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What are Endometritis?

When a mare’s reproductive system becomes contaminated with bacteria, her body responds with the release of the immune cells, neutrophils. Usually, the neutrophils are able to destroy the bacteria. If they are unable to stop the spread of the bacterium, inflammation occurs within the uterus.  This hostile environment reduces the mare’s ability to conceive or to carry a foal to full term. Symptoms may present with discharge from the vagina but this is not always seen in an equine with endometritis. Frequent estrous cycles may point to this condition as well. Treatment may be extensive including daily uterine lavage and antibiotics.

Endometritis is the inflammation of the lining of the inside of the uterus. Endometritis is the most common reason for infertility in mares.

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Symptoms of Endometritis in Horses

Venereal Infectious Endometritis

  • Vaginal discharge
  • Unable to conceive

Persistent Post-Mating Endometritis

  • Common in older mares and multiparous mares
  • Short cycling
  • Vaginal discharge
  • Embryonic death

Non-venereal Infectious Endometritis

  • Infertility
  • Early embryonic death
  • Short cycling

Chronic Infectious Endometritis

  • Repeated inflammation and infections
  • Infertility

Chronic Degenerative Endometritis

  • Usually occurs in older mares and multiparous mares
  • Degenerative changes to the uterus
  • Fluid accumulation in the uterus
  • Delayed uterine clearance
  • Low fertility 


  • Venereal infectious endometritis 
  • Persistent post-mating endometritis
  • Non-venereal infectious endometritis
  • Chronic infectious endometritis
  • Chronic degenerative endometritis

Causes of Endometritis in Horses

  • Venereal Infectious Endometritis - The three most common microorganisms that cause venereal infectious endometritis in mares are Klebsiella pneumoniae, Taylorella equigenitalis, and Pseudomonas aeruginosa
  • Persistent Post-mating Endometritis - The mare is unable to eliminate bacteria, fluids or debris from the uterus. Usually caused by damaged myometrial contractility
  • Non-venereal Infectious Endometritis - Infections caused by bacteria such as Streptococcus or Staphylococcus; fungal infection in the uterus such as candida
  • Chronic infectious endometritis - Persistent and recurring infections caused by a poor conformation such as pneumovagina or vaginal wind-sucking
  • Chronic Degenerative Endometritis - The repeated inflammation to the uterus causes degenerative changes

Diagnosis of Endometritis in Horses

If the veterinarian suspects an infection in the uterus he will perform a vaginal exam.  Using a light the veterinarian will be able to evaluate whether there are any lacerations, scars and inflammation. The veterinarian may want to take a culture and/or a biopsy of endometrial tissue. He may also perform a rectal exam and in addition, a uterine flush can help obtain cells and bacteria to be examined under a microscope. A blood test can reveal if an infection is present. Urine and fecal samples may be analysed as well. 

The veterinarian may also suggest an ultrasound of the mare’s uterus. The horse may be sedated for this procedure. The horse’s tail will be secured to the side before performing the diagnostic test.  An ultrasound transducer will produce sound waves that are transmitted from the rectum walls to the uterus.  The ultrasound will be able to take images that can help determine if the mare has endometritis.

Treatment of Endometritis in Horses

Once the veterinarian diagnoses endometritis he may recommend a uterine lavage using sterile, isotonic saline or a diluted povidone iodine solution.  This procedure can help remove debris and bacteria from the uterus; it can also stimulate the uterus to contract. The uterine contractions will also aid in removing the contaminants from the uterus. The uterine lavage is administered to the mare using a uterine catheter. 

Antibiotics will be administered and the veterinarian may also prescribe an anti-inflammatory.  Probiotic supplements may be recommended to restore normal flora. Some patients will also be prescribed immune stimulants, to help build up the immune system.

Recovery of Endometritis in Horses

The patient will need follow up visits, to ensure that the infection has cleared.  The veterinarian will need to perform a vaginal examination.  He may want the patient to undergo a second ultrasound to insure that there is no uterine inflammation.  Mares that had significant loss of the endometrial glands are unlikely to carry a foal to full-term. Mares that were diagnosed and treated for venereal diseases have a good recovery prognoses. It is important to prevent recurring sexually transmitted diseases.  Mares should only be breed with stallions that are CEM certified free.