Silicosis in horses is a respiratory condition caused by exposure to certain types of silicate dust found in some geographic regions. While silicosis is not a commonly diagnosed equine ailment in most areas of the country, Matthew Durham, DVM, of Steinbeck Country Equine Clinic in Salinas, Calif., said he sees cases far too often in his practice. Durham presented research he and co-author Coral Armstrong, DVM, conducted on 18 horses with clinical signs of silicosis, including numerous fractures, and bone deformities 2006 American Association of Equine Practitioners convention in San Antonio, Texas, held Dec. 2-6

A 19-year-old Arabian gelding used in Durham’s study, showing scapular bowing and lordosis.

Silicosis is typically a chronic condition in humans causing mild to severe respiratory disease that’s often accompanied by rheumatoid arthritis and lupus (a chronic autoimmune disease). In horses it causes respiratory disease, and it appears to be associated with osteoporosis (reduction of bone mass, and its associated fractures) and bone deformity. Silicosis is caused by the inhalation of certain types of silicate dust, including quartz and cristobalite. While quartz does not tend to be dusty, cristobalite is chalky and its dust becomes airborne easily, making horses in areas with high amounts of cristobalite rock particularly susceptible to the condition