Manganese is essential for correct bone formation and plays a critical role in cartilage metabolism. The manganese supplement for joints is a part of chondroitin sulfate in the body. A deficiency in this mineral will show as bone abnormalities such as chondroitin sulfate cannot be created properly withoutminerals. When chondroitin sulfate was not good, the bones cannot be trained. Manganese is found in lower concentrations compared to the horse's body to other minerals.
Significant forage generally has usually not a problem with magnesium deficiency. But, horse's hay is like most. Your horse probably getting a lot more manganese than he needs. There are no any researches showing manganese deficiency to arthritis or a benefit for horse joint supplementing manganese. Therefore, avoid manganese in the lowest dose you can.