Determination and prediction of the apparent and standardized ileal amino acid digestibility in soybean meal fed to the pullets

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This experiment was conducted to evaluate the chemical composition, apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of amino acid (AA) in 10 different sources of soybean meal (SBM) fed to the pullets and established prediction equations based on the chemical composition of SBM. 792 Hy Line Brown hens aged 12-15 weeks were divided into 11 diet groups, the diets included one nitrogen-free diet (NFD) used to measure the basal endogenous losses of AA and 10 SBM test diets containing 35.2 % SBM as the sole source of AA. The 0.5 % titanium dioxide (TiO2) was used as an indigestible marker. The results shown that there was considerable variation in crude ash (Ash), ether extract (EE), and acid detergent fiber (ADF) content in the 10 SBM samples with a coefficient of variation greater than 10 %. The AID and SID of both indispensable and dispensable AA except for the Cys and Ala among the 10 SBM differed (P < 0.05). The AID of AA was correlated with the dry matter (DM), gross energy (GE), crude protein (CP), EE, Ash, and reactive Lys (rLys) (P < 0.05), and SID of AA was correlated with the GE, CP, EE, CF, neutral detergent fiber (NDF) and rLys (P < 0.05). With R2 values exceeding 0.39, significant linear regression equations for the AID of Met, Phe, Lys, Asp, and Gly, as well as SID of Met, Phe, Lys, Ser and Tyr were obtained. The best fit equation for the AID of Asp was the DM, GE, Ash and rLys (R2 = 0.820, P = 0.042), and the SID of Lys was the GE, CP, CF, Ash, ADF and rLys (R2 = 0.989, P = 0.005), respectively. In conclusion, this experiment suggested that the rLys can be used to predict the AID and SID of AA in SBM with reasonable accuracy together with the basal chemical composition, and prediction equations for AID and SID could be used to evaluate the digestibility of SBM in the pullets.