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Dealing with endometritis

Sally Scholle
This mare's history of a vulval tear places her at higher risk for endometritis. Photo by Sally Scholle.

You’ve chosen the perfect stallion, checked his history and your mare’s genetic tests are clear. The calendar is set for tracking heat cycles and your plan is sound. What could go wrong?
One relatively common issue that wreaks havoc in breeding mares is equine endometritis – an infection of the uterus that’s usually caused by bacteria such as Streptococcus, Actinomyces, Staphylococcus or Pseudomonas.

Veterinarian Rick Leone, equine reproductive specialist at Peak View Animal Hospital in Fowler, Colorado, explains that endometritis can also be due to fungal infection or an inflammatory process. “If the cervix isn’t closed, any urine or air that’s enclosed in the vaginal vault gains access to the uterus,” he said. “Loss of cervical integrity can lead to mechanical endometritis.”

Leone says endometritis is relatively common in horses, accounts for 60 to 70 percent of mares that fail to become pregnant, and can be difficult to treat. The most likely candidates for the problem are mares older than 10 to 12 years, mares in poor body condition, mares with a tipped vulva and mares with a history of having an extremely large foal that resulted in cervical damage. Mares that have had a minor tear of the vulva or vagina at foaling are also at much higher risk, and multiparous mares become more prone to endometritis.

“Wet mares, because they typically carry less body condition, are more prone to tipping of the vulva because their body condition causes the vulva to tip forward,” Leone explained. “If that happens, urine or feces can enter the cervical canal and lead to infection.”

While older mares are the most likely candidates for this reproductive challenge, Leone has seen relatively young maiden mares with raging endometritis. “Younger mares normally have a healthy uterine environment,” he said, “but it can occur at any age. If you’ve bred your mare, live cover or A.I., and she goes beyond two cycles following breeding, we consider that abnormal.”

Although it’s uncommon, mares that have never been exposed to a stallion or A.I. can be diagnosed with endometritis. “It can even occur in young mares with a completely normal cervix,” said Leone. “In many cases, such mares are treated, become pregnant and never have problems again.”

A placenta that doesn’t pass for more than one to two hours postpartum is a problem and can start to damage the uterine environment, so ensuring the complete passage of an intact placenta following birth is critical.

Mares typically have a fertility rate of about 70 percent per cycle, so it isn’t uncommon for a mare to require repeat service. However, Leone recommends a complete workup if a mare remains open after two failed breedings. “The workup includes a culture and a biopsy so we know what her uterine lining is like and if any infectious agent is present,” he said. “When mares’ uteruses are biopsied, the biopsy is sent to Colorado State University and scored 1A, 1B, 2A, 2B, 3A or 3B. 1A is ideal, and 3B is very altered and unhealthy. Fertility rates decrease with poor uterine biopsy scores, and the culture can reflect the presence of fungal agents that indicate bacteria.”

Leone explains that at the time of the culture, the veterinarian visually and manually assesses the health of the cervix. While damage to the cervix is often the result of a difficult foaling, mares without that history may have damage that prevents the cervix from closing tightly between cycles.

“If there’s a compromised cervix, we need to be aware of that,” said Leone. “We may treat systemically with antibiotics (injectable or oral), infuse the uterus with antibiotics, or use steroids or a combination of all of those treatment options to reduce inflammation and/or infection in the uterus and give the mare the best chance to maintain and carry a pregnancy once she’s bred.”

Mare owners can watch for the early clinical signs of endometritis. The first, and most obvious sign is short cycling intervals. Mares normally ovulate every 21 days and come into heat every 15 to 16 days, but if a mare comes into heat every 10 to 14 days, Leone suspects endometritis. Evidence of vulvar drainage beyond the normal few days of drainage during ovulation is also considered abnormal.

Mares with either endometritis or endometriosis typically have lower conception rates. Those that do become pregnant, which can be determined at 10 to 12 days via ultrasound, are more likely to lose the pregnancy within the first week. “They may re-cycle, and we can treat mares during the cycle they’re being bred,” said Leone. “We can even treat mares for infection a few days after breeding while we’re trying to improve the uterine environment for the embryo that’s going to come down into the uterus around day six to seven after fertilization.”

Leone says in the thoroughbred industry, which requires live cover, breeders dealing with endometritis will lavage the uterus to remove any excess fluid within a few hours after breeding. Because semen moves to and remains in the oviduct within two hours post-breeding, this measure won’t interfere with conception. The uterus can be lavaged for several days afterwards to improve the chances of a good uterine environment and successful embryo implantation.

Any mare being considered for purchase should be suspected of having endometritis if she does not have a foal at her side or isn’t confirmed pregnant.

“Be highly skeptical of any dry mare you buy,” said Leone. “If it’s a four-year old mare coming out of a performance career, that’s different. But a mare that’s been used for breeding and is not pregnant is suspect.”

Leone says a routine workup prior to the breeding season is well worth the investment. The workup includes ultrasound to check for abnormal fluid and status of the ovaries. “If the mare has no previous history of failing to get pregnant, we’ll frequently breed them one or two cycles without the expense of a workup,” said Leone. “But if there’s any concern about the mare’s ability to become pregnant, whether she had a difficult foaling, has repeated opportunity to become pregnant but hasn’t produced a foal, if she has aborted, or if she’s at risk due to conformation, we recommend a workup.”

While a pre-breeding workup costs several hundred dollars, Leone says it’s a small price to pay considering the cost of shipping semen and multiple breeding attempts.

“Endometritis is a common problem, and the risk of a mare developing it increases with age, but it’s treatable,” said Leone. “It will add expense, and the number of times you have to expose your mare to semen will go up. I tell people it’ll double breeding expenses, and they’ll have treatment expenses. If in doubt, get the workup done.”


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