Published December, 2009

Placentitis, which often is caused by an ascending infection that enters the mare's uterus through the cervix, is the single most important cause of premature delivery of a foal. Placentitis accounts for nearly one-third of late-term abortions and fetal mortality in the first day of life. During the past six years, the University of Kentucky (UK) Livestock Disease Diagnostic Center has diagnosed 1,429 cases of placentitis.

Mats Troedsson, DVM, Dipl. ACT, is the chair of UK's Department of Veterinary Science and director of the Gluck Equine Research Center. Troedsson served as professor and service chief in theriogenology and director of equine research programs at the University of Florida's College of Veterinary Medicine before coming to the Gluck Equine Research Center in 2008.

In the early 1990s, Troedsson began using ultrasound to examine placentas in clinical cases. That led to a study establishing normal values for transrectal ultrasound examination of the combined thickness of the uterus and placenta. During the last 10 years, Troedsson's research has had a different focus, and his contribution has been limited to evaluating the efficacy of different treatment regimens for placentitis and case reports of clinical cases in collaboration with Margo Macpherson, DVM, MS, Dipl. ACT, associate professor of theriogenology in Large Animal Clinical Sciences at the University of Florida. .

Because there are still many unanswered questions about an accurate diagnostics, prognostics, monitoring of fetal well-being, and treatment in high-risk pregnancies, Troedsson plans to revisit this research topic with the reproduction group at the Gluck Center.

Efficient diagnosis relies upon cautious monitoring of mares in late stages of pregnancy. However, available treatment approaches are far from perfect and treatment outcome is hard to predict. Early intervention in treatment of placental infections is likely the key to treatment success.

In some chronic cases of placentitis accelerated fetal maturation will commence. Mares will deliver these foals prematurely, but the foal will not be mature enough to survive outside the uterus after birth. Delaying premature labor long enough to allow accelerated fetal maturation to proceed full development may improve the chance of foal survival.

The most common clinical signs of placentitis in mares are premature udder development and vulvar discharge. Ultrasonography is an excellent tool for monitoring fetal and placental changes in mares affected by placentitis. But since serial ultrasonographic evaluations are not commonly employed in late-gestation mares, a veterinarian can miss diagnosis in subclinically affected mares. Subclinical disease might also result in subtle ultrasonographic changes that are not easily distinguished from normal findings. However, in spite of these hurdles, transrectal ultrasonography remains one of the best tools available for diagnosing equine placental infections.

Another type of ultrasonography, transabdominal, can be a useful tool for placental evaluation in mares with suspected placentitis. Using transabdominal ultrasonography, the clinician cannot image the caudal portion of the allantochorion (the part of the placenta that is attached to the back of the uterus close to the cervix), which prevents diagnosis of ascending placentitis in its early stages. However, placental thickening and partial separation of the placenta from the uterus using transabdominal ultrasonography in mares with placentitis originating from a hematogenous infection (infection spread to the uterus via the mare's blood).

Treatment strategies for mares with ascending placentitis are currently vague. Many treatment regimens have been extrapolated from research in other species, such as humans. Treatment efforts are directed at several targets including combating infection, reducing inflammation, and controlling uterine contractions.

According to Troedsson, the outcome of any treatment was previously found to be poor.

"We found that treatment of subclinical cases diagnosed by ultrasonography resulted in quite acceptable and much improved outcome of affected pregnancies," he said.

Common treatment for placentitis is broad-spectrum antibiotics, Regu-Mate (double dose) and pentoxifylline for the remainder of the pregnancy, and a non-steroidal anti-inflammatory agent. This treatment, however, is not 100% effective and often results in the birth of an underdeveloped and compromised foal.

"But while success is hard to achieve when treating placentitis in mares, having a live foal that has been delivered successfully and is healthy is a great reward," Troedsson said.

Alexandra Harper is a UK equine intern and undergraduate majoring in communications.