Women aren’t the only ones suffering from decreased bone density and bone mass loss–horses in Central California have experienced a systemic osteoporotic disorder. At the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif., Amanda Murray, DVM, MPVM, of the University of California, Davis, presented a paper on equine bone fragility syndrome, a systemic osteoporotic (characterized by a decrease in bone mass) syndrome identified in specific areas of California and thought to be caused by exposure to cristobalite. This mineral is found in chalk rock in the Carmel/Monterey Bay region and is thought to occur in volcanic formations in Sonoma and Lake Counties of California. Exposed cristobalite-rich soils are readily aerosolized when the ground is disturbed by excavation.

This syndrome is thought to be associated with pulmonary silicosis (a silicate dust-caused respiratory disease that in humans might be accompanied by rheumatoid arthritis). With disease progression an affected horse suffers from skeletal deformities and, ultimately, pathologic fractures.

In a previous study 19% of horses affected by bone fragility syndrome had concurrent pulmonary silicosis, and 58% of horses with chest radiographs had signs of lung disease. In many cases the pulmonary disease can be silent (no obvious clinical lung signs). This disease is not restricted to any particular age, breed, or gender.

Skeletal deformities most often begin with bowing of the scapula (shoulder blade). While bone disease can manifest years after exposure to the mineral, scapular bowing might be noted suddenly, beginning on one side and progressing to both shoulders. Excessive bone production leads to thickening of the scapular spine and irregular contours of the scapula due to ongoing bone destruction and resorption