These days, it seems like there's a supplement available to fix almost any deficiency or ailment in a horse, including behavioral issues. One of the most popular temperament issues supplement manufacturers may try to solve is nervousness or excess energy, which prompts many horse owners to reach for a magnesium-based product.
Magnesium is thought to help soothe nervous horses because it works in concert with calcium on muscle contractions. Calcium stimulates muscle contraction, while magnesium stimulates relaxation of the muscle. Relatively little research had been done on the effectiveness of magnesium supplements for calming before researchers from the University of Guelph in Ontario, Canada tackled the issue in a study published in the most recent edition of the Journal of Equine Veterinary Science.
Study co-author Dr. Wendy Pearson wanted to learn whether a magnesium supplement had acute effects on a horse's response to stress. To test a supplement's short-term impacts, Pearson randomly assigned horses to treatments including the supplement, or a dose of acepromazine (a medication used for sedation), or a placebo paste. Each group was then asked them to perform tasks such as loading into a trailer, spending 10 minutes in a stall with an unfamiliar object, riding alone in a trailer, and having a blood sample taken. All of these activities, which are fairly routine in the course of a horse's management, were known to escalate heart rate and the amount of cortisol (stress hormone) in a horse's blood.
Both acepromazine and the magnesium supplement blunted the response of heart rate to the stressful activities when the horse was asked to perform the tasks 30 minutes after administration of each.
Pearson said she wasn't surprised to see the magnesium have an impact similar to the ace.
“There is abundant evidence in the research literature linking magnesium status to anxiety, and supplementary magnesium has been associated with reduced stress in a number of different species, including humans and rodents,” Pearson said.
It's important to note the study tested the usefulness of a magnesium supplement only in the short term; the amount of cortisol in the horses' blood, which would have given a hint as to their long-term stress level, did not change significantly with the supplement or the acepromazine. It's also likely owners would give the supplement with a regularly-scheduled meal, rather than timing it ahead of a given activity. Pearson said the experiment was structured this way because the acepromazine group was the control for the magnesium supplement group, and ace administration is traditionally timed according to an anticipated stressful situation.
“That is not to say that repeated administration of a magnesium-rich supplement as a daily feed additive would not be expected to have similar results,” said Pearson. “In fact, results may be more pronounced in daily feeding as dietary magnesium does appear to have marked effect on anxiety.”
Another consideration is the danger of oversupplementing magnesium in the equine diet. As we noted on the Paulick Report earlier this year, some experts believe magnesium is one of the most over-fed minerals, and it's believed too much of it can cause similar symptoms to calcium deficiency – namely, developmental orthopedic disease, loose teeth, and weight loss.
Although the study suggests this particular magnesium supplement (the study used Calm and Collected, by Herbs for Horses) does indeed, live up to the hype in the short term, Pearson cautions that nutraceuticals like this one are not all created equal.
“I think an important take-home message is that nutraceutical products are not subject to the same regulatory oversight as drugs or feeds, and a beneficial effect observed with this product in this study does not necessarily translate to similar products from different manufacturers,” said Pearson. “As a community, the horse industry is desperately in need of more research in this area, and an important contributor to achieving this is for consumers of nutraceutical products to support manufacturers that invest in research on their products.”
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