Dietary magnesium increases calcium absorption of ovine small intestine in vivo and in vitro

(Received 25 May 2001; accepted 15 January 2002)

Abstract
The purpose of this study was to investigate whether or not an increase in dietary Mg intake increases Ca absorption in the ovine gastrointestinal tract. In an in vivo experiment, an increase in the infused MgCl ₂ level (0.0, 25.0 and 75.0 mg Mg kg BW ^-1 day ^-1 with 75.0 mg Ca kg BW ^-1 day ^-1 as CaCl ₂) into the rumen for ten days significantly decreased fecal excretion but increased urinary excretion ( P < 0.05) of Ca in five castrated male sheep. Apparent Ca absorption tended to increase ( P = 0.067) whilst the retention and plasma concentration of Ca were not changed. In an in vitro experiment with isolated segments from the rumen, upper jejunum, cecum and upper colon under the presence of an electrochemical gradient, the mucosal to serosal Ca flux rate was significantly greater in the presence of 60.0 mM as compared with 1.2 mM MgCl ₂ ( P < 0.05). From these results, we conclude that the mucosal Mg has the ability to increase the Ca absorption in the gastrointestinal tract in sheep when the dietary Mg level is raised.