retained fetal membranes in mares

Most mares naturally and uneventfully pass their fetal membranes (the placenta) shortly after foaling. If the tissues don’t pass within three hours, however, they’re considered “retained.” These retained fetal membranes in mares can cause serious side effects such as metritis (inflammation of the uterine wall), sepsis (infection), and laminitis.

Veterinarians use a variety of techniques to remove retained membranes in mares; one that can be controversial is manual removal. Chelsie Burden, DVM, Dipl. ACT, of Goulburn Valley Equine Hospital, in Victoria, Australia, described how to perform this procedure safely and the pros and cons of its use during the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

“Retained fetal membranes (RFMs) represent one of the more common postpartum problems in mares,” she said. “While the overall incidence is low (2-10.6%), the consequences, if left unattended, can be severe.”

Existing treatments for retained fetal membranes in mares include:

  • Administering oxytocin, which is a hormone that causes uterine contractions (an inexpensive and effective first line of treatment, said Burden);
  • Performing uterine lavage to promote uterine clearance;
  • Passing a catheter through the umbilical cord to achieve vascular distension; and
  • Removing the membranes manually.

Although veterinarians have used the manual technique for years, said Burden, it can be tricky to perform; therein lies the controversy.

She said the benefits of manual membrane removal include:

  • Rapid and efficient removal—“It only takes 5 minutes of your time,” said Burden, whereas other techniques can take 20 to 30 minutes;
  • The ability to assess the membranes immediately for disease or damage and treat the mare and foal as needed to avoid septic or dummy foals (aka those suffering from neonatal maladjustment syndrome—exhibiting behavioral or neurologic abnormalities unrelated to infectious or toxic conditions, congenital or developmental abnormalities, or metabolic disorders); and
  • Less risk of complications associated with RFM.

Possible consequences include:

  • An increased risk of postpartum hemorrhage after membrane separation from the endometrium (“If this starts to happen, stop,” said Burden.);
  • Membrane tearing;
  • Retained microvilli (the tiny fingerlike projections that help connect the uterus and placenta), which can lead to metritis; and
  • Uterine horn intussusception (in which the horn telescopes into itself).

To evaluate this procedure’s safety and efficacy, Burden and her colleagues performed a study on 18 pregnant mares, 12 of which had induced placentitis (inflammation of the placenta, which can put mares at risk of complications such as RFM). Shortly after foaling, she performed manual membrane removal on the 12 of those mares that had not passed their placentas spontaneously. She did so with mares either standing or in sternal recumbency (lying on their side). Burden said she prefers the latter technique because she doesn’t have to deal with the placenta’s weight while performing the procedure.

Burden removed nine of the 12 (75%) retained fetal membranes in mares without complications. The three mares that did have side effects experienced uterine horn eversion or prolapse (when a portion of the uterus protrudes through the cervix).

Four of the five mares (80%) that expelled their placentas naturally suffered complications. Burden noted, however, that most of these mares had placentitis and abnormally heavy fetal membranes.

“Controlled manual removal of fetal membranes allowed for rapid membrane removal with relatively low risk to both normal foaling and high-risk mares in this study,” she said. “Controlled fetal membrane removal is a practical, efficient tool that, when performed correctly, can improve the health of postpartum mares.”

Veterinarians should base their decision to use this technique on the mare and foal’s health, delivery location, degree of retention, and other circumstances surrounding the birth, said Burden. If there’s bleeding or no progress being made during the procedure, stop and pursue other options.