Pregnant Broodmare Management

So you’ve gone through the trials and tribulations of breeding your mare, and the vets at Henderson Equine Clinic have confirmed the presence of an embryo at 14 days post breeding. Congratulations! Now what? Do you just sit back and relax for 11 months until foaling time? While there’s some aspect of patience that’s important when waiting for a foal, there are a lot of things that you can do to help your mare give birth to and care for a healthy foal.

Ultrasounds

While humans typically have very frequent ultrasounds during their pregnancies, we often don’t need to ultrasound pregnant mares as often unless we suspect severe complications.

The most important ultrasound we will perform is 14 days post-breeding. This is when we confirm the pregnancy by visualizing a tiny embryo in the uterus. It is important not to delay this appointment because we will also be checking for the presence of twin embryos. Twins are extremely dangerous for mares to attempt to carry to term, and it is safest to terminate one of the twins at the 14-day mark rather than later in the pregnancy.

The next ultrasound we perform is 28 days post-breeding. This is very exciting for owners (and us vets!) because by this point, we can visualize a heartbeat on the tiny embryo and confirm that it is a viable pregnancy.

Some owners will opt for an ultrasound to help them predict the sex of the fetus. We will typically perform this ultrasound at approximately 60 days post-breeding, but for most vets this is far from an exact science. Fetal sexing heavily depends on what position the fetus is in within the uterus when we check, and it is very difficult to definitively differentiate even in the best circumstances.

Later in pregnancy, the fetus sinks below the brim of the pelvis, so it’s difficult/impossible to visualize via rectal ultrasound. We can still attempt to visualize it via transabdominal ultrasound, but this also depends heavily on the fetus’ position in the uterus.

For mares that we have a higher level of concern for, whether from a history of pregnancy complications or another suspicion, we may perform an ultrasound around 9 months of gestation. This is to measure a baseline Combined Thickness of the Uterus and Placenta, or “CTUP”. If later in gestation we suspect any complications, such as placentitis (infection/inflammation of the uterus), we will take this measurement again to confirm our suspicions, which is why it can be helpful to have a baseline.

Body Condition

Mares need to maintain a good body condition as they carry a pregnancy in order to provide the growing fetus with nutrients as well as avoiding stress to the mare. A body condition of 5-6/9 is ideal, meaning the ribs can be felt easily but not seen, and their topline should be well cushioned with muscle/fat. Mares with a lower body condition need better nutrition. Mares with a higher body condition should embark on a reasonable weight loss journey in order to avoid complications such as laminitis. Consult your veterinarian to make sure your mare continues to get appropriate nutrition while decreasing to a more appropriate body condition.

Nutrition

Good quality legume hays (like alfalfa and clover) are recommended for broodmares over grass hays (like timothy), especially in late gestation. This doesn’t mean grass hays are bad to feed your broodmare; it just means that broodmares fed exclusively grass hays may need more concentrate supplementation (grain) to meet their protein requirements. One study by the University of Kentucky suggests that broodmares should eat slightly more than 2 lbs of hay per 100 lbs of body weight per day.

However, one grass (whether it be hay or pasture) is very important to avoid for pregnant mares - fescue grass. This grass is sometimes infected by fungal spores that can cause many birth complications, including abortion and inability to produce milk.

We will generally recommend supplementing your mare with a concentrated feed (either a grain or a balancer), especially during late gestation, but the specific kind will depend heavily on your mare’s specific breed and needs.

Vaccination Schedule

The typical vaccination schedule that Henderson Equine recommends for pregnant mares consists of two major vaccine groupings.

The first is to protect against Equine Herpes Virus (EHV, rhinopneumonitis), which is a contagious disease known to cause abortions in pregnant mares. We recommend a 3-vaccine series during your mare’s pregnancy, at 5-, 7-, and 9-months of gestation.

At 10 months of gestation (one month prior to the due date), we will booster your mare with a “core” vaccine grouping. This vaccine group consists of Rabies, Eastern Equine Encephalitis, Western Equine Encephalitis, Influenza, and West Nile Virus. This helps her produce antibodies for these diseases, which will then be passed to her foal in her colostrum.