Merck Manual

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Male Genital Abnormalities


Ahmed Tibary

, DMV, PhD, DACT, Washington State University

Last full review/revision Aug 2015 | Content last modified Aug 2015
Topic Resources

Abnormalities of the Testis and Epididymis:

Cryptorchidism is a failure of one or both testicles to descend into the scrotum. It is seen in all domestic animals; it is common in stallions and boars and is the most common disorder of sexual development in dogs (13%). Cryptorchidism is caused by a combination of genetic, epigenetic, and environmental factors. Bilateral cryptorchidism results in sterility. Unilateral cryptorchidism is more common, and the male is usually fertile because of sperm production from the normally descended testicle. The undescended testicle may be located anywhere from just caudal of the kidney to within the inguinal canal and can be identified by transrectal or transabdominal ultrasonography. Abdominal testicles produce male hormones, and cryptorchid animals have normal secondary sex characteristics and mating behavior. Cryptorchidectomy is recommended for all companion animals because of the suspected inherited nature of the condition and predisposition to testicular neoplasia (seminomas, interstitial cell tumors).

Testicular hypoplasia has been described in several domestic species and is associated with chromosomal abnormalities in some cases. It is common in some family lines in camelids.

Anorchism is the complete absence of development of one or both testes. Unilateral anarchism has been described in horses and camelids. In camelids, the kidney ipsilateral to the missing testis is also missing.

Partial or complete segmental aplasia of the structures originating from the mesonephric duct (epididymis, ductus deferens, ampullae and seminal vesicles) has been described in bulls. Bilateral epididymal hypoplasia has been described in azoospermic stallions and camelids. In camelids, segmental aplasia of the epididymis is often associated with epididymal and rete testis cysts.

Abnormalities of the Penis and Prepuce:

Persistent penile frenulum is not uncommon. Affected bulls are unable to protrude the penis from the sheath and, in most cases, cannot achieve intromission. Attachment can be minimal (eg, 0.5 cm), or the preputial mucosa can be attached the full length of the ventral raphe of the free part of the penis. Genetic association is suspected in some breeds. Surgical correction should not be performed in bulls intended for seedstock breeding. Many male foals may appear to have a persistent frenulum at birth, but the condition resolves within a few days. If the condition persists, correction should not be attempted until the foal is at least 1 mo old.

Preputial prolapse occurs due to a lack of or a weak preputial retractor muscle in polled breeds. The condition is exacerbated when these breeds are crossed with Brahman cattle.

Congenital short penis has been described in bulls and may be associated with short retractor penis muscles, which prevent full erection. Bulls may breed satisfactorily in the first season, but copulation becomes impossible as their body size increases.

Short retractor penis muscle may occur congenitally or after injury to the penis or prepuce. Affected bulls have normal libido, but during attempted service the penis is only partially protruded from the sheath and the ejaculatory thrust does not occur. Failure of erection in bulls may be a congenital condition but is generally a sequela of trauma and/or hematoma of the penis.

Congenital vascular shunts have been described in bulls with partial erection or erection failure.

Hypospadias is an abnormal opening of the urethra due to failure or incomplete closure of the embryonic urethral groove.

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