Magnesium is an essential mineral in your horse’s diet that plays a key role in muscle function, nerve health, energy production, and metabolic balance. Despite being required in relatively small amounts, magnesium is one of the most common mineral deficiencies seen in horses, especially those under stress, in work, or grazing on magnesium-deficient pastures.
Feeding magnesium correctly can support your horse’s calm behaviour, muscle recovery, and overall performance. However, it's important to understand how much your horse needs, when to supplement, and how to avoid overfeeding.
Why Do Horses Need Magnesium?
Magnesium is involved in hundreds of enzyme reactions in the horse’s body and is vital for:
- Normal nerve transmission and muscle relaxation
- Maintaining a steady heartbeat
- Energy production at the cellular level (ATP synthesis)
- Bone development and strength
- Insulin sensitivity and glucose metabolism
A magnesium deficiency may cause muscle tension, irritability, reduced performance, and nervous behaviour—often mistaken for training or behavioural issues.
Signs of Magnesium Deficiency in Horses
Magnesium deficiency can be mild and chronic or acute and severe, depending on the diet and stress levels.
Common signs include:
- Nervous or anxious behaviour
- Muscle tremors, twitching, or stiffness
- Difficulty relaxing after work
- Poor focus or ‘spooky’ attitude
- Teeth grinding or sensitivity to touch
- Cramping or tying-up episodes in performance horses
- Insulin resistance or metabolic syndrome symptoms
These signs often become more obvious when horses are in heavy work, travelling, exposed to loud environments, or during spring grass growth, when potassium spikes and magnesium levels drop in the pasture.
How Much Magnesium Does a Horse Need?
The average 500 kg horse requires approximately 10–15 grams of elemental magnesium per day, depending on:
- Workload
- Diet composition
- Body condition
- Level of stress or excitement
Horses in intense work or with metabolic conditions (like Equine Metabolic Syndrome or Cushing’s Disease) may require more.
Natural Sources of Magnesium in the Diet
Magnesium is naturally found in:
- Grass and hay (levels vary widely based on soil content)
- Lucerne (alfalfa) – often higher in magnesium
- Beet pulp
- Soybean hulls
- Commercial feeds and mineral supplements such as the all purpose Equilibrium Mineral Mix
However, magnesium levels in pasture, especially during spring flush or drought conditions can be low, making supplementation necessary for some horses.
Supplementing Magnesium: What Are the Options?
The most common forms of magnesium supplements for horses include:
- Magnesium oxide (highly bioavailable, cost-effective)
- Magnesium sulphate (Epsom salts – use with caution, can cause diarrhoea)
- Chelated magnesium (bound to amino acids, may have improved absorption)
When choosing a magnesium supplement, look for elemental magnesium content, not just the weight of the compound. Always introduce supplements gradually and consult with a veterinarian or equine nutritionist for tailored advice.
Equlibrium Mineral Mix provides a balanced supply of minerals
Is Too Much Magnesium Dangerous?
While magnesium toxicity is rare in horses with normal kidney function, excessive supplementation, especially with magnesium sulphate can lead to:
- Loose manure or diarrhoea
- Lethargy
- Imbalance of other important minerals (especially calcium and phosphorus)
Always assess your horse’s entire diet, including feeds, balancers, and supplements, to avoid over-supplementation.
Which Horses Benefit Most from Magnesium Supplementation?
Horses that may benefit from magnesium include:
- Nervous, spooky, or anxious horses
- Horses on lush spring or potassium-rich pasture
- Horses with Equine Metabolic Syndrome or Insulin Resistance
- Horses prone to tying up or muscle stiffness
- Performance horses in regular, high-intensity work
Stance Magnesium Supplements
Final Thoughts: Is Magnesium Right for Your Horse?
Feeding magnesium to horses can help support calmness, muscle function, metabolic health, and performance but only when done properly. Magnesium should always be part of a balanced diet and supplemented based on your horse’s individual needs.
If you suspect a deficiency or want to support a horse in work or under stress, magnesium oxide is often the most practical and effective option. Pair with a complete vitamin and mineral supplement such as Equilibrium Mineral Mix to maintain proper balance and avoid the risks of over-supplementing one nutrient at the expense of others.
