Availability of Magnesium from Magnesium Oxide Particles of Differing Sizes and Surfaces

Abstract

Magnesium oxides were unground prills sieved to between 30 and 100 screen mesh size (30–100), or 12 and 40 mesh (12–40), or forms ground from the 12–40 to pass a 200 mesh (−200) or a 20 mesh (−20) screen. In the first experiment, magnesium recoveries, the increase in urinary excretion of magnesium above baseline for 2 days following oral administration of 100 g of magnesium oxide to cattle, were 0, 0, 10.2%, and 6.29% for the respective screen sizes. Recovery from 12–40 increased to 4.47% following a series of four daily 100-g oral loads. These amounts represent the relative availability of magnesium and magnesium oxide forms examined, not the absolute availability of magnesium from any one form. In a second experiment, magnesium oxide supplementation, as either 12–40, 30–00, or −20, to a control restricted roughage-ad libitum concentrate diet fed to lactating Holstein cows increased milk fat concentrations (2.84 versus 2.19%), total fat production (580 versus 470 g/day), and magnesium concentrations in blood serum (2.96 versus 2.68 mg/dl). In general the −20 produced a greater increase above control in these traits than did the unground 12–40 or 30–100 forms. The rumen proportion of propionate was decreased by the −20 and 12–40 sizes (32.0 versus 35.4), but only the −20 increased the molar proportion of acetate (55.3 versus 51.0). Although degree of availability differed, magnesium from all magnesium oxide forms examined is available for absorption. The differences may result from the lower rate of solubilization in rumen fluid of the unground versus ground magnesium oxides that was noted during 24-h in vitro incubation. © 1981, American Dairy Science Association. All rights reserved.