Five mixed-age Coopworth ewes were offered a pelleted low Mg (1.0 g Mg/kgDM) diet at the rate of 800 g/d for 2 months. Five levels of MG (0, 0.5, 1, 2 and 4 g Mg/d) in 230 ml deionised water were infused into the distal ileum for 48 h, followed by a recovery period of 24 h. The treatments were randomly allocated to each animal using a latin square design. Mg absorption from the large intestine was estimated from changes in plasma Mg concentration and urinary Mg excretion rate. Twelve h after commencement of infusion, plasma Mg concentration was higher at 4 g Mg than at 0g. There was a positive relationship between the amount of Mg infused and urinary Mg excretion. However, the percentage of infused Mg that was absorbed declined from 18.2% to 6.9% when Mg infusion rate was increased from 0.5 to 4 g Mg/d. In a second experiment, using a cross-over design, increasing the amount of water infused, with 4g Mg/d, from 230 to 2300 ml decreased urinary Mg excretion. The results show that Mg can be absorbed from the large intestine in significant amounts and indicate that a passive transport mechanism may be involved.
Proceedings of the New Zealand Society of Animal Production, Volume 49, , 191-196, 1989
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