 Oversaturation of urine with crystals is by the far the biggest factor in stone formation in dogs and cats.This oversaturation can be caused by increased excretion of crystals by the kidneys, water reabsorption by the renal tubules resulting in concentration of the urine, and changes in urine pH that influence crystallization.Other contributing factors include diet, frequency of urination, genetics, current medications, and the presence of a urinary tract infection.