FieldDxMare reproductive loss syndromeClinical signs, differential diagnosis, treatment and prevention in horses.
Overview
A regional cause of late-term abortion and early fetal loss in mares, linked to a specific caterpillar species. Exposure to Eastern tent caterpillars (Malacosoma americanum); their hairs (setae) penetrate the gut wall, allowing bacteria to seed the placenta/fetus.
Clinical signs
- Early fetal loss, late fetal loss, fibrinous pericarditis, and unilateral uveitis (as noted in the master list)
Predisposing factors
- Historically, many epidemiologic studies were performed to determine the source of the epidemic.
Treatment
Treatment of affected foals is primarily supportive in nature. Horses with pericarditis should have the fluid drained to relieve or prevent cardiac tamponade and to minimize the accumulation of fibrin.
Drugs mentioned: Tissue Plasminogen Activator Atropine
Prevention
This is based on prevention of ingestion of ETC by horses. Preventing horses from ingesting caterpillars by minimizing access to pasture and feeding hay in stalls is likely to be beneficial. Other control measures include removing wild or black cherry trees, the favored host species for ETCs, from pastures, hedges, and fence rows
Source
A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER — Mare Reproductive Loss Syndrome (Early Fetal Loss, Late Fetal Loss, Fibrinous Pericarditis, And Unilateral Uveitis)
A Textbook of the Diseases of Cattle, Horses, Sheep, Pigs and Goat by ELSEVIER (Not specified in source excerpts)
MSD Veterinary Manual — Mare Reproductive Loss Syndrome (accessed 2026-08-11)
Condensed and attributed, never reproduced whole. Open the full entry in the app.