The effect of site and quantity on the extent of absorption of Mg infused into the gastro-intestinal tract of sheep

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Abstract
Summary: Balance trials were carried out in which different amounts of Mg (0·44–2·9 g/day) were infused alternatively into the rumen and into the omasum, abomasum or duodenum of sheep consuming a low Mg diet (0·2 g Mg/kg D.M.). Absorption from the region between the infusion sites was measured from the change in urinary excretion and apparent absorption caused by changing the site of infusion.Absorption was greater from a ruminal than from a comparable duodenal infusion. There was evidence, however, that the absorption mechanism within the stomach area was becoming saturated at the higher infusion rates in that the relationship between the amount absorbed and infused was curvilinear. The proportion of infused Mg which was absorbed from the stomach area fell from 0·61 to 0·14 as the infusion rate increased from 0·44 to 2·80 g/day.The main site of absorption within the stomach area was the rumen; a small amount was absorbed from the omasum, but none from the abomasum. Positive differences between omasal and duodenal infusions were seen in plasma concentration at the two lowest and in urinary excretion at all infusion rates.Increasing the amount of Mg infused into the duodenum caused an increase in plasma concentration and a linear increase in absorption.When the ruminal and duodenal infusions were repeated with the sheep consuming hay, the results were similar but the proportion of infused Mg absorbed was reduced.