Prediction of the concentration of standardized ileal digestible amino acids and safety margins among sources of distillers dried grains with solubles for growing pigs: A meta-analysis approach

The concentration of standardized ileal digestible (SID, g/kg) amino acid (AA) is variable among sources of distillers dried grains with solubles (DDGS). The range in SID Lys among sources of DDGS reported in the literature varies among studies from 0.8 to 8.2 g/kg (88% DM basis). A meta-analysis was conducted using a database representing 23 published studies, with 118 sources of DDGS, to develop prediction equations for estimating the content of SID essential AA based on chemical composition. Sources of DDGS were separated into subgroups according to the type of grain used: corn (n = 90), wheat (n = 12), sorghum (n = 2), corn and wheat blend (n = 7), and other grains (rice, blend of corn and sorghum, or blend of more than 2 grains; n = 7). Descriptive statistics included means of nutrient composition among publications, types of grains, and pig body weight. After testing for normal distribution and outliers, data were analyzed using a mixed model with publication as a random effect. Redundant variables were removed after collinearity analysis. A validation step was performed for all models to compare predicted vs. observed values. Compared with corn DDGS, wheat DDGS had greater (P < 0.05) content of crude protein (336 vs. 271, g/kg), acid detergent fibre (ADF, 151 vs. 115 g/kg), and tryptophan (3.1 vs. 2.0 g/kg), but less ether extract (48 vs. 88, g/kg), lysine (6.0 vs. 8.0, g/kg) and lysine SID coefficient (0.533 vs. 0.617). For all types of DDGS, the best predictor of SID AA content was the corresponding total AA content (R² ranged from 0.97 to 0.99). Neutral detergent fibre (NDF) or ADF had negative effects on the SID content of AA with small slopes for NDF (−0.005 to −0.002) and ADF (−0.028 to −0.001). An interaction (P = 0.048) between essential AA content and ADF was only observed in the SID threonine. Safety margins for diet formulation can be estimated using the radius of the 95% confidence interval for lysine (0.37, g/kg), methionine (0.15, g/kg), threonine (0.31 g/kg), and tryptophan (0.10, g/kg). In all models that predicted essential AA content, the intercept (=0) and slope (=1) were not different (P > 0.10) between model predicted and observed SID AA values, suggesting high accuracy of the models. In conclusion, accurate prediction equations were developed for estimating the SID essential AA content and suggested safety margins for DDGS from various grain sources.