Effect of Acetylsalicylic Acid on Uterine Blood Flow, Gestation Length, Foal Birth Weight and Placental Weight in Pregnant Thoroughbred Mares - A Clinical Pilot Study.
Authors: Sielhorst Jutta, Roggel-Buecker Ute, Neudeck Kim-Carolin, Kahler Anne, Rohn Karl, Luettgenau Johannes, Bollwein Heinrich, Hollinshead Fiona, Sieme Harald
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Low-dose acetylsalicylic acid (ASA) is occasionally used in equine reproduction to improve placental perfusion, yet evidence supporting this practice remains limited. This double-blinded, placebo-controlled pilot study examined whether oral ASA administration altered uterine blood flow dynamics, gestation length, and neonatal outcomes in 16 Thoroughbred mares, with treatment groups receiving either 5,000 mg lactose daily (control, n=4), 5,000 mg ASA daily from day 120 of gestation (ASA1, n=7), or 5,000 mg ASA daily until day 285 then twice daily thereafter (ASA2, n=5). Serial ultrasonographic assessments of both uterine arteries from mid-gestation through parturition revealed that mares receiving twice-daily ASA dosing (ASA2) demonstrated significantly elevated time-averaged maximum velocity in the ipsilateral uterine artery during late pregnancy (day 305–346, P=0.03) and a trend towards increased total uterine blood flow volume (P=0.07), whilst gestation length, foal birth weight, and placental weight did not differ significantly between groups. For practitioners considering ASA supplementation in mares with suspected placental insufficiency or poor obstetric history, these findings suggest that higher-frequency dosing in the final weeks of gestation may enhance uterine perfusion; however, the small sample size and lack of clinical outcome differences—such as improved foal vigour or reduced perinatal complications—limit conclusions about whether haemodynamic improvements translate to meaningful health benefits.
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Practical Takeaways
- •Twice-daily ASA dosing in late pregnancy may enhance uterine blood flow, which could be beneficial in mares with placental insufficiency concerns, though clinical outcomes (birth weight, placental weight) were not affected in this pilot study
- •The study was small (n=16) and results warrant larger controlled trials before clinical recommendations can be made for routine use in pregnant mares
- •ASA appeared safe in this population with all mares delivering healthy foals, but the lack of differences in actual foal or placental outcomes limits immediate clinical application
Key Findings
- •ASA 5,000 mg twice daily from day 285 onwards significantly increased time average maximum velocity in the ipsilateral uterine artery during late pregnancy (P = 0.03)
- •Mares receiving twice-daily ASA showed a tendency toward increased total blood flow volume during late pregnancy (days 305-346, P = 0.07)
- •All 16 mares delivered live foals with normal pregnancies regardless of treatment group
- •No differences reported in gestation length, foal birth weight, or placental weight between treatment groups