Diagnostic tools help to monitor health of pregnancy and anticipated foal

by Robin Stanback

A great deal of time, effort, and research goes into the successful mating of a stallion and a broodmare. While many breeders heave a huge sigh of relief when a mare is pronounced in foal, their job of producing a viable offspring is far from over. Besides the need for proper nutrition regimens, inoculations, and general health care, mares need to be monitored for a variety of potentially life-threatening problems that, if recognized and addressed quickly, can often be corrected.

Amniocentesis, widely used in human medicine to study fluids withdrawn by needle from the mother's womb, is not a process that can be safely used for broodmares. Michelle LeBlanc, D.V.M., a board-certified theriogenologist (reproductive specialist) at Rood & Riddle Equine Hospital in Lexington, explained. "In the human, it is possible to use ultrasound technology to study the entire uterus [and] see the placenta and the fetus," she said. "This enables doctors to find the right spot for a needle aspiration of fluids. In horses, there is just so much more tissue for the ultrasound to probe that it is impossible to see the entire uterus. There are areas within it that cannot safely be penetrated."

Theriogenologists most frequently study the health of an equine pregnancy using tools that include a combination of transrectal ultrasonography, transabdominal ultrasonography, and assays of serum progesterone concentrations.

Ultrasonography has come a long way in the past 30 years--from grainy pictures that barely provided a glimpse of a pregnancy to images that are clear enough to determine the gender of a fetus. It is this technology that makes the first problem facing an equine pregnancy considerably easier to correct.

Twinning

The number one cause of non-infectious abortion in mares used to be twin pregnancy. The use of ultrasound technology to identify a twin pregnancy and eliminate one of the twins has changed that statistic. Karen Wolfsdorf, D.V.M., a board-certified theriogenologist at Hagyard Equine Medical Institute's McGee Fertility Center in Lexington, said it is wise to begin ultrasounding a mare at 13 to 15 days after ovulation to check for pregnancy and to determine if the mare is carrying twins.

"If so, it is usually possible to pinch one of the embryos while leaving the other unharmed," she said. "Then you should monitor again two to three days post reduction [after one embryo has been eliminated] to be certain that the remaining embryo is still viable. Waiting past the second week of pregnancy to try to eliminate one of the twins can be a challenge. After day 35, if a mare aborts [naturally or in an attempt to eliminate one] she will have already developed endometrial cups and will not cycle again for 120 to 150 days. In most cases, this means the loss of the entire breeding season."

The veterinarians at the McGee Fertility Center recently have used ultrasound technology to develop a new procedure that helps salvage pregnancies in mares that are presented to the clinic at 60 to 100 days gestation and carrying twins.

"During the past three breeding seasons, we have developed a method of cranio-cervical dislocation that allows us to destroy one of the fetuses before the placenta has fully formed," Wolfsdorf said. "The result has been a 60% success rate in mares delivering normal, healthy-sized foals."

Placentitis

Placentitis, an infection of the placenta responsible for up to 80% of equine abortions or premature deliveries, causes the placenta to become insufficiently attached to the uterus to supply the fetus with its necessary nutrition and oxygen. This leads to the death and subsequent abortion of the fetus or, if the fetus survives, to the premature or full-term delivery of a live but weak foal.

"Unlike women, premature birth in horses usually results in the delivery of a nonviable foal because final fetal maturation in the horse occurs only during the last five to seven days of development in utero," LeBlanc said.

Many bacteria and some fungi can cause placentitis. Most commonly, the condition is triggered by an infection that enters through the cervix while the mare is pregnant. Another cause is a blood-borne infection that lodges in the placenta. This type of placentitis is very difficult to predict or to understand, and even more difficult to prevent.

Most horse owners first discover the problem when a broodmare prematurely begins making a milk bag or when vaginal discharge is apparent. At this point, most experts agree it already may be too late to achieve a positive outcome, but a veterinarian should be called in to assess what can be done.

If the placenta is infected but premature labor can be delayed, the fetus may respond by maturing more quickly so that its organs can cope with the challenge. Consequently, suppressing labor with the use of drugs could significantly improve the survival of the fetus, but its health must be monitored carefully to assure it remains viable and to make certain the mare does not retain a dead fetus.

Ultrasound technology can be used to monitor the health of the placenta, but many veterinarians use a multifaceted approach. Mats Troedsson, D.V.M., Ph.D., professor and chief of the theriogenology section at the University of Florida, said: "There is no definitive, stand-alone diagnostic for equine placentitis. Ultrasonography is one of the tools that we have, and even small changes can often be detected. The problem is more related to interpretation of what we see.

"While some mares with placentitis don't show much increased thickness of the placenta or placental separation, there are other mares that have ultrasonographic changes, but these changes may be normal during a follow-up examination. We definitely need more research in this area.

"From a practical standpoint, we try to gain as much clinical information as possible when we examine mares with suspected placentitis. That is the reason we use a combination of transrectal ultrasonography, transabdominal ultrasonography, and serum progesterone concentrations."

The equine placenta appears not to synthesize progesterone, but it does secrete progestins, which serve the same function for maintenance of pregnancy. Toward the end of gestation, blood levels of these progestins are typically 100 times the maximal level of progesterone. Monitoring these blood levels is one way to determine the health of the pregnancy.

"When a fetus is in distress, total estrogens drop and progestins rise," said Robert Douglas, Ph.D., of BET Labs in Lexington, who performs amino assays on blood samples drawn from broodmares that are referred to him.

"We have a scale we use to help determine the health of the placenta," he said. "When the progestins sit at a range between four and 15 and remain steady at that level, we feel comfortable that the fetus is in good shape. If that level changes, if the initial blood test we run indicates progestin levels over 15 or under four, then we know we have a problem. We use that information to help us determine the hormonal therapy we are going to use."

LeBlanc agreed with the use of the scale, though her scale runs between two and 15. "If we determine that the blood levels we have drawn indicate a possible problem, we will come back and do repeat blood tests two to four days apart," she said.

Differing opinions

One place the experts differ is their response to the results of blood tests:

•Troedsson routinely treats mares with placentitis with a combination of antibiotics, altrenogest (Regu-Mate), and anti-inflammatory drugs;

•LeBlanc favors a conservative treatment that utilizes Regu-Mate to block inflammation. She is not opposed to the use of antibiotics, but she prefers to move very cautiously to introduce them to avoid other complications such as diarrhea; and

•Douglas said he has had success using broad-spectrum antibiotics in conjunction with hormone therapy.

While Douglas recommends running routine blood tests, and does so for his clients who have very valuable broodmares, the average horse owner typically relies on keen observation of vaginal discharge or any changes in the udder.

"First, it's important to remember that although placentitis is a significant problem in horses, only 3% to 5% of all broodmares will be affected by this disease," Troedsson said. "As far as time intervals between examinations, sampling of blood, we don't know how often we need to monitor mares to detect early signs that respond to treatment. It's not possible to say if once per week, once every second week, or once every month is an optimal interval between treatments. My clinical recommendation has often been to examine mares that are at risk once per month, and increase the frequency of examinations if signs that support an ongoing placentitis are detected. Dr. Walter Zent at McGee Fertility Center has used transrectal ultrasonography once per month with encouraging results in mares with placentitis [about 80% live foals]."

Other abortion causes

While twin pregnancies and placentitis are frequent causes of abortions in broodmares in the United States, they are not the only causes. According to Troedsson, the most common cause of fetal deaths and abortion in the United Kingdom is long, twisted umbilical cords.

"We had the first reported cases of late-term abortion from MRLS [mare reproductive loss syndrome] in Florida last spring," Troedsson said, "and there are idiopathic fetal deaths, hydrops [fluid accumulation in the fetus], and pregnancy losses secondary to systemic diseases such as colic."

In almost every case, the horse owner's first line of defense is an observant eye, LeBlanc said.

"Any sign of premature edema in the mare's udder, swelling in the underbelly, or discharge from the vagina are reasons for calling in a veterinarian," she said. "If the mare has had a history of placentitis or is overly stressed, it might be wise to monitor her more closely. Early detection, while sometimes difficult, is most important."