Prediction of the concentration of standardized ileal digestible (SID) amino acids among sources of distillers dried grains with solubles (DDGS) for growing pigs: A meta-analysis

Abstract Text: The concentration of SID AA is highly variable among DDGS sources. The range in SID Lys content for DDGS sources reported in the literature varies from 0.088 to 0.929% (DM basis). Therefore, accurate prediction of SID AA content in DDGS sources is essential to capture the greatest nutritional value and manage variability when formulating DDGS diets for swine. A meta-analysis was conducted using a database representing 19 published studies and 99 DDGS sources to predict the SID essential AA content of DDGS based on chemical composition. Samples of corn (n = 85), wheat (n = 6), sorghum (n = 2), corn-wheat (n = 4), corn-sorghum (n = 1), and rice (n = 1) DDGS were included in the analysis. Wheat DDGS had greater CP (39.8 vs. 30.9%), ADF (20.8 vs. 13.0%), and Trp (0.39 vs. 0.23%) content, but lower crude fat (4.9 vs. 9.7%), Lys (0.64 vs. 0.92%) and Lys digestibility (44.6 vs. 61.8%; P < 0.05) compared with corn DDGS, respectively. For all types of DDGS, the best predictor of SID AA content was the corresponding total AA content (R² ranged from 0.984 to 0.995). Fiber content (NDF, ADF or hemicellulose) had negative effects on SID content of AA, but the coefficient for fiber in prediction equations was small (-0.006 to -0.003 for NDF and -0.019 to -0.001 for ADF). For example, when NDF increased from 20.4 to 49.6% (minimum and maximum), the concentration of SID Lys and Thr decreased by 0.09 and 0.15%, respectively. The prediction models showed that the mean of radius (half the width) of the 95% confidence interval for the mean SID AA prediction was 0.030, 0.021, 0.024, and 0.012, respectively, for Lys, Met, Thr, and Trp. The radius of the 95% confidence interval provides a reference for establishing feed formulation safety margin coefficients. The prediction error and bias were 0.37 and 0.19 for Lys, 0.20 and -0.28 for Met, 0.32 and 0.48 for Thr, and 0.06 and -0.27 for Trp, respectively. In addition, internal validation of the model showed non-significant (P> 0.10) intercept (= 0) and slope (= 1) for established equations of predicted values against observed values for all SID AA. In conclusion, accurate prediction equations were developed for estimating individual SID essential AA content and suggested safety margins for DDGS from various grain sources.

Keywords: amino acids, distillers dried grains with solubles, meta-analysis, pigs