Broodmare Health: High-Risk Pregnancies Benefit from Early Aspirin Intervention

Low uterine blood flow may contribute to pregnancy loss in mares. Despite the fact that aspirin, known also as acetylsalicylic acid or ASA, is often prescribed for certain conditions, including placentitis, few studies support its use. A new study revealed that ASA administered throughout mid and late gestation increased uterine blood flow and appeared safe for both the mare and foal.^*

In that study, 16 pregnant Thoroughbred mares ranging in age from 9 to 17 years were included. All mares were considered high risk, as they had a history of placentitis or spontaneous abortion. From day 120 of gestation until parturition, mares were administered either a placebo or 5,000 mg of ASA once or twice daily. The ASA dose was chosen empirically, estimated from the few previously reported studies of ASA use in pregnant mares.

Prior to ASA administration, mares were examined through ultrasound, and uterine blood flow was evaluated on three separate occasions. During those examinations, maximum velocity of blood flowing in the uterine arteries and total blood flow volume were calculated.

Researchers repeated those tests every 21 days beginning on day 120 of pregnancy and ending at birth. The results showed increased uterine blood flow in mares treated with 5,000 mg ASA twice daily compared to the mares treated with ASA only once daily and to control mares.

Two doses of 5,000 mg ASA can enhance uterine perfusion by increasing blood flow velocity, according to the study.

“This team of researchers indicated that early detection of high-risk pregnancies and early intervention with ASA for mares with placentitis or placental insufficiency due to endometriosis, for example, may increase the likelihood of producing a live foal,” said Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research.

Other ways of supporting mares during gestation are (1) ensuring a balanced diet that supplies sufficient energy to support the growth of the foal and prepare the mare for lactation, and (2) offering omega-3 fatty acids throughout pregnancy.

“In humans, research shows that increased intake of the omega-3 fatty acids DHA and EPA prevent premature labor and delivery through a reduction in prenatal stress. Further, studies also report reduced perinatal mortality rate and higher birth weights in babies whose mothers were supplemented with omega-3 fatty acids during gestation,” she explained.

Similar data are not yet available in pregnant mares. “However, we do know that mares supplemented with omega-3 fatty acids derived from fish oil, which is high in DHA and EPA, have improved colostrum quality and enhanced passive transfer of antibodies from colostrum,” Crandell said.

In terms of safety, all 16 mares included in the study had normal pregnancies and delivered live foals. Gestation lengths, time to placental expulsion, and foal birth weight were all considered normal in mares treated with ASA.

^*Sielhorst, J., U. Roggel-Buecker, K.-C. Neudeck, A. Kahler, K. Rohn, J. Luettgenau, H. Bollwein, F. Hollinshead, and H. Sieme. 2022. Effect of acetylsalicylic acid on uterine blood flow, gestation length, foal birth weight and placental weight in pregnant Thoroughbred mares: A clinical pilot study. Journal of Equine Veterinary Science 118:104107.