EC November/December, 2006
Sometimes a pregnant mare develops a problem that puts the fetus at risk for abortion or premature delivery. Some of these foals can be saved, however, if the problem is discovered early and the mare given proper treatment to reverse the condition or improve the fetus’ chances for survival.
Elizabeth Santschi, DVM (veterinary surgeon at the University of Wisconsin-Madison School of Veterinary Medicine) says the most common cause of premature delivery in mares is placentitis–some degree of inflammation and infection of the placenta. “It is most commonly ascending (coming from the cervix), but it doesn’t have to be. It may be a silent infection elsewhere in the uterus that is present at breeding, and later becomes a problem,” she says.
“With ascending placentitis you can generally, by examining the cervix, get some indication that this is the case. Mares in the last month of gestation can have a fairly loose cervix. It usually doesn’t mean anything, but in certain susceptible mares (for reasons we know or we don’t know), this can create a problem. The loosening cervix can allow bacteria to enter, and the mare gets an infection in the rear portion of the placenta. This, in itself, may not cause much trouble. But if it extends forward on the placenta, the mare’s mammary gland develops and she starts to lactate prematurely,” says Santschi.
“Typically what most mare owners will see is that the mare fills her udder much sooner than she should. Occasionally there will also be some discharge from the vulva, but you may or may not see it,” she says.
“Placentitis, in my experience, is the most common cause for mares to deliver early. Others may deliver early as a result of a serious medical condition or surgical condition. 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 predispose a mare to have the cervix open and cause an ascending placentitis. I haven’t observed this myself, but it probably could happen,” says Santschi.
“This is one of the reasons we try to delay any surgery (if a mare needs it in the last 2 months of gestation) until after she has foaled–if it can be delayed. If surgery is needed in the middle of gestation, it usually doesn’t bother the fetus. The foal does most of its growing in the last 2 months,” she explains.
There are also some mares that just seem to foal early every year. “Whether this is because the foal outgrows the size of the uterus or whether it is because the endometrium is damaged in some way (so the foal gets to the point where it is not getting enough nutrients through the placenta for proper growth and initiates parturition), we are not always sure. A fair number of mares foal early but we never know why,” she says.
“One of the biggest problems in trying to identify high risk pregnancies is that the vast number of normal pregnancies can lull us into a false sense of security. When you do identify them, it’s generally because either you are already treating some other condition in that mare, or you start to see premature lactation.”
The best thing to do with a high risk pregnancy is to treat the primary cause. “If it’s colic, or diarrhea, or some other serious condition, the best way to take care of the foal is to take care of the mare, rather than get the foal out early,” she says. Deal with the primary disease.
TREATMENT – If the primary disease is an ascending placentitis, you must treat that. “Almost always these cases are bacterial, but there was a type of placentitis (Nocardio-form) that went through Kentucky a couple years ago that was caused by a fungus. Most, however, are bacterial, so the mare will need antibiotics. In many mares that start to lactate too soon, at 300 days of gestation or less, if we put them on antibiotics the udder cools down. They quit making milk.” This treatment may be enough to help them get farther along before foaling, says Santschi. If the mare has already leaked milk, however, she may have lost much of the immunoglobulins in the colostrum. The passive transfer status of the foal after birth, after nursing, should be closely checked.
The antibiotic selected will depend on the type of bacteria causing the problem (as revealed by a culture of fluids from the vagina and cervix). “Part of the problem in choosing an antibiotic is that we are always limited in the kind of drugs we have available for horses, whether because of cost or because they may cause inappropriate reactions in horses. There are only a few we can choose from. Most of the time Streptococcus is the cause of ascending placentitis, so penicillin is the drug of choice. As long as the client can afford some good I.V. doses, I put the mare on penicillin and gentomycin for a few days (because these have a synergistic activity, acting more effectively together than by themselves). Then, since this is quite expensive, we usually go to intramuscular penicillin,” she says.
“I have used trimetheprim sulfa quite successfully in these mares. There is some suggestion that it can cause some fetal problems, but this is relatively uncommon. If it’s late in gestation, I don’t worry much about this. Enrofloxacin is another oral drug that has some detrimental effects on cartilage and is not recommended for use on young foals, so I avoid the use of this in pregnant mares,” says Santschi.
Additional therapy for these conditions may include use of non-steroidal anti-inflammatory drugs such as bute or Banamine. “These can reduce the inflammation, and I have no problem using these. They also seem to have a certain quieting effect on the uterus. One of the things we think may cause these foals to have problems and be compromised is that when the uterus is inflamed, it wants to contract. As it contracts, it compromises the blood flow; there is less blood supply to the foal. You want a relaxed and happy uterus,” she explains. Anti-inflammatory drugs can reduce or ease the spastic contractions.
“The same is true with Regumate or any of the synthetic progesterones. These have a calming effect on the uterus. The use of these is somewhat controversial but I still 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 than a single dose,” she says.
“There are a few other treatments. Some people will use a rheologic agent (which is a drug that changes the deformability of red blood cells), with the idea that it allows blood cells to get through vessels that are small or inflamed for some reason.” If the circulation to the placenta has been compromised, this might help. This is one of the things your veterinarian might choose to use, says Santschi.
“In an intensive care situation with a high risk pregnancy, some veterinarians will hospitalize the mare and give her intra-nasal oxygen, trying to increase her delivery of oxygen to the foal.” If her blood oxygen is increased, this can help keep the foal from being compromised. There have been some successes with this, she says.
Beyond that, it’s just standard supportive care–such as fluids, anti-inflammatory drugs, etc. “The rule is, always take the best care of the mare, and that is how you will be most likely to save the foal,” says Santschi.
