Effect of duodenal infusion of leucine and phenylalanine on intestinal enzyme activities and starch digestibility in goats

The present research evaluated the effect of duodenal infusion of leucine (Leu) and phenylalanine (Phe) on the activity of α-amylase, trypsin, and lipase, and starch digestibility in the small intestine of goats. Sixteen yearling ewes (body weight=29.7±1.4 Kg) fitted with duodenal catheters were used in a completely randomized design experiment. All goats were fed the same diet (700 g/d, dry matter (DM) basis) twice daily at 0800 and 1800, and were randomly assigned to one of the following four treatments for 21 d: duodenal infusion of water, 3 g/d Leu, 9 g/d Leu, or 2 g/d Phe. On day 21, all goats were slaughtered for collecting samples of the blood and the digesta. The total length of the small intestine from the distal region of the pylorus to the ileal-cecal junction was defined as 100%. Digesta samples at the 0, 20, 40, 60, 80, and 100% relative sites along the small intestine were collected and frozen at −80 °C for the subsequent analysis. The α-amylase activity was increased (P<0.05) with the infusion of 3 g/d Leu at the 0% relative site, 9 g/d Leu at the 0, 20 and 80% relative sites, and 2 g/d Phe at the 0 and 80% relative sites of the small intestine. The 9 g/d Leu also improved (P<0.05) the trypsin activity at the 0, 20 and 40% relative sites, and the lipase activity at the 0 and 20% relative sites of the small intestine. Duodenal infusion of Leu and Phe showed no significant effects on intestinal digestibility of DM (P=0.223) or starch (P=0.116), Leu and 2 g/d Phe numerically increased DM digestibility by 4.3 and 6.5%, and starch digestibility by 6.0 and 5.7%. Linear relationships (P<0.05) were identified between digesta α-amylase activity and intestinal digestibility of DM and starch. These data indicate that duodenal supply of Leu and Phe may increase digesta α-amylase activity, and numerically improved starch digestion in the small intestine.