iO Yellow Sulphur is a very important macro mineral to your horse?s health due to the fact that it is present in so many places in his body. Quick Facts & Benefits: With iO Yellow Sulphur, you can be sure your horse will be given the proper nutrients to keep it happy inside and out! Can also be used as a insect repellent in horses. iO Yellow Sulphur is known to relieve equine cold symptoms. iO Yellow Sulfur is necessary for amino acids, B vitamins, insulin, and chondroitin sulfate in your horse. It?s a bright yellow powder obtained from naturally-occurring volcanic brimstone deposits.Â