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It is widely accepted that supplementing magnesium can be of great benefit to 
both the horse’s health and behavior. As a result, it is common for a calmer to contain magnesium, so why do they not all give the same result?

Magnesium is vital in the body for a huge range of processes. Horse’s burn off magnesium in response to stress, be it from stabling, breaking, schooling, travelling, competition, a change of routine etc. The domesticated horse is exposed to extremely high levels of stress and it is therefore common for magnesium requirement to far exceed dietary intake.  This can cause generally highly strung or sharp behavior as well as more specific problems such as spooking, aggression, nervousness, bad travelers, box walking, weight loss and even head shaking.

These problems result from changes in both the nervous and hormonal systems. Low magnesium levels mean that calcium can overload the muscle and nerve cells making the nerves overly sensitive. Hormonally, there is an increase in levels of stress hormones, notably of adrenaline and cortisol.

Unfortunately, the solution is not as simple as it may seem. Getting the required result from the magnesium you supplement very much depends on the type, quality and quantity used. Magnesium oxide for example, is a very cheap and readily available form of magnesium but unfortunately it is almost entirely insoluble, so absorption is very poor.     

Magnesium sulfate and magnesium phosphate are examples of readily available salts that would be in the horse’s natural dietary intake. The problem with these forms is that the complex sulfate and phosphate groups limit absorption. As a horse in the wild would be grazing large quantities of rough grassland and continually roaming, their intake would be far greater. Modern feeding not only decreases the consumption of magnesium by limiting roaming, but also hinders absorption through feeding of competitive nutrients in rich feed and because it reduces the amount of time food spends in the gut. Supplementing compounds such as magnesium sulfate is therefore rarely effective as the absorption rate is too low to overcome the problems of modern feeding and the stress of domestication.

Know what type of magnesium you are feeding.

Unfortunately, comparing the quantity of different magnesium compounds in various supplements is pointless because it comes down to how much is being absorbed rather than how much you are feeding. Also bear in mind that the food only stays in the small intestine (where magnesium absorption takes place) for a relatively short period. This means that each type of magnesium will have a different upper limit to the amount that can be absorbed from one feed. For example, if you take two different magnesium compounds; magnesium-A and magnesium-B. If magnesium-A absorbs twice as well as magnesium-B it would be reasonable to assume that feeding twice as much of magnesium-B would achieve the same result but, all that would happen is that you would be increasing the amount that ends up in your horses’ bed without ever entering his circulation. What you would actually need to do is feed one amount of magnesium-B, allow time for complete absorption and then feed the same amount again a few hours later just to match one amount of magnesium-A.

To get the best from the magnesium you supplement, look for a liquid that has been specifically developed. The compound of choice is undoubtedly magnesium aspartate hydrochloride which has been scientifically and independently (i.e. not from the manufacturers own in-house research) proven to provide a level of absorption which far exceeds that of magnesium aspartate and magnesium citrate as well as the more readily available forms (oxide, sulfate, phosphate and protein bound forms).

The ultimate deciding factor is how much your horse needs because this varies greatly and comes down to the combination of the amount of stress your horse is exposed to and how well it naturally copes with that stress. If you are lucky enough to have a horse that is mostly laid back, you may well see an improvement with cheaper forms of magnesium. It is worth bearing in mind though that this may be a false economy; you could deliver the same amount of magnesium by feeding a lot less of a more effective compound.

To make matters more complicated, many calmers are not really magnesium calmers at all. Although they contain magnesium, it is often inadequate to make any real difference and if you see an improvement it is likely to be coming from an array of other ingredients, the more common of which are listed below:

Valerian this is a known herbal sedative which will cause drowsiness. If you are looking for a mild sedative this will work but it should not be used if you need your horse to be alert and it is totally banned for competition use. Long-term use of valerian in humans can result in depression, stomach ache, anxiety and nightmares. Whether or not these effects exist in the horse is unknown.

L-Tryptophan this is a form of the amino acid Tryptophan, supplementation increases the secretion of certain suppressive, good mood hormones such as serotonin thus producing a mild sedative effect. There is no dietary reason to supplement L-Tryptophan as the horse’s diet already contains far higher levels of amino acids (protein) than is natural to them.

B-Vitamins among other vitamins have different mechanisms of action but generally, when given in excess they have a suppressive effect on the nervous system which results in calming. Again, there should be no dietary need for these vitamins as the horse’s needs are adequately met by dietary intake and by absorbing vitamins produced by bacteria in the hindgut, indeed B-Vitamins only have a calming effect when given in excess i.e. be aware that companies will play on the we don’t eat enough vitamins concept that is so familiar to us.

In addition to these there is an array of herbs which may be included, in most cases it is not really known exactly how they work or proven that they do work at all, but many people believe in them and they may well have the desired effect.

To conclude, if you are looking for a calmer consider what you want to achieve from giving it. If it is the magnesium you are after be aware of other contents because it is probable that you will think you have solved the problem when in actual fact you are merely masking it. The great thing about magnesium is that it works not by manipulating the bodies control mechanisms to create an artificial calm, but by returning your horse to normal function, thus helping to overcome the negative effect of modern feeding and domestication.

 Classen, HG et al. Comparative Experimental Study in Animals on Magnesium Absorption from the Gastro-Intestinal Tract in the From of Sulfate, Chloride, Aspartate-Hydrochlorida. Arzneimittle_Forschung (Drug Reaserch) 1973; 23: 267-271