It's a well-known human disease, known to affect those that routinely inhale fine dust in their jobs as miners, masons, sandblasting or construction work--anywhere rock is crushed into an easily inhaled dust. 

For the past few years, silicosis, caused by the inhalation of silica dust particles that lodge in airways, has been affecting horses in northern California. The source of the dust is pumice like stone that is exposed and pulverized in the construction process. Horses inhale the dust while feeding off the ground.

In a report co-written by University of California-Davis veterinarian John Madigan, Matthew Durham, DVM, of Steinbeck Country Equine Clinic in Salinas, Calif., noted that the disease was first diagnosed in horses in the late 1970s in the Monterey-Carmel area.

In the June 1 issue of the Journal of the American Veterinary Medical Association, a study of horses with fragile bones showed an apparent link between osteoporosis and compromised lung function, although no one knows exactly why. There is no surgical procedure to correct silicosis.