Although it isn’t an established essential nutrient — or even a “legal” ingredient — MSM is present in the horse’s natural diet.??A horse maintained at pasture takes in between 1 to 2 mg/kg of body weight/day of MSM, which amounts to 500 mg to 1 g/day for a 1,100-pound horse.??This is below the current recommended therapeutic dose of 20 g/day, but it may provide a good starting point to estimate maintenance dosing in horses with chronic conditions that respond well to MSM. However, it’s wise to remember there’s something to the saying “too much of a good thing.”
A woman taking high-dose MSM as a treatment for skin and hair problems — and giving a high dose to her horse as well — began to notice muscular pain and cramping after a few weeks. The horse’s performance also fell off, again looking like muscle pain. This case caught our attention, as we had a similar case in a test horse receiving high-dose MSM (30 to 40 g/day) for joint inflammation. We found a reference to DMSO enhancing the efficiency of energy generation in muscle cells when present in the precisely correct concentration but interfering with it in high concentration. MSM is closely related to DMSO, and DMSO partially metabolize to MSM in the body.
We asked manufacturers of patented MSM if they knew of similar reports. They didn’t. Mike Uckele of Uckele Animal Health reports a few cases where excessive use of MSM resulted in lethargy or poor performance. He theorized the excessive sulfur may be binding to copper and interfering with trace minerals key in anti-inflammatory activities. These were isolated incidents, and the horses seemed normal otherwise. The connection to high-dose MSM is unproven, but the problems did correlate in time with its use and disappeared rapidly when stopped.
We aren’t suggesting anyone stop using MSM. We like MSM. It’s one of the safest supplements in terms of side effects. However, we’d stay within suggested dosage limits, and if a horse receives a copper and other trace minerals, we’d feed MSM in a separate feeding.