Page 87 - December 2017

An equine embryo at 7-8 days old.
(corpus luteum, a temporary endocrine struc- ture involved in the production of progester- one) that keep producing progesterone—which protects the pregnancy by keeping the mare from coming back into heat,” according to Tibary. “If the endometrial cups are already formed and producing hormone, the mare may enter a pseudo-pregnancy state which can last up to 4 months.
“There have been many studies done over the years, looking at how many mares failed to foal after they were diagnosed pregnant at 14 days,” Tibary says. “There is a wide range of reported incidence of pregnancy loss, depending on the studies—ranging from about 2.5% all the way up to 30%.” Some mares will be at higher risk than others for losing the pregnancy early.
“The next time we’d check a mare is around 60 days of gestation, to make sure everything
is going according to schedule,” says Sheerin. “This is also the window (60 to 70 days) in which we can detect sex of the fetus if the client wishes. Sometimes, we will check a mare again at 90 days. If the mare looks good at 60 days, there’s not a whole lot 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 (has no infection).”
“These later ultrasound examinations look at the fluid and membranes,” says Tibary. “We can detect things like a dislodged vesicle, loss of fluid, etc. These indicate whether the pregnancy is viable or not. We may decide to help the preg- nancy with progesterone or altrenogest. If I see a good vesicle but the tone is not what I’d like,
I may put that mare on altrenogest (synthetic progesterone, such as Regumate®). I like the Altrenogest because it allows me to check the endogenous progesterone of the mare (what she herself is producing) because the test does not cross-react with the synthetic hormone. Now, with Doppler ultrasonography, we can glean even more information about the quality of the pregnancy and the CL. It is important to follow up on mares after breeding to sort out the ones that may be easy and the ones that may be at
high risk of losing the pregnancy or having some complications.”
Sheerin checks mares again at around 5 months, or 150 days. “This is typically when we start the 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 preg- nant mares usually go to one spot and the open mares to another group.
“Beyond that, any further monitoring of pregnant mares is variable; the client may weigh the cost versus the benefit,” Sheerin continues. “This may also depend on whether it’s a high-risk mare. If it’s a mare that has 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 every- thing is normal.
“What we would monitor in that situation would be the placental thickness (using ultra- sound). We also look for edema in the placenta and monitor fetal fluids to see how much gray material is floating around. This kind of check- ing and monitoring is a little dicey because
it’s more subjective; results of the assessment depend a bit on the person checking. With fetal fluids, for example, is this a grade 2 or a grade 3? Is it significant or not significant? This type of monitoring and checking can be a challenge.
“There has been some work looking at mea- suring 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.
“Some farms check all their pregnancies monthly, by palpation and ultrasound, to make sure that things are okay,” Sheerin says. “Others check them at 14 and 18 days, and if the mare is pregnant, they don’t look at her again until it’s time to foal.”
A lot will depend on the age and the his- tory 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 has had problems,” Sheerin explains. “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.”
“We generally assume that a young maiden mare in good health, good body development, and with no problems settling on the first cycle would have less than 5% chance of losing the pregnancy,” says Tibary.
“The other extreme is the aged mare— greater than 18 years, and one that has had problems with uterine infection, pregnancy loss or abortion in the past,” Tibary says. “This mare would be in the highest risk category. There are many mares somewhere in between. Mares with a recent history of weight loss or systemic dis- ease, or treatment during the previous cycle for uterine infection, may be at a higher risk of early embryonic death than the healthy maiden mare.
“When we look at what might cause embry- onic loss, we blame the uterus (the mare and the uterine environment for that embryo) or we can blame the embryo itself, or even the stallion in some instances,” says Tibary. “There may be some outside environmental factors, as well.”
“If it’s a mare that had a dystocia, this is usu- ally just a chance occurrence and not something that you can change or do much to impact things,” says Sheerin. “You can check mares after 9 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,” says Sheerin. “If the foal will be coming backward, this would be a mare you’d obviously want to monitor closely at foaling time.”
Check the mare early in gestation, especially if there is a concern about twins, since the embryo doesn’t stop its migration until around day 16. The safe delivery of healthy twins is extremely low and can result in the loss of one or both of the foals as well as of the mare. If twins are found early, the embryos can be separated to allow one to develop normally.
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equine health