Placentitis (Mares) in Horses

Placentitis (Mares) in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
Placentitis (Mares) in Horses - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Placentitis (Mares)?

This condition is caused by bacteria entering the vagina and traveling up and into the placenta. Placentitis is devastating to discover in the last three to four months of gestation. Usually, the foals are born prematurely and do not survive. But if diagnosed early in the infection stage and treated appropriately, the chance of the foal surviving to lead a healthy life is greatly increased. Your veterinarian assistance is vital to determine what neonatal care will be required as not all organs mature at the same rate; therefore, early birth foals may need extra assistance until the development is complete.

Placentitis is an inflammation within the placenta that is responsible for approximately up to forty percent of late term abortions in your mares.

Symptoms of Placentitis (Mares) in Horses

  • Very hard to predict as there are usually no outward clinical signs that anything is wrong to give warning to the owner 
  • The abortion of the foal due to this condition is usually the first sign that there is any problem 
  • Past history of your mare’s pregnancy may provide a warning if she has had trouble before
  • Visual signs such as evidence of a vaginal discharge may be present 
  • Premature udder development can be an indication 


  • Most types of placentitis in your mare is caused through infection which means the infection arrives through the cervix 
  • But infections can arrive via the bloodstream while others have been lying dormant and are triggered by pregnancy 
  • Viral cases of placentitis such as equine herpesvirus (EHV) do occur and cause early abortions or weak foals
  • A fungal infection may follow the initial infection as a secondary infection


Causes of Placentitis (Mares) in Horses

  • The production of prostaglandin which is a hormone that may cause uterine contractions thus leading to premature labor
  • Bacterial infection of the uterus that gained entry via the vagina and broke through the cervical barrier 
  • The eating of the body parts of various species of caterpillar has been shown to lead to abortions
  • Injury to the mare from previous foalings that allows infection from weak areas 
  • Inflammation of the placenta causes it to pull away from the uterine lining
  • Poor confirmation of the vulvar open allowing feces into the vagina
  • Infection is usually in the area known as the cervical star area
  • This in turn decreases oxygen and nutrients to the unborn foal


Diagnosis of Placentitis (Mares) in Horses

Early diagnosis is not easy to make but if it is found early in the beginning stages, it would improve the chances of positive clinical outcomes. Causes of this condition can be hard to determine, but if your mare has previously given birth then the history of her health and knowledge of any previous problems can help with diagnosis. Ultrasound screening has been the main tool in diagnosing placentitis. It helps to measure the thickness of the uterus and placenta to determine any variables. The only downside of this diagnosis tool is the expense because of the frequent monitoring required. 

Testing your mare’s hormones is another way to determine the health of the pregnancy showing elevated progesterone levels that may indicate something is not right.  The third method is known as SAA tests which explore the use of inflammatory blood protein levels to test the body’s level of inflammation. One other way to provide early diagnosis is if there is a discharge from the vaginal area, your veterinarian may take a sample and from a culture may be able to tell if infection is present.



Treatment of Placentitis (Mares) in Horses

Treatment of placentitis is aimed at reducing the infections and inflammatory responses, while supporting the mare with care. Combining both antibiotics and medications to reduce inflammation, and administering progesterone until the birth of the foal can help overcome this condition. The earlier this condition is discovered, the better for the unborn foal. Delaying the early delivery to allow the complete formation of the foal will assist with the pregnancy going close to full term. 

A few antimicrobials such as sulpha-trimethoprim and penicillin have been shown to cross the the fetal membranes to effectively inhibit the common bacteria from causing placentitis. 

Upon delivery, a regular practise should be to inspect the placenta. Even with a seemingly normal birth inspection of the placenta can show abnormalities that can alert you to the fact the mare and foal may both need further attention. It can also lead to considering the mare as an at-risk mare for future breeding purposes. Your veterinarian will be able to show you what to look for in the future if you are going to be breeding this horse or others to ensure your mares get the attention they need.



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Recovery of Placentitis (Mares) in Horses

As throughout her pregnancy, the mare usually displays no obvious signs of ill health right up to going into labour. Once the foal has been born, the mare usually recovers immediately but for her health may need a course of medication to clear up any infection remaining. This will apply to the foal if it has been born alive. The foal may need oxygen to assist it to recover due to a reduced supply due to the infection of the placenta. 

Small foals that are normally the result of this condition have been known to grow into strong healthy animals given the right care and attention at birth. After the birth, management comes down to care given to ensure your mare has no ill effects afterwards and special attention to the foal as it develops. Checking for any after effects and providing quality feed and water, combined with observation and recording details for later breeding will help to provide correct breeding protocols.



Placentitis (Mares) Questions and Advice from Veterinary Professionals

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