Optimizing broiler growth performance through balanced net energy, standard ileal digestible lysine, and amylose/amylopectin ratios: a Box-Behnken response surface approach

This study investigated the effects of net energy (NE), standard ileal digestible lysine (SID Lys), and amylose/amylopectin (AM/AP) ratios on broiler growth performance using a Box-Behnken design. A total of 936 male Arbor Acres Plus broilers (15-35 days post-hatch) were allocated to thirteen treatments with three factors at three levels including NE (2,000, 2,250, 2,500 kcal/kg), SID Lys (1.00 %, 1.20 %, 1.40 %), and AM/AP ratios (0.17, 0.22, 0.27, composed of different ratios of pea starch and waxy corn starch). Growth performance was measured weekly. At the growth stage of 15-20 d, quadratic relationships between dietary NE (P = 0.038), SID Lys (P = 0.010), AM/AP ratios (P = 0.021), and broiler 20 d body weight (BW), with optimization occurring at 2,303 kcal/kg NE, 1.24 % SID Lys, and an AM/AP ratio of 0.22. The 15-25 d feed-to-gain ratio (F/G) decreased linearly with increasing dietary NE (P = 0.038) and SID Lys (P = 0.010). At the growth stage of 21-27 d, linear increases in broiler 27 d BW (P = 0.007) and 21-27 d body weight gain (BWG) (P = 0.013) were observed with higher dietary SID Lys levels, reaching a peak at 2,500 kcal/kg NE, 1.40 % SID Lys, and an AM/AP ratio of 0.17. The 21-27 d F/G decreased linearly with increasing dietary NE (P < 0.001) and SID Lys (P < 0.001) levels. At the 28-35 d growth stage, a significant interaction between NE and SID Lys levels was observed for 35 d BW (P = 0.016) and 28-35 d BWG (P = 0.007). At 2,500 kcal/kg NE, both 35 d BW and 28-35 d BWG increased with higher SID Lys, whereas at 2,000 kcal/kg NE, they initially increased and then decreased as SID Lys levels rose. There was a significant interaction effect of NE and AM/AP ratio on broiler 28-35 d BWG (P = 0.017). Further quadratic curve fitting of 28-35 d BWG and 15-35 d BWG against dietary SID Lys/NE ratio revealed that 28-35 d BWG and 15-35 d BWG were optimized at dietary SID Lys/NE of 5.68 and 5.80 mg/kcal, respectively. These data indicate balancing dietary NE and SID Lys can optimize broiler growth, while lowering the dietary AM/AP ratio further enhances growth performance, likely due to improved starch digestibility and energy release dynamics. This study provides actionable insights for precision nutrition strategies in broiler production.