CHAPTER 19Congenital Abnormalities Involving the Cervix and Uterus
Congenital abnormalities involving the uterus or cervix are rare in the horse. However, these abnormalities are frequently associated with infertility, even sterility. Many mares with congenital abnormalities of the cervix or uterus are bred on repeated cycles and for years before a thorough examination identifies the abnormality. Congenital abnormalities of the cervix or uterus may be associated with normal or abnormal estrous behavior patterns and ovarian function.
CHROMOSOMAL ABNORMALITIES
Mares with chromosomal abnormalities, such as 63XO, 64XY, 65XXY, and others, usually have gonadal dysgenesis. In addition to very small ovaries or even testicular tissue, the mares usually have very underdeveloped uteri and an infantile, open cervix. A cytogenetic evaluation (see Chapter 10) should be performed on blood or tissue samples from mares with developmental abnormalities of the cervix, uterus, oviducts, or ovaries.1 On rare occasions, mares with congenital absence of the cervix or uterus may have normal ovaries. The reproductive tract of mares with gonadal dysgenesis may still be responsive to progesterone and estrogen. Pregnancy has been established in XO mares in an embryo transfer program when the mares were treated with estrogen and progesterone.2
