Rapidly Digestible Protein Influences Starch and Protein Digestive Dynamics, Digestibility and Concentrations of Amino Acids in Portal Circulation in Broiler Chickens

A ‘slow protein’ foundation diet and a ‘rapid protein’ summit diet were offered to male Ross 308 chicks from 7 to 28 days. The foundation diet contained protein derived from soybean and canola meals, maize and limited quantities of supplemental lysine, methionine and threonine. The summit diet contained casein and additional supplemental amino acids as partial replacements for soybean meal. The transition from foundation to summit diets accelerated protein (N) disappearance rates in the three posterior small intestinal segments to highly significant (P < 0.001) extents. However, this transition significantly increased starch digestibility coefficients in three posterior small intestinal segments by 4.46% (0.844 versus 0.808) in the distal jejunum (DJ), 3.96% (0.946 versus 0.910) in proximal ileum (PI), 3.11% (0.962 versus 0.933) in distal ileum (DI) and accelerated (P < 0.01-0.001) starch disappearance rates in all four small intestinal segments by 16.2% (26.78 versus 23.04 g/bird/day) in PJ, 14.4% (32.38 versus 28.30 g/bird/day) in DJ, 14.0% (36.14 versus 31.71 g/bird/day) in PI and by 13.1% (36.72 versus 32.46 g/bird/day) in DI. Rapid protein positively influenced amino acid digestibility coefficients to highly significant extents and the summit diet significantly increased plasma concentrations of methionine (16.5 versus 11.6 μg/ml; P < 0.005) and threonine (81.8 versus 58.8 μg/ml; P < 0.005) in the portal circulation. Thus the inclusion of rapidly digestible protein as casein and synthetic amino acids increased protein and starch digestibility and disappearance rates and influenced post-enteral availability of amino acids.