Vitamins and minerals have important functions in a horse’s body. A shortage or excess of any of these substances can have negative effects on your horse’s health. In this article, we will discuss magnesium deficiency. 

Magnesium is a mineral that, together with calcium, causes contraction of muscles. Magnesium and calcium are each other’s antagonists, which means that they act as opposed to each other. Where magnesium provides muscle relaxation, calcium provides muscle tension. Magnesium also plays a role in the building of enzymes and bone tissue and the transmission of stimuli in the nervous system. 

A horse needs magnesium every day through its feed. Unlike other minerals, such as copper, magnesium cannot be stored in the liver. In case of a temporary shortage, the horse cannot gain some magnesium from its liver. But nature has created another reserve, namely the bones. The building blocks of bones are magnesium, calcium and phosphorus. In times of emergency, a horse can use the magnesium in the bone tissue. The horse does this by breaking down bone tissue, which among other things releases magnesium into the body, and then forms new bone again. 

Making use of these emergency reserves does not have to be an immediate problem, provided it is temporary. If the deficiency lasts for a longer time, it has consequences for the quality of the bone. The bone is broken down to release magnesium to be used by the muscles. But when building a new piece of bone, magnesium is also needed. The new bone tissue will then contain fewer minerals than before. This process is called demineralization. The moment a horse has a long-term magnesium deficiency, its skeleton will gradually deteriorate in quality. This can cause injuries more easily. In addition to demineralizing the bone, there are other consequences of a magnesium deficiency. It can cause poor appetite, nervousness, sweating, muscle cramps, ataxia (balance disorder) and accelerated breathing. 

A magnesium deficiency occurs regularly in horses, but it can be difficult to determine. A blood sample can be taken to determine magnesium levels. The problem with this is that in case of a deficiency, magnesium is removed from the bone and brought to the place in the body where it is needed, such as muscle or nerve tissue. As soon as a blood sample is taken, this can indicate normal or increased magnesium levels. You would think that there is no problem, but the horse may indeed have a magnesium deficiency. A sample of muscle tissue (muscle biopsy) should be taken to make a better diagnosis. 

It is important that your horse receives minerals in the right ratios. For example, a surplus of calcium can cause a magnesium deficiency. The horse then absorbs too much calcium, so that there is no longer any room for magnesium. 

Do you suspect magnesium deficiency in your horse? Then first check whether the diet contains enough magnesium. Good quality roughage, pasture grazing and a minimum amount of concentrates is often sufficient to cover the need. The need for magnesium cannot usually be met with roughage alone, but you can only be sure of this if you have had a roughage analysis carried out. On the basis of this analysis you know the mineral contents in your roughage. Are there any shortages? Then you can supplement it with concentrates or supplements. So if your horse shows symptoms of magnesium deficiency, you could add magnesium for a few weeks to see how your horse reacts to this. An excess of magnesium is not harmful to the horse, this is simply excreted in the urine without additional burden on the kidneys. But: if your horse does not need it, there is no point in adding extra magnesium. If you do not notice a difference after a while, it is wise to look for another explanation for your horse’s behaviour.