Horse owners in California and other states where silica composites make up pasture soil should be aware that ingestion of some minerals, including silica can lead to health problems in their horses with the lungs and limbs being affected.
In these areas, foraging and eating hay off the ground may contribute to problems of osteoporosis and lung disease.
In recent years, veterinarians in California noticed a correlation between cases of pulmonary silicosis, an equine respiratory inflammation caused by inhaling dust from silica-rich soils, and problems involving lameness, loss of bone strength, and musculo-skeletal changes in some horses.
The disease was first diagnosed in the late 1970s in the Monterey-Carmel area. Before this time, area veterinarians had noted signs of respiratory disease, but had been unsure of its cause. For years, silicosis in horses was believed to be isolated to this small region. But as awareness of the disease increased, cases started to be diagnosed in other parts of the state.
Given the name, silicate associated osteoporosis (SAO), the disease usually affects the upper portion of bones in the limbs and the vertebral spine. Horses that are mildly affected have intermittent lameness which may affect one or more limbs. Horses appear stiff and reluctant to move. As the disease progresses, the bones begin to deform and fractures occur.
Diagnosis of Silicate Associated Osteoporosis (SAO) is confirmed by bone scans. The results of routine blood tests are usually normal. Radiographs of the legs are not generally helpful in disease diagnosis because the bones in the lower part of the limbs are minimally affected. Good quality radiographs of the lower cervical vertebrae in the base of the neck may be useful for detection of bone changes in moderately to severely affected horses.
A study completed at UC Davis identified the effects as equine bone fragility syndrome (EBFS). A recent study of nine horses with EBFS and three horses without signs showed no bone loss in the control horses, while postmortem examination of the EBFS horses showed osteoporosis. The researchers concluded that horses with EBFS have a type of osteoporosis that is associated with inflammation of the lungs and lymph nodes caused by silicosis.