NSHP develops when horses eat rations low in calcium or rations high in phosphorus and low or normal in calcium. If the ration is low in calcium, the calcium in the blood is only mildly reduced. But if it has too much phosphorus, it can severely decrease calcium absorption. So, the phosphorus in the blood increases and the calcium decreases. This often happens when horses eat large amounts of grain or concentrates and little hay.
Grains are generally high in phosphorus, and hays are high in calcium.
Forages high in oxalates also bind calcium, making it unavailable for absorption. Too much wheat bran or minerals high in phosphorus can raise phosphorus intake. Chewing problems occur late in the disease, but may be the first sign owners notice. Weight loss and anemia can occur as the disease progresses. Bones enlarge as minerals pulled out by PTH are replaced by fibrous connective tissue.