EQUINE CARE

Monitoring Preg The Importance of

gnancy in Mares

By HEATHER SMITH THOMAS T he mare has been bred, and checked with ultrasound a couple weeks later to make sure she conceived, and at that point everything looks good. Not every conception ends in a successful pregnancy, however. There can be various reasons for pregnancy loss, and it pays to monitor broodmares during their pregnancy—to make sure they are actually still pregnant (especially in early pregnancy) and that everything is going smoothly.

Dr. Peter Sheerin, owner of Nandi Veterinary Associates in New Freedom, Pa., says there are typical times that mares are examined for pregnancy. “We usually look at them 14 to 16 days after they’ve ovulated or 15 to 17 days after they were bred, to see if they conceived. We may check them again a couple days later, depending on the situation and if there’s a concern about twins. We want to find twins early, so we can eliminate one of them,” he says. “The next time a mare would be examined would be somewhere between 28 and 30 days gestation, to check the pregnancy for a heartbeat. This would be to make sure the conceptus is continuing to grow and that there is a heartbeat present.”

Examinations after that would depend on the client and the veterinarian’s preference. “When I practiced in Lexington, we would check mares at 28 to 30 days, and then again at 42 to 45 days, to make sure the fetus is continuing to grow, and doing the things that it should. If for some reason the mare has lost the pregnancy by that point, you could get a culture on her to make sure infection wasn’t the cause. You may be fortunate enough that she lost it before the endometrial cups formed (which usually happens around 36 days). If that’s the case, you may have a chance to breed her again during this breeding season,” he says.

In that situation, the mare could return to heat and be bred, whereas if she lost the pregEquine C are

nancy after the endometrial cups have formed and start producing the hormones that keep her from coming back into heat, you are probably out of luck. The endometrial cups are outgrowths on the placenta that produce the important hormone eCG in the pregnant mare, which triggers production of accessory CL that keep producing progesterone—which protects the pregnancy by keeping the mare from coming back into heat. If the endometrial cups are already formed and producing hormone, the mare may enter a pseudo-pregnancy state which can last up to four months. “The next time we’d check a mare is around 60 days of gestation, to make sure everything is going according to schedule. This is also the window (60 to 70 days) in which we can detect the sex of the fetus, if the client wishes. Sometimes we will check a mare again at 90 days. It depends on the client or the farm, and how much checking they want to do. If a mare looks good at 60 days, there’s not much you’d check for again at 90 days, other than to make sure she has not lost the pregnancy, and if she has, that she’s not dirty (no infection),” he says.

“We check mares again at 150 days (five months), which is typically when we start mares on their vaccinations to protect against herpes virus (to prevent viral abortion). We want to make sure they are pregnant before we start that vaccination schedule, because if by chance they are no longer pregnant we don’t want to waste money on the vaccines. This stage (150 days) is usually in the fall, which is the time when mares on most farms are moved around for where they will spend the winter, based on which group they fall into. The pregnant mares usually go to one group and the open mares to another.”

Those are the routine times to check mares for pregnancy. “Beyond that, further monitoring of pregnant mares is variable—a gray area in which the client may weigh the cost versus the benefit. This may also depend on whether it’s a

high-risk mare. If it’s a mare that’s had placentitis in the past, there’s a chance she will have this problem again. In that case, it would be potentially beneficial to examine her more frequently during pregnancy—to make sure she is maintaining the pregnancy and that everything is normal,” he says.

“What we would monitor in that situation would be the placental thickness (using ultrasound). We’ll also look for edema in the placenta and monitor fetal fluids to see how much gray material is floating around. This kind of checking/monitoring is a little more dicey because it’s more subjective; the results of the assessment depend a bit on the person checking. With fetal fluids, for example, is this a grade two or grade three Is it significant or not significant? This type of monitoring/checking can be a challenge,” says Sheerin.

“There has been some work done, looking at measuring progesterone and total estrogens through the pregnancy, to see if these levels give an indication of impending fetal issues. The thing we don’t yet know is how frequently you’d need to do this, to have meaningful results. So again, it’s a cost-benefit question,” he says.

“Some farms check all their pregnancies monthly, by palpation and ultrasound, to make sure things are okay. There are others that check mares at 14 and 18 days and if a mare is pregnant they don’t look at her again until it’s time to foal,” he says.

A lot depends on the age and the history of the mare, with the history being most important. “A mare that typically has not had problems in the past usually does not need to be examined as frequently as a mare that’s had problems. Her history will tell you what the problems were, and if it’s a placentitis there is a chance that this would recur and you’d want to address that as soon as possible. In that case, more exams would be worthwhile,” he explains.

“If it’s a mare that had a dystocia, this is usually just a chance occurrence and not something you can change or do much to impact for next time. You can check mares after nine months of pregnancy, however, to see if the fetus is in the proper presentation— and will be coming headfirst—or butt first.” After a certain time, the fetus has grown so large that it can no longer move around freely in the uterus, and won’t be able to change that basic position. There is no room to turn around.

“This can give you an idea of whether you need to be concerned. If the foal will be coming backward, you’d obviously want to monitor that mare closely at foaling time,” says Sheerin.

Some people worry about progesterone deficiency causing early embryonic loss, and like to put some mares on a progesterone supplement. If the mare’s history has indications that she may be at higher risk of losing the pregnancy or if she had loss of pregnancy before, the client often puts the mare on progesterone supplementation. It’s hard to prove whether or not this helps. “The mare’s CL will produce progesterone initially, so many people pull blood and evaluate her progesterone level at the time they do the first pregnancy exam. If it’s low, they can treat the mare at that point. After about 110 to 120 days of pregnancy, the placenta starts to take over the job of producing the progesterone,” he says.

“After that point, checking for progesterone is a little dicey because the placenta isn’t actually producing progesterone per se. It produces progestin. Depending on the lab that you use for the test, results will vary. Some assays are more specific for just progesterone, so if you measured the levels of a pregnant mare later in gestation, the levels will be low. There are other assays that have more cross-reactivity, so the test can pick up other progestins. It may not pick up 100%, but can pick up some of it, to say that it’s there. Those levels will be a little higher. So it all depends on the specificity of the assay that the lab is using,” he explains.

“This can be very confusing, to try to explain to the client, because we have to get into how the assay works. If we are going to sample the mare for progesterone or progestin later in pregnancy, we need to know the assay that the lab is using, and if it has crossreactivity with other progestins. The only way to know is to call the lab,” he says.

Another form of monitoring pregnant mares is simple external observation, watching the mare, looking at her udder and vulva. Some mares will show signs of udder development earlier than others, and sometimes too early. Others may not develop much udder until right before they foal, and can surprise you.

“The mare might have a vaginal discharge, which could signal a problem, but if you don’t pick up her tail and look, you might miss this clue. Depending on the situation and how the mares are housed, it may be easy or not so easy to check them closely, and the frequency of those examinations will vary from farm to farm.” The mares may be in stalls or small paddocks or they may be out in a field somewhere. “You can use the mare’s history as a guideline as to how frequently she should be checked. Even if mares are outside, whoever feeds them will be seeing them every day, and you’d hope they would look at udders,” says Sheerin. You can compare what a mare’s udder looks like today compared to yesterday, or last week.

“The person feeding them may not pick up all their tails, but could at least look at the udders, to see if there are any changes. If a mare does show signs of development too early, this would be an indication that it would be a good idea to have the veterinarian palpate and ultrasound her, to examine placental thickness, fetal fluids, and pull blood to evaluate progesterone and total estrogen. After these assessments the veterinarian can decide what therapy should be utilized.” This moves into the realm of a high risk pregnancy. ■ Equine C are

Early pregnancy ultrasound image “ Some farms check all their pregnancies monthly, by palpation and ultrasound, to make sure things are okay. There are others that check mares at 14 and 18 days and if a mare is pregnant they don’t look at her again until it’s time to foal. ” —Dr. Peter Sheerin