Equine Reproduction Specialists Urge Late Gestation Ultrasound Exams

With foaling season right around the corner, specialists in the UC Davis Equine Reproduction Service are urging their clients to schedule ultrasounds late in their mares’ pregnancies.

Once a mare is confirmed pregnant early in gestation, she is often rechecked shortly afterward to confirm embryo or fetal viability.

“In many cases, no further examinations are performed until foaling,” said Dr. Catherine Renaudin, chief of the Equine Reproduction Service at the William R. Pritchard Veterinary Medical Teaching Hospital (VMTH). “However, additional ultrasound examinations later in pregnancy are strongly recommended to improve pregnancy outcomes and reduce the risk of complications for both mare and foal.”

A brief, non-invasive transrectal ultrasound can provide valuable information.

Between 9 and 11 months of gestation, the fetus typically settles into its final presentation. Using ultrasound, veterinarians can determine whether the foal is in a normal anterior presentation (head first). This is done by identifying the fetal head or eye.

If the fetus is in an abnormal position, such as posterior (hindquarters first) or transverse (sideways), the tail, thighs, or spine may be detected. Although fetal malpresentation is uncommon, it can lead to dystocia (difficult birth), posing serious risks to both mare and foal.

“Early detection allows to plan appropriately—such having the mare foal out at the VMTH or another facility equipped for assisted delivery or cesarean section—thereby reducing the risks associated with abnormal foaling,” Dr. Renaudin stated.

Another benefit of a late gestation ultrasound is screening for placentitis, the leading cause of infectious abortion in mares. It often develops near the cervix, making it detectable via transrectal ultrasound. Early signs include thickening of the placenta or partial separation of the placenta from the uterus. UC Davis recommends monthly placentitis screenings beginning at 7 months of gestation through to foaling. If abnormalities are detected, treatment can be started early, significantly improving the chances of a successful pregnancy and reducing the risk of abortion.

“In summary, late-term ultrasound exams provide crucial information about fetal presentation and placental health,” said Dr. Renaudin. “By identifying problems early, we can take proactive steps to safeguard the health and well-being of both mare and foal.”

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If you have any questions, would like more information, or would like to schedule a late term pregnancy examination for your horse, please contact the VMTH Large Animal Hospital at 530-752-0290 or email the Equine Reproduction Service at reproduction@ucdavis.edu.