Is Your Horse Getting Too Much Calcium?

Excessive Calcium Supplements May Be Harmful

Before you go jumping on the band wagon and feeding your horse extra calcium because you think that will help laminitis or build strong bones, consider this study which showed: “Hypercalcemia and excessive administration of calcium have the potential to increase urinary excretion of electrolytes, especially magnesium.” The study also showed extra calcium in feeds increased diuresis (excessive urination). Toribio, R.E., et al., Effects of hypercalcemia on serum concentrations of magnesium, potassium, and phosphate and urinary excretion of electrolytes in horses. Am J Vet Res, 2007. 68(5): p. 543-54.

Calcium and Magnesium Are Antagonists

Calcium and magnesium are antagonists in that when magnesium is low, excessive calcium can block the effects of magnesium, thereby becoming a ‘bully’. Calcium contracts, and magnesium relaxes. When muscle fibres need to contract for action, adrenaline is released to temporarily remove the magnesium gatekeeper from calcium channels. This allows the calcium to move in to stimulate and cause contraction. When it’s time to relax magnesium moves back into the calcium channel, kicks out the calcium to the extracellular space, and brings more hydration back into the cell. This allows expansion, stretching and relaxation again. In a healthy system we should have a see-saw balancing action that can move quickly from one state to another as needed without getting ‘stuck’.

Low magnesium is known to cause metabolic syndrome and insulin resistance, which in turn can trigger hoof degeneration and laminitis. As magnesium levels drop, cells become more prone to lower pH (acidification), which is a low oxygen state that leads to tissue degeneration and premature ageing. Basically, sugar metabolism results in higher acid byproducts, low oxygen environments, lower energy metabolism and prevalence to inflammatory states as the immune system becomes compromised.

To counteract acidity, and when magnesium reserves are low, the body leaches calcium out of bones and deposits into soft tissue and joints. This commonly happens at sites that have been prone to injury, repetitive stress and inflammation, these sites being lower in pH. Calcium can buffer acidic states, but the downside is that it can lead to hypercalcaemia as well as osteoporosis if not enough magnesium is available to control how the calcium is used in the body. We need enough magnesium to take calcium into bones to strengthen the bone matrix (along with other trace minerals). Magnesium is also needed in plentiful supply to keep the muscles and joints flexible and stretchy.

Excessive Calcium and Grass Tetany

It is now well known that as magnesium reserves drop lower, calcium deposits excessively in soft tissue, making ligaments and joints stiff.  It can also cause involuntary muscle movements (calcium being a nerve stimulant);  as well as increase anxiety and stress sensitivity. You will see these symptoms of magnesium deficiency also in other animals in the form of grass tetany, whereby muscles spasm uncontrollably.

Australian soils are commonly low in magnesium, magnesium salts being very water soluble and easily lost from surface soils.  Grasses are therefore often high in sugars, but low in magnesium.  When excessive grasses, grain carbohydrates and molasses etc are consumed it can lead to acidosis and even horse diabetes.  To make matters worse, grains usually contain a lot more calcium than magnesium, which can lead to electrolyte imbalance.  High oxalate grasses can also block the uptake of both magnesium and calcium.

A moderate addition of natural food grade magnesium chloride salts to feeds (approx half a cup per day) can help to supplement a horse’s diet with vital natural magnesium that is easy to absorb and palatable.

In addition to magnesium chloride salts, horses need a varied diet containing also quality fats and proteins.  In the case of acidosis you can use a course of toxin binders to remove gut irritants that may have been consumed in the grasses.  It is recommended to treat the gut and restore proper digestion before commencing oral magnesium chloride supplementation.  So as not to miss out on valuable magnesium supplementation in the case of acidosis and gut disorders, magnesium chloride can also be diluted in water and used as a spray, or used as a lotion, to be absorbed by the horse transdermally.

See Feeding Method…


A 9kg bucket of magnesium chloride flakes, at half a cup per day average, lasts one horse about 5 months.

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