Comparison of two diet types in the determination of metabolizable energy content of corn distillers dried grains with solubles for broiler chickens by the regression method

The objective of this study was to compare 2 diet types, practical and semi-purified, in the determination of ME and MEn contents of corn distillers dried grains with solubles (CDDGS) for broiler chickens by the regression method. Two hundred eighty-eight 14-d-old Ross 308 broiler chickens were assigned to 6 diets consisting of 2 factors in a 2 x 3 factorial arrangement: diet type (practical corn-soybean meal or semi-purified nitrogen-free diet) and CDDGS (0, 300, or 600 g/kg). The birds were fed for 7 d, and there were 6 birds per cage and 8 replicate cages per diet in a randomized complete block design. The CDDGS sample used in the present experiment contained (by analysis) 895 g/kg of DM, 4.811 kcal/g of gross energy, 265.7 g/ kg of CP, 107.6 g/kg of crude fat, 61.3 g/kg of crude fiber, and 41.8 g/kg of ash. There was the expected interaction (P < 0.001) between diet type and CDDGS level in nitrogen retention response of the birds with a decrease as CDDGS level in the practical diet increased but an increase in the semi-purified diet. There were interactions (P < 0.001) between diet type and CD-DGS level in energy retention response, ME, and MEn. Energy retention linearly decreased (P < 0.0001) from 78.6 to 58.6% as CDDGS increased from 0 to 600 g/kg in the practical diets, whereas the decrease was from 86.8 to 75.4% in the semi-purified diet. The ME and MEn (kcal/g) contents of the diets linearly decreased (P < 0.0001) from 3.615 and 3.414 to 2.753 and 2.642, respectively, as CDDGS increased from 0 to 600 g/kg in the practical diets. Corresponding linear decrease (P < 0.0001) values for semi-purified diets were 3.210 and 3.227 to 2.732 and 2.697, respectively. Regression of CDDGS-associated ME intake in kilocalories against grams of CDDGS intake generated the following equations for practical and semi-purified diets respectively: Y = 2.904X + 52, r² = 0.987 and Y = 3.013X + 67, r² = 0.983. The regression equations for CDDGS-associated MEn intake in kilocalories against grams of CD-DGS intake were Y = 2.787X + 46, r² = 0.989 and Y = 2.963X + 66, r² = 0.983 for practical and semi-purified diets, respectively. Comparison using ANOVA procedures indicated the slope for semi-purified diet type was greater (P < 0.05) than that for the practical diet type. These data indicate that the respective ME and MEn values (kcal/g) of the CDDGS sample evaluated were 3.013 and 2.963 when semi-purified nitrogen-free diet was used as the basal diet; and 2.904 and 2.787 when practical corn-soybean meal diet was used as the basal diet. These differences imply that broiler chicken nutritionists should exercise due caution regarding the source of data for ME values of CDDGS when formulating diets containing CDDGS.