The objective of this study was to determine the net energy (NE) concentration in soybean meal (SBM) fed to broiler chickens using the comparative slaughter technique. Two different types of SBM containing 460 g/ kg crude protein (SBM-46) and 480 g/kg crude protein (SBM-48) were used in the current study. On d 17 post hatching, 108 male broiler chickens were fasted for 12 h. On d 18 post hatching, birds were individually weighed (initial body weight = 701 ± 68 g) and divided into the initial (8 birds) and final group (96 birds). The initial group was euthanized by CO2 asphyxiation and immediately frozen. Remaining 96 birds were assigned to 3 experimental diets with 4 birds per cage in a randomized complete block design with body weight as a blocking factor. Experimental diets consisted of a basal diet and 2 test diets in which 20% of SBM-46 or SBM-48 replaced the energy-yielding ingredients in the basal diet. The experiment lasted for 7 d and excreta collection was conducted during the last 3 d. On d 25 of age, birds were euthanized by CO2 asphyxiation after a 12 h-fast, individually weighed, and immediately frozen. Whole frozen carcasses in the same cage were ground together, thoroughly mixed, and dried at 55°C for gross energy analysis. Nitrogen-corrected metabolizable energy (MEn), energy retention, and NE in the basal diet were greater (P < 0.05) than values in the test diets containing SBM-46 and SBM-48. No difference was observed in MEn between the SBM-46 and SBM-48 diets, but NE in the SBM-46 diet was greater (P < 0.05) than those in the SBM- 48 diet. On a dry matter (DM) basis, MEn in SBM-46 (2,835 kcal/kg DM) and SBM-48 (2,697 kcal/kg DM) did not differ, whereas NE was greater (P < 0.05) in SBM-46 (2,094 kcal/kg DM) compared with SBM-48 (1,241 kcal/kg DM).
In conclusion, NE concentration in SBM with low protein was greater than that in SBM with high protein.