Equine Urolithiasis Study Guide

Overview and Clinical Importance

Urolithiasis refers to the formation of calculi (stones) within the urinary tract. In horses, this is an uncommon but clinically significant condition with a reported prevalence of approximately 0.11% of equine admissions to veterinary teaching hospitals. Despite this low prevalence, urolithiasis represents approximately 7.8% of diagnoses of urinary tract disease in horses, making it an important differential for horses presenting with signs of urinary dysfunction.

The unique composition of equine urine predisposes horses to calcium carbonate stone formation. Unlike other species, equine urine is naturally alkaline (pH greater than 7.0) and supersaturated with calcium and carbonate ions. The presence of large amounts of calcium carbonate crystals in normal equine urine is a normal finding, contributing to the characteristic turbid, mucoid appearance of horse urine.

Epidemiology and Risk Factors

Signalment

Sex: Males are more commonly affected than females, with geldings being overrepresented. Approximately 69% of all equine uroliths are from males. This predisposition is attributed to the longer, less distensible male urethra, which impedes passage of calculi.