Mar 152019

By Patty Wilber

I looked at Equine Appeasing Pheromone (some data-driven evidence supports its efficacy) and tryptophan (no data-driven evidence supports it) as calming agents in horses over the last two weeks.

One of my favorite pictures of LT. Magnesium supplementation did not seem to change her outlook on life, but Vitamin B and tryptophan pastes did.

This week is magnesium, and still to come are fat and Vitamin B.  Oh boy!

When looking into magnesium as a calmer in horses, I figured it would be super easy.  There are tons of supplements with Mg in them, and the sellers make a lot of “backed by science” claims, so my plan was to go read those studies, summarize them and ta da! Done!

But Nooooo.

It turns out, while there is a lot of interest in magnesium, there are NOT many studies done on horses and the “based on science” claims are stretching it a bit in some cases….So here is my new plan.

First, a bit about magnesium and studies not in horses; second a quick review of the few studies in horses; third, an analysis of some of the claims made by companies selling stuff to us I’ll-spend-anything-on-my O’-Dobbin horse owners.  And no one should take offense at that, because I am in very much in that club, especially, for some reason, with feed supplements.


I read (skimmed) three reviews. Magnesium basics,  Jahnen-Dechent and Ketteler(2012); Magnesium and Stress, Cuciureanu and Vink (2011); and The Importance of Magnesium in Clinical Healthcare Schwalfenberg and Genuis (2017).

There are 92 naturally occurring elements on Earth.

Magnesium is the eighth most abundant and is readily bioavailable. The Dead Sea is high in magnesium (Jahnen-Dechent and Ketteler).

In fact, “Mg is the fourth most abundant cation in the body and the second most abundant intracellular cation” (Cuciureanu and Vink).

Enzymes are proteins that basically run metabolism and “more than 325 enzymes are Mg dependent” (Cuciureanu and Vink).

Cuciureanu and Vink say that “many of these are nervous system enzymes.” And Jahnen-Dechent and Ketteler add  “chronic latent magnesium deficiency has been linked …. to psychiatric disorders.”

Magnesium has antidepressant effects (), Mg counteracts some of the negative biochemical effects of stress (), low brain Mg levels in mice increases sensitivity to stress (), and Mg enhances serotonin receptor function  () in Cuciureanu and Vink.

A 2012 study found that Mg deficiency produced anxiety in mice.

Serotonin is a feel good chemical in the brain (tryptophan is a precursor).

If Mg has similar effects in equines as described above, then it sure stands to reason that Mg supplementation would work as a calming agent. But hardly anyone has looked!

Studies in horses

In 2002, Wijnberg et. al. found that horses with subclinical hypomagnesemia  exhibited hyperirritability of nerves and noted that  endurance folks might want to know this.  They stopped short of recommending Mg supplementation.

Dodd et al., 2015, noted that supplement sellers like to claim that Mg is a great calming agent, without any evidence.  So Dodd et. al., decided to test it.  They found oral Mg worked as well as the sedative Acepromazine (Ace) on six mature standardbred geldings. Then they said, “This is the first time an objective measurement of behavioral change due to oral magnesium supplementation has been reported in the horse.”  This was in 2015. Four years ago.

A study attempting to repeat the 2015 test was reported in a non-peer reviewed blog in 2018 and they did not find a consistent calming effect of Mg on horses.

Natalie Voss reported on a 2017 study in the Journal of Equine Veterinary Science.  Ms. Voss says that the study showed that Mg was as effective as Ace.  The study was on short-term use of Mg, but one of the study authors, Dr. Wendy Pearson at the University of Guelph in Ontario, Canada was quoted as saying, “… results may be more pronounced in daily feeding as dietary magnesium does appear to have marked effect on anxiety.”

In a weird contrast, Equifeast, who seems to be really really high on and slightly defensive about selling tryptophan, drew the absolutely opposite conclusion from the Dr. Pearson study and said this: “All-in-all this experiment shows no significant calming effect (that horse handlers might want to see) from either veterinary sedation or from magnesium.”

Unfortunately, I could not access this article to see who was actually right!

And in a tangential side note and interesting article, MgCl can be used as an anesthetic in squids and octopuses.

In summary, there is one published study that I could read that definitely found a calming effect of Mg on horses (Dodd et al, 2015).  There is one non-peer reviewed article that found inconsistent effects, and one peer reviewed article that I could not access, but Dr. Pearson is a professor, as noted above, and could be emailed about that pub… Ok.  Gonna do it. Did it. Emailed.

Some claims by sellers

Kelato Animal Health

“Now is the time where you ask whether there is any scientific evidence behind the alleged ‘calming properties’ of magnesium. Until recently, we were mainly relying on anecdotal evidence and reports from owners who saw a significant improvement in their horses’ behaviour. In 2015, researchers investigated the effects of magnesium aspartate supplementation on the reaction speeds of six Standardbred geldings (Dodd et al. 2015). They found that adding 10g of magnesium aspartate to a roughage diet (clover/ryegrass hay), which already provided the recommended daily intake of magnesium, reduced their reaction speed response by more than one third. More research is warranted to determine the repeatability of this study, but it certainly provides some food for thought.”

That was pretty spot on.

An article.

“Magnesium is involved in relaxation of the muscles and nervous system and has been studied extensively using laboratory animals and horses. Not enough magnesium can induce anxiety. Typically, such horses will appear “sensitive” where they may spook easily, avert their attention away from you, become irritable, or are uncomfortable and nervous.”

Extensively? As in one published study? I want citations, people, citations.

Performance Equine

“Magnesium plays an important part in nerve and muscle function, and horses deficient in this important element can show signs of nervousness, wariness, excitability, jumpy,  tight sore backs not related to saddle fit, muscle tremors and skin is hypersensitive. Magnesium deficient horses are likely to have a poor tolerance to work, fatigue quickly and are prone to tying up. They also build up lactic acid more readily. Magnesium deficient horses often have behavioral problems due to muscle cramping and a poor tolerance for work. They fatigue quickly and have poor recovery from hard workouts.”

I guess I missed those articles. Where are the citations for horses? I found this: Hypomagnesemia and this Magnesium disorders in horses, but neither match up with the claims above. It seems like there may have been some extrapolation somewhere along the line from studies on other other species, maybe even humans, to horses.  Citations. Necessary.

(Anecdote disclaimer: I actually use Mg from this company, and, uh, well, it has worked as a calmer for a young horse I was starting that was having some anxiety issues.)


“Supplementing horses with magnesium to manage stress, erratic behavior, anxiety, and even to relax tight muscles is not a new concept.”

True that, but “concept” and “proof of concept” are not the same thing.

So, I guess the same old warning applies.  We have got to be critical and thoughtful consumers!

My recommendation on Mg is, “might as well try it”.  It could make a difference and there is biochemical evidence that it is an exceedingly important element, whether or not supplementation produces calming effects.