NSH is a metabolic bone disease of horses, caused by a calcium deficiency. The deficiency is the result of horses consuming a diet with excess phosphorous (more than 20% of rations contain wheat-bran based feeds), or ingestion of fresh pasture grass, weeds, hay, or receiving large quantities of treats that contain large amounts of oxalates (oxalic acid).

Upon ingestion, oxalates bind calcium (Ca), magnesium (Mg) and other trace minerals such as iron (Fe), making them unavailable for absorption by the small intestine. This leads to disturbances in the Ca/P ratio and results in excessive mobilization of bone mineral. By demineralizing the bones, the horse becomes weakened and misshapen, resulting in deformation of the face and lameness.