05/28/2025
EDS offers a PCR and culture for R. equi. It has been widespread this spring!
🦠 Rhodococcus equi in Foals: What I’ve Learned
This is the first time I’ve had a foal diagnosed with Rhodococcus equi, and before answering all the questions that have come in, I’ve spent the past few days digging deep—reading veterinary journals, consulting our vet, and trying to wrap my head around this infection.
It’s scary, serious, and sneaky—but it’s also something we can fight effectively if we catch it early. So here’s what I’ve learned and what I think every foal owner or breeder should know:
❓ What is Rhodococcus equi?
It’s a bacteria that lives in the soil—especially in warm, dry, dusty environments where manure builds up. Foals inhale it, and it settles deep in the lungs, where it forms abscesses. That’s what makes it so dangerous—it hides, spreads, and doesn’t respond to short-term treatments like most infections.
🧬 How do foals get it?
🌬️ Foals are exposed by inhaling dust from contaminated ground
🧫 The bacteria hide inside immune cells, making them hard to eliminate
🚫 It’s not contagious horse-to-horse in the traditional sense, but multiple foals on a farm can be affected due to shared exposure
⚠️ Early signs are incredibly subtle:
🌡️ Low or fluctuating fever
😴 Mild lethargy
😮 Slight cough or increased breathing effort
Later stages may bring:
🤧 Nasal discharge
😓 Labored breathing
📉 Poor weight gain
🦵 Swollen joints or diarrhea (in rare cases where it spreads beyond the lungs)
In Callie’s case? Just a fever and a bit of tiredness. That’s it. No cough, no discharge. But that fever told us everything we needed to know.
📊 How serious is it?
According to the AAEP, R. equi is one of the leading causes of severe pneumonia in foals, affecting up to 20% of foals on some endemic farms. That doesn’t mean every farm will see it—but when it shows up, it hits hard.
The survival rate is around 70–90% with early detection and aggressive treatment. But foals that are untreated—or treated too late—can decline rapidly. Some don’t make it. Others may suffer long-term lung damage or complications.
That’s why catching it early can mean the difference between a few weeks of meds… and a heartbreaking outcome.
💊 Treatment is not quick.
This shocked me: most infections resolve in a week or two. Rhodococcus? You're usually looking at 6 to 12 weeks of treatment. Antibiotics have to work their way into the lung abscesses, and stopping early can cause the infection to come roaring back.
Treatment plans vary depending on the case and should always be guided by your veterinarian. One of the most common and effective combinations is a macrolide paired with rifampin. In Callie’s case, she’s receiving erythromycin alongside rifampin—an established treatment that’s helping her respond well so far.
But there’s an important catch:
☀️ Sun sensitivity and risk of hyperthermia:
Macrolides like erythromycin, clarithromycin, and azithromycin can interfere with the body’s ability to regulate heat, putting foals at risk for dangerously high internal temperatures. That’s why foals on these meds need to be kept out of the sun and as cool as possible. For Callie, that’s meant nighttime-only turnout and a fan blowing fresh air into her stall during the day to keep her comfortable.
Even if a foal looks great, overexertion or a warm stall could trigger a dangerous spike in temperature.
🔍 How it’s diagnosed:
🧪 Chest ultrasound is the gold standard—abscesses don’t show up with just a stethoscope
📊 Bloodwork helps monitor inflammation (fibrinogen, white cell count)
🧫 Some cases may require a tracheal wash and culture, especially if the foal isn’t improving
📚 Other FAQs I’ve Learned Along the Way:
🍼 Why are foals most at risk?
Foals between 1 and 6 months old are the most vulnerable because their immune systems are still developing and they spend a lot of time with their noses close to the ground—inhaling dust stirred up by hooves. That combination makes them the perfect target.
🧒 Should I be worried about my yearling?
Yearlings and adult horses are rarely affected. Healthy older horses are usually immune carriers—they may harbor the bacteria in their gut or environment but don’t develop symptoms. So it’s not typically a concern for them unless they’re severely immunocompromised.
🩸Why didn’t the plasma or maternal antibodies prevent it?
Great question—and one I asked too. While good colostrum and hyperimmune plasma provide some protection, they’re not a guarantee. The antibodies help reduce severity and may even prevent disease in some cases, but they can’t stop all exposure—especially in high-risk environments. Think of them as an extra layer of defense, not full armor.
💉 Is there a vaccine?
Sadly, no—not yet. Researchers have been working on it for decades, but so far there’s no commercially available vaccine proven to prevent R. equi in foals. That’s why early detection and management remain our best tools.
🌾 Can you test for it or remove it from your farm?
This was one of my first questions, too—especially after realizing just how serious it can be. And here’s what I found:
🧪 Yes, you can test for Rhodococcus equi in soil or manure, but it’s not often done because:
– It’s expensive and not widely available
– A positive test doesn’t necessarily mean your foals will get sick
– And a negative test doesn’t guarantee you’re in the clear
Soil cultures might confirm the bacteria is present, but it’s considered endemic on many farms—especially in major breeding regions like Kentucky. That means it's just part of the environment in many places.
🧼 Can you get rid of it? Unfortunately, no—not completely.
R. equi lives in:
– Soil
– Manure
– Dust particles kicked up by hooves
Once it’s in the environment, it’s nearly impossible to eliminate. Even on the best-managed farms, it lingers in dry areas near gates, around feeders, or where pasture gets worn down.
But—here’s what can make a difference:
✅ Manure management (removing or composting manure away from foaling areas)
✅ Watering dusty zones or rotating paddocks to avoid erosion
✅ Planting grass in bare or overgrazed areas to reduce dust
✅ Limiting stocking density and separating younger foals from high-traffic zones
✅ Daily temp checks and proactive monitoring (like microchips + EquiTrace)
Even with good pasture and responsible management (like we do here), you may still see cases. That’s not a sign your farm is dirty—it’s a sign you’re raising foals in a world where some pathogens just live in the dirt.
🧼 And no—having this on your farm does NOT mean you did something wrong.
This part is important.
Our foals go out in well-managed grassy pastures. We mow regularly. We drag to break up manure. We don’t overgraze. But like most farms, there are still dusty spots near gates or eroded areas where hooves break down the soil.
That’s all it takes.
R. equi is in the soil and dust on many breeding farms. You can do everything right and still have a foal exposed. Even the biggest, cleanest, most prestigious operations deal with this bacteria. It’s not a sign your farm is dirty—it’s a sign your foal was born into a world where certain pathogens live in the dirt.
The goal isn’t perfection—it’s preparedness. Early detection is everything.
📈 Why we caught it early
We use bio-thermo microchips and the EquiTrace app to monitor temperatures multiple times a day. Without that, I honestly don’t think I would have caught Callie’s fever in time. She looked fine. She was only a little quiet. But that one number changed everything.
Because we caught it early, we were able to start treatment before things progressed. And that’s our best chance at avoiding complications—or a much harder road ahead.
📌 Final thought: Don’t wait for a cough.
I’ll say that again: Don’t wait for a cough. If something feels off, check a temp. If there’s a low-grade fever and you’re not sure why, call your vet. Rhodococcus equi can move fast, but early detection can absolutely save lives.
This isn’t the post I thought I’d be writing this week—but I’m grateful we caught it in time. I hope this helps someone else do the same.
And if you’ve been through this with one of your foals—whether recently or years ago—I’d love for you to share what you learned in the comments. The more we talk about it, the more tools we give others to catch it early and act fast. Your experience might be exactly what someone else needs to hear.
