Correlation of an immobilized digestive enzyme assay with poultry true amino acid digestibility for soybean meal

The immobilized digestive enzyme assay (IDEA) was run on 6 soybean meal (SBM) samples and compared with true amino acid digestibility (TAAD) content, as determined using cecectomized roosters. The IDEA values were excellent TAAD predictors as evidenced by R(2) values of 0.90 and 0.88 for lysine and cystine, respectively. The original IDEA took 2.5 d to run, and therefore we modified the protocol to reduce the time to 18 h. This modified IDEA procedure was run on 17 SBM samples, and IDEA values were shown to be excellent predictors of TAAD content. This IDEA SBM kit was validated by predicting the TAAD of 5 SBM not included in the 17-sample set above and the comparison of the predicted vs. determined TAAD. Finally, the IDEA SBM kit was used to compare the predicted TAAD of 338 SBM samples from around the world. The predicted lysine digestibility on the world survey samples ranged from 70.6 to 95.5% with an average of approximately 89%, and the ranges and means of the other amino acid digestibilities were also calculated.