If you soil is low in magnesium, the grass that grows in it will be low in mineral as well. Considering that your horse receives the majority of its daily magnesium needs through a normal forage diet, it is important to understand if your soil is helping or hindering those needs.You can hire a soil testing service or test it yourself using a commercial test kit.
The easiest way to avoid magnesium deficiency in your horse is to properly maintain your pastures.
 Depending on the soil that they grow in, grasses can be magnesium deficient. The same is true of horse feed. In turn, this can cause your horse to develop a magnesium deficiency. Make sure that the grass and feed that your horse is eating are high in magnesium and other important minerals.Your retailer or distributor should provide information on the mineral make up of their feed.
 Because magnesium is water-soluble, it is easily leached from the ground during rainy seasons. If it has recently rained a lot, the grass will likely not have enough magnesium in it, leading to your horse developing a deficiency. You can increase the magnesium in the soil by sprinkling dolomite or Epsom salts in the field or pasture where your horse feeds., Many consider skittishness a symptom of magnesium deficiency in horses. In fact, magnesium is often recommended as a supplement to help horses relax. If your horse seems more timid than usual, they may be suffering from a magnesium deficiency.There is little scientific evidence to support this claim. If your horse is acting anxious, consult your veterinarian before giving it any supplements.
Research your soil’s mineral makeup.
Evaluate magnesium levels in new grass or feed.
Consider what time of year it is.
Observe if your horse seems nervous or skittish.
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