The impact of soybean meal and field peas inclusion on growth performance, carcass traits and nutrient digestibilities in broiler chickens offered wheat-based diets

Abstract

Replacing soybean meal (SBM) in broiler diets with only other plant-based protein-rich ingredients or only non-bound amino acids (NBAA) may compromise growth performance in broiler chickens. However, combining both to replace SBM may be feasible while maintaining broiler performance. A 3 × 2 full factorial designed experiment was conducted to include three levels of SBM inclusions (conventional, medium, and low/nil) and with supplementation of field peas or not (50, 80, 100, and 120 g/kg in the starter, grower, finisher, and withdrawal phases, respectively). The variation of SBM inclusions in the diets led to changes in NBAA inclusions and total dietary crude protein. Each diet was offered to 10 replicates of 5 birds per bioassay cage, or a total of 300 straight-run, Ross 308 broilers, from 0-42 days post-hatch. From 0-10 days post-hatch, medium inclusion of SBM reduced feed conversion ratio (FCR) compared to conventional SBM inclusions (1.171 versus 1.129, P = 0.044). From 0-24 days post-hatch, pea inclusions improved the body weight gain by 2.08% (1371 versus 1343 g/bird; P = 0.038) and reduced FCR from 1.297 to 1.276 (P < 0.001) regardless of dietary SBM inclusion levels. Similarly, from 0-35 days post-hatch, pea inclusion increased body weight gain from 2632 to 2731 g/bird (P = 0.001) and reduced FCR from 1.405 to 1.369 (P < 0.001). Overall from 0-42 days, field peas inclusion improved body weight gain by 2.87% (3421 versus 3519 g/bird, P = 0.025), and reduced FCR by 3.1 points (1.518 versus 1.487, P = 0.024) regardless of SBM inclusion levels from 0-42 days post-hatch. Dietary treatment did not influence carcass yield and energy utilisation (P > 0.05). From 27-29 days, broiler chickens offered diets containing the standard SBM inclusion generated the lowest total tract nitrogen retention regardless of pea inclusion rates (P = 0.001). Reducing SBM inclusions, which corresponded with a reduction in dietary crude protein, increased apparent distal jejunal and ileal protein (N) digestibility coefficients (P < 0.05) and total tract nitrogen retention (P = 0.001), regardless of field pea inclusion. Dietary treatments did not influence protein disappearance rates in both the distal jejunum and the distal ileum (P > 0.05). Diets containing the least SBM had increased apparent distal ileal digestibility coefficients of valine, glycine and proline (7.07%) compared to the conventional diets (P < 0.05). In conclusion, replacing SBM with 5%-12% field peas and NBAAs in wheat-based broiler diets to achieve a 20 g/kg dietary CP reduction did not compromise growth performance in broiler chickens. The mechanism by which peas enhanced growth performance is unclear, as the inclusion of peas in the present study did not alter the starch digestion rate.