Feeding magnesium to horses

Last Updated on April 5, 2022 by Allison Price

Psom salts or magnesium sulfate are becoming a more common supplement for horses.

Magnesium is an essential element in nerve and muscle function. Horses deficient in this vital element may show signs of nervousness and wariness as well as excitability and muscle tremors.

Magnesium is known for its calming effect on horses because of this.

Horses with poor work tolerance are more likely to be unable to tolerate stress and will tend to tie up quickly.

Magnesium can also be used to reduce equine obesity. It can also help to lessen the risk for laminitis in horses that are prone to it during strong spring grass growth.

You can, however, end up giving too much to your horse as with most things.

Epsom salts are expensive and horse owners might be giving their horses too much.

Epsom salts are best known for their ability to relieve constipation. Do not give your horse too much Epsom salts. They will feel diarrhoea just as people. A case of diarrhoea is possible if your horse consumes more than one tablespoon per 100g of their body weight.

Although it can be taken at the right rate, it is still a good source of magnesium. However, magnesium oxide or magnesium aspartate, which are the Rolls-Royces of magnesium supplements, will work better.

Magnesium To Horses

Magnesium excreted in excess will be excreted from the urine. However, major overdoses have been linked with heart problems and kidney trouble.

Six veterinarians from the Department of Veterinary Biosciences College of Veterinary Medicine at Ohio State University conducted a study on magnesium uptake in horses.

A horse’s magnesium needs are approximately 13 mg per kilogram of bodyweight each day. Horses who are pregnant, lactating, and/or working will require more magnesium each day.

Magnesium can also be lost through sweat. This could mean that the amount of magnesium in the animal’s system can be increased by 1.5 to 2x.

There seems to be a wide range of opinions on the need for magnesium supplementation. This will depend on the magnesium content of the soils where horses are grazing. The grass will reflect any such deficiencies.

A horse will generally get 60 to 100 percent of its daily magnesium requirements through a regular forage diet.

Deficiencies are more common in spring during periods of high grass growth and winter in milder areas where grass is being pulled with fertiliser.

In both cases, grass is low in magnesium, sodium and soluble carbohydrate. It’s also likely to be high in potassium and nitrogen. This double-whammy is because high potassium levels can slow down the absorption of magnesium, while low sodium levels (which are common in these circumstances) can help with its uptake.

The mechanisms that affect magnesium uptake in horses are complex and may not be related to a low magnesium diet. Too much potassium can also cause magnesium deficiency.

This complex equation does not only include potassium. Horses can use magnesium in their diets depending on the amount and the proportions of calcium, protein, and fats.

Horses only have a limited capacity to store magnesium. Any magnesium deficiency can cause problems quickly.

Magnesium oxide (MgO), magnesium carbonate(MgCO3) or magnesium sulfate(MgSO4) are the most popular forms of supplementation. Also known as Epsom Salts.

Horses can expect to use about 70% of the magnesium available in each of these minerals.

To get the 13mg elemental magnesium per kilogram bodyweight, you will need:

 • 31 mg/kg/day of MgO (Magnesium Oxide) or
• 64 mg/kg/day of MgCO3 (Magnesium Carbonate) or
• 93 mg/kg/day of MgSO4 (Magnesium Sulfate – Epsom Salts)

There are 1000mg to a gram, so the total daily magnesium requirements of a 500kg horse would be 15.5 grams of magnesium oxide, 32 grams of magnesium carbonate, and 46.5 grams of magnesium sulfate.

This equation shows that magnesium oxide has the highest amount of magnesium available among all three.

The newcomer, at least for horse owners, is magnesium aspartate, more properly known as magnesium-L-aspartate.

It is the magnesium salt in aspartic acid. It is very water-soluble. It is easily absorbed by the intestinal wall once it has been dissolved.

Its biological uptake rate is higher than that of the magnesium supplements.

Magnesium Aspartate is approved in many countries to maintain normal magnesium levels.

It actually contains 20 percent magnesium. Therefore, a horse of 500 kg will need 32.5 grams per day to get 13mg/kg/day magnesium.

Another material that horses are often given is dolomite. It contains approximately 80% calcium carbonate (23% of which is calcium) and 20% magnesium carbonate (12% magnesium).

Only 5.7% of all dolomite actually contains magnesium. A tablespoonful of dolomite contains just one gram of magnesium. Its bio-availability, however, is low.

Evidence suggests that animals are more likely to absorb magnesium if they have salt (sodium chlorineide) and magnesium supplements. Equestrian specialists recommend adding a mixture of 95% salt and 5% magnesium oxide to horses’ diets.

There are many factors that can affect horses’ ability to use magnesium. Common-sense solutions must be used.

You run the risk that you supplement your horse’s diet by adding all kinds of minerals. This could leave your horse’s kidneys vulnerable to the many additives you think your horse requires.

A blood test can be ordered. You can always order a blood test.

Monitor one thing at a given time, if possible. A magnesium supplement might be a good option if you have concerns about unusual or frightening behavior. A mycotoxin binder might also be an option.

If you do both, and get positive results, there is no way to know which one delivers the desired outcome.

Magnesium supplementation in horses with magnesium deficiencies will have a significant impact on their wellbeing.

Be sure that your horse is getting what he needs, and don’t give too much.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!