Triplicate nylon bags were put into the rumen of each dairy cows to be incubated for 2, 4, 8, 16, 24, 48, and 72 h (3 bags for each dairy cow at each time point) respectively except for the 16 h time point, the number of bags was twice that of the other time points, as the rumen residues left after that time point were needed to be collected to determine DRUP values.
Determined DRUP values derived from the mobile nylon bag method, the OTS method and the MTS method were calculated by the following equation:
DRUP (%) = (rumen undegraded protein content - residual protein content) x 100/rumen undegraded protein content
Predicted DRUP values derived from the ADIN estimated method were calculated by the following equation:
DRUP (%) = (rumen undegraded protein content - ADIN protein content) x 100/rumen undegraded protein content
The PROC CORR procedure of SAS (1999) was used to make the correlation analysis for DRUP values between the MNB method and other methods.
Determination of DRUP values of feed by three methods and correlation analysis
The determined DRUP values of the concentrates using the MNB, MTS, and OTS methods are presented in Table 2.
For the roughages in Table 2, alfalfa (Zhaodong, Longmu 801, and Longmu 803) had higher determined DRUP values (above 60%) using the MNB method than other roughages.
Correlation coefficients of the determined DRUP values in three types (protein supplements, energy feeds, and roughages) between the MNB method and other methods are presented in Table 6, and a correlation matrix of determined DRUP values between the MNB method and other methods is list in Table 7.
Correlation analysis between the estimated DRUP values using the ADIN method and the determined DRUP values using the MNB method
Regression relation between the DRUP values and routine nutrient content of the feed