A two-day exclusive gathering of the leading reproductive researchers and practitioners from around the world convened at the Gluck Equine Research Center in Lexington, Ky., Dec. 5-6, to discuss the equine placenta. From the evolutionary development of the placental layers to Mare Reproductive Loss Syndrome, no topic was left untouched if it dealt with the fine, and sometimes little understood, relationship between mare and fetus.
In 1950s, the researchers said, it was thought the fetus was a passive passenger. In 1960s, it became known that the fetus an active participant in the gestational process, and that the fetus plays an active role in parturition. The equine fetus has an active endocrine system prior to birth, and even as early Day 35 conceptuses they have enough organogenesis (development of their own organs) to be active.
How active the conceptus can be and how early that interaction begins to happen isn't fully understood. It is known that relatively minor environmental changes can have a profound effect on conceptus outcome, especially early in gestation. In fact, in other species it has been shown that nutritional status of the mare prior to conception can have an effect on the birth weight of the upcoming offspring and affect gestational length.
While the pathologists, scientists, and practitioners acknowledged a need to better communicate their understanding of the mare/fetus bond, the question also was raised by the practitioners: For our clients, how do we diagnose placental problems and economically do something about them?
First, it is worth noting that the relative importance of causes for pregnancy loss is changing. Twinning used to be the number one problem, but better management of twin pregnancy has reduced that importance. Now, placentitis ranks at the top of the list. There was much discussion of infections that invades the uterus through the cervix (ascending placentitis), and the placental infections that seem to originate in the middle of the uterus (nocardioform placentitis). In many cases, nocardioform placentitis is difficult to diagnose and treat. But both may be associated with fetal loss.
One problem mentioned was the normal opening and closing of the cervix during pregnancy. Another problem discussed was stress and its effect on premature foaling. For example, Thoroughbred mares that go through November and January breeding stock sales, then foal earlier than their due dates. For that topic, researchers in other species and equine researchers suggested that high doses of progesterone in the face of that type of stress might benefit those mares in "holding" their pregnancies to term.
Other problems included the over-long umbilical cord that causes death of foals. In the United Kingdom, it is the leading cause of non-disease-related fetal death. While human umbilical cords also are long, they are designed to have a certain amount of twist to their nature (like a telephone cord). While it is normal for the umbilical cord of equine fetuses to twist, the longer cords can make the fetus more prone to death or compromise due to twists cutting off transportation of nutrients and wastes. An equine umbilical cord over 80 cm is considered long.
Another topic that was new to many of those in the room was the remnant of the yolk sack that can mineralize/ossify in the umbilical cord and potentially cause problems. More specific articles from this placenta conference can be found on-line at www.TheHorse.com.