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Four experiments were conducted to evaluate the effectiveness of a computer-controlled simulated digestion system (CCSDS) for predicting apparent metabolizable energy (AME) and true metabolizable energy (TME) using in vitro digestible energy (IVDE) content of feeds for roosters. In Exp. 1, the repeatability of the IVDE assay was tested in corn, wheat, rapeseed meal, and cottonseed meal with 3 assays of each sample and each with 5 replicates of the same sample. In Exp. 2, the additivity of IVDE concentration in corn, soybean meal, and cottonseed meal was tested by comparing determined IVDE values of the complete diet with values predicted from measurements on individual ingredients. In Exp. 3, linear models to predict AME and TME based on IVDE were developed with 16 calibration samples. In Exp. 4, the accuracy of prediction models was tested by the differences between predicted and determined values for AME or TME of 6 ingredients and 4 diets. In Exp. 1, the mean CV of IVDE was 0.88% (range = 0.20 to 2.14%) for corn, wheat, rapeseed meal, and cottonseed meal. No difference in IVDE was observed between 3 assays of an ingredient, indicating that the IVDE assay is repeatable under these conditions. In Exp. 2, minimal differences (<21 kcal/kg) were observed between determined and calculated IVDE of 3 complete diets formulated with corn, soybean meal, and cottonseed meal, demonstrating that the IVDE values are additive in a complete diet. In Exp. 3, linear relationships between AME and IVDE and between TME and IVDE were observed in 16 calibration samples: AME = 1.062 × IVDE - 530 (R(2) = 0.97, residual standard deviation [RSD] = 146 kcal/kg, P < 0.001) and TME = 1.050 × IVDE - 16 (R(2) = 0.97, RSD = 148 kcal/kg, P < 0.001). Differences of less than 100 kcal/kg were observed between determined and predicted values in 10 and 9 of the 16 calibration samples for AME and TME, respectively. In Exp. 4, differences of less than 100 kcal/kg between determined and predicted values were observed in 3 and 4 of the 6 ingredient samples for AME and TME, respectively, and all 4 diets showed the differences of less than 25 kcal/kg between determined and predicted AME or TME. Our results indicate that the CCSDS is repeatable and additive. This system accurately predicted AME or TME on 17 of the 26 samples and may be a promising method to predict the energetic values of feed for poultry.

Two experiments were conducted to investigate the feasibility of using corn starch as the basal diet to determine the ME of protein feedstuffs using the TME assay in Chinese Yellow chickens. In the first experiment, the TME of corn starch were determined by force-feeding 25 or 40 g of feed. To test the repeatability of the bioassay, the same experiment was repeated 4 times. In the second experiment, the TME of soybean meal and cottonseed meal was determined by considering corn starch as the basal diet, while corn was fed alone to the chickens. To test the accuracy of the TME assay for individual ingredients, the additivity was evaluated by determining the TME of 3 mixed diets: corn-soybean meal diet, corn-cottonseed meal diet, and corn-soybean meal-cottonseed meal diet. In experiment 1, the value of endogenous energy loss was 16.76 to 18.46 kcal/48 h, and no significant differences between the 4 assays were noted. The TME and energy metabolizability of the 25-g corn starch treatment (4.06 kcal/g and 98.06%) were higher than those of the 40-g treatment (3.79 kcal/g and 91.45%; P < 0.01); whereas the CV were less than that of the 40-g treatment, indicating that it is reasonable to use the TME value of the 25-g treatment in feed formulation. In experiment 2, the TME values for corn, soybean meal, and cottonseed meal were 4.02, 3.39, and 2.92 kcal/g, respectively. The observed and predicted TME values of the corn-soybean meal, corn-cottonseed meal, and corn-soybean meal-cottonseed meal diets were in high agreement with differences ranging from -0.02 to 0.01 kcal/g. None of the differences was significant, indicating an accurate measure of the TME of the individual ingredients. Thus, using corn starch as the basal diet to determine the TME of protein feedstuffs was validated.