Mare Vaginal Discharge: Normal Heat, Infection or Reproductive Problem?

Not every discharge means infection. A mare in estrus may have a small amount of clear to slightly cloudy mucus because the cervix relaxes during heat. That kind of discharge is usually mild, short-lived, and not foul-smelling. If your mare seems bright, is eating normally, and the discharge only appears around her cycle, your vet may decide monitoring is reasonable.

Abnormal discharge is more concerning. Common causes include endometritis or metritis, especially after breeding, foaling, retained placenta, or contamination of the reproductive tract. Merck notes that mares with genital infection may have tail matting, uterine discharge, inflammatory cells on cytology, and fluid in the uterus on ultrasound. Postpartum metritis can cause a fetid, copious discharge and may be accompanied by fever, lethargy, dehydration, and even laminitis risk.

Some mares leak discharge because urine pools in the vagina rather than because the uterus is infected. This is called urovagina. Merck describes urine staining on the inner thighs and direct visualization of urine in the vagina on vaginoscopy as important clues. Poor vulvar seal, pneumovagina, older broodmare conformation changes, and previous foaling injuries can all make contamination more likely.

Pregnancy changes the picture. Mucopurulent discharge in a pregnant mare raises concern for ascending placentitis, which Merck describes as a common cause of abortion and is associated with discharge, premature udder development, and increased uteroplacental thickness on ultrasound. After breeding, contagious equine metritis is another important but uncommon infectious cause; AAEP notes affected mares can develop mucopurulent discharge for 2 to 3 weeks and the disease is reportable in the US.

See your vet immediately if the mare is pregnant, recently foaled, or seems systemically ill. Red flags include fever, depression, poor appetite, repeated straining, colic-like behavior, a bad odor, blood, thick pus, retained fetal membranes, or a foal that is nursing often but still seems unsatisfied. These signs can go with metritis, placentitis, vaginal trauma, or other reproductive emergencies.

A postpartum mare needs especially close attention. Merck states fetal membranes should normally pass within about 3 hours after foaling, and retained membranes beyond that point can lead to metritis, endotoxemia, laminitis, and death. If any membranes are hanging from the vulva, do not pull them out. Call your vet right away.

You may be able to monitor briefly at home if the mare has only a scant amount of clear mucus around heat, is bright and comfortable, has no odor, no fever, and no pregnancy or recent foaling history. Even then, if the discharge lasts more than a day or two, keeps returning, stains the tail, or affects breeding plans, schedule an exam.

When in doubt, take photos of the discharge, note the mare's temperature, appetite, breeding dates, and foaling date if relevant, and share that information with your vet. Exact timing matters because discharge 10 to 14 days after breeding, discharge during late gestation, and discharge after foaling each point to different problems.

Your vet will start with history and a hands-on exam. Expect questions about the mare's age, breeding status, pregnancy stage, foaling date, recent breeding or insemination, prior reproductive problems, urine scalding, and whether the discharge is clear, bloody, or foul-smelling. A temperature, heart rate, hydration check, and inspection of the tail, vulva, and inner thighs help separate a local reproductive problem from a whole-body illness.

A reproductive exam often includes transrectal ultrasound and vaginal or speculum examination. Merck describes ultrasound as useful for finding uterine fluid, enlarged or flaccid uterus, placental thickening, and vaginal fluid. Vaginoscopy can help identify urine pooling, cervical problems, trauma, or discharge coming from the uterus rather than the lower tract.

If infection is suspected, your vet may collect samples for uterine culture and cytology, and sometimes biopsy in chronic fertility cases. These tests help distinguish inflammation from contamination and guide treatment choices. If the mare is pregnant, ultrasound of the placenta and fetus becomes especially important. If contagious equine metritis is a concern, testing and regulatory steps are more specific because it is a reportable disease in the US.

Treatment depends on the cause and the mare's status. Options may include uterine lavage, oxytocin to help clear fluid, anti-inflammatory medication, targeted antimicrobials, repair of reproductive tract injuries, or procedures that improve vulvar seal such as a Caslick in selected mares. Pregnant and postpartum mares often need faster, more intensive monitoring because the stakes are higher for both mare and foal.

Home care should support your vet's plan, not replace it. Keep the mare in a clean, dry area and gently keep the tail and hindquarters free of dried discharge so your vet can better monitor changes. Do not put creams, washes, or home remedies inside the vagina unless your vet specifically instructs you to do so.

Take and record her rectal temperature once or twice daily if your vet recommends monitoring. Also track appetite, manure, urination, attitude, breeding dates, pregnancy stage, and whether the discharge is clear, cloudy, bloody, or foul-smelling. Photos taken at the same time each day can be surprisingly helpful.

If the mare recently foaled, watch closely for retained membranes, depression, reduced milk production, or signs of foot soreness that could suggest laminitis risk. If any fetal membranes are hanging from the vulva, do not pull on them. Call your vet. If the mare is pregnant, any discharge should be treated as more urgent than the same sign in an open mare.

Until your vet has examined her, avoid breeding the mare and avoid sharing breeding equipment. If contagious equine metritis or another infectious reproductive disease is even a small concern, your vet may recommend temporary isolation and testing steps. Early evaluation usually gives the most treatment options and the best chance of protecting both fertility and overall health.