THE U.S. HAS THE FOURTH LARGEST CATTLE POPULATION IN THE WORLD BY HEAD COUNT YET IS THE LARGEST BEEF PRODUCER. THERE IS A SIGNIFICANT AMOUNT OF GENETIC VARIATION BETWEEN ANIMALS IN THEIR ABILITY TO CONVERT INPUTS (FEED) TO FINAL PRODUCT (GROWTH) E.G. SOME ANIMALS GROW WELL WHILE EATING VERY LITTLE WHILE OTHERS GROW POORLY WHILE EATING A LOT. THE COST OF FEED REPRESENTS UP TO 75% OF THE DIRECT COST ASSOCIATED WITH BEEF PRODUCTION. IN ORDER FOR THE U.S. TO CONTINUE TO LEAD IN BEEF PRODUCTION AND INCREASE PROFITABILITY OF BEEF PRODUCTION, EFFICIENCIES IN PRODUCTION MUST BE OPTIMIZED. OUR OVERALL OBJECTIVE IS TO IDENTIFY DNA VARIANTS INFLUENCING GENE EXPRESSION LINKED TO VARIATION OF FEED EFFICIENCY OF CATTLE AND INCLUDE THESE VARIANTS ON COMMERCIALLY AVAILABLE ASSAYS TO ENABLE PRODUCERS TO MORE ACCURATELY SELECT THE MOST EFFICIENT ANIMALS. TO ACHIEVE THIS, WE WILL PROFILE THE GENE EXPRESSION OF THREE RELEVANT TISSUES IN A LARGE NUMBER OF ANIMALS SELECTED FOR EXTREMES OF FEED EFFICIENCY.WE EXPECT THAT ALL THE PRODUCTS OF THIS RESEARCH WILL ENHANCE OUR UNDERSTANDING OF THE GENETIC/GENOMIC MECHANISMS UNDERLYING THE COMPLEX TRAIT OF FEED EFFICIENCY AND SERVE AS A MODEL FOR FUTURE WORK IN RELATED TRAITS. INDEED, A BETTER UNDERSTANDING OF THE BIOLOGICAL MECHANISMS RESPONSIBLE FOR QUANTITATIVE VARIATION WILL HELP CREATE THE MAP THAT CAN BE USED BY MANY SCIENTIFIC DISCIPLINES FROM NUTRITIONISTS, PHYSIOLOGISTS, GENETICIST TO GENOME ENGINEERS, ENABLING THE SCIENTIFIC COMMUNITY TO HELP ACCOMPLISH THE GRAND CHALLENGE OF ADVANCING OUR NATION'S ABILITY TO ACHIEVE GLOBAL FOOD SECURITY AND FIGHT HUNGER.