Composition of Stones

• Most stones are composed of calcium carbonate, with struvite (magnesium-ammonium-phosphate) uroliths seen occasionally.
  
  

Predisposition to stones

• High mineral content and the pH levels of normal equine urine may predispose equines to crystal formation. Normal equine urine also contains large amounts of mucoproteins, a glycoprotein comprised mostly of mucopolysaccharides, which may serve as a bonding agent for crystals. Forages, which contain large amounts of calcium, ammonia and magnesium, predispose horses to stone formation. Grains with high phosphorus content can also contribute to uroliths.
  
  

Symptoms

• Symptoms include dysuria (painful or frequent short urinations), colic (acute abdominal pain) and hematuria (passing of blood in the urine). Hematuria is seen most often after exercise.
  
  

Diagnosis

• Diagnosis is tentatively based on the history and clinical signs, and confirmed by rectal palpation of a firm oval mass at or near the neck of the bladder. Transrectal ultrasonography allows a visual confirmation of the urolith. Urinalysis reveals red blood cells, white blood cells, proteinuria and calcium carbonate crystals.
  
  

Treatment

• Inserting a catheter into the bladder to decompress it may dislodge an impacted stone. Several surgical procedures are available for urolith removal, including laser lithotripsy--laser destruction of the stone. Prophylactic antibiotics and urinary acidifiers--such as ammonium chloride- after treatment may decrease the formation of new stones.