THE MERCK VETERINARY MANUAL
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Overview of Congenital and Inherited Anomalies of the Reproductive System

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Cryptorchidism is a failure of one or both testicles to descend into the scrotum and 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%). Predisposing factors include testicular hypoplasia, estrogen exposure in pregnancy, breech labor compromising blood supply to the testes, and delayed closure of the umbilicus resulting in an inability to increase abdominal pressure. Bilateral cryptorchidism results in sterility. Unilateral cryptorchidism is more common, and the male is usually fertile due to 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. Abdominal testicles produce male hormones, and cryptorchid animals have normal secondary sex characteristics and mating behavior. Because of the inherited nature of the condition, unilateral cryptorchids should not be used for breeding. After puberty the retained testis becomes hypoplastic, degenerate, and fibrotic. Affected animals should be castrated as sertoliomas, seminomas, and interstitial cell tumors tend to develop within cryptorchid testicles and because of the heritability of the condition.

Some cases of hereditary hypoplasia of the ovaries and testes are associated with a single recessive gene with incomplete penetrance. It has been described in Swedish Highland cattle and has marked association with white coat color; the incidence has been much reduced by a controlled breeding program. Bilateral, unilateral, partial, or total hypoplasia may be seen. A condition similar to the human Turner's syndrome, with severe bilateral ovarian hypoplasia associated with chromosomal abnormalities, absence of follicles, and fibrosis with consequent infertility has been described in grade mares and in Thoroughbreds, Arabians, Welsh Ponies, Tennessee Walking Horses, Standardbreds, American Saddlebreds, Paso Finos, Belgians, Quarter Horses, and Appaloosas. Affected mares may be smaller than average and show either an absence of estrous cycles or only occasional estrus. They have a small flaccid uterus, a flaccid cervix with an open os, and small to very small ovaries. The ovaries are smooth and firm and have no follicles or corpora lutea. Cytogenetic studies may be indicated in infertile mares that show some or all of the above signs. The most common chromosomal abnormality in these mares is an absence of one of the sex chromosomes, and these animals are designated XO. There is no treatment.

Prolapse of the prepuce is a common defect in bulls, particularly in Bos indicus cattle. In B taurus cattle, it is common in polled beef breeds. A long, pendulous sheath, a large preputial orifice, and absence or poor development of the retractor prepuce muscles are predisposing inherited anatomic abnormalities. Prolapse of the prepuce predisposes the animal to injury, which can lead to abscess formation, scarring, adhesions, or phimosis. Surgical correction of the prolapse is possible, but as genetic predisposition may play a role, castration should be carefully considered.

Penile deviation is a common cause of copulatory failure in bulls. Two types of penile deviation are described—premature spiral deviation of the penis (corkscrew penis) and ventral deviation of the penis. Both conditions are caused by insufficiency of the dorsal apical ligament of the penis. Trauma is rarely involved. Premature spiral deviation of the penis is the most common penile defect in polled beef bulls and has been reported in most beef and dairy breeds. Spiral deviation is abnormal when it occurs prematurely and prevents intromission on more than one occasion. In affected bulls, the condition can be mild to severe, and premature spiral deviations of the penis may range from <25% to >75% of all services attempted. This may occur within one mating season or over several seasons. Most affected bulls develop the defect between 3 and 6 yr of age. In ventral deviation of the penis, the free part of the penis curves downward and prevents intromission. Deviations of the penis are diagnosed by careful observation of bulls at the time of service or during test mating. Surgical correction can be done, but should not be performed if inheritance is possible.

The opening of the penile urethra may be dislocated on the ventral surface of the penis (hypospadias) or on the dorsal surface (epispadias).

Persistent penile frenulum is not uncommon and is regarded as an inherited defect. 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. 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.

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.

Hermaphroditism or intersexuality is occasionally described in goats and pigs. True hermaphrodites are rare and have both ovarian and testicular tissue and exhibit anomalies of the external genitalia. The chromosomal makeup is variable and may be a chimera: mosaic, XX, with or without the SRY gene, or unknown. Pseudohermaphrodites are more common; they have one or the other type of gonad and an anomaly of the external genitalia that resembles, to some degree, that of the opposite sex.

The most common intersex condition, the male pseudohermaphrodite, has testicular tissue in the abdominal cavity or beneath the skin in the scrotal region, and external genital organs that resemble those of females. Miniature Schnauzers, Basset Hounds, and, rarely, Persian cats may present with pseudohermaphroditism when affected by persistent paramesonephric (müllerian) duct syndrome. Undescended testes are attached to the uterine horns and the vasa deferentia are located in the wall of the uterus. There are bilateral oviducts, a complete uterus with a cervix, and a cranial portion of the vagina. Bilateral scrotal testes or unilateral or bilateral cryptorchidism may be present. Affected animals can present clinically with pyometra, urinary tract infection, prostate infection, or Sertoli cell tumor. The diagnosis is confirmed by presence of a 78, XY chromosome constitution, bilateral testes, and the presence of all paramesonephric (müllerian) duct derivatives. Androgen-dependent masculinization is that of a normal male. Treatment is limited to castration and hysterectomy. The defect is inherited as an autosomal recessive trait in Miniature Schnauzers, and both females and males can be carriers. Homozygous affected dogs with a descended testis are generally fertile and capable of transmitting the trait to all offspring.

The paramesonephric ducts are paired embryonic ducts that develop into the anterior vagina, cervix, uterus, and oviducts. Segmental aplasia of the paramesonephric ducts results in anomalies of those organs. Ovarian development is normal. Accumulation of secretions proximal to the obstruction occurs secondarily. Variable degrees of persistence of the hymen is the most commonly reported paramesonephric duct anomaly; it may result in development of a fluctuating swelling caused by the accumulation of uterine secretions that is palpable per vagina. Segmental aplasia of the cervix may result in either mucometra, hydrometra, or cystic enlargement of the cervix. Segmental aplasia of the uterus may involve one horn (resulting in a condition called uterus unicornis), both horns, or only part of one horn (which may result in cystic dilatation of the uterine horn anterior to the area of dilatation). Developmental anomalies involving the paramesonephric tracts occur in all breeds, but the hymenal defects are most common in white Shorthorn cattle (white heifer disease).

Double external os of the cervix is due to a failure of the paramesonephric ducts to fuse. It may present as a band of tissue caudal to, or in, the external os of the cervix. In other cases, there is a true double external os opening into a single caudal part of the cervical canal. Affected cows usually conceive normally. Rarely, a true double cervix, with a complete septum between the two cervical canals, each opening into its respective uterine horn (uterus didelphys), occurs.

Gartner's ducts, located beneath the mucosa of the floor of the vagina, may develop multiple cysts, which are generally of no clinical significance.

Freemartins are sterile females born twin to a male. In cattle with multiple conceptions, the chorionic placental blood vessels form a common circulation between the fetuses prior to sexual differentiation, allowing antimüllerian duct hormone and testosterone secreted by the male to inhibit development of the female tract. In ∼92% of cases of mixed-sex twins, the females are sterile. The tubular genital organs in affected animals range from cordlike bands to near-normal uterine horns. Freemartins have a short vagina that ends blindly without communication with the uterus. The cervix is absent. The ovaries usually fail to develop and remain small.

Normal and freemartin cattle can be differentiated on the basis of length of the vagina and on presence or absence of a cervix. In calves (1–4 wk old), the normal vaginal length is 13–15 cm, while in a freemartin vaginal length is 5–6 cm. Vaginal length is easily measured by gently inserting a well-lubricated probe with a blunt end into the vagina. Cytogenetic examination can demonstrate XX and XY chromosome patterns in free-martins. The interchange of cells that occurs in the placental circulation between the fetuses can also be demonstrated by detecting 2 different blood types in a single animal.

Rectovaginal constriction is a simple autosomal recessive defect of Jersey cattle resulting in a severe stenosis or constriction of the anus or vestibule. In females, it is characterized by inelastic constrictions at the junction of the anus, rectum, vestibule, and vulva. Males may have anal stenosis. Affected cattle can copulate and defecate, but rectal examinations are difficult to perform and the vaginal constriction can lead to severe dystocia. In addition, affected cows are prone to develop udder edema at calving, frequently followed by severe mastitis.

Last full review/revision July 2011 by Fabio Del Piero, DVM, DACVP, PhD

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