The impact of grain type and reduced crude protein formulation on postprandial glucose and amino acid responses

Two experiments were conducted to evaluate the post‑prandial glucose, insulin, and amino acid responses in broiler chickens offered diets containing standard and reduced crude protein (CP) levels. Exp. 1 used 120 straight-run Ross 308 broilers to compare standard (SCP) versus reduced crude protein (LCP) wheat‑based diets from 10 to 38 days post‑hatch where growth performance, starch and amino acid digestibility, carcass traits, abdominal fat deposition, and post‑prandial glucose and insulin dynamics were assessed. Exp. 2 used a 2 × 2 factorial design to examine the interactive effects of dietary crude protein level and grain type (wheat or sorghum) on post‑prandial glucose, insulin, plasma amino acids in 144 straight-run Ross 308 broilers from 14 to 35 days post‑hatch. In Exp. 1, the LCP diet reduced weight gain and increased feed conversion during the grower phase and decreased breast yield but did not affect finisher or overall performance. Increased starch intake, starch disappearance rates, starch‑to‑protein disappearance ratios and nitrogen retention were observed in birds offered LCP diet. Amino acid digestibility in the jejunum and ileum was generally enhanced under the LCP diet. In Exp. 2, wheat-based diets led to higher glucose concentrations at 30 min, and there was a treatment effect on postprandial insulin response. Wheat-based diets exhibited higher circulating Val and Ile but not Leu at 120 and 200 min regardless of dietary CP levels and LCP diets increased plasma glutamine concentrations and total area under the curve for glutamine. Overall, no clear relationship between post-prandial amino acid concentrations and growth performance was observed; no clear correlation between glucose, insulin, and fat pad weights was observed, which differed from our hypotheses. Reducing dietary crude protein with NBAA supplementation improved nitrogen utilisation and apparent amino acid digestibility; however, these benefits did not consistently result in improved growth performance.