When Magnesium Marketing Gets Ahead of the Science
By Annie Emery, MS CRC CESMT CENA
If you spend any time around horse supplements, you’ve likely seen ads suggesting that stressed or reactive horses are experiencing a drop in magnesium — and that this drop is what’s driving exaggerated adrenaline responses, anxiety, or spookiness.
That implication sounds tidy.
It also isn’t supported by equine nutrition research.
Magnesium deficiency is not common in horses.
Magnesium is naturally present in hay, pasture, forage, and commercial feeds. In fact, most typical forage-based equine diets already meet or exceed established magnesium requirements without supplementation.
True magnesium deficiency in horses is uncommon. When it does occur, it’s usually associated with specific medical or management issues — such as severe malabsorption, prolonged lack of intake, or specific disease states — not everyday stress or normal training demands.
The horse regulates magnesium tightly.
The equine body is quite good at maintaining magnesium balance. Serum magnesium levels tend to remain relatively stable across a wide range of intakes, which is one reason veterinarians do not routinely test magnesium levels unless there is a specific medical reason to do so.
The idea that stress alone reliably causes a meaningful drop in magnesium — enough to create deficiency or exaggerated adrenaline responses — is not supported by current evidence.
Response to a supplement is not the same as a deficiency.
Some horses do respond positively to added magnesium. That’s real, and it’s worth acknowledging. It’s used in many diets as a tool. That’s awesome!
However, a response to supplementation does not automatically mean the horse was deficient. Supplements can influence neuromuscular function, gut comfort, or overall dietary balance in subtle ways that improve how a horse feels or behaves — without correcting an actual deficiency.
This distinction matters. Improvement does not validate the claim that most reactive horses are magnesium-deficient or that stress is “draining” magnesium reserves.
Where marketing often goes wrong
Many supplement ads rely on implied cause-and-effect storytelling:
stress → magnesium drops → adrenaline spikes → behavior problems → supplement solution.
It’s a compelling narrative — but it oversimplifies equine physiology and stretches beyond what the data actually support.
Magnesium can be a valuable tool in select cases. It is not a universal fix, and it does not correct a widespread deficiency problem in the general horse population.
The bottom line
Magnesium supplementation isn’t inherently wrong — but the story often told around it is. Good nutrition decisions come from understanding the whole diet, the individual horse, and the evidence behind nutrient needs, not from assuming deficiency based on behavior alone.
If a horse is reactive, tense, or difficult to manage, magnesium may be one piece of the puzzle — but it should never be the default explanation or the first assumption.
Feeding with clarity means separating what sounds plausible from what’s actually supported by science.
Do you want help discovering if your horse needs a magnesium supplement? Reach out!
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