The Science Behind Magnesium for Horses
Magnesium (Mg) is gaining attention in equine health, and for good reason. Long praised anecdotally for its calming effects and muscular support, recent research is now backing up what horse owners and veterinarians have observed for years.
Anecdotal reports on the benefits of oral magnesium are numerous, with many owners and vets describing reduced skin sensitivity, ‘hot’ behaviour, tying-up, irritability, muscular cramping, weakness, insulin-resistance, cresty necks and stiffness when horses receive a Mg supplement. The possibility that a natural oral supplement might be useful is very attractive, and recently, some great research has confirmed the anecdotes and observations.
Magnesium vs. Sedatives
In an Australian study, researchers compared the effects of oral magnesium to the sedative acetylpromazine (ACE) using a ‘reaction speed test’. This test measures the time taken for a horse to cover 2 metres in a custom-built chute, after being startled.
Before treatment: Horses moved at 5.3 m/sec.
After ACE: Speed dropped to 3.5 m/sec.
After 7 days of 10g Mg/day: Speed dropped further to 3.1 m/sec.
The first time equine behavioural research has objectively shown that oral magnesium supplementation can reduce reactivity more effectively than a sedative.
A 2017 study investigated how horses respond to stress during a brief, 3-second weighbridge loading task—using heart rate and cortisol levels (a key stress hormone) as indicators. The findings were compelling:
Horses supplemented with magnesium or given the sedative acetylpromazine (ACE) showed significantly lower heart rates compared to unsupplemented horses.
The calming effect of magnesium was comparable to that of ACE, reinforcing its potential as a natural alternative.
Veterinarians from the University of Guelph, who conducted the study, weren’t surprised. The connection between low magnesium levels and increased anxiety is well-documented across species, including humans and rodents. Supplementing magnesium has consistently been shown to reduce stress and improve behavioural responses, making it a promising tool in equine care.
The Magnesium-Thiamine Connection
Magnesium doesn’t work alone. It plays a crucial role in activating thiamine (vitamin B1), which also has calming properties. A deficiency in magnesium can lead to a secondary thiamine deficiency, compounding stress and excitability.
Historical data support this synergy. In 1961, researchers noted that racehorses given thiamine were noticeably calmer, observations confirmed by both jockeys and trainers, unaware of the treatment.
Studies in rats have shown that thiamine can significantly reduce biomarkers associated with anxiety, while a combination of magnesium and thiamine has been found to alleviate postnatal depression in mice. In a Canadian equine study, administering magnesium and thiamine just 30 minutes before a stress-inducing event was as effective as the sedative ACE in preventing stress-related increases in heart rate.
Magnesium and Muscle Function
Magnesium plays a vital role in muscle relaxation, working in tandem with calcium, which stimulates muscle contraction. Calcium stimulates contraction, magnesium relaxation. When magnesium levels are low, muscles may struggle to fully relax, leading to spasms, cramping, and stiffness. While low magnesium in muscle tissue can sometimes be linked to genetic factors rather than diet, many horses have shown improvement with magnesium supplementation, particularly in cases of chronic tying-up.
A recent study found that horses receiving a daily magnesium supplement at clinically recommended levels showed:
Lower muscle enzyme levels post-exercise, indicating reduced muscle strain
Reduced heart rates, suggesting improved cardiovascular recovery
Magnesium is essential for energy production, as it activates the enzymes involved in the synthesis of ATP (adenosine triphosphate), the body’s main energy source. It supports oxygen delivery and uptake in working muscles, helping horses maintain the high oxygen consumption needed for optimum muscle function and peak performance.
Olympic-Level Insight: Magnesium Enhances Performance and Behaviour
International Olympic veterinarians, working with show jumpers, dressage horses, and 3-day eventers, and 4-in-hand horses, have reported that magnesium supplementation:
Reduced muscle fatigue and improved work tolerance
Decreased skin sensitivity and “hot” attitudes
Alleviated hindleg lameness of muscular origin
Helped with tying-up, irritability, and muscular cramping
Improved weakness and stiffness, particularly of the hindlimbs
Providing supplemental magnesium alleviated signs and symptoms of deficiency, improving behaviour and performance.
Magnesium’s Role in Equine Health Conditions
Magnesium is also involved in several important veterinary conditions, including:
Insulin Resistance (IR) and Equine Metabolic Syndrome (EMS). Horses with insulin dysregulation have lowered intracellular magnesium, which can cause higher blood insulin levels (Winter et al, 2020)
Synchronous Diaphragmatic Flutter (SDF) in endurance, event and racehorses
Developmental bone and growth disorders in young horses
Tetany (grass and transit-related)
However, magnesium is not involved in the condition known as “bighead” (nutritional secondary hyperparathyroidism). Multiple studies confirm that oxalates do not affect magnesium status in horses. While magnesium deficiency is linked to oxalate toxicoses in ruminants like cows and sheep, the opposite is true for horses, highlighting the importance of species-specific research.
Why It Matters
These studies show that magnesium, especially when paired with thiamine, powerful tool for managing stress and reactivity in horses. It also supports energy production, oxygen delivery, and recovery, helping to enhance both behaviour and performance.
Note on Tryptophan in Magnesium Supplements
Some magnesium supplements formulated for horses contain tryptophan, an amino acid known to influence behaviour in other species. While tryptophan has been shown to produce calming effects in rodents, its impact on equine behaviour is notably different. In horses, tryptophan does not produce consistent behavioural changes, and in some cases, may even have excitatory effects.
Despite being marketed globally as a calmative agent for excitable horses, there is no scientific evidence supporting the efficacy of tryptophan for this purpose. The limited studies available suggest that:
Low doses of tryptophan may cause mild excitement.
High doses can reduce endurance capacity and may lead to acute haemolytic anaemia when administered orally, due to the formation of a toxic hindgut metabolite.
Watch - Science-Backed Calm: Inside the Benefits of EzyMAG+
In this episode, we explore the latest scientific research on magnesium and its impact on equine behaviour and muscle health. Learn about the powerful benefits of vitamins B1, B6, and E, and discover how our supplement, EzyMAG+, supports your horse’s muscles and mind.
References
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Counotte, G. et al (2014) Feeding magnesium supplement to foals reduces osteochondrosis prevalence. Journal of Equine Veterinary Science
Davis, B.P., Engle, T.E., Ransom, J.I. and Grandin, T., 2017. Preliminary evaluation on the effectiveness of varying doses of supplemental tryptophan as a calmative in horses. Applied Animal Behaviour Science, 188
Grimmett, A. and Sillence, M.N. (2005). Calmatives for the excitable horse: a review of L-tryptophan. The Veterinary Journal, 170(1)
Harrington, D. (1975) Influence of magnesium deficiency on horse foal tissue concentration of Mg calcium & phosphorus. Br J Nutr
Kurtz (2009) Effect of dietary magnesium status on indices of muscular dysfunction in exercising horses. Master’s thesis Texas A&M
Noble, G.K., Brockwell, Y.M., Munn, K.J., Harris, P.A., Davidson, H.P.B., Li, X., Zhang, D. and Sillence, M.N., (2008). Effects of a commercial dose of L-tryptophan on plasma tryptophan concentrations and behaviour in horses. Equine Veterinary Journal
Nolan, M.et al (2010) Bone density in the juvenile racehorse fed differing levels of minerals in 17th Equine Nutr Physiol Soc Symp.
Vervuert, I. (2008) Major mineral & trace element requirements & functions in exercising horses. Nutrition of the exercising horse. EAAP publication
Stephens, T (2002) Mineral balance in juvenile horses in race training. Texas A&M University.
Stöckle et al (2019) Dose-dependent effects of magnesium supplementation on serum and intracellular magnesium concentrations in healthy horses Pferdeheilkunde – Equine Medicine 35
Winter et al (2020) Relationship between intracellular free magnesium concentration and the degree of insulin resistance in horses with equine metabolic syndrome. Pferdeheilkunde – Equine Medicine 36
Dr Jennifer Stewart
BVSc BSc PhD Equine Veterinarian and Consultant Nutritionist
