Availability of Different Inorganic Salts of Magnesium to Sheep

Two experiments were conducted with sheep to determine the relative biological availability of various inorganic magnesium compounds. In experiment I, 25 yearling wethers were fed a magnesium deficient diet to reduce feed intake and then the increase in voluntary feed intake was measured in response to 500 mg of supplemental magnesium daily in the form of feed grade magnesium oxide and reagent grade magnesium carbonate, magnesium oxide and magnesium sulfate. In a second experiment, 24 wether lambs were used in a balance study involving magnesite and reagent grade magnesium carbonate, magnesium oxide and magnesium sulfate. Voluntary feed intake in Experiment I, when expressed as a multiple of consumption prior to magnesium repletion was 2.19, 1.94, 1.65 and 1.26 for reagent grade magnesium carbonate, reagent grade magnesium oxide, feed grade magnesium oxide and reagent grade magnesium sulfate, respectively (P<.01). Magnesium sulfate caused an appreciable diuresis, and the lower feed intake obtained may not relate directly to the availability of its magnesium. Based on absorption and retention data obtained in Experiment II, magnesium as reagent grade magnesium carbonate, oxide and sulfate was well utilized. The magnesium in magnesite was essentially totally unavailable.