Saturation kinetics of magnesium efflux across the rumen wall in heifers

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 ( K m ; 11·43 mmol/l) and maximal efflux ( V max ; 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.