Pasture dusting with fine particle grade calcined magnesite (16kg Mg/ha) is an effective means for the prevention of hypomagnesaemia and clinical tetany in dairy cows, but almost double that rate was recommended for practical use as both leaf adherence and spreading distribution may be inefficient, (Todd and Morrison, 1964). Magnesium hydroxide powder has been demonstrated to have a significantly higher apparent magnesium availability and increased urine magnesium output for wether sheep than some granular calcined magnesites (Hemingway et al., 1997). Very fine particle size (0.95 ˂10μm) Mg hydroxide suspension (‘Neutramag 40’, Britmag Ltd, Hartlepool TS24 0BY) is available (405g dry matter (DM)/kg, 168g Mg/kg liquid suspension with S.G. of 1.3). The objective of the work was to examine the apparent availability and also the effectiveness of varying rates of application of this material in providing supplemental magnesium to grazing ruminants in spring.