A comparison of the true and apparent metabolizable energy measures using corn and soybean meal samples

This study was designed to compare the results of the true metabolizable energy (TME) and the conventional apparent metabolizable energy (AME) assays in detecting differences in the metabolizable energy content of different samples of corn and soybean meal. The samples assayed were three pairs of high and low protein soybean meals (SBM) and six corn samples of varying bushel weight. Also included in the study were two additional corn samples of a single variety of which one was a normal crop (corn ND) and the other (corn D) was obtained from plants earlier afflicted with "eye spot' fungal disease (Kabatiella zeae) so that the grain kernels did not fully mature. A somewhat larger difference was apparent in the metabolizable energy content of two of the three pairs of the high and low protein SBM using the AME assay as compared to using TME as a measure. Because of insufficient material the AME of two of the six corns that differed most in bushel weight could not be determined. The TME values for the six corns were very similar and so were the AME values for the four samples with sufficient assay material. In the case of the two corns of the same variety, corn ND showed an appreciably higher AME than corn D while the TMEs of these two samples were essentially the same. The multiplication factors for converting N-corrected AME to TME were greater for the low protein, high fiber SMB than for the high protein, low fiber samples, while the factors for corn samples were substantially smaller than those for either the high or low protein SBM. These results indicate that there may be no consistent relationship between AME and TME, although theoretically there should be a consistent relationship between these two energy measures regardless of the feedstuff assayed.