In this experiment,small intestinal digestibility of rumen undegraded protein(RUP) in 13 kinds of concentrates were measured by mobile nylon bag method(MBT),original three-step in vitro method(TSP),modified three-step in vitro method(MTSP) and acid detergent insoluble nitrogen(ADIN) estimation method,and correlation analysis of measured results between MBT and other methods and regression analysis between conventional nutrient contents and small intestinal digestibility of RUP were carried out.The purpose o...