Effects of grain type and soybean meal reduction on growth performance, carcass traits, and nutrient digestibility of broilers

Reducing reliance on soybean meal (SBM) in broiler diets using non-bound amino acids (NBAA) and alternative protein-rich ingredients is an important strategy for sustainable poultry production, yet the efficacy of this approach across different basal cereal grains remains unexplored. This study evaluated the feasibility of replacing SBM using a combination of NBAA and alternative protein-rich ingredients in broiler diets based on different grains. The experiment was conducted using a completely randomized design with a 3 × 3 factorial arrangement of treatments with three basal grains (wheat, sorghum, and barley) and three SBM inclusion levels (standard, medium, and low/nil), resulting in nine dietary treatments. Each treatment was offered to eight replicate floor pens of 20 birds, totalling 1440 one-d-old off-sex male Ross 308 broilers (body weight 38.65 ± 0.03 g), from 0 to 42 d post-hatch. Standard SBM inclusion levels were 250, 210, and 170 g/kg in the starter (d 0–14), grower (d 14–28), and finisher (d 28–42) diets, respectively. Medium and low/nil SBM inclusion levels represented reductions of 25% and 50%, 50% and 75%, 75% and 100% of SBM inclusions for three phases, respectively. Soybean meal reduction was achieved by including NBAA, canola products, and field peas. Nutrient digestibility was assessed on d 28, and carcass traits were evaluated on d 42. An interaction between grain type and SBM inclusion level was observed during the starter phase, where low/nil SBM inclusion reduced body weight gain (BWG; P = 0.005), and feed intake (FI; P = 0.002) in sorghum-based diets, but not in wheat- or barley-based diets. Over the grower and finisher phases, no interaction effects were detected for BWG, FI, or feed conversion ratio (FCR) ( P > 0.05). Low/nil SBM inclusion reduced overall BWG compared with standard and medium SBM inclusion levels ( P < 0.001). Sorghum-based diets reduced overall BWG compared with wheat- and barley-based diets ( P < 0.001). An interaction between grain type and SBM inclusion for relative pectoralis major weight was observed ( P = 0.002), with low/nil SBM inclusion reducing breast yield in wheat- and sorghum-based diets. As main effects, sorghum-based diets and low/nil SBM inclusion diets increased relative abdominal fat pad weight ( P < 0.001). Sorghum-based diets resulted in the lowest apparent jejunal starch and protein digestibility, and apparent ileal starch digestibility ( P < 0.001). In conclusion, 25%, 50%, and 75% SBM reduction in the starter, grower, and finisher phases, maintained growth performance and carcass yield, particularly in wheat- and barley-based diets.