The bioavailability of magnesium from different types of calcined magnesites of Greek origin

Abstract

The objective of this work was to determine the apparent bioavailability of magnesium from four different types of calcined magnesites of Greek origin. These four types (A, B, C, D) were different in particle size fractions and production process. The solubility of the above four magnesium samples and their fractions were determined: (a) in the laboratory using ammonium nitrate solution after 24-h shaking and (b) in vivo using a nylon bag technique after 24-h incubation. Solubility was correlated with apparent bioavailability as determined in a balance experiment with five wether sheep in a 5 X5 Latin-square design. Sheep were kept in metabolism cages and were given daily a basal diet (500 g hay + 700 g concentrate) plus 2 g magnesium supplements from types A to D. The magnesium bioavailability of the basal diet was used as a base for the determination of the bioavailability of magnesium in A, B, C and D supplements. Magnesium apparent bioavailability of the basal diet was found to be 0-203 and, for the supplements A, B, C and D, 0-381, 0-339, 0-315 and 0-292 respectively. The solubility of supplements A, B, C and D in ammonium nitrate solution and in vivo (using the nylon-bag technique) was found to be 0-812, 0-805, 0-784 and 0-773 or 0-294, 0-152, 0-102 and 0-200 respectively. The solubilities of the magnesium supplements in ammonium nitrate solution and in vivo both reflected dietary bioavailability differences up to a point, but neither was well enough correlated with the apparent bioavailability as determined by the balance experiment, this being judged to be the most precise method for bioavailability determination.

Influence of manufacturing conditions on the bioavailability of magnesium in calcined magnesites measured in vivo and in vitro

“…Solubility in molar ammonium nitrate of magnesites calcined at different temperatures tended to be better correlated with urinary magnesium output than with apparent availability. However, there were correlations between solubility and both availability and (more significantly) with urine output for particle size fractions, in agreement with Zervas & Papadopoulos (1993). Whilst Durrant & Draycott (1976) have reported that solubility in molar ammonium nitrate is of value in assessing magnesium availability in fertilizer-grade calcined magnesites for sugarbeet, this may be more suitable for much larger particle sizes and over the long growing period of the crop.…”

“…The extent of loss of materials calcined at different temperatures was well correlated with both urinary magnesium output and availability. Zervas & Papadopoulos (1993) did not establish such a relationship using four granular magnesites of mixed particle size (Greek origin) with fistulated sheep given hay and concentrates and using bags of 30-60 urn mesh. The potential value of a nylon bag method of appraisal will depend on the use of standardized conditions and recognition that different particle size fractions may have different rates of passage through the rumen.…”

Importance of appropriate amounts of magnesium in rations for dairy cows

“…Such changes in polarity reduce the driving force for electropositively charged Mg ions to be taken up by rumen epithelial cells. In another study, 16 investigators used a wider range of particle sizes and determined that MgO was most soluble at a particle size < 500 µm, moderately soluble at 500 to 1,000 µm, and poorly soluble at > 1,000 µm. Because of the high amounts of potassium in many feedstuffs, especially forages, rations for lactating dairy cattle should contain high concentrations of Mg.…”