Magnesium for horses: when does it make sense?

What does magnesium do in the horse?

Magnesium plays a key role in the transmission of signals between nerves and muscles. A deficiency can lead to increased irritability, muscle tremors, or a horse that struggles to relax. In addition, magnesium is essential for the production of ATP, the energy source at cellular level, and for healthy bone development. The mineral works closely together with calcium and phosphorus: the ratio between these three minerals in the ration partly determines how well magnesium is absorbed. A daily requirement of approximately 13–15 mg per kilogram of body weight serves as a guideline for an adult horse in light to moderate work.

When does a deficiency occur?

Pasture management and season play a major role. Young, rapidly growing spring grass contains relatively little magnesium compared to potassium and nitrogen, which reduces absorption from the gut. Stress, intensive training, and prolonged stabling without fresh roughage can also increase magnesium requirements. Horses fed exclusively hay from calcium-poor or sandy soils are likewise at risk. A blood value below 0.7 mmol/l is considered a deficiency, but blood values are not a perfect measure since most magnesium is stored intracellularly.

Signs that may indicate a deficiency

• Increased nervousness or spookiness without an obvious cause
• Muscle tremors or cramps, even after normal exercise
• Difficulty relaxing through the back during riding
• Excessive sweating with minimal exertion
• Teeth grinding or a tense jaw
• Poor coat condition combined with lethargic behaviour

Not every nervous horse needs magnesium

Nervousness often has multiple causes: too little exercise, insufficient roughage, a high sugar and starch content in the ration, or simply a spirited temperament. Do not automatically reach for magnesium without first checking the basic ration. Have the full ration calculated, including hay or grass silage analyses. Only when an actual deficiency is identified does supplementation add value. If you use EquiSight, you can record feeding data and behavioural observations in the horse dossier, allowing you to recognise patterns over time and make more targeted adjustments.

Forms and dosages of magnesium supplements

The most commonly used and well-absorbed forms are magnesium oxide and magnesium chloride. Magnesium oxide is inexpensive and widely available; a standard maintenance dose is around 5–10 grams per day for a 500 kg horse. Magnesium chloride (bischofite) is also used mixed into feed or as a foot bath. Overdosing is difficult in healthy horses with functioning kidneys, but diarrhoea can be a sign that the dose is too high. Start low, around 5 grams per day, and increase after two to three weeks if you see no effect.

Practical: incorporating magnesium into the ration

• First have a hay or roughage analysis carried out to determine the current content
• Calculate the daily requirement: approximately 13 mg per kg of body weight
• Use magnesium oxide as the default option: affordable and effective for most horses
• Divide the daily dose over two feeding moments for more stable absorption
• Record behavioural changes and muscle tension in the EquiSight horse dossier to measure effect
• Re-evaluate after four to six weeks: is supplementation still necessary or can the dose be reduced?

Combination with other minerals and vitamins

Magnesium never stands alone. An excess of calcium in the ration, which occurs with intensive use of alfalfa, inhibits magnesium absorption. Vitamin B6 and vitamin D support the utilisation of magnesium at cellular level. If your horse also has a zinc or selenium deficiency, address those deficiencies in parallel. Never give multiple individual supplements simultaneously without an overview: you risk creating imbalances. Ask EquiCoach in the app to combine an overview of your current supplementation with signals from the dossier into concrete advice for your next consultation with your vet or nutritional adviser.