Protease supplementation of sorghum-based broiler diets enhances amino acid digestibility coefficients in four small intestinal sites and accelerates their rates of digestion

Apparent amino acid digestibility coefficients in the proximal jejunum, distal jejunum, proximal ileum and distal ileum of broilers fed sorghum-based diets without or with exogenous protease were determined at 28 days post-hatch. The digestion kinetics of amino acids were determined using an exponential mathematical model to relate digestion coefficients at four intestinal sites with mean retention times in each small intestinal segment. Protease increased average digestibility coefficients in the distal jejunum by 12.6% (0.681 vs. 0.605; P<0.05), in the proximal ileum by 5.0% (0.783 vs. 0.746; P=0.055) and in the distal ileum by 4.7% (0.822 vs. 0.785; P<0.05). In distal ileum, protease significantly increased the digestibility of thirteen amino acids, which ranged from a 4.5% increase in histidine (0.820 vs. 0.785, P<0.05) to a 7.9% increase in proline (0.779 vs. 0.722, P<0.01). Protease supplementation significantly increased digestion rates of twelve amino acids from 34.2% for histidine (2.57 vs. 3.45×10−2 min−1, P<0.05) to 55.7% for proline (2.28 vs. 3.55×10−2 min−1, P<0.01). Protease did not significantly influence retention times in each intestinal site. Protease significantly increased predicted glycaemic response by 18.8% (P<0.05). There were no significant correlations between digestion rates of starch and amino acids. The present study indicates that the Bacillus lichenformis-derived protease has the capacity to improve amino acid digestibility coefficients in sorghum-based diets and accelerate the digestion rate of protein and amino acid absorption.