Integrity Matters' vets continue their look at electrolytes, this time with a focus on magnesium.

What is magnesium?

Magnesium is not the most abundant electrolyte in the horse's body but it plays a vital role in many physiological processes. Magnesium, like its close relative calcium, is vital for life.

What magnesium does:

Magnesium plays a role in over 300 biochemical reactions in the body. It is a vital part of energy production, nerve and muscle function and regulation of heart rate.

While calcium performs a vital role in bone structure, recent research suggests that magnesium is the rate limiting substance in Vitamin D and calcium levels. About 60% of magnesium in the body is in the bones of the skeleton and a further 30% is found in the muscles. The remaining 10% is found in the blood plasma and in many enzymes, including those that regulate inflammation and body sugar.

Calcium causes muscle contraction while magnesium causes the muscle to relax. Inadequate magnesium is associated with muscle spasm and nerve over excitability.

Where does magnesium comes from?

Magnesium is a relatively common component of forages (hay, pasture, silage) and grain and commercial rations.

What happens if magnesium levels are too high or too low?

Gross magnesium deficiencies are rare in the horse, but a "relative" deficiency may impact on a horse's reactiveness and ability to recover from exertion.

Other "positive" ions such as excess potassium and calcium as well as phosphate and excess fats in the diet may inhibit the uptake of magnesium.

CSU researchers found that adding 10% magnesium aspartate over the recommend level of magnesium intake reduced the reaction times in six standardbred geldings. There is no other evidence that pastes and injections containing magnesium have a calming effect on horses nor assist with managing laminitis. 

Low magnesium levels have been associated with increased bone fractures in humans, but this research has not been repeated in horses. 

Too much magnesium is only seen when a horse has been treated with a magnesium containing substance orally or intravenously. Signs include sweating, muscle weakness, high heart rate, high respiratory rate, collapse and even death. 

How do you ensure your racehorse gets the right amount of magnesium?

Research suggests that horses need about 13 milligrams per kilogram body weight of magnesium per day. Horses that are growing, lactating or in hard work will need more. This is particularly the case for race horses as magnesium, like sodium, potassium and chloride is lost in sweat.

The form that the magnesium is in affects how much it is absorbed and therefore how much needs to be administered.

Epsom salts (magnesium sulfate) have been used as a form of magnesium supplement historically but can induce diarrhoea as it is poorly absorbed. Magnesium oxide and magnesium aspartate are safer forms of magnesium supplementation. It is important that you consult with a trained equine nutritionist to ensure that your horse has a balanced intake of positively charged ions like magnesium, calcium and potassium as too much of one will inhibit the intake of the others.


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