Pregnant Mares: What owners need to know as foaling time approaches

Tuesday, March 2, 2021

During a mare’s pregnancy, moderate exercise such as vigorous walking or riding will help control her weight and maintain muscle tone and strength needed for the last two months of pregnancy.

To maintain her body condition, feed her a high-quality forage diet using the same pre-pregnancy amounts with an increase in energy as pregnancy demands. In cold weather, consider the extra requirements needed to maintain body condition and adjust her ration accordingly. As with all animals, she should always have plenty of clean, fresh (not frozen) water.

With your veterinarian, establish an effective, safe deworming schedule. Deworm the mare within several weeks of foaling because she is the primary source for infecting her foal with parasites. Vaccinations should be current since infectious diseases can trigger abortions. Again, consult your veterinarian for your specific scenario as mares in crowded boarding stables have different requirements than solitary mares on pasture. Boosters for selected vaccines should be administered one month prior to foaling to increase antibody levels in the mare’s colostrum, which in turn, will help protect the newborn foal from disease.

Foaling season can be both an exciting and an anxious time. Remember, nature has developed a wonderful system of birth in the mare. Because the uterus determines the size of the foal, with the exception of miniature horses, mares usually do not have complications from a foal that is too large. Unlike cattle, mares have a lower occurrence of difficult deliveries. They can have, on occasion, malpositioned foals or other complications.

On average, a mare’s pregnancy lasts 338 to 343 days. Labor and delivery are generally very uneventful. Mares seem to have some control over their delivery and prefer to foal in privacy at night.

While foaling is usually problem-free, have your veterinarian's telephone number handy. Your mare will need a clean, safe, quiet place to foal. If the weather is good, a clean pasture is great. If not, she will need a stall large enough to freely lay down with room on both ends. Avoid a situation where at delivery the mare or her foal are forced into a corner or up against a wall.

If available, use a stall with a floor that can be readily cleaned and disinfected. After a thorough cleaning, a 10 percent solution of normal laundry bleach and water sprayed on the floor and walls is a good disinfectant. Clean bright straw or clean grass hay for bedding is preferable to shavings. It is less dusty and won't cling to the wet newborn or mare like small wood particles will. Also, wood shavings can be a source of some germs and toxins. Always keep the stall well ventilated and clean.

A few things can cause abnormally long pregnancies and should be investigated. If a mare's pregnancy extends past 360 days, your veterinarian should examine her to determine if she is still pregnant and confirm that all is well. Just as with human babies, using an ultrasound your veterinarian can assess the viability of the unborn foal. Also, the degree of fetal maturity can be assessed by checking calcium levels in the mare’s colostrum or first milk.

It is vitally important that the foal nurses colostrum within the first 12 hours of life. Colostrum is extremely rich in antibodies that help prevent disease in the foal until its own immune system kicks in, especially if the mare was vaccinated appropriately. Without adequate colostrum, the foal is at an increased risk of infections. Your veterinarian can test the colostrum to determine whether it is rich in antibodies.

Also, the foal's serum can be tested at 18 to 24 hours of age to evaluate IgG antibody levels. If its concentration of IgG is inadequate, specially prepared serum can be given intravenously or a dose of colostrum from a tested resident mare, if given before 24 hours of age, could be the difference in the foal’s survival.

A few key points and when to call your veterinarian:

If your mare starts to drip milk before 320 days of pregnancy.
If your mare does not have a filling udder (colostrum) within one week of her due date.
If the mare runs milk consistently prior to foaling for more than three to four days.
If heavy labor (pushing) persists for 20 minutes without any sign of the foal protruding from the vulva.
If the feet are presented with the soles up; front feet and nose should come first.
An emergency note: Premature placental separation or "red bag" requires immediate attention. If the bag protruding from your mare’s vulva, covering the foal’s feet, is velvety red instead of milky white, break (tear or safely cut) the bag immediately and assist in delivering the foal or it will suffocate within minutes. Call your veterinarian once the foal is delivered.
If the placenta is not eliminated within three to six hours of foaling.
If the foal does not rise within one hour of birth, nurse within two to three hours of birth, or pass the meconium (first stool) within one hour after rising and receiving an enema.
Finally, about 24 hours after birth, have your veterinarian examine the mare, foal and placenta for any signs of abnormalities.

For owners who want relief from the worry or when nature goes awry, OSU’s College of Veterinary Medicine Ranch offers foaling services, a service most North American veterinary colleges do not provide. Senior clinicians, with fourth-year veterinary students, monitor mares and their unborn foals during the late term of pregnancy using ultrasound and udder secretions. As the mare’s delivery nears, she is placed under 24-hour observation, including closed-circuit TV, until after her baby is safely delivered. If needed, mares and foals can be quickly transported to OSU’s Veterinary Medical Hospital for neonatal intensive care. The ranch foaling program has proven to be a very effective tool in training future veterinarians and a valuable resource to horse owners and the horse industry in Oklahoma and surrounding regions.

About the author: G. Reed Holyoak, DVM, Ph.D., Dipl. ACT, is a professor and holds the Bullock Equine Reproduction Endowed Professorship at the Oklahoma State University College of Veterinary Medicine. He is a board-certified diplomate of the American College of Theriogenologists.

Veterinary Viewpoints is provided by the faculty of the OSU Veterinary Medical Hospital. Certified by the American Animal Hospital Association, the hospital is open to the public providing routine and specialized care for all species and 24-hour emergency care, 365 days a year. Call 405-744-7000 for an appointment or more information.