Magnesium Supplementation: Is It Necessary?

In an equine society dominated by supplements for everything imaginable--from joint health and calmers to antioxidants and vitamins and minerals--some horse owners likely wonder what, if any, feed additives they should provide their horses. Take magnesium for example: Science has shown us that horses require this macromineral to keep their bodies functioning properly, so should owners provide a supplement to ensure their animals get enough in their diet? According to an Auburn University researcher, hold off on buying that magnesium supplement, as it likely isn't needed by your horse.

Magnesium is an essential macromineral for horses that aids in maintaining normal nerve and muscle function, as well as the production of protein and DNA. Previous research from Cornell University indicates that horses need to consume just under 5 mg of the mineral to carry out normal body functions.

According to Allison J. Stewart, BVSc(hons), MS, Dipl. ACVIM, ACVECC, associate professor of equine internal medicine at Auburn, who recently composed a literature review on magnesium deficiencies in horses, "As there is generally a large amount of magnesium in vegetative matter (i.e., grass, hays, and grains), deficiency is rare in horses."

Stewart explained that in very rare cases, broodmares can suffer neurologic problems and rapid death from magnesium deficiency brought on by long bouts with no feed while nursing a foal

Magnesium toxicity also is rare in horses, and there's little scientific research on the topic.

She explained that incorrect administration of Epsom salts (magnesium sulfate) during treatment for a colonic impaction could lead to magnesium toxicity, so it's important for veterinarians to ensure a horse is adequately hydrated and has normal electrolyte and renal (kidney) function before such therapy.

Treatment for both magnesium deficiency and toxicity requires quick action, Stewart explained. "If a horse is very sick seek specialist care at a 24-hour referral facility as soon as possible so that electrolyte, fluid and acid base imbalances can be corrected quickly and aid in his recovery from colic, diarrhea, pneumonia, or sepsis," she said.

"There are rumors that magnesium supplementation can be used to help treat equine metabolic syndrome and improve insulin sensitivity," she said; however, she added there is no scientific evidence that confirms or denies these suggestions.

So should you purchase that magnesium supplement for your horses?

"If your horse is receiving a good quality balanced diet, or has access to good quality hay or pasture, (magnesium) deficiency is unlikely to be a problem," Stewart concluded. However, if you have concerns about a particular horse's magnesium intake, consult with your veterinarian or equine nutritionist.

The article, "Magnesium disorders in horses," appeared April in the Veterinary Clinics of North America: Equine Practice. The abstract is available on PubMed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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