Hello horse owners with upcoming foals or those thinking about breeding! This will be a three-article piece that will cover gestation, the foaling process, and what to do once the foal is born. Our hope is that this will help educate you and get you excited for your mare’s upcoming parturition. A new article will be posted each week, so be sure to continue checking our website for more information!
Article 1: Gestation
Equine gestation should last from 335 to 342 days. The length of gestation can vary based on season (may carry up to 10 days longer in the winter or early spring). This is a normal phenomenon and usually does not cause any problems for the mare or foal. On the other hand, fescue exposure can also result in longer gestation periods, but this is not desirable. It is a disease condition that can cause issues for both the mare and foal. An endotoxin that lives within the fescue plant can increase gestation length to 360 days causing the foal to be abnormally large when born. Unfortunately, this endotoxin can also cause the mare not to have milk once she foals. This is especially concerning because the “first milk” or colostrum is the milk that gives the newborn foal antibodies to protect it from diseases in the environment. Without those antibiodies, foals are at high risk of becoming extremely ill within the first few days of being born. Several things can be done to prevent this condition including keeping the mare off of fescue for the last trimester of pregnancy and administration of domperidone to the gestating and lactating mare (begin ten to fifteen days prior to foaling and continue after foaling).
Pregnancy diagnosis can be confirmed via rectal ultrasound as early as fourteen days into gestation. Often veterinarians like to check this early to confirm the pregnancy and check for twins. Twinning in horses is fairly rare, and it is even rarer for a twin pregnancy to result in the birth of two live foals.
Nutritional requirements during pregnancy are very similar to adult maintenance for the first 8 months. Pregnant mares should be kept at a body condition score of 6-7/9. Following the first 8 months, energy and protein requirements begin to increase. This is because the majority of fetal growth takes place during the last trimester. Increasing calorie intake the last trimester is also important because the mare needs to be in a positive energy balance going into foaling. Lactation is very taxing on a mare’s body due to it’s a high demand for energy. Mares need to be fed appropriately to maintain body condition when going into the period where they will be feeding their foals. Mares in the last trimester should be fed high quality forage and grain in order to meet their metabolic demands. Feeding alfalfa hay and a quality grain formulated for pregnant mares can also increase the protein of the diet.
Mares should be vaccinated with their annual vaccines (Rabies, EWT, WNV) prior to breeding season. Do not vaccinate during first 90 days of pregnancy. Most modified live vaccines are not used in pregnant mares (They can cause abortions.). By vaccinating during the last month of gestation, colostral antibodies can be passed to the foal.
- Vaccinate for rhinopneumonitis (EHV1) at 5th, 7th, and 9th months of gestation
- EHV1 of Herpes virus can cause abortion in mares and rhinopneumonitis in foals and growing horses. So, this is an important vaccine for all brood mares to receive prior to being bred.
- Vaccinate for EWT, influenza, WNV at 10th month of gestation
- ± Botulism – to protect foal – for mare’s first foal vaccinate at 8th, 9th, and 10th month of pregnancy, do at 10th month on subsequent pregnancies
- ± Rotavirus – 8th, 9th, 10th month of pregnancy
- Rotavirus is the most common cause of infectious diarrhea in foals.
- ± PHF – for dam – usually April and August
Regular deworming throughout the pregnancy is important. Most horses stay on their normal deworming program (dewormed based on fecal egg counts or consistent deworming every several months). It is important to confirm that the dewormer you give can be used on pregnant mares. Most ivermectin products are for administration during pregnancy, but you should always check the label to be sure.
Ultrasound fetal check-ups:
Fetal viability can be assessed via transrectal ultrasound throughout gestation. On ultrasound the veterinarian can see fetal movement, count fetal heart rate and assess the health of the uterus and placenta. Once the fetus gets too big to be viewed via ultrasound, your vet can rectally palpate and feel fetal movement.
Mares can be exercised during gestation, and often, fit mares have an easier time with the birthing process. Normal work (similar to what work you were doing before the mare was bred) can be continued up until about the 7th-8th month of gestation. After that light riding is still possible until about a month before foaling. It is important not to over-work or over-heat pregnant mares, but some exercise is beneficial.
Mares should be moved to the area where they will foal about 4-6 weeks before her due date. This not only lets her get familiar with the area, but also exposes her to the environment the foal will come into, letting her develop antibodies to pass to the foal in her colostrum. The area where the mare foals should be clean and dry.
We hope you enjoyed the first article in our series on foaling. Now you and your mare are ready for the pregnancy! Check back next week for more information on the foaling process. If you have any questions, please give our office a call at 540-788-6094. One of our large animal veterinarians would be happy to give you a call back and discuss your questions with you.