The objective of this study was to compare broiler growth performance at the market ages d35, 42 and 56 when fed enzyme-treated soy protein (ESP; Hamlet Protein A/S, Denmark), representing extremely low anti-nutrition- al factors, to exogenous protease in starter diets. A total of 552 day-of-hatch Yield Plus x Ross 708 male broiler chickens were used to assess the effect of two dietary treatments: Starter period (d0-14) chickens were fed either T1 (31.46% SBM, protease: 137.5 U/metric ton) or T2 (26.90% SBM, 5% ESP). In the grower (d14-28), finisher (d28-42) and withdrawal periods (d42-56), all birds received common corn-soybean meal based diets. T1 group continued to receive protease (137.5 U/metric ton) throughout the entire trial. Feed and water were provided ad libitum. Body weight and feed intake by pen were recorded at d0, 14, 28, 35, 42 and 56. Body weight gain (BWG) and feed conversion ratio (FCR) were calculated. FCR was adjust- ed for mortality and fixed BW (d35=2.42kg, d42=3.34kg, d56=4.88kg). Data were analyzed using the statistical software R (R Core Team 2020 version 4.0.0) by Student’s T-test. Differences were considered significant at p<0.05. For BWG, no significant difference was observed between treatments. ESP inclusion in starter feed had a significant effect on mortality adjusted FCR on day 35 (SBM+protease=1.45, SBM+ESP=1.42; p=0.001), day 42 (SBM+protease=1.52, SBM+ESP=1.48; p<0.0001) and day 56 (SBM+protease=1.71, SBM+ESP=1.68; p=0.046). Fixed BW adjusted FCR was significantly improved by ESP inclusion at day 35 (SBM+protease=1.44, SBM+ESP=1.42; p=0.018) and day 42 (SBM+protease=1.52, SBM+ESP=1.48; p=0.0006).
In conclusion, replacing part of the SBM in broiler starter diets with 5% ESP improved performance at day 35, 42 and 56 by reducing mortality adjusted FCR by 3, 4 and 4 points over exogenous protease. Feeding ESP in starter diets reduced BW adjusted FCR at day 35 and 42 by 2 and 4 points over exogenous protease.