ABOMASAL GLUCOSE, MAIZE STARCH AND MAIZE DEXTRIN INFUSIONS IN CATTLE - SMALL-INTESTINAL DISAPPEARANCE, NET PORTAL GLUCOSE FLUX AND ILEAL OLIGOSACCHARIDE FLOW

Three castrated male Holstein cattle (423 (SD 19) kg live weight) fitt ed with elevated carotid artery, portal, and mesenteric venous cathete rs, and abomasal and heal cannulas were used to study small-intestinal starch digestion. The cattle were infused abomasally with water (275 ml/h), glucose (66 g/h), maize dextrin (66 g/h) or maize starch (66 g/ h) in an incomplete Latin square design, with eight infusion periods. Infusion with carbohydrate resulted in higher arterial glucose concent rations and greater net portal glucose flux than when cattle were infu sed with water. Arterial glucose concentration and net portal glucose flux were highest when glucose was infused. In the small intestine, 85 % of abomasally-infused glucose, 78% of infused dextrin, and 66% of in fused starch disappeared. Of the carbohydrate that disappeared in the small intestine, that which could be accounted for as net portal gluco se flux was 73% for glucose, 60% for dextrin, and 57% for starch. Ilea l digesta contained unpolymerized glucose, and short-chain soluble alp ha-glucoside. Of the infused dextrin flowing past the ileum (14 g/h), 0.3 g/h was glucose, 6.2 g/h was soluble alpha-glucoside, and 7.5 g/h was insoluble alpha-glucoside. Of the infused starch flowing at the il eum (22.2 g/h), 0.9 g/h was glucose, 5.3 g/h was soluble alpha-glucosi de, and 15.9 g/h was insoluble alpha-glucoside. The average chain leng ths of the soluble alpha-glucosides in heal digesta were 2.07 and 2.36 for dextrin and starch infusions respectively, indicating mostly di- and to a lesser extent trisaccharides. We conclude that (1) when 66 g raw starch is presented to the small intestine per h, about half of th e intestinal disappearance appears as glucose in the portal vasculatur e, and (2) alpha-1,4 glucosidase (EC 3.2.1.20) activity at the brush b order is the rate-limiting step to small-intestinal starch digestion i n cattle.