🌾 Vet Guide: Feeding Moldy Hay to Horses | 2025 Respiratory Risks, Palatability & Testing Tips 🐴

By Dr Duncan Houston, BVSc

Moldy hay is more than a nuisance—**it’s a health hazard**. Whether it's due to poor weather at harvest or improper storage, feeding moldy hay to horses can lead to **nutrient loss, respiratory disease, and reduced feed intake**. Understanding when hay is dangerous—and how to prevent mold formation—is essential to protect your horse’s health. 🧠🐎

In this 2025 guide, we’ll explore how mold develops in hay, what the risks are, and how to **test questionable hay before feeding**. 🌬️🧪

🦠 Why Moldy Hay Is a Concern

Dr. Sally Flis of Equi-Analytical explains that once mold forms in hay, two key problems arise: 🔍

• 📉 **Loss of dry matter and digestible nutrients** – Mold literally “eats” the hay before your horse can
• 🌬️ **Respiratory irritation** – Mold spores trigger inflammation in the airways, especially in sensitive horses

Mold doesn't just lower hay quality—it can **cause disease**, especially in horses with pre-existing respiratory conditions. 🧬

😷 Mold & Respiratory Disease

Horses with **heaves**, **COPD**, or **inflammatory airway disease (IAD)** are highly sensitive to airborne allergens—including mold spores found in dusty, old, or poorly cured hay. 😮‍💨

Clinical Signs of Respiratory Reaction:

• 💨 Increased respiratory rate
• 🤧 Coughing, nasal discharge
• 🫁 Flared nostrils or labored breathing
• 📉 Poor performance or exercise intolerance

Even low levels of mold can trigger **severe respiratory distress** in susceptible horses. Prevention is key. 🔑

🤢 Palatability & Feed Refusal

Horses have **sensitive noses and taste preferences**. Many will instinctively refuse moldy hay, which leads to **reduced intake and nutrient gaps**. But not all horses are that discerning—some will eat moldy hay anyway, putting them at risk. 🧠

Just because your horse eats the hay doesn’t mean it’s safe. ❌

🌧️ How Mold Forms in Hay

Mold usually forms during **wet or humid weather**—either in the field or during storage. Common causes include: 🌧️

• 🌱 **Wet weather before harvest** – Moist grass can develop mold even before it’s cut
• 💧 **Rained-on hay** – If hay is cut and gets rained on before baling, drying takes longer, increasing mold risk
• 🌫️ **Baling too wet** – Hay baled with >14% moisture is at high risk for internal mold growth
• 🚜 **Poor storage** – Hay stored directly on the ground or without airflow traps moisture and grows mold

Raking and fluffing hay after rain helps, but proper timing and **moisture testing** before baling are crucial. 📏

🧪 Testing Hay for Mold

If hay looks dusty, smells musty, or you’re unsure—it’s always better to **test before feeding**. Not all “dusty” hay is dangerous, but some mold is invisible and still harmful. 🔬

How to Test Hay:

• 🔩 Use a **hay probe** to sample at least 10 bales
• 📦 Mix samples and send 1 lb to a lab like **Equi-Analytical**
• 🧪 Request a **mold spore count** or **mycotoxin screen**

Testing is affordable and fast—and it can save your horse from weeks of coughing or worse. 💡

🧼 Managing Mold Risk Year-Round

✅ Best Practices:

• 📏 Never bale hay over 14% moisture
• 🌬️ Store hay off the ground, with airflow between stacks
• ❄️ In winter, rotate hay to prevent “sweating” and mold growth
• 📉 Don’t feed hay that smells moldy, feels damp, or looks off-color

Even during drought or high hay prices—**resist the urge to feed questionable hay**. Vet bills cost more than quality hay. 💸

📲 Use Ask A Vet for Hay Decisions

The Ask A Vet app gives you quick support when evaluating feed quality:

• 📸 Upload hay photos for condition evaluation
• 📊 Ask about mold risk, testing options, or how to manage hay-sensitive horses
• 🧪 Get recommendations for soaking, steaming, or replacing poor hay

It’s a must-have for nutrition and hay safety questions year-round. 🐴📲

✅ Moldy Hay Takeaways

• 🦠 Mold can reduce hay nutrition and cause severe respiratory issues
• 😷 Sensitive horses may react to even small amounts
• 🧪 Test hay if it smells, looks, or feels questionable
• 🚫 Don’t clip corners by feeding poor hay—it’s not worth the risk
• 📱 Use Ask A Vet to assess mold risks and manage sensitive horses

📲 Final Thoughts from Dr Duncan Houston

Feeding moldy hay may seem like a quick fix—but it’s rarely worth the risk. Whether you’re dealing with respiratory disease, poor appetite, or just uncertainty, **your best defense is information and prevention**. 🧠💙

Download the Ask A Vet app today to test smarter, feed safer, and keep your horse healthy—every season of the year. 🐎📱