Effects of Soybean Meal Concentration at a Fixed 12% Dietary CP on Growth and Carcass Performance of Finishing Pigs from 115 to 136 Kg

Research has reported performance reduction when finishing pigs are fed corn-soybean meal diets formulated below 12% CP even when diets are fortified with all AA at or above minimum NRC (2012) requirements relative to Lys. A total of 280 pigs (DNA 600×241, initially 114.2 kg) were used in a 23-d trial to determine the effects of SBM concentration with CP fixed at 12% on finishing pig performance. Pens of 7 or 8 pigs (balanced number of pigs per treatment) were randomly assigned to 1 of 6 dietary treatments with 6 replications. Treatments consisted of 5 levels of SBM (10.6, 7.7, 4.9, 2.7, and 0%) with 12% CP and a negative control (NC) treatment with 4.0% SBM and 10% CP. All diets were formulated to 0.55% SID Lys with increasing levels of corn gluten meal used as SBM was decreased to maintain the 12% CP. Data was analyzed with PROC GLIMMIX procedure in SAS with pen as the experimental unit and initial BW as a blocking factor. For growth performance, decreasing SBM while maintaining 12% CP marginally decreased (linear, P=0.06) ADG (0.95, 0.94, 0.93, 0.90, and 0.90 kg/d), increased (linear, P=0.01) ADFI (3.36, 3.37, 3.43, 3.56, and 3.50 kg/d), worsened (linear, P<0.01) G:F (0.284, 0.278, 0.273, 0.253, and 0.257) and marginally worsened (linear, 0.07) final BW (136.2, 135.7, 135.7, 134.9, 134.9 kg). Feed intake was lowered (P<0.01) in pigs fed the diet with 12% CP and 10.6% SBM compared with pigs fed the NC diet (3.36 vs 3.60 kg), resulting in a marginal improvement (P=0.06) in G:F for pigs fed the 12% CP, 10.6% SBM diet (0.284 vs 0.267). For carcass characteristics, decreasing SBM decreased (linear, P=0.03) carcass ADG (0.73, 0.72, 0.71, 0.69, and 0.69 kg/d) and worsened (linear, P<0.01) carcass feed efficiency (0.218, 0.213, 0.209, 0.193, and 0.197). Pigs fed the diet with 12% CP and 10.6% SBM had improved (P=0.04) carcass G:F compared with pigs fed the NC diet (0.218 vs 0.204). Reducing the concentration of SBM worsened ADG, G:F, BW, carcass ADG, and carcass feed efficiency. Additionally, pigs fed the 12% CP and 10.6% SBM had improved G:F and carcass G:F compared with pigs fed the NC diet . These results suggest that reduced SBM concentration could be one of the reasons finishing pig performance is decreased when low CP diets are fed.