The Reactivity of Magnesium Oxide in Relation to Its Use as a Feed Additive

The reactivities of a number of commercial magnesium oxide products used as feed additives have been determined by pH-static titration at 37°C, both at pH 2.7 and at pH 6.5–6.84. Calcined magnesites are significantly less reactive than magnesium oxide manufactured from dolomite. Grain size is an important factor, but grinding does not always lead to the desired increase in reactivity, because hornblende impurities produce soluble silicic acid, which inhibits dissolution. Some of the products cannot be considered 100% biologically available.