Abstract:To analyze effect of grinding degree on the digestibility of bone protein and ammonia nitrogen content of bone powder，pig bone was taken as raw material，with the high pressure cooking and enzyme assisted hydrolysis，the bone was crushed with colloid mill into particle size larger than 150 μm，less than 37.4 μm，and sizerange of 150 μm-92.9 μm，92.9 μm-75 μm，75 μm-58.9 μm，58.9 μm-48.9 μm，48.9 μm-41.8 μm，41.8 μm-37.4 μm. Ammonia nitrogen content，fat and moisture contents，protein digestion ratio of bone meal were determined，and the protein pattern，bone morphology were analyzed. Results showed that the bone size smaller than 37.4 μm accounted for 83.2 %. With the decrease of particle size，the content of fat increased，and the content of ammonia nitrogen decreased. The digestion ratio of protein in the bone meal showed an increasing trend with the decrease of the size of the bone meal，and the digestion ratio of the bone size less than 37.4 μm was significantly（P＜0.05）higher than others. The result of SDS-PAGE of bone meal showed that the content of low molecular protein increased with the decrease of the size of the bone particle. The microstructure of bone meal showed that the surface of the crushed bone meal was smooth.