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 from the diet, the net portal flux of L-lactate, ammonia-N, acetate, propionate, isobutyrate, and 3-methylbutyrate were reduced (P < 0.05). These reductions were largely the result of decreased portal blood flow. In both experiments, dietary ionophores affected net flux across portal-drained viscera for several metabolites. These changes may differ, however, with roughage level and ionophore fed.
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Harmon et al. (1988) studied this question.
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