SKELETAL MUSCLE IS A DYNAMIC TISSUE THAT DAIRY CATTLE CAN DRAW UPON IN EARLY LACTATION AND THEREFORE MUST BE ACCRETED AT OTHER STAGE OF LACTATION. IT IS UNCLEAR WHAT ROLE NUTRITION AND GENETICS PLAY IN EXTENT AND AMOUNT OF MUSCLE THAT CAN BE DEPLETED DURING THE TRANSITION TO LACTATION. THEREFORE OUR GOALS ARE TO DETERMINE IF FEEDING GREATER METABOLIZABLE PROTEIN PREPARTUM PROMOTES MUSCLE ACCRETION, ALTERS MUSCLE HISTOLOGY, AND RESULTS IN IMPROVED LACTATION PERFORMANCE. SECONDLY, TO DETERMINE IF DIFFERENCES IN GENOTYPES REFLECT THE PATTERN OF MUSCLE ACCRETION AND DEPLETION FROM LATE-GESTATION TO PEAK LACTATION. OUR SPECIFIC AIMS ARE TO: 1) DETERMINE IF INCREASING MP DURING THE NON-LACTATING, LATE-GESTATION PERIOD WILL INCREASE MUSCLE MASS, SUPPORT INCREASED MILK PRODUCTION IN EARLY LACTATION, AND RESULT IN CALVES WITH LARGER BODY WEIGHT AND MUSCLE MASS, 2) DETERMINE IF INCREASING MP TO THE DAIRY COW WILL RESULT IN CHANGES IN HISTOLOGICAL MUSCLE FIBER CHARACTERISTICS AND MOLECULAR SIGNATURES OF MUSCLE BIOPSIES, AND 3) DETERMINE IF GENETIC MARKERS EXIST FOR COWS THAT CAN ACCRETE AND DEPLETE THEIR SKELETAL MUSCLE RESERVES TO A GREATER EXTENT. THE CHARACTERIZATION OF THE ROLE OF MUSCLE DURING THIS TRANSITION PERIOD MAY CHANGE THE WAY WE FEED AND MANAGE LATE-GESTATION ANIMALS TO MORE CLOSELY MEET THEIR REQUIREMENTS. THE ROLE OF GENETICS ON MUSCLE CHARACTERISTICS IN DAIRY CATTLE IS NOT ESTABLISHED AND BECAUSE OF THE KEY ROLE THAT MUSCLE PLAYS ON GLUCOSE METABOLISM AND ENERGY SYNTHESIS, DETERMINING GENETIC MARKERS FOR MUSCLE DYNAMICS WILL ENABLE POTENTIAL GENETIC SELECTION IN THE FUTURE. FINALLY, WE WILL TRAIN GRADUATE STUDENTS IN THE INTERSECTION OF NUTRITION, MUSCLE BIOLOGY, AND GENETICS IN ORDER TO PRODUCE MULTIDISCIPLINARY FUTURE RESEARCHERS.