When a pregnant mare develops a problem that puts her fetus at risk, what can be done? Some of these foals can be saved if the problem can be discovered early and the mare given proper treatment to reverse the condition.
Jon Palmer, VMD, associate professor of medicine and director of the neonatal and perinatal programs at the Connelly Intensive Care Unit at New Bolton Center (part of the University of Pennsylvania), deals with many pregnant mares and their problems. "When we talk about high-risk pregnancies, there are two general classifications of mares," he says. "One group includes mares that are having problems during their current gestations that may compromise the pregnancy--such as a mare with colic or laminitis or something else that interferes with her health and may have an impact on the foal. This group includes mares that may have a placental inflammation or evidence of premature placental separation.
"The other group are mares that had problems in the past," Palmer adds. "Perhaps in their last few gestations they had foals born with problems, or foals that had problems with placental function near the end of gestation. Those mares are at higher risk of having this again."
The primary cause for premature labor in the mare is placental disease, and the most common placental disease is infection. Even in human medicine, prematurity in babies is most often caused by placental problems. Whenever there is placentitis (inflammation of the placenta), there is a much higher risk of having the foal delivered early, Palmer says. This occurs most often in older mares; they tend to have more instances of vaginal infection from a tipped vulva. Sometimes there are other problems with older mares--their uteri might have more scarring and the placentas have poor attachment and are not functioning well.
Elizabeth Santschi, DVM, Dipl. ACVS, a veterinary surgeon at the University of Wisconsin-Madison School of Veterinary Medicine, says that infection of the placenta is usually ascending (coming from the vagina and cervix), but not always. "It may be a silent infection elsewhere in the uterus that is present at breeding and later becomes a problem," she says.
"A mare in the last month of gestation may have a fairly loose cervix, but this usually doesn't mean anything," she adds. "In certain susceptible mares, however (for reasons we might not know), this can cause problems. The loosening cervix can allow bacteria to enter and the mare gets an infection in the rear portion of the placenta." This in itself might not cause trouble, unless the infection extends forward on the placenta, says Santschi.
Some mares might deliver early if they undergo surgery during late gestation. "Some people feel that surgery in itself will compromise the pregnancy--that the anesthesia, or having the mare on her back (which we often do for surgery)--can cause the cervix to open and result in ascending placentitis," she says. "I haven't observed this myself, but it could happen. This is one reason we try to delay any surgery until after she has foaled--if it can be delayed. Surgery in the middle of gestation usually doesn't bother the fetus. It does most of its growing in the last two months."
There are also some mares which seem to foal early every year. "Whether this is because the foal outgrows the size of the uterus or whether the endometrium is damaged (the foal gets to the point it is not getting enough nutrients for proper growth and initiates parturition), we are not always sure," Santschi explains. "A fair number of mares foal early, but we never know why."
Signs of Trouble
A mare which develops an udder sooner than she should, or begins to drip milk, is getting signals from her body that the foal is ready to be delivered, even if it is premature. "This gives us an indication that something is wrong, such as impending abortion or premature birth," says Palmer. "Udder changes in the mare are often the best indication that something is wrong. Occasionally there will also be a discharge from the vulva, but you may or may not see it. If a mare shows udder development or vaginal discharge, she should be examined by a veterinarian."
Michelle LeBlanc, DVM, Dipl. ACT, of Rood and Riddle Equine Hospital in Lexington, Ky., says part of the challenge in identifying mares with compromised pregnancy is that only about 70% of them show clinical signs. The mare might lose the foal before you even realize she was in trouble.
She says it is extremely important to identify these mares early, if possible, and halt the inflammatory process before it gets too far along. Monitoring pregnant mares closely is crucial, since you might only see very subtle signs that anything might be wrong. LeBlanc says if you suspect a problem, your veterinarian can examine the mare, measure her progestins (any of several steroid hormones that prepare the uterus for egg implantation and pregnancy), and do other diagnostic tests to see if something serious is going on. Always keep a close eye on mares which had problems in earlier pregnancies. They are much more apt to have problems again.
"Mares that have twins may bag up and make an udder early, but rarely have a discharge," says LeBlanc. "In those cases, I would check for twins (trans-abdominal scan with ultrasound), and if so, I would let those mares abort, or abort them with drugs (see "Twins" on page 66)."
"If a mare has udder development and/or vaginal discharge before nine months, my suggestion is to treat her, but be aware that the foal might have so much abnormality it will never be a performance horse," she says. It might be better to let nature take its course, and allow the mare to lose the pregnancy.
"The mare should have a vaginal exam to look at the cervix, and a culture of the fluids in the vagina to determine presence of bacterial or fungal infection," says LeBlanc.
An ultrasound of the uterus can often show if the foal is doing all right or not. A transrectal ultrasound, in which the probe is placed in the mare's rectum, can show the part of the uterus at the back of the abdomen, near the pelvis. This is the area most often affected with placentitis because most infections come up through the vaginal canal. Ultrasound can show if the placenta has separated or thickened and is not functioning well. It won't show the whole placenta, but it reveals a fair portion of it.
"We can also image the uterus by ultrasounding through the abdomen (trans-abdominal scan, through the belly of the abdomen)," says Palmer. "A late-term mare's uterus is lying on the floor of the abdomen."
Ultrasound in this area will show the foal's anatomy and whether he is the right size for the mare's stage of pregnancy. An ultrasound check can be reassuring if the foal looks normal, although sometimes it might look all right even if the foal has problems.
"If we detect serious abnormalities, however, we can try therapy, and also be ready when the mare gives birth, to assist the foal," he says. Ultrasound can reveal twins, which might have been missed when the mare was checked soon after breeding. If one twin is dying, it will put the other at risk.
The attending veterinarian must try to determine if the fetus is in trouble, looking for any changes that might reflect distress. "We put a telemetry monitor on all hospitalized high-risk pregnancy mares at night, and every couple of hours record the fetal heart rate," says Palmer. "Usually we see a reassuring heart rate pattern that suggests the foal is okay (although sometimes, he says, they are fooled). If we see a heart rate that suggests the foal is not okay, we try to do things to relieve the foals's distress--such as giving the mare IV fluids and more oxygen."
LeBlanc says that if a mare has become compromised before 310 days of gestation, a veterinarian might want to measure her progestins. "Progestins are hormones produced by the placenta throughout pregnancy, but by 310 days they are also produced by the fetal adrenal glands," LeBlanc explains. "After 310 days, the progestin levels go up in a normal pregnancy as an indication the foal is maturing."
If there is placental disease, however, the progestins might go up sooner than they should because of fetal stress, she adds.
Between 180 and 310 days, the level should remain steady. In cases of chronic stress, it can become very high.
"If it's acute stress the fetus can't handle (as when the mare has severe colic and is on the table for surgery, and the fetus is not getting enough oxygen under anesthesia), the progestins may drop very quickly," explains LeBlanc. "In this acute stress, the mare may abort."
Treating the Mare
The best thing to do for the fetal foal is treat the mare, rather than try to get the foal out early. "A foal in trouble in the uterus is more likely to survive than a foal in trouble in my intensive care unit," says Palmer. He tries to keep the foal in the uterus as long as it can possibly survive there. If it reaches a point where it looks like the foal will die, then they get him out quickly, but most often the best thing is to try to make the mare's uterus a better environment for the foal, rather than trying to reproduce those conditions in the neonatal ICU, which is very difficult.
When the problem is an infected placenta, there are several treatments veterinarians can use. "Some of these treatments are used by many veterinarians and some by only a few," says Palmer. "All of us, from our own experience, have a feeling of what works and what doesn't, but we don't have any scientific data to guide us. When there's placental infection, however, usually the mare is placed on antibiotics, because most often the infection is caused by bacteria," he says. The mare might also be given progestins (such as Regumate) and sometimes an antiprostaglandin (a non-steroidal anti-inflammatory drug such as flunixin meglumine, or Banamine).
"Some of the signals in the mare's body, telling her to make a bigger udder and that she's getting close to foaling, are mediated through prostaglandins, which Banamine blocks," Palmer says.
Santschi says that phenylbutazone (Bute) or Banamine might halt the udder development and have a quieting effect on the uterus--reducing its spastic contractions. When the uterus is inflamed, it wants to contract. "When it contracts, it compromises the blood flow and there is less blood supply to the foal," she said. "You want a relaxed and happy uterus."
She says Regumate and other synthetic progesterones also have a calming effect on the uterus. "The use of these is somewhat controversial, but I use them. Regumate is often used at twice the recommended dose for other purposes, because the higher dose has been shown to be more effective for this."
Palmer says he always uses three things in treating at-risk mares: Antibiotics, Regumate, and Banamine. "Beyond that, some veterinarians use other treatments, such as drugs that hopefully will increase blood flow to the uterus," he adds. "Some veterinarians also use vitamin E. This might help prevent some of the damage that could occur if the foal experiences a drop in oxygen."
Some people also use a rheologic agent (a drug that changes the deformability of red blood cells) with the idea that it allows the blood cells to get through vessels that are small or inflamed. If circulation to the placenta has been compromised, this might be one of the things your veterinarian might choose to use, says Santschi.
In many mares which start to lactate too soon (at 300 days or less of gestation), antibiotics are often enough to halt the milk production. This treatment might be enough to get the mare further along before foaling. If the mare has already leaked milk, however, she might have lost the antibodies in her colostrum, so the foal might need antibodies from another source at birth to prime his immune system.
A culture of fluids from the vagina and cervix can give the veterinarian a clue in choosing the proper antibiotic for treating a bacterial placentitis. "We are limited, however, in the kind of drugs we can use in the horse--either because of cost or because they may cause inappropriate reactions in horses," says Santschi. "Most of the time Streptococcus is the cause of ascending placentitis, so penicillin is the drug of choice. If the client can afford some IV doses, I put the mare on penicillin and gentamicin for a few days (these have a synergistic activity, being more effective together than by themselves). Then, since IV administration is quite expensive, we usually switch to intramuscular penicillin."
Palmer says, "The first key to helping any mare with a problem is to recognize that it is a high-risk pregnancy. The next key is to determine whether the foal is in distress, and the final key is to relieve that distress. There are a number of things that Mother Nature has built in to help the mare and foal avoid problems, but these only go so far." Sometimes, these veterinarians agree, we have to give Mother Nature a little help.
NEONATAL CARE: Helping the Foal
As a clinician, when Jon Palmer, VMD, associate professor of medicine and director of the neonatal and perinatal programs at the Connelly Intensive Care Unit at New Bolton Center (part of the University of Pennsylvania), looks at a mare with a problem, he tries not to see it in terms of how serious the mare's condition is, but rather at how the problem is affecting the fetus' life. "I ask myself if there are things I can do to relieve that stress on the fetus," he says.
For example, if a mare has colic and abdominal pain, she can't be fed (because of the gastrointestinal problem), yet this will be hard on the fetus, says Palmer. Any mare that is sick might stop eating. There are metabolic changes that occur in the mare when she goes off feed that will affect the fetus and might even tell it to come early. Putting the sick mare on intravenous solutions that include glucose (sugar) can make a difference to the fetus in terms of survival. "Despite the fact we can't feed the mare, we can still try to make sure the mare is able to feed the foal," he says.
If a mare has a placental problem that might interfere with blood or oxygen delivery to the foal (even though her own lungs and blood oxygen are normal), she can be put on oxygen. "It may not help the mare, but may enhance the amount of oxygen the foal gets via her bloodstream," says Palmer.
"The effect of oxygen is peculiar to the horse's placentation," he adds. "By increasing the mare's blood oxygen a little bit, we may help transfer a significant amount to the foal. This process is more efficient in the horse than in other species," he says. "The oxygen is administered to the mare with a simple cannula (small tube) in her nostril. As she breathes in, she takes in a higher percentage of oxygen than what is present in normal room air. Most mares don't like having a tube in their noses, but some tolerate it well." Palmer feels it makes a difference for the foal.--Heather Smith Thomas
Premature birth--the foal is born before term, but after the point of viability. With help, such as in a neonatal intensive care unit, he might survive.
Abortion--birth before viability; the fetus is not far enough along in its develop-
ment to survive outside the uterus.
Stillbirth--death before delivery; the foal is born dead.
THE COMPROMISED UTERUS: Inflammation Research
Managing inflammation in a pregnant mare's uterus is complicated business. "Preliminary data indicate that placental inflammation is an inflammatory event in which the mare produces pro-inflammatory cytokines. Those are substances produced by white blood cells when there is inflammation in the body," says Michelle LeBlanc, DVM, Dipl. ACT, of Rood and Riddle Equine Hospital in Lexington, Ky.
This leads to production of the hormones prostaglandin E2 (PgE2) and lower amounts of the prostaglandin PGF2alpha. Prostaglandins are found in the allantoic fluid that surrounds the fetus. The levels of those hormones become very high when there is inflammation--much higher than in a normal pregnancy. Prostaglandins will cause uterine contractions, initiating labor, and it's a very rapid event. The foal is unfortunately taken along for the ride and is kicked out too soon, she says.
"In humans, we can block those cytokines with other cytokines that are not pro-inflammatory (such as IL10, which is a modulating cytokine), but these are expensive drugs that are not used in horses," says LeBlanc.
Another experimental treatment is to put dexamethasone inside the uterine fluids. "It blocks all the cytokines and thus blocks the generation of prostaglandins, since cytokines are what make the prostaglandins," she says. Dexamethasone is put into the uterus by amniocentesis--injection through the abdominal wall and on into the uterus. This is easier to do in women than it is in horses, however, because the horse has a different type of placenta.
LeBlanc feels this is a treatment that might be beneficial in the mare, but the procedure itself can sometimes lead to abortion. "Right now we don't have a good way to do all the treatments that might be helpful to halt the inflammatory process. This is probably why, in many cases, it appears that the drugs don't work," she says.--Heather Smith Thomas
TWINS: Trapped with Two
When twin pregnancies are discovered early (in the first weeks after breeding), the mare owner usually chooses to have the veterinarian terminate one of the embryos. If twins are allowed to develop, there is a high health risk for them and the mare.
"Your choices of what to do will depend on how far along the mare is when you discover them," says Elizabeth Santschi, DVM, Dipl. ACVS, a veterinary surgeon at the University of Wisconsin-Madison School of Veterinary Medicine. "If they were missed at three weeks and you don't see them until 60 days, your option is to get rid of them both," says Santschi. You end up with an empty mare, she says, but the mare has an excellent chance of rebreeding quickly. This is preferable to the risk of losing her or permanently impairing her reproductive abilities by trying to give birth to twins, she adds.
"As you get toward 100 to 150 days, one option is a procedure in which one of the fetuses is injected with potassium chloride or procaine penicillin," Santschi advises. "You euthanize one and allow it to mummify and just sit there to let the second one grow."
In the mare's uterus, it's all about space. The two fetuses tend to outgrow their space and make life hard for themselves and the mare.
What Santschi tells the client when doing this procedure is that the mare will not have twins, but 50% of these mares will kick out both fetuses. The other 50% will go ahead and have one normal foal. She says veterinarians don't know enough about this procedure yet to tell which twin would have been the most viable (which one to keep) and which one Mother Nature would have culled.
"What you don't want is a late-term abortion with twins," says Santschi. "It can be difficult to get them sorted out; you usually lose them and may also lose the mare. Another problem is that the uterus in mares that deliver twins is so stretched that the mare may not rebreed. Even if she lives, you have two dead twins and a mare that can't get back in foal. She may have cervical lacerations and other damage, as well as the stretched uterus."
"Once you get past five months, I am not comfortable about injecting one, so then your option is a selective abortion, which is basically just ending the pregnancy," notes Santschi. "At that stage, you are not putting the mare at much risk. The foals are still quite small, even up to seven or eight months."
The mare can abort them with no problem and usually needs no assistance nor follow-up treatment. These mares generally do well, especially if they can be turned out for exercise so the uterus can involute and shrink down more readily, says Santschi.--Heather Smith Thomas
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.
POLL: University Equine Hospitals