"Apart from the genetic makeup, the most important determinant of how a neonatal foal does is the placental integrity," said Peter R. Morresey, BVSc, Dipl. ACT, of the University of Pennsylvania's New Bolton Center, at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004. He explained that examination of the placenta can yield important information relating to the reproductive health of the mare and the medical prognosis of the foal. That information can lead to better or more complete referral information if either mare or foal is admitted to an equine hospital.

"It is said that what does not kill you makes you stronger, but I do not agree," he added. "The fetal inflammatory response leads to death, premature delivery, and disease."

The Client's Role in Placental Evaluation

The examination of a well-preserved placenta adds value to a post-partum checkup. "What clients can do to help us is the timeliness of placental examination," he added. "There is little you can draw from a placenta that has been exhumed from beneath an azalea bush after three days."

The client should store the placenta in a waterproof container, so if the placenta is grossly edematous (fluid-filled), the veterinarian will be able to get an accurate reading for the weight of the placenta. A falsely normal reading could impact the prescribed care for the foal.

Additionally, the client should make sure the placenta is stored in an animal-proof place. "I've had more than one placental evaluation that could not be completed due to the canine (mouth)," he added with a chuckle.

Examining the Placenta

Morresey said that veterinarians should develop a systematic, repeatable, and relevant examination. Additionally, he encouraged veterinarians to develop a form on a single side of one sheet of paper--the simpler it is, the more likely it is to be completed. He said to include the following information on the form:

  • Date
  • Client information
  • Dam information
    • Signalment of dam
    • Parity (foaling history)
  • Parturition information
  • Foal information
    • Signalment
    • Gestational age
    • Weight
    • Status - alive or dead
    • Any comments
  • Placental information
    • Time to expulsion (how much time between parturition and placental expulsion)
    • Measurements--weight, length (especially of the umbilical cord)
  • Diagram of a placenta so you can mark the problem or missing areas

Normal parameters should be listed on the form to enable rapid identification of abnormal values.  Additionally, if samples are to be sent for laboratory examination, note this on the form as well.

Then Morresey listed some tips for performing a placental examination.

"The placenta is usually passed with the inside surface (the one touching the foal) on the outside. My preferred technique is to expose the chorionic surface (red velvety layer that contacted the endometrium) and lay this out in a capital F formation on a clean, flat surface," he said. He examines the parts of the placenta in this order:

  • Allantochorion: the part of the placenta that contacts the endometrium of the mare. It's formed by the fusion of the allantois, a sac-like outgrowth of the hindgut, and the chorion, derived from the outermost cell layer or the early conceptus;
  • Allantoamnion: This fusion of the allantois and the amnion is formed from the early embryo;
  • Umbilical cord; and
  • Placental weight.

It is vitally important to assess the pregnant and especially non-pregnant uterine horn for completion. For comparison, lay the pregnant and non-pregnant horns beside one another. The pregnant horn should be larger, more thickly walled, and more edematous (fluid-filled) than the non-pregnant horn.

There may be some areas that appear bald, that is, there are no signs of the red velvety surface that allows attachment of the placenta to the mare. Some of these are of no concern; sites where the endometrial cups have been sloughed, areas along the remnants of the cervical star, and longitudinal folds at the site of umbilical cord attachment and the very end of the horn tips regularly appear this way. Other areas, however, are of concern and should be noted. In addition, "You should never see an intact cervical star," he explained, only white remnants. An intact cervical star is an indication of abnormal foal delivery and possible placentitis.

Both surfaces of the placenta must be examined, and Morresey prefers to weigh the placenta at the end of the exam using a fishing scale.

"Sample both horns, the body and the area of the cervical scar. Make sure you get some of the amnion and a piece of the umbilical cord, and get normal and abnormal pieces for comparison," he said. Information on the cost of this process is included below. Use a pencil on the identification tags, because the pen ink will bleed and run in the formalin preservative.

Associated Costs:

  • Scale and measuring tape=$10
  • Bags, containers, formalin, scalpel, and tags that can go in formalin (see purchasing information for these tags below)=$5
  • Sample testing=$50 (or more, depending on what is done).

He adds, "Gaining information on the future reproductive potential of the mare and medical management of the foal--priceless."

Suitable tags for tissue submitted to the laboratory will be available from many sources. Morresey listed the following vendor:

Howard Enterprises
147 N Cameron Street
Harrisburg, PA 17101

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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