postpartum metritis in mares
Inflammation of the uterine wall known as metritis is one of the most common yet serious postpartum diseases seen in mares. Veterinarians can treat it using antimicrobials but, because it takes at least four days to get culture results indicating which antibiotic is most effective against the bacteria present, most practitioners treat postpartum metritis in mares before culture results return.

During the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California, Maria Ferrer, DVM, Dipl. ACT, associate professor of theriogenology in the University of Georgia’s Department of Large Animal Medicine, in Athens, described how to best manage affected mares.

“Metritis is a serious, life-threatening disease that requires immediate treatment,” said Ferrer.

While early clinical signs include vulvar discharge, lethargy, and fever, the bacteria or their toxins can quickly reach high levels body-wide, potentially leading to laminitis, organ dysfunction, and even death.

Ferrer conducted a retrospective study to develop treatment recommendations for affected mares. She evaluated veterinary records of 45 mares that had been diagnosed with metritis within six days of foaling and treated with a variety of antimicrobial types. Treating veterinarians had confirmed on culture that 28 (62.2%) of the mares were infected with more than one bacterial species, with the most common one being Escherichia coli (30.7%).

Ferrer said 65.5% of mares were infected with both Gram-negative and Gram-positive bacteria, which have structural or functional differences that make some drugs more effective against them than others. For this reason she recommended choosing a broad-spectrum antibiotic that acts on both types when making treatment decisions for these mares.

Ferrer said 59.8% of the bacteria were multidrug resistant (MDR), with Gram-negative bacteria having especially high MDR (85.4%).

Based on these findings, Ferrer recommended treating postpartum metritis in mares with a combination of penicillin and amikacin or enrofloxacin. Nonantimicrobial treatment steps might include flushing the uterus daily (uterine lavage), administering the hormone oxytocin, giving non-steroidal anti-inflammatory drugs as needed, and adding domperidone to stimulate lactation if necessary.

Ferrer noted that seven mares had been treated for placentitis (inflammation of the placenta) during gestation, which resulted in antibiotic resistance, making metritis treatment particularly challenging. “One third of the study mares had a history of placentitis,” she said. “This says to us that we need to check in on these mares after foaling.”

Ferrer said the main goals to in keep in mind when treating postpartum metritis in mares are to control bacterial growth, evacuate uterine contents, and prevent complications.

“Uterine culture should be incorporated into routine metritis management because it’s important for monitoring MDR and guiding antimicrobial choice,” she concluded.