🩺 Equine Abortion: A Vet’s 2025 Guide | Dr Duncan Houston BVSc

Meta description: A complete 2025 vet’s guide by Dr Duncan Houston on equine abortion—identifying causes, treatment options, diagnostics, and prevention for breeders.

1. 📘 Definition & Timing

An abortion in mares refers to fetal loss before 300 days gestation (term ≈340 days). Delivery after 300 days is classified as stillbirth or premature delivery :contentReference[oaicite:2]{index=2}.

2. ⚠️ Clinical Signs

• Vaginal discharge, often bloody or cloudy :contentReference[oaicite:3]{index=3}
• Udder enlargement or milk production before the due date :contentReference[oaicite:4]{index=4}
• Presence of fetal or placental tissues in the stall or pasture :contentReference[oaicite:5]{index=5}
• Behavioral changes: colic-like signs, abdominal discomfort, restlessness :contentReference[oaicite:6]{index=6}

3. 🔬 Causes

3.1 Infectious Causes

• Equine herpesvirus‑1 (EHV‑1): Leading viral cause; abortions in last trimester without mare illness. Diagnosis via PCR or virus isolation. Vaccinate at 5, 7, and 9 months :contentReference[oaicite:7]{index=7}.
• Equine viral arteritis (EVA): Abortion occurs 1–4 weeks after infection. Prevent via stallion/mare vaccination and isolation strategies :contentReference[oaicite:8]{index=8}.
• Potomac horse fever (Neorickettsia risticii): Bacterial abortion mid-late gestation; placentitis and retained fetal membranes may occur :contentReference[oaicite:9]{index=9}.
• Leptospirosis: Emerging viral/bacterial cause in 6–9 months with usually single cases :contentReference[oaicite:10]{index=10}.
• Bacterial/fungal placentitis: Caused by Streptococcus, E. coli, Aspergillus, Candida… leads to late-term abortions :contentReference[oaicite:11]{index=11}.
• Mare Reproductive Loss Syndrome (MRLS): Linked to eastern tent caterpillars; can cause abortion storms in early or late gestation :contentReference[oaicite:12]{index=12}.

3.2 Non-Infectious Causes

• Twinning: Most common non-infectious cause; often results in abortion at 7–9 months due to insufficient uterine capacity :contentReference[oaicite:13]{index=13}.
• Umbilical cord torsion: Especially in horses with long cords; leads to fetal death via circulatory compromise :contentReference[oaicite:14]{index=14}.
• Premature placental separation (“red bag”): Can cause fetal hypoxia and loss :contentReference[oaicite:15]{index=15}.
• Toxic fescue endophyte: Infected fescue grass can cause placental thickening, abortion in late gestation :contentReference[oaicite:16]{index=16}.
• Nutritional or toxic issues: Starvation, plant toxins, or corticosteroid use :contentReference[oaicite:17]{index=17}.
• Genetic anomalies or congenital defects may also result in fetal loss :contentReference[oaicite:18]{index=18}.

4. 🧪 Diagnosis

Diagnose via veterinary exam, ultrasound, and detailed testing of fetal and placental tissues. Submission includes formalin-fixed specimens for histopathology and fresh samples for bacteriology or PCR :contentReference[oaicite:19]{index=19}.

5. 💊 Treatment

• If infection suspected: tailored antimicrobial or antifungal therapy.
• For retained placenta: aggressive uterine lavage, oxytocin, systemic antibiotics, and NSAIDs to prevent toxemia or laminitis :contentReference[oaicite:20]{index=20}.
• Supportive care: IV fluids, anti‑inflammatories, nutritional support.
• Twin reduction: Prosthetic or manual reduction early in gestation :contentReference[oaicite:21]{index=21}.

6. 🛡️ Prevention

• Vaccinate pregnant mares at 5, 7, 9 months against EHV‑1; EVA vaccination for seronegative mares :contentReference[oaicite:22]{index=22}.
• Ensure clean breeding hygiene and Caslick’s procedure to prevent ascending infections :contentReference[oaicite:23]{index=23}.
• Monitor twin pregnancies via early ultrasound; reduce if detected :contentReference[oaicite:24]{index=24}.
• Manage pastures: avoid fescue with endophyte, control caterpillars, feed hay during risk periods :contentReference[oaicite:25]{index=25}.
• Boost nutrition: quality forage, mineral supplements, body condition monitoring :contentReference[oaicite:26]{index=26}.
• Isolate new horses, maintain biosecurity to prevent viral spread :contentReference[oaicite:27]{index=27}.

7. 🩺 Prognosis

Most mares return to fertility after a single abortion if treated promptly. Prognosis depends on timely intervention and addressing underlying cause.

8. 📝 Client Advice

• Immediate vet assessment if abortion signs observed.
• Collect fetus and placenta for lab analysis to guide management.
• Maintain strong vaccination and biosecurity routines.
• Plan for early ultrasound to detect twins.
• Ensure balanced diet and pasturing strategies year-round.

9. 📚 Final Words

Equine abortion has many triggers—infectious pathogens like EHV‑1/EVA/Neorickettsia, bacterial/fungal placentitis, twin pregnancies, toxins, and cord abnormalities. 30–50% of cases remain undiagnosed :contentReference[oaicite:28]{index=28}. Proper preventive strategies—vaccination, pasture management, hygiene, ultrasound screening—plus swift veterinary care can dramatically reduce risk and preserve mare reproductive health.

📞 For tailored reproductive plans, diagnostics, or pasture management advice, contact Ask A Vet. As Dr Duncan Houston, I’m here to support breeders and veterinarians with expert guidance, care protocols, and preventive strategies in 2025 and beyond.