from the Vet Corner Archives

Part of Horse Previews Magazine website. Posted on 2/1/98; 10:00:00 AM.

Veterinary Corner 2/98: Abortion in the Mare

by Frosty Franklin, DVM
Edgecliff Equine Hospital
S. 1322 Park Road, Spokane, WA 99212 * 509/924-6069

In the mare, abortion brings a frustrating end to your planning and anticipation. Abortion is one of the most common problems affecting mares and losses have been placed as high as 15%. In miniature horses, studies suggest this number might be as high as 27% when combining both early and late term losses.

Expelling a premature fetus can be dangerous for the mare. Commonly, fetal death occurs prior to abortion. Therefore, it is unable to position itself properly in the uterus in preparation for parturition (birth). This results in the mare being unable to expel the dead fetus. Signs indicating the fetus has died include fluid coming from the vulva of the mare, the mare's wet bloody tail, or a small string of placenta hanging from the vulva of the mare.

Once the dead fetus has been delivered, one needs to be sure the placenta has not been retained in the uterus. Fetal membranes that are not passed in a timely manner, generally within 3-4 hours, can act as a source for uterine infection. Chronic uterine infection results in subfertility. Severe uterine infection can result in a toxic condition that leads to laminitis (founder) and even death of the mare. Your mare should be examined by your veterinarian following an abortion so any potential problems can be diagnosed and treated properly.

An autopsy should be performed on the fetus, including samples collected for viral, fungal, and bacterial isolation. Approximately 50% of the time the cause of abortion goes undiagnosed. Of the 50% of abortions that are diagnosed placentitis (infection of the placenta), is the most common diagnosis. Equine herpesvirus (Rhino) is the most frequently diagnosed viral cause of abortion in mares and has been reported to account for up to 15% of all diagnosed abortions. Twinning also remains a common cause of abortion despite the availability of ultrasonography. All three of these problems, placentitis, Equine herpesvirus, and twinning, do not usually occur until the fetus is more than 6 months gestation.

The most common signs of impending abortion in the mare are premature udder development ("bagging up") and vaginal discharge. Recently, Dr. Mats H. T. Troedsson and coworkers developed a technique using ultrasound to diagnose placentitis. Using the diagnostic probe transrectally, the thickness of the placenta can be measured. An increase in the thickness of the placenta indicates inflammation and swelling, possible placentitis. Once this diagnosis is made, the mare can be placed on antibiotics, progestins, and uterine anticontraction medication. Unfortunately, in many cases, the disease has progressed too far for treatment to be successful. This technique is most useful in monitoring mares with a previous history of abortion.

Mares with endometrial (uterine lining) biopsies that have inflammatory cells and fibrosis are not only subfertile, they are also more likely to experience abortion after they finally conceive. Studies indicate inadequate support for the rapidly growing fetus in late gestation due to the compromised endometrium can lead to abortion. A very small percentage of diagnosed abortions are caused by chromosomal factors, poor nutrition, vitamin/mineral deficiencies, poisonous plants, toxins, medications, and other physical and environmental factors.

To prevent abortion in the mare, good mare care and husbandry practices must be used. First, identify the mares at risk (i.e. mares that have aborted before, old mares with poor perineum conformation, mares with abnormal uterine biopsies, mares with other health problems). Second, excellent nutrition is essential. Good quality, mature hay and complete vitamin and mineral supplements are paramount to mare care. Third, keep mares in small groups and relatively isolated, especially from horses new to the farm. Fourth, vaccinations for equine herpesvirus should be given at the 5th, 7th and 9th months of gestation. Fifth, progesterone supplementation is widely used in an attempt to prevent abortion, as experience has shown that fetal loss can be reduced with progesterone therapy. Regardless of the quality of the prevention program, the mare and fetus must be examined regularly by your veterinarian.


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