The most common congenital abnormality of the ovary is ovarian dysgenesis or ovarian hypoplasia. Ovarian dysgenesis has been described in several domestic animal species and has been associated with various chromosomal abnormalities (monosomy X or Turner syndrome, trisomy XXX, or Klinefelter syndrome XXY). The ovaries are very small and lack follicular activity.
The paramesonephric ducts are paired embryonic ducts that develop into the anterior vagina, cervix, uterus, and uterine tube. Segmental aplasia of the paramesonephric ducts results in anomalies of those organs. The aplasia (obstruction) may be located in a segment of the uterine tube, uterine horn, cervix, or vagina. Ovarian development is normal. Accumulation of secretions proximal to the obstruction occurs secondarily (hydrosalpinx, hydrometra, mucometra, colpometra).
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). Uterus unicornis has been described in several domestic animal species. The condition seems to be relatively common in camelids. These females can become pregnant and carry the pregnancy to term. Cervical aplasia has been described in a few cases but is not as common.
True persistence of the hymen or imperforation of the hymen is the most commonly reported paramesonephric duct anomaly in domestic animals. Fluid accumulates in the vagina and uterus, resulting in protrusion of the hymen at the vulva when the animal is lying down or straining. 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.
Vaginal stricture or vestibulovaginal hypoplasia has been described in mares, dogs, and camelids.
Gartner's ducts, located beneath the mucosa of the floor of the vagina, may develop multiple cysts, which are generally of no clinical significance.
Vulvar atresia or hypoplasia (atresia vulvi) has been described primarily in camelids. In extreme cases, the labia are completely fused. The condition is believed to be due to an autosomal recessive gene.
Rectovaginal constriction is a connective tissue disorder of Jersey cattle characterized by stenosis of the anus and/or vestibulovaginal sphincter. Bilateral stenosis of the milk veins has also been described and results in udder edema and ischemic necrosis. It is a simple autosomal recessive defect. Anal stenosis renders transrectal palpation difficult. Affected females experience severe dystocia. The prevalence of the disease has been substantially reduced because of identification of carrier bulls.