Ammonium urate (or biurate) crystals generally appear as brown or yellow-brown spherical
bodies with irregular protrusions ("thorn-apples"). Though possible in urine of any pH, their
formation is favored in neutral to alkaline urine.
These crystals are fairly common in dogs and cats with congenital or acquired portal vascular anomalies, with or without concomitant ammonium urate uroliths. They can be seen in urine from normal Dalmatian dogs. Both Dalmations and Bulldogs are predisposed to urate urolithiasis. They are rarely, if ever, seen in urine from normal cats or dogs of other breeds.