💩 Diarrhea in Horses Vet Guide 2025 by Dr Duncan Houston

Diarrhea is a frequently encountered issue in equine practice—from mild loose droppings to life-threatening colitis. In this extensive guide, I’ll walk you through causes (both non-infectious & infectious), complications, diagnosis, treatment, prevention strategies, and how to work effectively with your veterinarian to ensure rapid recovery and long-term gut health. 🐴✨

1. What Is Diarrhea & Why It Matters

Diarrhea is defined as the increased passage of liquid or semi-solid feces. Though often mild, it can escalate rapidly—especially in adults where fluid losses of 90 L/day may occur—leading to dehydration, electrolyte imbalance, colic, endotoxemia, and laminitis :contentReference[oaicite:2]{index=2}.

2. Causes of Diarrhea

• Non-Infectious Triggers

• Diet changes or carbohydrate overload: Overfeeding grain or sweet pasture disrupts hindgut microbiota :contentReference[oaicite:3]{index=3}.
• Stress & transport effects: Hospitalization and travel can trigger dysbiosis :contentReference[oaicite:4]{index=4}.
• Medications: Antibiotics, NSAIDs, deworming, or halothane stress may upset gut flora :contentReference[oaicite:5]{index=5}.
• Inflammatory or neoplastic conditions: IBD, lymphoma, or hepatic disease affect absorption :contentReference[oaicite:6]{index=6}.
• Toxins & plants: Ingestion of artemisia, acorns, castor bean, linseed, arsenic etc. :contentReference[oaicite:7]{index=7}.

• Infectious Causes

• Bacterial: Salmonella; Clostridioides difficile & C. perfringens cause enterocolitis often fatal :contentReference[oaicite:8]{index=8}.
• Clostridial colitis (“Colitis‑X”): Fulminant diarrhea with 90–100% mortality :contentReference[oaicite:9]{index=9}.
• Potomac Horse Fever (Neorickettsia risticii): Seasonal, watery diarrhea, fever :contentReference[oaicite:10]{index=10}.
• Viral: Equine coronavirus, rotavirus in foals :contentReference[oaicite:11]{index=11}.
• Parasitic or protozoal: Cyathostomes larvae, Lawsonia, Cryptosporidium in foals :contentReference[oaicite:12]{index=12}.

3. Complications to Monitor

• Dehydration & colic pain
• Electrolyte imbalance; loss of sodium/potassium, metabolic acidosis
• Endotoxemia leading to fever, tachycardia, vascular collapse :contentReference[oaicite:13]{index=13}.
• Laminitis from systemic inflammation or carbohydrate overload
• Protein-losing enteropathy or weight loss with chronic diarrhea

4. Diagnostic Approach

• History & exam: Appetite, temp, vitals, mucous membranes, hydration
• Bloodwork: CBC, chemistry, PCV/TP, electrolytes to assess dehydration or endotoxemia
• Fecal tests: Salmonella culture, toxin ELISA/PCR (C. difficile/perfringens), PCR for PHF :contentReference[oaicite:14]{index=14}
• Ultrasound & endoscopy: For right dorsal colitis, necrosis, cycle lesions :contentReference[oaicite:15]{index=15}
• Biopsy: If chronic inflammatory or neoplastic process suspected

5. Treatment Strategies

• Restore Fluid & Electrolyte Balance

Severe dehydration from diarrhea can exceed 90 L/day in adult horses :contentReference[oaicite:16]{index=16}. Immediate IV isotonic fluids—boluses then maintenance—plus electrolytes and colloids/plasma help prevent shock :contentReference[oaicite:17]{index=17}.

• Provide Nutritional Support

• Low-bulk, pelleted feeds or quality grass/alfalfa hay during recovery :contentReference[oaicite:18]{index=18}.
• Water, free choice plus balanced electrolytes; molasses-enhanced options improve intake :contentReference[oaicite:19]{index=19}.

• Targeted Therapies

• Oxytetracycline for PHF :contentReference[oaicite:20]{index=20}.
• Metronidazole (20–25 mg/kg) for confirmed or suspected clostridiosis :contentReference[oaicite:21]{index=21}.
• Careful use of broad-spectrum antibiotics if severely neutropenic or septic :contentReference[oaicite:22]{index=22}.
• NSAIDs (e.g., flunixin) to control endotoxin inflammation; monitor hydration.
• Colloids (plasma/HES) for volume expansion as clinically indicated :contentReference[oaicite:23]{index=23}.

• Supportive Measures

• Probiotics—Saccharomyces, Lactobacillus—to support microbiome restoration; results vary :contentReference[oaicite:24]{index=24}.
• Fecal microbiome transplantation (FMT) under exploration, especially in recurrent cases :contentReference[oaicite:25]{index=25}.
• Toxin binders (e.g., activated charcoal) for acute toxin absorption.

6. Monitoring & Recheck Care

• Track vitals, hydration, manure, appetite, and weight daily
• Reassess labs (PCV/TP, electrolytes) as diarrhea improves
• Monitor for laminitis signs—pulse, hoof warmth
• Consider follow-up fecal testing to confirm resolution

7. Prevention & Management

• Avoid abrupt diet changes—introduce feeds gradually over 1–2 weeks :contentReference[oaicite:26]{index=26}.
• Regular deworming, avoid overuse of antibiotics and NSAIDs
• Practice good biosecurity—especially with hospitalized or stressed horses; isolate new arrivals
• Clean stalls and paddocks; avoid toxic plants
• Maintain forage-focused diet with minimal concentrates
• Plan calm transport and hospitalization strategies (electrolytes/hay access) :contentReference[oaicite:27]{index=27}.

8. Owner–Vet Partnership

• Share treatment logs: manure, hydration, vitals, appetite diariamente
• Discuss triggers—diet changes, meds, travel
• Plan recheck schedules based on severity and diagnostics
• Adapt diet and protocol based on recovery stage and lab results.

9. Core Summary Table

🔚 Final Thoughts

Diarrhea is often a symptom rather than a disease—but can escalate quickly without prompt, informed veterinary action. Restoration of hydration, accurate diagnosis, targeted therapy, and supportive care are essential. A collaborative vet-owner approach ensures recovery and minimizes future risk. Want help designing a prevention plan, diarrhea log templates, or post-diarrhea diet guides? Contact our Ask A Vet team. Download the Ask A Vet app for 24/7 monitoring, tailored protocols, and expert support right on your phone. 🌟