Small intestinal starch digestion in steers: effect of various levels of abomasal glucose, corn starch and corn dextrin infusion on small intestinal disappearance and net glucose absorption.

Eight Holstein steers (four at 300 kg, four at 406 kg) fitted with an elevated carotid artery, hepatic portal and mesenteric venous catheters, and abomasal and ileal cannulas were used in several 4 x 4 Latin square experiments to evaluate small intestinal starch digestion. They were fed alfalfa hay at 1.5% of BW and abomasally infused with water or glucose, corn starch or corn dextrin (one carbohydrate per Latin square) at 20, 40 or 60 g/h, with subsequent determination of small intestinal disappearance and net portal glucose absorption. Increasing the amount of all three carbohydrates infused abomasally increased the amount of carbohydrate disappearing in the small intestine. Increased infusion of glucose caused a continual increase (linear, P less than .01) in net glucose absorption, whereas net glucose absorption for starch and dextrin was maximal at the 20 g/h infusion (quadratic, P less than .05). With the 60 g/h infusion, 94% of the glucose but only 38% of starch and 29% of small intestinal dextrin disappearance could be accounted for as net glucose absorption, leaving a large portion of starch and dextrin disappearance unaccounted for. Of the infused starch and dextrin passing the ileum, 5.8 and 7.3%, respectively, was unpolymerized glucose, indicating that, at least in the distal small intestine, complete starch hydrolysis exceeded the capacity for glucose disappearance. It is concluded that only about 35% of the raw corn starch disappearing in the steer's small intestine resulted in net portal glucose absorption.