The objective of the study was to investigate the effect of reduced- crude protein (RCP) diets with soybean meal (SBM), canola meal (CM), or corn-dried distiller’s grains with solubles (cDDGS) on ileal amino acid (AA) digestibility and relative gene expression of protein utilization in pectoralis major of broilers under coccidiosis vaccination. A total of 1,296 male chicks were allocated in a 4 × 2 factorial arrangement (diet × vaccination) with 6 replicates. All birds were fed a starter diet from d 0 to 7. Four experimental diets were formulated for the grower (d 7-28) and finisher (d 28-42) phases, namely positive control (PC) corn-SBM-based diet, with 200 or 180 g/kg CP for the grower and finisher phases, negative control (NC) with 40 g/kg CP lower than PC (NC-SBM), an NC diet where 80 g/kg CM replaced 60 g/kg SBM (NC-CM), and an NC diet where 100 g/kg cDDGS replaced 50 g/kg SBM (NC- cDDGS). All diets were isocaloric and formulated to have similar digestible AA concentrations. On d 0, half of the birds were vaccinated with Coccivac B52. Ileal digesta were collected from 2 birds per pen and pooled to generate 6 digesta samples for the non- vaccinated and vaccinated groups on d 7. Ileal digesta on d 15 and 23 were collected from 5 birds per pen. Jejunal tissue and breast muscle were collected on d 23 for relative gene expression of nutrient transporter and protein utilization. On d 7, vaccination numerically decreased the ileal AA digestibility. Ileal digestibility of N, His, Ile, Lys, Phe, and Val in NC-cDDGS was lower (P < 0.05) compared to the PC diet on d 15. There was no interaction effect on ileal AA digestibility on d 23; the ileal digestibility of N, His, Ile, Lys, and Phe in NC-CM and NC-cDDGS was lower (P < 0.05) than in the PC diet. There were no treatment differences in the relative gene expression of jejunal peptide and AA transporter, however, protein synthesis gene (EIF4EBP1) expression was lower (P < 0.05) in the vaccinated group compared to the non- vaccinated group on d 23. In conclusion, reduced-CP diets with CM and cDDGS may lead to lower ileal AA digestibility compared to the standard-protein diet. However, protein utilization genes in the pectoralis were not affected by the dietary treatments, irrespective of the coccidiosis vaccination.

Hyeok Yoon, J., A. Ajao, R. Shamugasundaram, A. Oladeinde and O. Olukosi. 2025. Ileal amino acid digestibility and relative gene expression of ileal nutrient transporter, and pectoralis protein synthesis and degradation in broiler chickens fed reduced-crude protein diets containing soybean meal, canola meal, or corn dried distiller’s grains with solubles under coccidiosis vaccination.  2025 International Poultry Scientific Forum, Abstract M98.