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

Abstract

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.

Magnesium absorption in mature ewes infused intrarumenally with magnesium chloride

“…In other studies, similar observations were made when the Mg intakes of sheep infused with MgCl, were decreased below approximately 2.5 g/d (Strachan & Rook, 1975;Tomas & Potter, 1976;Field & Munro, 1977). The decline of the marginal Mg absorption rate proximal to the pylorus was complemented by an increase in absorption distal to the pylorus.…”

“…In contrast, Mg absorption at the two lower levels of Mg intake took place against the observed electrochemical gradients, suggesting that active transport across the rumen epithelium was occurring. Other studies in sheep (Field & Munro, 1977;Brown et al 1978;Martens et al 1978;Martens & Rayssiguier, 1980) and cattle (Martens, 1983) have provided evidence that absorption of Mg across the rumen epithelium is achieved by an active transport process which reaches saturation at high Mg concentrations. The results of this present study are consistent with these findings.…”

“…Recent studies have shown that the major site of magnesium absorption in the sheep is located at the rumen and that Mg uptake from this site is achieved by an active transport process (Martens et al 1976(Martens et al , 1978Field & Munro, 1977;Brown et al 1978;Martens & Rayssiguier, 1980). In addition, a number of studies have shown that Mg absorption can also occur from sites distal to the pylorus (Grace & MacRae, 1972;Ben-Ghedalia et al 1975;Field & Munro, 1977).…”

“…In addition, a number of studies have shown that Mg absorption can also occur from sites distal to the pylorus (Grace & MacRae, 1972;Ben-Ghedalia et al 1975;Field & Munro, 1977). However, it is not clear whether Mg absorption from both of these sites can vary in proportion to Mg supplementation or what transport mechanisms are involved.…”

Effects of Faunation, Protein Source and Surgical Modification of the Intestinal Tract Upon Flows of Calcium, Phosphorus and Magnesium in the Digestive Tract of Sheep

“…Endogenous secretion of Ca occurs in the ileal section (Ben-Ghedalia et al 1975). The rumeno-reticulum and not the small intestine is the major site for the absorption of Mg (Field and Munro 1977 …”