本试验旨在比较粉碎粒度对氧弹式量热法测定全混合日粮（TMR）总能的影响。试验选取奶牛TMR样品15个，分别粉碎至18、40、60、100目，采用氧弹式量热仪分别测定各样品的总能，同时采用国标法测定样品的干物质、粗脂肪、粗灰分、粗纤维含量，参照NY/T 34-2004方法计算总能，比较不同粉碎粒度的TMR样品所测得的总能的差异，确定采用氧弹式量热法测定TMR总能时最适的粉碎粒度。结果显示：18、40目粉碎组的总能较低，极显著低于60、100目粉碎组及国标法计算所得总能（P<0.01）；60、100目粉碎组的总能较高，与国标法计算所得总能接近，无显著差异（P>0.05）；18和40目粉碎组的相对平均偏差高于60和100目粉碎组。上述结果表明，对TMR进行60或100目粉碎时，采用氧弹式量热法测定的总能更为准确，精确度更高，与国标法计算所得总能可互为替代；综合分析认为，采用氧弹式量测法测定奶牛TMR总能时，粉碎至60目即可满足测定需要。

This experiment was to study the effect of grinding particle size on gross energy (GE) of total mixed ration (TMR) measured by oxygen bomb calorimetry. Fifteen samples of total mixed ration (TMR) for dairy cow were selected and pulverized to 18, 40, 60 and 100 mesh, respectively. The GE of each sample was determined by oxygen bomb calorimeter, the contents of nutrients such as dry matter (DM), crude fat (EE), ash (Ash) and crude fiber (CF) were determined by national standard method, and the GE was calculated reference to the NY/T 34-2004 method, to compare the difference in GE with different degrees of comminution and to determine the optimum grinding particle size for the determination of GE of TMR by the oxygen bomb calorimetry. The results showed that the GE of the 18 and 40 mesh grinding groups was lower, which was significantly lower than that of the 60, 100 mesh grinding groups and the GE calculated by national standard method (P<0.01); the GE of 60 and 100 mesh grinding groups was higher, compared with the GE calculated by the national standard method, there was no significant difference (P>0.05); the relative average deviation of the 18 and 40 mesh grinding groups was higher than that of the 60 and 100 mesh grinding groups. It is shown that when the measured TMR is subjected to 60 or 100 mesh pulverization, the GE measured by oxygen bomb calorimetry is more accurate and has higher precision, and GE which is calculated by the national standard method can be substituted for each other. Comprehensive analysis reveals that the TMR for dairy cow is pulverized to 60 mesh can meet the need of GE determination by oxygen bomb calorimetry.