INFLUENCE OF IONOPHORE ADDITION TO ROUGHAGE AND HIGH-CONCENTRATE DIETS ON PORTAL BLOOD FLOW AND NET NUTRIENT FLUX IN CATTLE

Two experiments using cattle with chronic hepatic-portal and arterial catheters were conducted to investigate effects of ionophore addition to roughage and high-concentrate diets on net nutrient flux across portal-drained viscera. Monensin and salinomycin added to a high-concentrate diet fed to three beef heifers in a Latin square design (exp. 1) increased the net portal flux of propionate (P < 0.05) and glutamate (P < 0.05) with a tendency for increased portal blood flow. Two beef steers (exp. 2) were fed alfalfa with monensin (300 mg d−1) for 22 d prior to dietary monensin and samples were taken on days −3, 0, 1,2, 4, 9, 16, 32, and 35 relative to monensin removal. Portal blood flow and gut oxygen consumption decreased (P < 0.05) following monensin removal until day 9, then remained relatively constant. Use of glucose by portal-drained viscera decreased (P < 0.05) until day 16, then returned towards initial values, while net appearance of L-lactate decreased linearly (P < 0.05). After monensin removal f...