Abortion in Mule Mares: Pregnancy Loss Causes and Veterinary Next Steps

Quick Answer
  • Pregnancy loss in a mule mare is a veterinary concern because infectious disease, placental disease, twins, toxins, and maternal illness can all be involved.
  • Common warning signs include vulvar discharge, premature udder development or milk dripping, colic-like discomfort, fever, and passage of a fetus or placenta.
  • Save the fetus and placenta if possible, keep other equids away, and call your vet promptly because testing the tissues often gives the best answer.
  • A basic farm-call exam with reproductive ultrasound and sample submission often falls in the $600-$1,150 cost range, while more complete workups and herd biosecurity can cost more.
Estimated cost: $600–$1,150

What Is Abortion in Mule Mares?

Abortion in a mule mare means loss of a pregnancy before the foal is viable. In equids, pregnancy loss can happen early and go unnoticed, or it can occur later in gestation with obvious passage of the fetus and placenta. Because mules are equids, vets usually approach pregnancy loss using the same reproductive principles used for mares, while also considering the individual animal, breeding history, and stage of gestation. (merckvetmanual.com)

Late-term abortion is especially important because it may be linked to contagious disease, placental infection, or management problems that could affect other pregnant equids on the property. Equine herpesvirus-1, placentitis, leptospirosis, equine viral arteritis, twin pregnancy, and toxic fescue exposure are among the better-recognized causes in equids. (merckvetmanual.com)

For pet parents, the key point is that abortion is not one single disease. It is a clinical event with many possible causes. Your vet’s job is to stabilize the mare if needed, protect the rest of the herd, and collect the right samples quickly enough to improve the odds of finding an answer. (merckvetmanual.com)

Symptoms of Abortion in Mule Mares

  • Passage of a fetus, fetal membranes, or obvious placental tissue
  • Vulvar discharge, especially bloody, brown, or pus-like discharge
  • Premature udder development, waxing, or milk dripping before expected foaling
  • Fever, depression, reduced appetite, or signs of systemic illness
  • Colic-like discomfort, restlessness, tail raising, or repeated lying down and getting up
  • Retained placenta after pregnancy loss
  • No outward signs at all before a late-term abortion

Some mule mares show warning signs for hours to days before pregnancy loss, especially with placentitis, where vulvar discharge and premature mammary development can appear first. Others may abort with little or no warning, which is common with some EHV-1 cases. See your vet immediately if your mule mare passes a fetus, develops a fever, has abnormal discharge, or retains placenta after the loss. Keep aborted tissues away from other equids and use gloves during handling because some infectious causes can spread, and a few carry zoonotic concerns. (merckvetmanual.com)

What Causes Abortion in Mule Mares?

Placentitis is one of the most important causes of late-term pregnancy loss in equids. It often starts as an ascending infection that moves past the vulva and cervix, though blood-borne spread can also happen when the mare is systemically ill. Bacterial and fungal infections can damage the placenta enough to trigger abortion, premature delivery, or a weak newborn. Risk factors include poor reproductive conformation, cervical problems, chronic disease, and a history of placental compromise. (merckvetmanual.com)

Infectious causes also include equine herpesvirus-1, the most important viral cause of abortion in horses, and equine viral arteritis in some breeding populations. EHV-1 abortion usually happens after 7 months of gestation and may not be preceded by obvious illness in the mare. Leptospirosis is another recognized cause and can produce placental and fetal lesions. Because mules share susceptibility to many equine infectious diseases, your vet may consider these causes even if only one animal appears affected. (merckvetmanual.com)

Noninfectious causes matter too. Twin pregnancy can lead to pregnancy loss because the equine uterus usually cannot support both fetuses to term. Toxic fescue exposure in late gestation is more often linked to prolonged gestation, agalactia, placental thickening, and perinatal problems, but abortion can occur in the last 2 months in severe cases. General maternal illness, poor body condition, and severe stress may also contribute. (merckvetmanual.com)

How Is Abortion in Mule Mares Diagnosed?

Diagnosis starts with the history and the stage of gestation. Your vet will ask when the mare was bred, whether she had prior pregnancy checks, vaccine history, exposure to new horses, fever, discharge, toxic fescue, or shipped semen, and whether any other equids on the property are pregnant or sick. A physical exam and reproductive ultrasound help assess the mare’s uterus, retained membranes, fluid, and any signs of placental thickening or ongoing infection. (merckvetmanual.com)

The most useful samples are often the fetus and placenta. For suspected EHV-1 abortion, PCR, virus isolation, and tissue evaluation of the aborted fetus are key. For leptospirosis, testing may include PCR plus fluorescent antibody or immunohistochemical testing on placenta, umbilical cord, fetal liver, or fetal kidney. If equine viral arteritis is a concern, your vet may submit placenta or fetal tissues for PCR or virus isolation and may also test the mare. (merckvetmanual.com)

If the mare has not yet aborted but placentitis is suspected, serial ultrasound exams and selected blood or hormone testing may be used to monitor the pregnancy. Even with a careful workup, some cases remain unexplained. Still, prompt sample collection improves the odds of identifying an infectious cause and helps guide herd-level biosecurity decisions. (petmd.com)

Treatment Options for Abortion in Mule Mares

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$600–$1,150
Best for: Stable mule mares after an isolated pregnancy loss when finances are limited and the goal is to protect the mare, submit key samples, and reduce spread risk.
  • Farm call and physical exam
  • Basic reproductive exam after pregnancy loss
  • Collection of the most important samples if fetus and placenta are available
  • Retained placenta check and basic uterine monitoring
  • Short-term anti-inflammatory or antimicrobial plan if your vet feels it is appropriate
  • Immediate isolation and basic biosecurity guidance for the property
Expected outcome: Often fair for the mare’s recovery if retained placenta, metritis, and systemic illness are addressed quickly. Prognosis for identifying the exact cause is moderate and depends heavily on sample quality.
Consider: Lower upfront cost, but fewer diagnostics may leave the cause unconfirmed. That can make future breeding plans and herd prevention less precise.
Most Common

Recommended Standard Treatment

$1,100–$2,200
Best for: Most mule mares after abortion, especially when the cause is unclear, there are other pregnant equids on the farm, or the mare appears ill.
  • Everything in conservative care
  • Reproductive ultrasound and uterine assessment
  • CBC and chemistry panel for the mare
  • Targeted infectious disease testing such as EHV-1 PCR and selected placental or fetal testing
  • Treatment for retained placenta, uterine infection, pain, fever, or dehydration as indicated
  • Written herd biosecurity and monitoring plan for exposed equids
Expected outcome: Good for maternal recovery in many cases when complications are treated early. Better chance of finding an infectious or placental cause than with a minimal workup.
Consider: More complete and practical for most farms, but costs rise with lab testing and repeat visits. Some cases still remain undiagnosed.

Advanced / Critical Care

$2,800–$4,800
Best for: Mule mares that are systemically ill, have severe retained placenta or uterine infection, or are part of a multi-horse breeding situation where contagious abortion is a major concern.
  • Referral hospital care or intensive on-farm management
  • IV fluids, intensive monitoring, and treatment for endotoxemia, metritis, or severe retained placenta complications
  • Expanded laboratory testing and pathology on fetus and placenta
  • Serial ultrasound and repeat bloodwork
  • Outbreak-level biosecurity planning when EHV-1 or another contagious cause is suspected
  • Future breeding consultation for high-risk mares or mares with repeated pregnancy loss
Expected outcome: Best chance to stabilize a sick mare and define the cause, though future fertility depends on the underlying disease and how quickly treatment begins.
Consider: Highest cost range and more intensive handling. Not every case needs referral-level care, but it can be appropriate when the mare is unstable or herd risk is high.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Abortion in Mule Mares

Bring these questions to your vet appointment to get the most out of your visit.

  1. What are the most likely causes of this pregnancy loss based on her stage of gestation and exam findings?
  2. Which samples should we submit from the fetus, placenta, and mare to give us the best chance of finding an answer?
  3. Do we need to isolate this mule mare from other equids, and for how long?
  4. Are you concerned about EHV-1, leptospirosis, placentitis, EVA, or another contagious cause on this farm?
  5. Does she have retained placenta, uterine infection, fever, or signs of endotoxemia that need treatment now?
  6. What monitoring should we do over the next 24 to 72 hours for appetite, temperature, discharge, and laminitis risk?
  7. If we breed her again in the future, what prevention plan would you recommend before and during pregnancy?
  8. What cost range should we expect for basic testing versus a more complete diagnostic workup?

How to Prevent Abortion in Mule Mares

Prevention starts before breeding. A pre-breeding reproductive exam can help identify conformational problems, cervical injury, chronic disease, or a history that raises concern for placentitis. Early pregnancy checks are also important because twin pregnancies are a known cause of loss in equids, and reduction is recommended when twins are found early enough. Good body condition, sound breeding hygiene, and prompt treatment of reproductive tract disease all support a healthier pregnancy. (merckvetmanual.com)

Vaccination and biosecurity are major tools. AAEP guidance for pregnant mares recommends an inactivated EHV-1 vaccine during the fifth, seventh, and ninth months of gestation, and many vets also consider an earlier dose depending on risk. Even with vaccination, abortion can still occur, so minimizing exposure matters too. Pregnant equids should be kept away from horses returning from shows, sales, or other high-traffic events when possible, and any abortion event should trigger immediate isolation and careful cleanup. (aaep.org)

Management details matter in late gestation. Avoid toxic endophyte-infected fescue, watch for vulvar discharge or premature udder development, and schedule extra monitoring for mares with prior placental problems, poor reproductive conformation, or chronic illness. Routine ultrasound surveillance may help detect placental trouble earlier in high-risk pregnancies. Your vet can tailor a prevention plan to the mule mare, the breeding method used, and the disease risks on your farm. (merckvetmanual.com)

Find a Vet Near You