MSM (methylsulfonylmethane) is a naturally occurring form of sulfur that is found in plants and animals. MSM is used to support joint comfort in aging horses and performance horses.
Horses and other mammals cannot utilize pure sulfur in its elemental form. MSM is an organic sulfur compound found in fresh alfalfa and grains. It has high bioavailability and is safe to consume.
Sulfur is involved in many metabolic functions including carbohydrate metabolism, protein synthesis and protection from oxidative stress. It is also a component of glucosamine and collagen, both components of healthy connective tissue and cartilage in your horse.
Horses that are deficient in sulfur may experience inflammatory or degenerative issues like slow recovery from exercise, poor hoof quality, or joint pain.
Horses with arthritis, poor hoof condition, or aging horses are likely to benefit from MSM supplementation. It may also slow the progression of arthritis by preventing cartilage degradation, as shown in human studies.  
MSM has benefits for heavily exercised horses by minimizing oxidative damage and inflammation allowing their muscles to recover quickly. It is frequently given to high-level performance horses to keep them in peak competition condition.
Toxicity from MSM has not been reported in horses. It is derived from the natural compound DMSO (dimethyl sulfoxide). Both MSM and DMSO have been used as supplements for horses since the 1980s.
Why do Horses Need MSM?
MSM is primarily consumed as a highly bioavailable form of dietary sulfur. Sulfur is an essential macromineral that represents ~0.3% of total body weight in horses. It is required for the formation and proper functioning of proteins.
The NRC recommends a minimum sulfur intake of 0.15% of dry matter intake. Good quality hay and forages are likely to meet the minimum requirement for maintenance and leisure horses. Older horses or those that are heavily exercised would likely benefit from additional MSM for comfort and optimal performance.
Horses and other mammals obtain sulfur in the diet primarily in the form of two sulfur-containing amino acids called methionine and cysteine. Methionine is required in a horse’s feeding program because they can not synthesize it internally or endogenously. Cysteine can be made from methionine in the body. 
These amino acids are important building blocks for proteins. Cysteine molecules within proteins form connective links to each other that help the protein fold into the correct shape. This helps proteins such as enzymes, hormones, and structural proteins function properly and keep cells healthy. 
Collagen and glucosamine are the most abundant proteins in connective tissues such as ligaments, tendons, and within hooves, and joints. They are very high in the sulfur-containing amino acid cysteine.
When sulfur is low in the horse’s diet, the structure of collagen and glucosamine might be unstable making hooves and joints weak. This can cause pain and poor performance.
To understand whether your horse is meeting its sulfur requirement, you can submit your horse’s diet for analysis and one of our nutritionists will be happy to provide a complementary review.
MSM Benefits for Horses
When tissues require sulfur, cells break down proteins to release methionine and cysteine which are further broken down to release their sulfur content. These amino acids are then no longer available to make proteins.
Adding MSM to the diet as a readily available source of sulfur spares methionine and cysteine from being degraded, making them more available for protein synthesis. Supplementing with MSM also has direct therapeutic effects on its own.
Below are the top 9 benefits of MSM in horses:
- MSM is involved in making the detoxifying antioxidant glutathione, one of the most important intracellular antioxidants. Having enough glutathione keeps tissues healthy, especially when they are stressed by exercise or disease.
- It reduces oxidative stress after exercise, which could improve recovery after heavy work. It is also purported to increase circulation which may further support muscle recovery.