Effect of extrusion processing of soybean meal on ileal amino acid digestibility and growth performance of broiler chicks

The present experiments were conducted to investigate the efficacy of extrusion of inadequately processed soybean meal (SBM) on amino acid (AA) digestibility and performance of broiler chicks. In Exp. 1, 180 day-old Ross broiler chicks were randomly distributed between 6 pen replicates (15 chicks each) of 2 dietary treatments; diets based on SBM or extruded SBM (ESBM) as the main protein sources. Based on the results of Exp. 1 and AA digestibility assay, Exp. 2 was designed using 216 day-old Ross broiler chicks (6 replicates of 18 chicks each), in which dietary SBM content was replaced by 86% using ESBM. This replacement caused about a 9% decrease in dietary crude protein (CP) level. Results showed that coefficients of CP and AA digestibility were greater (P < 0.05) for ESBM than those of SBM. Extrusion processing of SBM increased digestibility coefficients of Lys, Thr, Cys, Leu, Phe, Tyr, Pro, Ser, and Gly. Except during the starter period, dietary inclusion of ESBM increased (P < 0.05) average daily feed intake (ADFI) in Exp. 1 and caused increases (P < 0.01) in average daily weight gains (ADWG) throughout the trial period. Also, using ESBM improved the (P < 0.01) feed conversion ratio (FCR) during starter and finisher periods. In Exp. 2, reducing dietary CP level using ESBM decreased both ADFI (P < 0.05) and ADWG (P < 0.01) in the starter period. During grower, finisher, and entire trial periods, however, ADFI and ADWG were not influenced by dietary treatments. Dietary inclusion of ESBM improved (P < 0.05) FCR value in the finisher period. Although carcass yield was not affected by dietary treatments, reducing dietary CP level resulted in an increase (P < 0.05) in abdominal fat percentage. Moreover, a decrease in dietary CP level reduced (P = 0.08) breast yield. The present findings indicate that extrusion of SBM could improve its nutritive value for broiler chicks. Using ESBM, one can reduce dietary CP level by about 9% without any detrimental effect on performance parameters of broiler chicks.