Magnesium deficiency is a common problem amongst horses and can cause a myriad of health problems, from behavioural issues to muscular, cardiovascular and neurological problems.  This article shares some of the causes of magnesium deficiency, signs of magnesium deficiency in horses and treatment options.

What Causes Magnesium Deficiency?

1. Magnesium Deficient Soils

In the first instance, magnesium deficient soils result in pastures which are low in magnesium.  Conditions which result in magnesium deficient soils include:

  • Low soil pH
  • Dry soil
  • Sandy soils
  • Lack of organic matter (humus)
  • High levels of competing minerals such as calcium and potassium, which reduce the uptake of magnesium by plant matter.

While soil analysis will provide the most thorough information about your soil composition, it is possible to assess the health of your pasture based upon the plants (or weeds) growing within the pasture.

A significant number of any of the following plants growing on your land is an identifier of low magnesium levels:

  • Capeweed (Arctotheca calendula)
  • Sour sobs / Oxalis / Wood sorrel (Oxalis spp)
  • Dock (Rumex spp)
  • Onion grass (Romulea rosea)
  • Hoary cress (Lepidium draba)
  • Heliotrope (Heliotropium spp)
  • Buttercup (Ranunculus spp)
2. Stress and Strenuous Exercise

Magnesium is assimilated by the body quickly in times of stress and heavy exercise.  Magnesium is lost through sweat and urine, meaning that horses in a rigorous training programme or under stress due to factors such as travel and competition will have a higher demand for magnesium.  If this need is not met, magnesium deficiency will result and is often more commonly noticed towards the end of competition season.

3. Calcium-Rich Diets

The body requires a balance of magnesium to calcium in the ratio of 1:1 or 2:1 in favour of magnesium.  Diets too high in calcium may result in magnesium deficiency by creating an imbalance in the magnesium to calcium ratio.

4. Spring Grass

Magnesium tends to be deficient in Spring grasses due to the fast rate of growth.  This is part of the reason why horse’s exhibit signs of Spring Flush (silly behaviour), as magnesium deficiency commonly results in behavioural problems in horses.

Signs of Magnesium Deficiency in Your Horse

The following are signs of magnesium deficiency in your horse.  Your horse may exhibit any combination of these signs, but not necessarily all:

  • Over-reactive to stimuli, such as sound and movement
  • Stringhalt
  • Tying-up (Recurrent Exertional Rhabdomyolosis)
  • Physical tension
  • Muscle pain, spasm, cramping, twitches, tremors and flinching
  • Loss of appetite
  • Irregular or pounding heartbeat
  • Teeth grinding
  • Difficulty swallowing
  • Failure to thrive in foals
  • Behavioural problems, including:
    • Stress and anxiety
    • Aggression when being brushed and rugged
    • Spooking
    • Inconsistent behaviour from one ride to the next
    • Increased excitability or bucking / rearing late in the training session (rather than fatiguing or calming down)

How to Treat Magnesium Deficiency

1. Balanced Diet

Ensure that your horse is being fed a balanced diet.  This is the best way to ensure that your horse is getting the right amount of nutrients in their diet and the correct balance of minerals.

A couple of points to note:

  • While lucerne / alfalfa provides an excellent source of protein, ensure that your horse is not consuming more than 20-40% of this legume in their diet (depending on their physical demands), as lucerne is high in calcium and can negatively affect the magnesium to calcium ratio, resulting in magnesium deficiency.
  • Also, ensure that your horse is not eating too many oxalate-rich grasses, such as tropical grasses and kikuyu. Oxalate-rich grasses bind to calcium and prevent absorption, which again affects the magnesium to calcium ratio.

If you need assistance to ensure that you are feeding a balanced diet, call upon the guidance of a qualified Equine Nutritionist.

2. Manage Your Pasture

Pastures low in magnesium can be treated with dolomite, which provides high levels of both magnesium and calcium carbonate.  You will know that the magnesium level in the soil is improving when the plants mentioned above begin to die or reduce in number.

If you want provide very specific treatment to your pasture, have the soil professionally tested by sending core samples to a specialist just prior to harvest time.  The professional can then make specific recommendations to get the balance of nutrients in your soil just right.

3. Supplementation

Supplementation with dolomite provides high levels of both magnesium and calcium carbonate to your horse, which can help to resolve a magnesium deficiency.  Alternatively, there are a multitude of magnesium supplements and multi-vitamin supplements on the market that can help bring your horse back into balance.

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