Saturation kinetics of magnesium efflux across the rumen wall in heifers

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Abstract
1. Absorption of magnesium from the temporarily-isolated, emptied and washed rumen of four 10–12-month-old heifers was measured at five different Mg concentrations (2·5, 5·0, 7·5, 12·5 and 20 mmol/l).2. Net absorption of Mg was observed at all concentrations. Saturation occurred at a concentration of 12·5 mmol Mg/l.3. Using an Eadie–Hofstee plot, the Michaelis–Menten constant (Km; 11·43 mmol/l) and maximal efflux (Vmax; 120·3 μmol/min) were estimated.4. The phenomenon of saturation supports the assumption that Mg transport across the rumen wall of heifers is an active process.