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Informational Articles

Abortion In The Mare


How heartbreaking to get your mare in foal and start preparing for the new baby, but then have the mare lose her foal. When the mare loses the foal before day 30 it is called early embryonic death and the mare could come back in heat without showing any signs of having been pregnant. If the mare loses her foal after about day 37, she may not come back in heat for several months because of the hormonal changes caused by the pregnancy. If the mare loses her foal between 150 to 300 days it is considered a late abortion, but after day 300 it would be called a stillborn, premature birth or full term birth, depending on the circumstances of the birth.

A late abortion can be very hard on the mare because the mare's pelvic muscles and cervix may not be relaxed enough to deliver a large fetus. Therefore it may be several months before the mare may be ready to be rebred. 

Signs of impending abortion
A mare that loses her foal early in gestation may not show any signs prior to the abortion. Later in gestation, the two most common signs of impending abortion are premature udder development and vaginal discharge. Generally the mare will start developing an udder a few weeks before she is due to give birth, but if she starts "bagging up" much before that time you might want to have her checked by your veterinarian. Vaginal discharge also warrants a call to your veterinarian.

If your mare seems to have a problem, you may want your vet to check the thickness of the placenta. An increase in the thickness of the placenta indicates inflammation, which could be placentitis. If this is the case, your vet may prescribe antibiotics, progestin, and anti-contraction medication. However, by the time your mare exhibits these signs it may be too late for treatment to be successful.

If your mare does abort her foal, her own health may also be in danger. Generally the fetus will die before the mare aborts and therefore the fetus cannot position itself properly in the uterus for delivery. Some signs that the fetus has died include a fluid discharge, a bloody tail, and a string of tissue hanging from the mare's vulva. Your mare probably needs your vet's help at this point.

Whenever a mare loses her foal, you should treat it as an infectious event; at least until you find out differently.

  • Disinfect all surfaces that came in contact with the aborted material.

  • Isolate the mare from other pregnant mares.

  • Disinfect her stall and keep it vacant for a few weeks.

Once the fetus has been delivered, you must ensure that the entire placenta is passed in a timely manner. The mare can develop a uterine infection if all of the fetal tissue has not been passed within about three to four hours. This type of infection can cause subfertility. A severe infection can lead to founder and even death of the mare.

Causes of abortion
About half of the time, the cause of the abortion goes undiagnosed. Despite this, you should request an autopsy on the fetus, including lab tests on fetal tissue. The most common diagnosis is placentitis, or infection of the placenta. Equine herpesvirus (Rhino) is the second most common cause of abortion. Despite the availability of ultrasound examinations, twinning is another cause of abortion. Unfortunately these three problems, placentitis, Rhino, and twinning, usually do not occur until after six months of gestation. This means that you not only lose one foal, but because it's so late in the season, the mare can't be bred back until the next year. Other causes of abortion include chromosomal factors, poor nutrition, poisonous plants, toxins, medications and other physical or environmental factors.

So what can you do to prevent abortion?

First, identify mares that are at risk. This includes mares that have aborted before, older mares, mares with poor reproductive conformation, mares with abnormal uterine biopsies, and mares with other health problems.

Second, give your broodmares excellent nutrition - good quality hay with a complete vitamin and mineral supplement.

Third, keep broodmares isolated from other horses, particularly from horses new to the farm or returning from competition.

Fourth, vaccinate for equine herpesvirus (Rhino) at the 5th, 7th and 9th months of gestation.

Fifth, check the broodmare's hormone levels and provide progesterone supplementation, if necessary.

Finally, pay attention to your mare:  How does she generally act? What is her normal temperature? How does she look?  Something out of the ordinary should put you on alert and may warrant an examination by your veterinarian.  Good luck!


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