Magnesium for Horses – What you Should Know

Magnesium for Horses 

The macromineral magnesium is known as the mineral superhero due to its involvement in regulating over 325 enzymes in the body. Magnesium for horses plays an essential part in several metabolic functions. 

Magnesium is vital for musculoskeletal and neurological health and is a critical nutrient in growing horses, lactating mares, and high-performance horses. 

A magnesium deficiency in horses is rare, yet many equestrians advocate its supplementation in horses with anxiety or high energy demands. 

men with white horse

The Uses of Magnesium Supplement for Horses

Horses require magnesium for healthy muscle and nerve function, making it an essential macromineral. Sixty percent of a horse’s magnesium lies within the bone, and the remaining forty percent occurs in the extracellular fluids and soft tissue. Maintaining optimal magnesium levels is vital in young foals that are growing, lactating mares, and heavily exercised horses. 

Magnesium supplements in horses offer several benefits, according to many equestrians. Listed below are a few common reasons some people use magnesium supplements: 

  • Improves equine moods and behavior.
  • Supporting athletic performance and promoting electrolyte balance by replenishing reserves lost through sweat during exercise. 
  • Promotes metabolic health by improving insulin sensitivity. 
  • Growth support in young foals with high metabolic needs during growth spurts.
  • Treatment of impaction colics and support during recovery. Horses who suffer from enterocolitis show low magnesium levels. If enterotoxemia occurs after bacteria enter the bloodstream due to altered gut permeability, the immune response triggered results in depletion of magnesium levels. 

Symptoms of Too Much Magnesium in Horses

Too much of a good thing is bad for you, as the adage goes. Magnesium overdose is known as hypermagnesemia. The condition occurs when the blood’s plasma Mg concentration exceeds 1.1 mmol/L. 

Hypermagnesemia is a condition that rarely happens and is more common in animals with monogastric digestive systems. The main concern of too much Mg in the blood is the effect it has on the circulatory system.

Horses are at risk of hypermagnesemia if they receive an overdose of oral magnesium sulfate (Epsom salts) during conservative medical management of impaction colics in the large intestines. 

The magnesium sulfate is administered through a nasogastric tube into the stomach to act as a hygroscopic agent. The salts create an osmotic pull to encourage water to be absorbed into the gastrointestinal lumen to help soften the impaction and relieve colic symptoms. 

A horse with too much magnesium in its system will start to sweat profusely, show signs of muscle weakness, and then cardiovascular symptoms begin to worsen. Horses become recumbent with tachycardia (heart rate of 120 beats per minute) and tachypnea (increased respiration rate of 60 breaths per minute). 

Echocardiogram changes occur when blood plasma concentration exceeds 2.5mmol/L with prolonged PR intervals. Deep tendon reflexes disappear after the concentration reaches 5mmol/L, and then hypotension and respiratory depression ensue. Death due to cardiac arrest is possible at levels above 6-7mmol/L. 

Treatment for hypermagnesemia is a slow intravenous infusion of calcium borogluconate, ideally while attached to an ECG machine to monitor any cardiac anomalies. 

Magnesium ions taste sour, which is why mineral water has a tart flavor. This bitter taste is one of the reasons why horses find magnesium unpalatable and rarely overindulge in magnesium-rich substances.

10 Science-Based Benefits of Equine Magnesium

Listed below are ten benefits of equine magnesium supplementation:

  1. Magnesium works together with calcium to ensure healthy and efficient muscle function. Nerve impulses control the calcium ion channels that facilitate muscle contraction.  Magnesium pushes the calcium back through the ion channel after the calcium contracts the muscle fibers. Muscles will cramp if magnesium levels are too low.
  2. Magnesium facilitates muscle relaxation, easing stiff muscles and supporting recovery after heavy days of work or competition. 
  3. The performance-boosting potential of magnesium in equine athletes is achieved by enhanced oxygen delivery to muscles, increased muscle tone, and enhanced protein synthesis.
  4. This macro mineral facilitates signal transmission from nerve cells to muscle fibers by regulating cell membrane balance through ion channels. 
  5. Researchers consider the calming effect of magnesium to be due to decreasing muscle tremors and tension. Horses with a nervous disposition, excitability, or behavioral issues may benefit from Mg. 
  6. Stress relief and improvements in coping with stress can lead to a healthier immune system. Stress depletes magnesium, and supplementation can regulate deficiencies even if they are subclinical. 
  7. Magnesium for cresty neck horses helps with the homogenous distribution of fat deposits and decreases fat pockets.
  8. Insulin sensitivity improves with magnesium as it helps cells respond better to insulin and may aid overweight horses who are showing signs of insulin resistance.
  9. Horses that are prone to laminitis, especially in the Spring, often have low levels of Mg, so supplementation can help avoid flare-ups of the condition. 
  10. Dietary calcium is better absorbed when the body has adequate magnesium levels. A healthy musculoskeletal system thrives with the correct nutritional balance of calcium and magnesium.

Why Do Horses Need Magnesium?

Magnesium has several functions in the body. These functions mostly center around the musculoskeletal and nervous systems. The balance of magnesium in the body is delicate, and there is an intricate balance with several other macrominerals needed to maintain homeostasis. 

Magnesium stores reside mostly in the bones; for this reason, around sixty percent of the total stores are unavailable to the body. The remaining forty percent is available for mobilization and use in several metabolic reactions. 

Over 300 enzyme reactions in the body require magnesium. The reactions range from generating cellular energy to decoding genetic information. Magnesium is crucial for nerve impulse transmission and muscle relaxation. The intricate balance between calcium and magnesium results in subclinical symptoms when disrupted. 

Homeostasis between intracellular and extracellular magnesium is an intricate balance act as very little of the mineral occurs in the extracellular fluid. Only around one percent, to be specific. Testing for hypomagnesemia through blood tests is inaccurate due to this fact. 

The use of magnesium as a calming supplement stems from the role it plays in nerve excitement and muscle contraction. Decreased levels may cause nervousness, and supplementation has shown some positive influences in research studies addressing horse behavior and management. 

Researchers confirm that magnesium modulates intracellular insulin into extracellular tissues. After a high starch or sugar meal, plasma levels of magnesium rise, indicating a functional role in aiding insulin’s uptake of glucose from the blood into storage. 

Low plasma levels of magnesium impair carbohydrate metabolism and may be a reason for a horse developing insulin resistance.

The fine balance between calcium and magnesium works antagonistically to contract and relax muscles, respectively. Magnesium deficiency may lead to muscle spasms as the calcium ion channels will not be blocked and will therefore keep contracting the muscles. 

These deficiencies having a genetic cause are more likely than a dietary cause, but reports of chronic tying-up being relieved by magnesium supplementation may leave room for debate. 

The role of magnesium in nerve excitability creates a problem when synchronous diaphragmatic flutter occurs. Synchronous diaphragmatic flutter is also known as Thumps. Thumps create spasmodic diaphragm contractions.

This condition often occurs in endurance horses with electrolyte imbalances. Competition vets will usually treat the condition with a combination of calcium and magnesium to speed up recovery.

horse in nature

Signs of Magnesium Deficiency in Horses

During spring, a flush of fast-growing grass species becomes available for grazing. Due to the rapid growth of these grasses, they are deficient in magnesium. Suboptimal magnesium levels may not reflect overt clinical symptoms in horses but can affect a horse’s mood and performance. 

These subclinical symptoms become more evident in horses during times of stress or while competing.

Magnesium deficiency is uncommon in horses, but three specific groups of horses may be prone to developing deficiencies and should undergo close monitoring if they begin to show any symptoms listed above. 

  1. Young growing horses are a risk group. They require a balanced diet to ensure that they can cope with the metabolic demands during growth spurts. 
  2. Lactating mares require higher magnesium levels to cope with increased demand during lactation. Mares who produce high volumes of milk have a higher magnesium requirement and are at a high risk of magnesium deficiency. Lactating mares’ magnesium requirement ranges from 0.35 to 0.44oz (8.7 to 11g) of magnesium per day. 
  3. High-performance athletes have significantly higher magnesium requirements even when just training with moderate exercise and especially during intense exercise and competitions. High metabolic demands require a magnesium increase of between 1.5 to 2 times. A 1,100 pounds (500 kilograms) horse during training and competition requires a magnesium supplement of up to 0.6oz (15g) per day to compensate for metabolic losses from sweating and increased activity levels. 

Symptoms associated with magnesium deficiency cause the following neurological and muscular dysfunctions:

  • Excessive irritation.  
  • Heightened nervousness, increased excitability, and anxiety.
  • Erratic behavior and resistance to long periods of work or training.
  • Hypersensitivity to sound, foreign objects, and movement.
  • Fatigue.
  • Painful heats in mares.
  • Behaviors, including unexpected bucking or rearing 20 to 30 minutes into a ride.
  • Requires long lunging periods before settling and focussing on work.
  • Refractory to or temporary relief from massage therapy or chiropractic adjustments. 
  • Grinding teeth. 
  • Muscle fasciculations, tremors, shivering skin, spasms, twitching and trembling.
  • Painful muscles and visible signs of cramping.
  • Cardiac arrhythmias.
  • Excessive sweating. 
  • Increased perspiration and anhidrosis

Rarely, in severe cases of hypomagnesemia, symptoms may progress to the following severe conditions:

  • Synchronous diaphragmatic flutter or thumps.
  • Chronic Exertional Rhabdomyolysis (tying up).
  • Dyspnoea and tachypnoea.
  • Muscle convulsions and possibly even death. 

The Causes of Equine Magnesium Deficiency

If a horse’s ration contains adequate grazing, hay, and grain, they are unlikely to have low magnesium levels. Unlike ruminants, horses absorb between 30-60% of the magnesium fed to them in their ration.

Magnesium deficiency has few causes, and most symptoms are often subclinical. Dietary analysis is the best way to determine if your horse’s ration is deficient in magnesium. 

Fast-growing grasses are low in magnesium, which can predispose a horse to a deficiency, especially as they may also be low in sodium and high in potassium. Sodium helps with magnesium absorption, so when it is also low.

Ration composition and digestibility affect magnesium levels. Pasture grasses have higher magnesium digestibility than grains do. High grain diets, therefore, make horses more susceptible to deficiencies in the macromineral.

High amounts of fat, phosphates, oxalates, and fiber may also decrease magnesium absorption in horses. 

Magnesium deficient pastures include winter pastures with little herbage fertilized with potash and /or nitrogen. 

Every bale of hay cannot be analyzed to determine if there is potential for a magnesium deficiency, but considering pasture deficiencies at various times of the year can be a clue when a deficiency is suspected. 

In order to evaluate magnesium levels in a horse, clinicians monitor renal and urinary excretion of Mg. If the levels are low, the magnesium level in the urine will be negligible. 

Urine is collected over twenty-four hours, and the fractional clearance of Mg is determined. A healthy horse that feeds on grass hay has a fractional clearance between fifteen to thirty-five percent. Values of less than six percent indicate inadequate dietary intake of magnesium. 

An Equine Magnesium Dosage Chart

Magnesium comes in several different forms. Listed below are a few types available: 

  1. Magnesium sulfate is more commonly known as Epsom salts. Nutritionists and vets do not recommend using it regularly as it may lead to diarrhea.
  2. Magnesium oxide comes in a fine white powder, which is commonly found in horse feeds. The risk of overdose is minimal as it is only absorbed if there is a deficiency. It also contains the highest concentration of magnesium when compared to other forms. 
  3. Magnesium chloride provides a good source of magnesium and is readily absorbed by the body.
  4. Magnesium chloride flakes have a bitter taste, making them unpalatable to horses even though they have a very high bioavailability rate. Owners can try dissolving the flakes in water to mask the bitterness and improve palatability. 
  5. Magnesium hydroxide requires the horse’s stomach to convert it with peptic secretions of hydrochloric acid into magnesium chloride to enable it to become bioavailable. This process hinders its appeal.
  6. Magnesium oil is liquid magnesium chloride that lets the body quickly absorb magnesium through the gastrointestinal tract. 

Deciding on how much magnesium to add to your horse’s diet requires some knowledge of the daily magnesium requirements of a horse. According to the NRC, a 1,100lb (500kg) horse requires 0.006oz (15mg) of magnesium per kilogram of body weight. This recommendation equates to a supplement of around 0.3oz (7.5g) per day, depending on the composition of the supplements. 

A qualified nutritionist will best be able to review and adjust a horse’s diet according to its individual needs. It is not ideal for reviewing the magnesium levels in isolation but rather for looking at a balanced mineral ratio to support optimal health and performance. 

Product Form Total Magnesium Per Serving
Magnesium 5000Pellet2.13oz (5,000mg)
Magnesium 3000Powder1.28oz (3,000mg)
Magnesium CarbonatePowder1.06oz (2,500mg)
Magnesium Oxide 58%Powder0.99oz (2,320mg)
Magnesium CitratePowder0.74 (1,750mg)
Grand CalmPellets2.55oz (6,000mg)

The absorption of magnesium occurs in the small intestine down a concentration gradient in cell membranes through passive diffusion. Small amounts of absorption occur through active transport over the cell membranes. Calcium’s transport occurs through the same transporters, meaning magnesium and calcium compete for absorption.

To ensure optimal absorption of both minerals, a dietary ratio of 2:1 is advisable.

How to Feed Your Horse Magnesium

There are several available ways to administer magnesium, including injectable forms, oral supplements, and transdermal applications.  

It is very important to note that any sudden and drastic changes to a horse’s diet will result in gastrointestinal upset. It is essential to always gradually alter a horse’s diet over several days to allow the gastrointestinal system to adjust slowly. 

When determining what magnesium source to feed a horse, several factors need to consider, namely absorption rate, concentration, cost, and palatability. 

Absorption rates in inorganic forms are around seventy percent, which is higher than common feedstuffs, which are only around forty-sixty percent. 

Supplement formulations vary, and some are less concentrated than others. Low concentrations mean owners must feed horses some supplements in larger quantities to provide the same amount of magnesium that a more concentrated product would.

Oral supplementation is the most popular and practical method to combat magnesium deficiency. Supplements with magnesium for horses with ulcers may include magnesium oxide as it acts as a buffer in horses suffering from or prone to gastric ulcers.

Of the numerous formulations of oral magnesium available, Di-magnesium malate for horses is the best form. Benefits range from a high absorption rate, high bioavailability, and low potential for laxative effects.  

Magenium comes in several forms, including citrate, oxide, and ascorbate ( a secondary ion). 

Owners should avoid magnesium sulfate for maintenance supplementation because it carries a high laxative effect. 

Magnesium oxide for horses is a top-rated supplement due to its high magnesium concentration and high absorption rate. If a client needed to supplement 0.2oz (5g) of elemental magnesium, they would need to feed 0.34oz (8.5g) of magnesium oxide compared to 3.72oz (93g) of magnesium gluconate. 

Magnesium oxide is more cost-effective and easier to feed to a horse. Products such as the 40 lbs Magnesium 5,000 for horses provide 320 servings in pellet form.

An equine nutritionist is just a click away on most websites, so help is available to consult on how to correctly and safely adjust a horse’s dietary intake of minerals. Some companies even offer complimentary evaluations. 

In order to determine how much magnesium to feed to achieve at least a 2:1 ratio of calcium to magnesium, owners must know the current nutrient levels of the feed. 

For example, if the hay contains 0.15% magnesium and 0.8% calcium, the following calculation will help determine how much magnesium you will need to supplement to achieve the desired ratio. 

In 15lbs (6.75kg) of hay :

15lbs (6.75kg) of hay x 18.16oz/lb (454g/0.45kg) x 0.0015 = 10.2g magnesium

15lbs (6.75kg) of hay x 454g/lb (454g/0.45kg x 0.008 = 54.5 g calcium

In order to achieve the 2:1 ratio: (54.5/2) – 0.41oz (10.2g) = 0.68oz (17g) of magnesium must be added.

Magnesium oxide is 60 percent magnesium: 17/60 = 1.12oz (28g) of the mixture will provide 0.68oz (17g) of magnesium. 

Some powders are unpalatable with a chalky texture. The recommendations are to split the dose over two meals to allow for increased tolerability and lower the risk of diarrhea. 

Transdermal magnesium is an economically efficient option to supply magnesium and is delivered via absorption through the skin. When using a transdermal application, the magnesium bypasses the gastrointestinal system and becomes absorbed directly into the musculature. 

Before competing, there are therapeutic applications in using transdermal magnesium, especially in nervous horses. Applying magnesium transdermally can be very therapeutic before athletic competition, especially for the nervous horse. Post-performance applications aid in muscle relaxation and recovery.

Transdermal magnesium formulations range from sprays, lotions, and magnesium chloride salts that can be dissolved in water and sponged onto a horse.  

Horses with renal insufficiency should not receive magnesium supplementation unless they are under veterinary supervision. It is also important to ensure that any horse receiving magnesium supplementation maintains a good hydration status and has access to fresh water daily. 

horse drinking water

Our Parting Words

Magnesium is a very safe mineral to supplement if a deficiency is suspected because toxicity is rare. Subtle or subclinical manifestations of magnesium deficiency make it difficult to diagnose. 

Nutritional supplementation should always be discussed with a qualified nutrition expert when it comes to finding the best diet for your horse. Magnesium and calcium have a balancing act to maintain homeostasis, and overdoing it with supplements can tip the scale. Ideally, owners should keep the calcium to magnesium ratio between 2.5:1 and 3:1. 

When indicated, the benefits of feeding a magnesium supplement to a horse can be quite rewarding as it will quickly correct the subclinical manifestations of a deficiency.