Vet Guide to Doxycycline in 2025 for Horses 🐾

Hello, I’m Dr Duncan Houston, BVSc—founder of Ask A Vet. In this detailed 2025 guide, we cover **doxycycline**—a broad-spectrum tetracycline antibiotic frequently used off-label in equine practice to treat tick-borne infections like Lyme and anaplasmosis, respiratory and joint infections, and intracellular bacterial illnesses. Read on for information on how it works, dosing, potential risks, administration tips, and close monitoring recommendations—all structured to keep your horse safe and well. 💊🐴

📘 What Is Doxycycline?

Doxycycline is a broad-spectrum tetracycline-class antibiotic that inhibits bacterial protein synthesis—effectively halting growth of many Gram-positive, Gram-negative, and intracellular bacteria (e.g., anaplasma, lyme, rhodococcus) :contentReference[oaicite:3]{index=3}.

✅ Common Uses in Horses

• Lyme disease: 10 mg/kg PO every 12 h for 1–2 months :contentReference[oaicite:4]{index=4}.
• Anaplasmosis (EGA): 10 mg/kg PO every 12 h for ~10–14 days :contentReference[oaicite:5]{index=5}.
• Respiratory and joint infections: alternative to oxytetracycline in foals (e.g., Rhodococcus pneumonia) :contentReference[oaicite:6]{index=6}.
• Other use cases: intracellular or tissue infections, such as Potomac Horse Fever :contentReference[oaicite:7]{index=7}.

📐 Dosing & Administration

• Standard dose: 10 mg/kg PO every 12 h for most tick-borne and intracellular infections :contentReference[oaicite:8]{index=8}.
• Lower-dose option: 10 mg/kg PO every 24 h may work for organisms with low MIC (<0.25 µg/mL) :contentReference[oaicite:9]{index=9}.
• Oral administration: best absorbed on empty stomach :contentReference[oaicite:10]{index=10}.
• Avoid IV: intravenous use causes severe cardiovascular effects—arrhythmias, collapse, sudden death :contentReference[oaicite:11]{index=11}.
• Missed dose? Consult your vet; generally, give when remembered unless close to next dose. Never double up :contentReference[oaicite:12]{index=12}.
• Duration: varies: 10–14 days for anaplasmosis; 30–60 days for Lyme and other chronic infections :contentReference[oaicite:13]{index=13}.
• Compounded forms: may be used if horses cannot take tablets :contentReference[oaicite:14]{index=14}.

⚠️ Side Effects & Risks

Common effects:

• GI upset or diarrhea, sometimes colitis—especially with higher doses :contentReference[oaicite:15]{index=15}.
• Reduced appetite—can be minimized by mixing in small feed or syringing directly :contentReference[oaicite:16]{index=16}.
• Photosensitivity—rare in horses but observed in other species :contentReference[oaicite:17]{index=17}.

Serious risks:

• Severe colitis or systemic reactions—requires immediate veterinary intervention :contentReference[oaicite:18]{index=18}.
• Kidney stress—rare but possible; ensure hydration and cautious use alongside nephrotoxic drugs :contentReference[oaicite:19]{index=19}.

🚫 Contraindications & Cautions

• Never inject or infuse intravenously—risk of fatal cardiovascular collapse :contentReference[oaicite:20]{index=20}.
• Care in dehydrated horses or those on nephrotoxic drugs :contentReference[oaicite:21]{index=21}.
• Use cautiously in young foals—empty-stomach dosing may affect GI flora :contentReference[oaicite:22]{index=22}.
• Not labeled for horses intended for human consumption—declare exclusion in passport :contentReference[oaicite:23]{index=23}.

🩺 Monitoring & Veterinary Oversight

• Check hydration and appetite daily—seek vet care if diarrhea occurs :contentReference[oaicite:24]{index=24}.
• Follow-up bloodwork for Lyme/anaplasmosis—verify clearance and organ function :contentReference[oaicite:25]{index=25}.
• Monitor for signs of colitis (fever, abdominal pain) and discontinue if needed :contentReference[oaicite:26]{index=26}.

🏡 Real‑World Examples

🐎 Lyme treatment

• 10 mg/kg PO every 12 h for 30 days. After two weeks, lameness improved and antibodies declined :contentReference[oaicite:27]{index=27}.

🐎 Anaplasmosis in adult horse

• 10 mg/kg twice daily for 14 days—fever resolved and platelet count normalized.

❓ FAQs

Can I give doxycycline IV if horse won’t take oral?

No—intravenous administration can cause arrhythmia, collapse, or death. Oral formulations or compounded paste should be used :contentReference[oaicite:28]{index=28}.

What if diarrhea starts?

Stop medication immediately and call your vet. Support with fluids and potentially probiotics or medications—colitis can be life-threatening :contentReference[oaicite:29]{index=29}.

Can I give with feed?

Yes—if doxycycline is mixed with a small amount of feed or syringed, it may reduce GI upset; avoid high-calcium products :contentReference[oaicite:30]{index=30}.

📌 Final Takeaways

• Doxycycline is a valuable broad-spectrum antibiotic for equine tick-borne, respiratory, joint, and intracellular infections.
• Standard dosing: 10 mg/kg PO every 12 h (or every 24 h for low-MIC infections), on an empty stomach when feasible.
• Avoid IV use and monitor for GI upset or colitis—ensure hydration and vet follow-up.
• Use responsibly—complete the full course, monitor labwork, and exclude from human-food chain when treated.
• Always administer under veterinary supervision, with proper monitoring for adverse effects. 🐾❤️

Considering doxycycline for your horse? Download the Ask A Vet app for dosage schedules, side-effect tracking, treatment reminders, and 24/7 veterinary support—helping your horse recover safely in 2025 and beyond. 🐴💊