCY OF GROWTH IS OF CRITICAL IMPORTANCE AS WELL AS COW-CALF OPERATIONS WHERE FEED REPRESENTS THE GREATEST EXPENSE FOR EACH COW. FURTHER, WITH NEW TECHNOLOGY BEING IMPLEMENTED FOR ROUTINE COMMERCIAL GENOTYPING OF CATTLE, AN ANIMAL'S MITOCHONDRIAL GENOTYPE WILL BE COLLECTED ALONGSIDE DATA CURRENTLY USED FOR ROUTINE GENOMIC EVALUATIONS ATNO ADDITIONAL COST. THIS INFORMATION CAN IMMEDIATELY BE UTILIZED TO BOLSTER GENOMIC EVALUATIONS LEADING TO IMPROVED EFFICIENCY AND SUSTAINABILITY OF BEEF PRODUCTION.