为了预测不同粒度玉米在泌乳奶牛中瘤胃可降解干物质( RDDM)和瘤胃可降解淀粉( RDS)的含量,本试验选用5头带有永久性瘤胃瘘管的荷斯坦泌乳奶牛进行尼龙袋降解试验。玉米的粒度分别为300、450、600、2360和6000μm。降解试验采用“同时投入,分次取出”的方法,取样时间点分别为0、2、4、8、12、24、48 h。结果表明,与玉米粒度之间：除了0 h的淀粉降解率的相关性较差( R2=0.3113)外,其他各时间点的干物质和淀粉的降解率均表现出了较好的线性相关(干物质R2为0.6790~0.9334,淀粉R2为0.7467~0.9931,P<0.10)；干物质的快速降解部分( R2=0.8540)、慢速降解部分( R2=0.9010)和RDDM( R2=0.8799),淀粉的慢速降解部分( R2=0.8620)和RDS( R2=0.9290)均表现出了显著的线性相关( P<0.05)。本试验建立了通过粒度( x,μm)分布预测 RDDM ( y1,%)和 RDS 含量( y2,%)的回归公式：y1=67.96-0.00548x,R2=0.88,P=0.019；y2=70.12-0.00536x,R2=0.93,P=0.008。%This study using five lactating Holstein dairy cows with ruminal cannulas was conducted to predict ruminal degradable dry matter ( RDDM) and ruminal degradable starch ( RDS) contents of corn with different particle sizes. The particle sizes of corn were 300, 450, 600, 2 360 and 6 000 μm, respectively. The nylon bags were put in at the same time and took off fractionally in the degradation test, and the sampling time were 2, 4, 8, 12, 24 and 48 h, respectively. The results showed as follows:with particle size of corn, excepting a poor correlation of degradation rate of starch at 0 h ( R2=0.311 3) , liner correlations were found in degrada-tion rates of dry matter and starch at the other time points (R2 of dry matter was 0.679 0 to 0.933 4, R2 of starch was 0.746 7~0.993 1, P<0.10);significant liner correlations were found in rapidly ( R2=0.854 0) and slowly degraded parts of dry matter (R2=0.901 0) and RDDM (R2=0.879 9), as well as slowly degraded part of starch ( R2=0.901 0) and RDS ( R2=0.929 0) ( P<0.05) . Regression formulas of predicting the con-tents of RDDM ( y1 , %) and RDS ( y2 , %) of corn using particle size ( x, μm) distribution are established, which are as follows: y1=67.96-0.005 4 8x, R2=0.88, P=0.019; y2=70.12-0.005 36x, R2=0.93, P=0.008.
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