Net Absorption of Glucose, L-Lactate, Volatile Fatty Acids, and Nitrogenous Compounds by Bovine Given Abomasal Infusions of Starch or Glucose

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Abstract
Three experiments were conducted to evaluate effects of abomasal infusion of glucose or starch on absorption of metabolites (glucose, L-lactate, volatile fatty acids, and nitrogenous compounds) from portal-drained viscera of a nonlactating Holstein cow and two Hereford .times. Angus heifers. Portal blood and plasma flow were determined by dilution of paraminohippuric acid. Net absorption was portal-arterial concentration difference times portal plasma flow. Plasma concentration and portal-arterial difference of glucose increased rapidly and directly in response to increased rates of abomasal glucose infusion in the cow (Experiment 1). In the cow (Experiment 2), net absorption of L-lactate was greater with carbohydrate than with water infusion; net absorption of L-lactate was greater and of n-butyrate was less with starch than with glucose infusion. These responses were not evident in the heifers (Experiment 3). Net absorption of .alpha.-amino-N in the heifers was greater with starch than with glucose infusion. Increased concentrate intake by the heifers did not interact with responses to abomasal infusions. Recovery of infused glucose as absorbed glucose was similar for the cow and the heifers (65%). However, heifers absorbed (as glucose) 35% of infused starch and the cow only 8%.