Optimizing dietary crude protein, branched-chain amino acids, and energy levels for broiler performance using a Box-Behnken design

TL;DR

This study optimized protein, amino acids, and energy in broiler diets to improve performance and nutrient use.

Contribution

The novel use of a Box-Behnken design reveals how dietary components interact to affect broiler performance.

Findings

Reduced protein diets with excess BCAA lowered feed intake and weight gain.

High NE improved energy intake and feed conversion in high-protein diets.

BCAA effects on breast yield and fat content depend on protein levels.

Abstract

This study aimed to investigate the limitations and interactive effects of dietary crude protein (CP; 15%, 17% and 19%), excess branched-chain amino acid (BCAA) inclusions (0%, 20% and 40%), and net energy (NE; 9.0, 9.7 and 10.4 MJ/kg) on performance and nutrient utilization for Cobb 500 mix-sex broilers, using a Box-Behnken design. The study consisted of 2 experiments: Exp. 1 involved 1092 chickens, and their performance was measured from d 19 to 35, and Exp. 2 employed 156 birds for NE measurements from d 25 to 28. Both experiments used the same diets (n = 13), each replicated 7 times for Exp. 1 and 6 times for Exp. 2. On d 35, 4 birds per pen (2 males and 2 females) were sampled to collect ileal digesta and weigh carcass parts. Feed intake (FI), NE intake (NEi), weight gain (WG), feed conversion ratio (FCR) and breast yield were affected by CP × NE (P < 0.001) and CP × BCAA (P = 0.041). Diluting NE in the reduced CP (RP)-diets led to a higher FI (P < 0.001) and breast yield (P < 0.001) than high NE, but the NE levels had no effect (P > 0.05) on FI and breast yield in high CP (HCP)-diets. Breast yield increased (P = 0.041) with BCAA in HCP-diets, whereas in the RP-diets, the yield lowered (P = 0.041) with increased BCAA. A similar trend was observed with fat content: in HCP-diets, fat content increased (P = 0.007) with BCAA, while in RP-diets, fat content decreased (P = 0.007) with higher BCAA levels. In addition, increasing BCAA in the RP-diets decreased (P < 0.001) FI, NEi, WG and increased FCR (P = 0.001) than low BCAA. However, BCAA levels had no effect (P > 0.05) on these measurements in HCP-diets. High NE increased (P < 0.001) NEi and decreased (P < 0.001) FCR compared to low NE in the HCP-diets. However, the NE effect on both measurements did not differ (P > 0.05) in RP-diets. These results indicate that increasing BCAA levels beyond the recommended amounts in RP-diets impairs energy utilization, leading to poor performance.

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