🦠 Vet Advice 2025: The Truth About Feeding Moldy Hay to Horses 🐎🌾

Every horse owner faces it sooner or later: the moment when you open a bale of hay and see or smell something off. But is all moldy hay dangerous—or are some batches still okay to feed? In this comprehensive 2025 guide, Dr Duncan Houston separates myth from fact when it comes to moldy hay and horses, from respiratory risks to testing strategies and feeding alternatives. 🧠🐴

🔬 What Causes Mold in Hay?

Mold growth starts when hay is exposed to moisture—either before or after baling. The most common causes include:

• 🌧️ Rain after cutting but before baling
• 💧 Baling hay at >14% moisture content
• 🧊 Cool, wet conditions that slow drying
• 🌿 Hay absorbing moisture from wet soil

Even before cutting, grass can develop mold in humid conditions. And after baling, improper storage can introduce new moisture that fosters microbial growth. 🦠

📉 How Mold Reduces Hay Quality

When mold sets in, it consumes nutrients that would otherwise benefit your horse. This results in:

• 🔥 Loss of dry matter (up to 10–20%)
• 🥕 Reduced total digestible nutrients (TDN)
• 🧂 Depletion of vitamins and minerals

Essentially, the mold eats the hay before your horse can. This reduces the caloric value and feeding efficiency—especially critical for performance horses, senior horses, and lactating mares. 📉

💢 Health Risks of Moldy Hay for Horses

1. 💨 Respiratory Irritation

Mold spores can cause or worsen respiratory issues, especially in horses with:

• 🫁 Heaves (recurrent airway obstruction)
• 🤧 Inflammatory airway disease (IAD)
• 😷 Chronic obstructive pulmonary disease (COPD)

Symptoms include coughing, nasal discharge, and increased respiratory effort. Horses with existing respiratory issues should never be fed moldy hay. 🚫

2. 🦠 Mycotoxins and Digestive Upset

Some molds produce mycotoxins, which are toxic to horses even in small amounts. Although more common in grain, some hay molds can trigger:

• 🤒 Colic
• 🧠 Neurological signs
• 🐾 Poor weight gain or appetite loss

These effects are more pronounced in young, old, or immunocompromised horses. ⚠️

3. 🐴 Palatability and Refusal to Eat

Even if the hay isn’t dangerous, many horses won’t eat moldy forage due to its odor and taste. This leads to hay waste and feeding inconsistency. 🐽

🧪 Should You Test Moldy Hay?

Absolutely. Not all moldy hay is unsafe—but you won’t know until it’s tested. Here’s what to do:

How to Test:

• 📦 Collect samples from different parts of multiple bales
• 🧫 Send to a forage lab for mold count and nutritional analysis
• 🔬 Optional: Request mycotoxin screening

Tip: If mold is visible or the hay smells musty, test before feeding. If horses have respiratory conditions, err on the side of caution. 🧠

✅ When Is Moldy Hay Still Usable?

Some lightly moldy hay can be fed to healthy cattle or non-breeding adult horses in small amounts—but only if:

• 🧪 Mold spore count is low
• 🧬 No mycotoxins detected
• 🐴 Horses show no signs of irritation

Mixing moldy hay with clean hay may help, but never feed visibly moldy hay to young horses, pregnant mares, or horses with heaves. 🚫

🛡️ Preventing Mold in Future Hay Cuttings

• 📅 Cut hay with a dry forecast window (3–5 days)
• 🌬️ Use conditioners to speed drying
• 🚜 Rake early to prevent mold buildup from wet soil
• 💧 Bale at 12–14% moisture
• 🏠 Store hay in a dry, well-ventilated space

📲 Ask A Vet: Hay Review on Demand

Unsure if that dusty bale is safe to feed? The Ask A Vet app makes it easy to upload hay photos and lab results for fast feedback from veterinarians like Dr Duncan Houston. 📱🌾

• 📸 Share bale photos
• 🧪 Submit forage analysis
• 💬 Get advice on palatability, safety, and risk factors

Download the Ask A Vet app today and protect your horse’s lungs, gut, and performance with smarter hay choices. 🐴💨

🏁 Final Thoughts: Don’t Guess—Test and Protect

Moldy hay isn’t just unpleasant—it can be dangerous or costly if fed blindly. While not all mold means you have to discard the bale, the only way to know is to test and observe. ✅

Always consider:

• 🧪 Mold count and mycotoxin levels
• 🧠 The individual horse’s health status
• 🌿 Quality of storage and harvest conditions

🐾 For expert advice on hay safety and feeding practices, visit AskAVet.com or download the Ask A Vet app to connect with Dr Duncan Houston and ensure your horse’s forage is safe and supportive—every meal, every bale. 🐎💙