Evaluation of prediction equations to estimate the concentration of GE, DE, and ME content of corn dried distillers grains with solubles (DDGS) based on variable chemical composition for growing pigs

Abstract Text: The objective of this study was to cross-validate prediction equations developed to estimate the concentration of GE, DE, and ME for growing pigs among sources of corn distillers dried grains with solubles (DDGS) with variable chemical composition. Concentrations (DM basis) of GE, CP, ether extract (EE), NDF, and total dietary fiber (TDF), along with particle size (PS, µm), bulk density (BD, g/cm³) and in vivo determinations of DE and ME from 45 sources of DDGS samples were obtained from 5 published studies. Prediction equations for GE (5 equations), DE (20 equations), and ME (19 equations) from these 5 studies were used to calculate the concentration of GE, DE, and ME among DDGS sources and compare these estimates with experimentally determined in vivo values. Each equation was evaluated using the entire data set, and data sets that excluded data from which the equations were developed (cross-validation). Equations were compared for their overall variance (R²), precision based on reduced prediction error (PE), and accuracy based on deviation of predicted means from overall observed means (bias). Prediction of GE concentration among DDGS sources was poor (PE < 200 kcal/kg DM and biases > 150 kcal/kg DM), despite a moderate explanation of the variance (R²< 0.6). Therefore, we tested DE and ME equations that included GE as an input using actual GE values. Under this condition, the most precise (PE = 144 kcal/kg DM) and accurate (bias = 19 kcal/kg DM) DE equation was DE = -2,161 + (1.39 × GE) – (20.7 × NDF) – (49.3 × EE). The most precise (PE = 149 kcal/kg DM) and accurate (bias = -82 kcal/kg DM) ME equation was ME = -261 + (1.05 × GE) – (7.89 × CP) + (2.47 × NDF) – (4.99 × EE). Predicting GE with equation GE = 4583 + (50.6 × EE) – (0.1 × PS), and using this estimate in the equation of ME = -261 + (1.05 × GE) – (7.89 × CP) + (2.47 × NDF) – (4.99 × EE), resulted in moderate precision (PE = 134 kcal/kg DM) and accuracy (bias = 48 kcal/kg DM). Cross-validation of equations that require PS, BD, or TDF as inputs was not possible because these variables were only measured in 1 of the 5 published studies used in this evaluation.

Keywords: distillers dried grains with solubles, energy, prediction equations