Magnesium is distributed widely among body tissues. Approximately 60 % is present in the skeleton and bones. It is found in extracellular body fluids and in blood serum. Magnesium supplementation is very important in order to prevent grass tetany (hypo - magnesemia) in dairy cattle and sheep. Magnesium is also necessary as an activator of enzymes and essential for nerve excitation and muscle contraction.
Main sources Magnesium oxide Magnesium sulphate

Magnesium chloride
Magnesium hydroxide Quality  and selection parameters
The particle size  should be adequate and adapted to the type and processing of feed. Bioavailability: “in vivo” experiments seem to be more reliable than “in vitro” laboratory tests. The colour / pigmentation is especially important in feed supplements.Also the reactivity of the product must be taken into consideration according the processing methods of feed.
Analytical methods
Pyro - phosphate gravimetric method
Complexometric method
X - ray fluorescence
Conversion factors:
MgO x 0,60 = Mg
Mg x 1,66 = MgO