Silica-containing urinary calculi in dogs (1981-1993).

Silica-containing urinary calculi obtained from 773 dogs and submitted by veterinarians throughout the United States were analyzed by quantitative crystallographic analysis to determine mineral composition. Specimens were composed of either multiple mineral layers (535 specimens) or 1 mineral layer (238 specimens). Most multiple-layer calculi were composed of 80% or greater silica (300 of 535, 56%) or 20% to 79% silica (184 of 535, 34%) in any mineral layer. Most 1-layer calculi were composed of 100% silica (212 of 238, 89%). Most dogs forming silica-containing calculi were of male gender (679 of 773, 88%). Bacterial cultures of calculus or urine or both were performed on 49% (376 of 773) of the specimens, and bacterial growth was obtained from 37% (139 of 376) of samples cultured. The prevalence of calculus-associated urinary tract infection was 35% (113 of 321) in males and 47% (26 of 55) in females. The gender prevalence for infection with Staphylococcus species was 16% (51 of 321) in males and 33% (18 of 55) in females. The breed and gender of dogs that formed calculi (silica population) were compared with the hospital population (Veterinary Medical Teaching Hospital [VMTH] population) and with a population of calculus-forming dogs (Stonelab population) to determine risk factors for silica calculus formation. For all breeds compared, the ratio of males to females was higher in the silica population. The German Shepherd Dog and Old English Sheepdog were significantly overrepresented when the silica population was compared with either the VMTH population or the Stonelab population. We conclude that male German Shepherd Dogs and Old English Sheepdogs are at increased risk for formation of silica-containing urinary calculi.