Global Herbs MSMAbsolutely Pure MSM for horses MSM is an essential form of Sulphur found in most plants and an important equine joint supplement. Naturally occurring in the pasture, it's a natural equine supplement. In horses, MSM is vital for the maintenance of strong joints in all horses, young and old, retired and competing. MSM is suitable for all horses and ponies. Benefits for equines. Pure MSM Helps soothe equine muscle tissue. Helps maintain healthy joints.