Merck Manual

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Urethral Defects Causing Hematuria in Adult Male Horses


Thomas J. Divers

, DVM, DACVIM, DACVECC, Cornell University

Last full review/revision Jul 2013 | Content last modified Jul 2013
Topic Resources


The cause of the urethral defects is not proved, but they are believed to occur because of high pressure in the corpus spongiosum at the end of urination in geldings or during ejaculation in stallions. This high pressure may cause a "blow-out" tear in the urethral mucosa.

Clinical Findings and Diagnosis:

The clinical signs are limited to hematuria at the end of urination, associated with contractions of the bulbourethral muscle in geldings or with hemospermia and decreased fertility in stallions. All breeds may be affected, although the disorder seems more common in Quarter horses.

Diagnosis is based on clinical signs and urethral endoscopic findings. The urethral defect is seen in most cases on the dorsal convex surface of the urethra at the level of the ischial arch.


Some cases may heal spontaneously, but most continue with intermittent hemorrhage; anemia is rare. Breeding rest is recommended for stallions. Subischial urethrostomy or subischial incision into the spongiosum penis reduces vascular pressure in the corpus spongiosum during urination, allowing the defect to heal. A buccal mucosal graft was used to repair the defect in a stallion.

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