BEEF CATTLE VARY IN HOW EFFICIENTLY THEY CONVERT FEED INTO ENERGY, WHICH AFFECTS THE VIABILITY AND COMPETITIVENESS OF US BEEF PRODUCTION. WHILE MICROBES IN THE RUMEN, THE STOMACH OF CATTLE, PLAY A KEY ROLE IN THIS PROCESS THROUGH FERMENTATION OF FEED, LITTLE IS KNOWN ABOUT THE SPECIFIC MICROBES ATTACHED TO THE RUMEN WALL AND HOW THEY INTERACT WITH THE ANIMAL'S TISSUE TO INFLUENCE ITS NUTRIENT ABSORPTION. UNDERSTANDING THIS RELATIONSHIP IS ESSENTIAL FOR IMPROVING FEED EFFICIENCY AND SUPPORTING US BEEF PRODUCTION. THE OVERARCHING HYPOTHESIS OF THIS PROJECT IS THAT THE GENETICS OF CATTLE AFFECT BOTH THE CATTLE CELLS AT THE RUMEN WALL AND THE MICROBES THAT LIVE THERE. IN TURN, THE MICROBES AND THE CATTLE CELLS INFLUENCE EACH OTHER'S GENE ACTIVITY, WHICH HELPS CONTROL HOW NUTRIENTS ARE USED AT THE RUMEN WALL. TO TEST THE OVERARCHING HYPOTHESIS OF THIS PROJECT, THE SPECIFIC OBJECTIVES INCLUDE, 1) IDENTIFY THE DIFFERENT CELL TYPES IN THE RUMEN WALL AND EXAMINE HOW THEIR GENE ACTIVITY IS RELATED TO FEED EFFICIENCY IN BEEF CATTLE, 2) DETERMINE THE TYPES AND FUNCTIONS OF ACTIVE MICROBES ATTACHED TO THE RUMEN WALL AND HOW THEY ARE CONNECTED TO GENE ACTIVITY IN THE RUMEN TISSUE, AND 3) IDENTIFY GENETIC MARKERS IN CATTLE THAT ARE LINKED TO BOTH GENE ACTIVITY IN THE RUMEN WALL AND THE MAKEUP OF THE MICROBIAL COMMUNITY. AT THE COMPLETION OF THIS PROJECT, WE EXPECT TO HAVE A COMPREHENSIVE UNDERSTANDING OF HOW DIFFERENT RUMEN WALL CELL TYPES AND THEIR GENE ACTIVITY INTERACT WITH WALL-ASSOCIATED MICROBES AND CATTLE GENETICS TO INFLUENCE FEED EFFICIENCY. THIS PROJECT WILL PROVIDE CRITICAL NEW KNOWLEDGE THAT CAN BE USED TO DEVELOP TARGETED BREEDING STRATEGIES AND MICROBIAL INTERVENTIONS AIMED AT IMPROVING FEED EFFICIENCY IN BEEF CATTLE. THE FINDINGS WILL SUPPORT ENHANCED CATTLE MANAGEMENT PRACTICES, ADVANCE GENETIC IMPROVEMENT EFFORTS, AND ULTIMATELY HELP TO STRENGTHEN US BEEF PRODUCTION AND US AGRICULTURE.