Additivity of apparent and standardized ileal digestibility of amino acids in wheat, canola meal, and sorghum distillers dried grains with solubles in mixed diets fed to broiler chickens

An experiment was conducted to investigate which method, apparent ileal digestibility (AID) or standardized ileal digestibility (SID), more accurately predicts the digestibility of crude protein (CP) and amino acids (AA) in mixed diets fed to broiler chickens. Male Ross 308 broiler chickens received a standard starter diet from d 0 to 16 post hatching, thereafter grouped into 8 blocks, based on body weight (BW), of 10 birds/cage, and randomly allotted to 6 diets in a randomized complete block design. The 6 diets consisted of a nitrogen-free diet, 3 semi-purified diets, and 2 mixed diets to test the additivity of AID and SID in mixed diets. On d 21 post hatching, digesta from two-thirds of the distal ileum was collected. Using the determined AID or SID for CP and AA in wheat, canola meal (CM), or sorghum distillers dried grains with solubles (DDGS), the AID or SID for 2 mixed diets based on wheat-CM or wheat-CM-DDGS were predicted and compared with determined AID or SID, respectively. The results revealed that the predicted SID of CP and AA in the wheat-CM mixed diet were consistent with determined values except for Asp and Ser, and all the predicted SID of CP and AA were consistent with the determined values in the wheat-CM-DDGS mixed diet. The determined AID of Ile, Met, Thr, Val, Ala, Cys, Ser, and Tyr in the wheat-CM mixed diet were greater (P < 0.05) than predicted AID values. For the wheat-CM-DDGS mixed diet, the determined AID of Trp, Cys, and Glu were greater (P < 0.05) than the predicted AID values. However, there were more inconsistencies between the determined and predicted values in AID values for wheat-CM than the wheat-CM-DDGS mixed diet than SID values for both diets. In conclusion, the present study confirmed that the SID of CP and AA was more additive than the AID of CP and AA when a mixed diet contained wheat, CM, and DDGS as protein sources in broiler chickens.