Magnesium: The Mineral Superhero

Very few people are aware of the enormous role magnesium plays in a horse’s body. After oxygen, water, and basic food, magnesium may be the most important element needed to maintain health. It is vitally important, yet hardly known. 

Magnesium is by far the most important mineral, regulating over 325 enzymes in the body.  Research shows that magnesium supplementation improves performance and allows human athletes to reach exhaustion later in their exercise routine. It increases oxygen delivery to muscle tissue, it promotes muscle strength, endurance, and relaxation. Magnesium also activates enzymes necessary for the metabolism of carbohydrates and amino acids which lead to protein synthesis.

Magnesium is often the most neglected mineral in horse feeds. 

Spring grass is typically deficient in magnesium due to the fast growth rate and at this time of year many horses seem hotter and more difficult to ride.  Owners often attribute this to too many carbohydrates in the grass.  While this may be part of the story, what is often overlooked is that these horses may be deficient in magnesium. 

Magnesium deficiency has varying effects on the horse population.  Some horses do not suffer any signs while others are almost unrideable due to their apparent silliness and hyperactivity.  Adding magnesium to their diet may have a dramatic calming effect.  To understand why magnesium affects the horse in a calming manner, it is important to know what is happening in your horse’s body on a cellular level when there is a magnesium shortfall.

The Role of Calcium and Magnesium

Magnesium and calcium work closely with each other.  Calcium needs magnesium to assimilate properly, however magnesium does not need calcium. Calcium is in charge of contracting the muscle and magnesium looks after the relaxation or release of the muscle: much like a gas pedal and a clutch work together.  When a muscle cell is triggered, the cell membrane opens, letting calcium in and raising the calcium level in the cell setting off a reaction and the muscle contracts.  When the contraction is done, the magnesium inside the cell helps to push the calcium back out of the cell releasing the contraction.  This happens very rapidly.  When there is not enough magnesium in the cell, calcium can leak back in causing a stimulatory effect and the muscle cannot completely relax. This can put the body into a continually stressed state.  Low magnesium makes nerve endings hypersensitive thus exacerbating pain and noise.  Nerves and muscles require magnesium for proper function.

Testing for Magnesium Deficiency

The use of magnesium today is often incorrect.  One reason is this: Calcium needs magnesium in order to assimilate into the body. However, when we consume too much calcium, it inhibits the body’s ability to absorb and utilize magnesium efficiently.  To maintain proper levels in the blood, the body will borrow magnesium from bones and soft tissue to make up for the shortfall in order to assimilate the calcium.  Over time, this creates an accumulative negative reaction in the body that actually triggers the body to release adrenaline adding to the excitatory behavior we see in deficient horses. 

To correct a deficiency, we must offer magnesium by itself, not with calcium.  Bodies store only approx. 1% of magnesium in the blood; the body stores the rest in soft tissue and bone. Bodies are very efficient at maintaining that level in the blood stream to facilitate organ function.  This is why blood level magnesium tests are rarely indicative of an animal’s true magnesium status.  A horse would be severely deficient and would be very ill by the time a blood test would indicate a shortfall.

Diagnosing Magnesium Deficiency

Horses with magnesium deficiency may have all or only a few of these signs so it is important be aware of them.  They may be borderline and only exhibit signs during competition or stress.  For instance, horses with magnesium deficiency often have very sore tight backs in spite of excellent saddles and pad, proper fit, conditioning and training.  They don’t respond well to chiropractic adjustments and massages or these treatments don’t last more than a couple days and the tension and soreness return.  They often resent or even act afraid of being touched leading the owner to ask themselves, ‘Is someone abusing this horse when I am not around?’  Their response to outside stimuli is over reactive and they tend to become fractious, worried, fearful, or resistant to training.

Signs of magnesium deficiency include:

  • Unable to relax physically or mentally
  • Muscle tremors, twitches, flinching skin, or all over body trembling especially after exertion (not related to outside temp)
  • Body tension
  • Does not tolerate long periods of work– often becoming more excited instead of working down
  • Has difficulty with collection or picking his back up under saddle, moves hollow
  • Random spooking, running through the bridle, inconsistent from one ride to the next
  • Angry about being brushed, blanketed or touched or palpated on either side of spine
  • History of tying up
  • Fatigue
  • Painful heats in mares
  • Bucking or rearing 20-30 minutes into a ride for no apparent reason
  • Requires long periods of lunging before being able to focus on work
  • Would be described as ‘thin skinned’ or over sensitive to sound or movement
  • Massage and chiropractic adjustments do not have lasting affects
  • Teeth grinding
  • Irregular heartbeat or pounding heart- endurance horses often experience this at vet checks

Other signs of magnesium deficiency

Horses assimilate magnesium quickly in times of stress, such as traveling or heavy training.  Horses lose magnesium through sweat and urine.  Many performance horses can become deficient as the season progresses as they are using the available magnesium more rapidly due to stress, travel and competition. Horses with low magnesium status will often crave salt, which exacerbates the shortfall.  Calcium-rich diets can create an imbalance.

These horses are often difficult to work with, so riders tend to over exercise in an effort to manage behavior.  They are worked harder and for longer periods of time in an effort to wear them down which only adds to the shortfall thus creating a vicious cycle.  This causes more sweating and muscle cramping while contributing to fatigue, soreness, post competition pain, and a negative association to work.  Behavior gets worse with more work and exposure to stress, not better. Subsequently, horses begin to resent the show arena often developing gate issues.

Magnesium Absorption and Utilization

There are many factors that affect magnesium absorption and utilization.  Working horses require 10-30% more magnesium for light to moderate exercise, respectively, due to sweat losses.  Horses who sweat heavily will lose magnesium at a more rapid rate as well.

Magnesium toxicity is rare because excess is naturally excreted.  You should split magnesium between morning and evening feedings to increase absorption and decrease its occasional laxative effects. Once a horse becomes low on magnesium, it is very difficult for them to catch up without supplementation.

What kind of magnesium should I use?  

There are injectables, oral supplements and transdermal applications.  The most popular is oral magnesium oxide.  It is the least bio-available form of magnesium but it is the most available and inexpensive to feed.  Some horses do not like the powdery texture so picky eaters may turn up their noses to it.  It can also act as a buffer in the horse’s stomach which can help horses who tend to develop ulcers. 

Oral magnesium

There are many oral forms of magnesium; the best form of which is Di-magnesium malate.  It is highly absorb-able, bio-available and has the least potential laxative effect.  Horse owners need to be aware that magnesium is in different forms. Some forms include citrate, oxide, and ascorbate, which is the secondary ion.  Horse owners should avoid magnesium sulfate because of its laxative effect.  We recommend feeding 6 to 10 grams daily or to bowel tolerance, for working horses exhibiting mild to moderate signs of magnesium deficiency.  Horses showing severe signs of deficiency respond may require more. Every horse is different and will have its own individual maintenance dose. This will also fluctuate depending on times of stress, showing, weather and pasture content. When signs of deficiency begin to subside, you can taper off the dosage.

Transdermal magnesium

Transdermal magnesium (delivered through the skin) is an efficient way to deliver magnesium to muscle tissue as it bypasses the digestive system all together and can be taken up by the muscles rapidly.  Applying magnesium transdermally can be very therapeutic prior to athletic competition especially for the nervous horse and also post work out helping the body to recover and relax muscles.  It is available in sprays, lotions and a magnesium chloride salt form that is dissolved in warm water, sponged on the horse and rinsed off after 20 minutes.  This is the most economical of choices.

How do you know how much magnesium your horse is getting? 

It’s very difficult without analyzing every bale of hay.  Many feed supplements only give you a percentage of mineral content, not a gram total.  One thing you can do to insure your horse is not deficient is to familiarize yourself with the signs of possible deficiencies in your horse.  If you think you may have a shortfall, it’s a very safe mineral to give in any case.  Toxicity is extremely rare.  Horses with reduced kidney function should not be supplemented with magnesium without vet supervision.  Make sure your horse has access to water.

Disclaimer: The information in this article in not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. It is intended as a sharing of knowledge and information. We encourage you to make your own health care decision for your horse based upon your own research and in partnership with a qualified veterinarian.

Do you think your horse may be deficient? Take our Magnesium Deficiency Questionnaire.