Late Term Abortion in Mares Reviewed for World Equine Veterinarians

Failure to conceive and early embryonic death both negatively impact the equine breeding industry; however, late-term abortions also occur and should not be ignored, said Michelle M. LeBlanc, DMV, Dipl. ACT, from Rood & Riddle Equine Hospital in Lexington, Ky., during the 11th Congress of the World Equine Veterinary Association, which was held Sept. 24-27, 2009, in Guarujá, Sao Paulo, Brazil.

Late-term abortion is defined as a loss of pregnancy after seven months of gestation.

"Mares at risk for late-term abortion include those with a surgical or medical crises, placentitis (inflammation of the placenta), (those that) are off feed for many days, have developed laminitis, or equine Cushing's disease," explained LeBlanc.

Clinical signs of impending abortion late in gestation include:

  • Early udder development;
  • Placental abnormalities noted on ultrasound examination; and
  • Vulvar discharge.

"Most often, there are no warning signs," advised LeBlanc.

A veterinarian can use a variety of tests to diagnose late-gestation abnormalities, including ultrasound examination of the placenta and fetus and measurement of maternal hormonal levels and electrolyte levels in the mare's milk. LeBlanc noted that it can be useful to measure the combined thickness of the uterus and placenta when assessing a mare for placentitis. Researchers have found that a combined thickness of greater than 1.5 cm could indicate placentitis (normal thickness at 10 months of gestation is 1.2 cm or less).

Mares diagnosed with placentitis require aggressive management.

LeBlanc said she recommends a combined therapy, including antibiotics such as penicillin, ceftiofur, or trimethoprim sulfa; an anti-inflammatory drug such as flunixin meglumine, phenylbutazone, or pentoxifylline (to decrease pro-inflammatory mediators called cytokines); and an immunomodulator such as a double dose of altrenogest, pentoxifylline, or low-dose dexamethasone.

According to LeBlanc, combining such drugs can block abortion of a dead fetus, resulting in the development of severe metritis (inflammation of the lining of the uterus). Alternatively, the deceased fetus can become mummified or crushed.

Mares undergoing treatment for placentitis that are at risk for late-term abortion require veterinary examinations at least once weekly, as complications can develop rapidly. These can result in loss of the foal, and sometimes they can even be fatal to the mare.

"If complications such as metritis or retention of a dead fetus develop, the mare is not likely to conceive again that season if not treated aggressively after the abortion, and she can remain open until the next breeding season," advised LeBlanc.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.