Equine Placenta Workshop: Placentitis

Mats Troedsson, DVM, Dipl. ACT, University of Florida (with co-author Walter Zent, DVM, of Lexington, Ky.), discussed clinical ultrasound in evaluation of the equine placenta to identify and treat mares with placentitis. He said placentitis is a common cause of abortion in the United States. Most cases are believed to be the result of an ascending infection (starting at the cervix) during late gestation.

UK College of Agriculture photo
Mats Troedsson, DVM, Dipl. ACT describes clinical ultrasound in evaluation of the equine placenta to identify and treat mares with placentitis. 

There are characteristic lesions, with a thickened area usually starting around cervical star and spreading up into the placenta. Clinical signs include vaginal discharge and premature lactation, but he said by the times these signs are evident, it might be too late to treat the mare and save the pregnancy.

The hypothesis he and Zent started with is that early detection of subclinical cases of placentitis will improve the efficacy of treatment.

Their first objective was to develop a method to diagnose subclinical placentits. Using transrectal ultrasound, a veterinarian can place the probe cranial and lateral of the cervix. They look at the combined thickness of the uterus and placenta (CTUP) and look for placental separation.

Zent and Troedsson took group of normal Thoroughbred mares and measured CTUP from four months of gestation up to term. This established normal values with which to compare mares that might be at risk. Troedsson said there is not much change until after 270 days, then he saw predictable increases in thickness.

The normal values they established: Day 270 of gestation or less, the CTUP should be less than 7mm thick; Day 270-300, less than 8mm; Day 301-330 less than 10 mm; Day 331 less than 12 mm.

In a field study of 33 pregnant Thoroughbred mares considered at risk to abort, they used transrectal ultrasound monthly from Day 150 to term. The CTUP measurements were recorded. They found that none of the 30 mares which carried foals without problems had significant deviation from the norms established. However, two mares aborted early, and both mares had significantly higher thicknesses of CTUP on the last recording prior to abortion. When the last mare showed increased thickness, she was immediately put on treatment. In spite of that thickening, she showed no clinical signs. Troedsson said they never got CTUP thickness down to normal, but the mare stabilized (the thickness did not increase) and she carried foal to term and delivered normal foal. Placentitis was confirmed on histology after the mare foaled.

He said transrectal ultrasound is a valuable diagnostic tool in detecting early cases of ascending placentitis. This has been confirmed by studies using an experimental model of placentitis developed by Michelle LeBlanc, DVM, Dipl. ACT.

Complete evaluation of the placenta requires transabdomal ultrasound, noted Troedsson. This is important when Nocardiaform placenittis (starting at an area other than the cervix) or hematogenous placentitis (blood-borne) is suspected.

Placentitis Treatment

Systemic antibiotics should be used because most placentitis cases are caused by bacteria, although some are fungal. Troedsson questions whether if the inflammation can be halted, but the placenta CTUP doesn't decrease, is the placenta compromised and thus the foal compromised?

Because of that question, the second objective of their research looked at determining if transrectal ultrasound of the placenta can be used to identify and follow the successfull treatment of mares with placentitis.

They did a retrospective study of records from a Thoroughbred farm in Central Kentucky where they followed 477 pregnant mares from 1977-2003. They monitored for CTUP and placental separation once per month from 150 days of gestation to term. Criterias for treatment were: An increase in CTUP, placental separation, or clinical signs (vaginal discharge and udder development). Treatment included antibiotics, (trimethprim-sulfa, ceftiofur, or penicillin and gentamicin), pentxifylline, altrenogest, and NSAIDs. Treatments continued until the mare aborted or foaled.

Birth weight was compared between foals from mares with placentitis and mares without clinical or subclinical signs. The results were statistically significant.

Troedsson said 3.1% of the mares were diagnosed and treated for placentitis. The average gestational age was 8.6 months when they were diagnosed. Abortion in mares ranged from seven to nine months.
He said 15.8% of the treated mares aborted, and that 87% of the maintained pregnancies resulted in live foals. Final results showed that 73.3% of mares diagnosed with placentitis produced live foals. Pregnancy loss in treated mares occur on an average 62 days after onset of treatment, ranging from seven to 90 days. The birth weight of surviving foals from mares treated for placentitis was not different from foals born to non-affected mares.

Of mares with placentitis with dead/non-surviving foals, the birth weights were significantly lower.

Troedsson said their conclusions were that transrectal ultrasound is useful in detecting early signs of placentitis. A majority of mares treated for subclinical or early clinical signs of  placentitis produced viable foals. Birth weights of surviving foals from treated mares wasn't lower.

They questioned how long to treat a mare with placentitis. Troedsson said mares diagnosed with placentitis were treated for the remainder of pregnancy. He said a study in 2003 showed that mares with experimentally induced placentitis were treated only seven days, and all aborted. At this time, data suggest to treat until the mare aborts or foals, but more research is needed to determine an optimal duration of treatment.



About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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