🌾 Vet Advice 2025: Understanding the Impact of Rain-Damaged Hay on Horses and Cattle 🌧️🐴🐄

Whether you’re feeding performance horses or beef cattle, hay is often the foundation of their diet. But what happens when a summer rainstorm hits your freshly cut hay before it can be baled? According to Dr Duncan Houston, rain-damaged hay isn’t just less appealing—it can be nutritionally compromised and even pose risks if fed without proper testing. In this 2025 nutrition guide, we break down how rain affects hay and how to protect your herd’s health. 🧠🌱

🌧️ The Problem: Rain After Cutting but Before Baling

Rain becomes a serious issue when it strikes hay after it’s been cut and is laying in the field to dry. At this stage, the plant is no longer rooted and can’t repair itself—so any damage is permanent. The key risks include:

1. 💧 Leaching of nutrients
2. 🔥 Extended plant respiration
3. 🍂 Leaf shattering
4. 🦠 Microbial breakdown of tissue

All four of these factors reduce hay quality and can affect the nutritional value and safety of the feed for your horses or cattle. 📉

1️⃣ Nutrient Leaching: What Washes Away?

The most immediate effect of rain on cut hay is the loss of soluble nutrients like:

• 🥕 Carbohydrates (sugars and starches)
• 🍊 Water-soluble vitamins (B-complex, C)
• 🧂 Key minerals like potassium and sodium

Leaching is worse when hay has already dried somewhat and then receives prolonged or heavy rainfall. A small shower right after cutting may have little effect, but multiple inches of rain over several days can significantly . 💦

2️⃣ Respiration: Nutrients Burned Away

Respiration is the natural process where plant tissues use stored energy. Normally, respiration stops when hay dries to below 30% moisture. But if hay is still “green” when it’s rained on, respiration continues—burning up carbohydrates that would otherwise benefit your livestock. 🔥

This means hay that was nearly ready to bale can lose even more nutritional value if moisture levels spike again. 🌡️

3️⃣ Leaf Shatter: Losing the Most Nutritious Parts

Leaves are the most nutrient-rich part of many forages. When hay is raked, flipped, and tedded repeatedly to dry it after rain, the fragile leaves often break off from the stem—a process known as leaf shattering. 🍂

Without the leaves, what’s left is mostly stem—lower in protein and energy, and harder for horses to digest. 💢

4️⃣ Microbial Breakdown and Dry Matter Loss

Wet hay lying on the ground becomes a buffet for microbes and fungi. This microbial activity breaks down cell walls and reduces dry matter yield. In fact, studies show hay can lose up to 5% of dry matter per inch of rainfall post-cutting. 📉

Less dry matter means less bulk to feed, and microbial degradation can also raise the risk of mold and mycotoxins. 🦠

🧪 The Solution: Hay Analysis Is Essential

If your hay got rained on, the best way to protect your herd is to send a sample to a forage lab. Here’s what to test for:

• 📊 Moisture content (especially if bales feel warm)
• 💪 Crude protein
• 🍬 Water-soluble carbohydrates (WSC)
• 🧬 Neutral detergent fiber (NDF)
• 🦠 Mold or mycotoxin presence (optional, but advised for horses)

Once you have the results, you can make informed decisions—whether that’s supplementing with grain, using the hay for lower-priority livestock, or discarding high-risk bales. 🧠

🐴 Feeding Rain-Damaged Hay to Horses: Special Concerns

Horses are more sensitive to mold and nutrient imbalances than cattle. With damaged hay, be especially cautious of:

• 🤧 Respiratory irritation from moldy hay
• 💢 Colic from low fiber digestibility
• 🧠 Weight loss from energy-deficient forage

Dr Duncan Houston recommends avoiding feeding moldy hay to horses entirely and always testing questionable hay for sugar content, especially if feeding to insulin-resistant or laminitic horses. 🧬

🐄 Feeding Rain-Damaged Hay to Cattle: More Flexibility

Cattle are more resilient and can often handle lower-quality hay, but watch for:

• 📉 Drop in average daily gain (ADG)
• 🧪 Mycotoxins in moldy bales (especially for breeding cows)
• 🐮 Refusal to eat hay with off smell or color

If necessary, blend lower-quality hay with high-protein supplements or rotate it with fresh forage to ensure adequate intake. 🥩

💡 Tips to Minimize Rain Damage in Future Cuttings

• 📅 Cut hay with a good weather window (at least 3–5 days dry forecast)
• 🚜 Use conditioners to speed drying
• 🔄 Minimize raking or flipping to preserve leaves
• 🌬️ Bale at optimal moisture (no more than 18% for square bales)

📲 Ask A Vet: Forage Review on Demand

Unsure if your rained-on hay is safe to feed? Use the Ask A Vet app to share hay analysis results or photos with veterinarians like Dr Duncan Houston for expert advice tailored to your livestock. 📱🐴🐄

• 📊 Upload forage test results
• 📸 Share hay photos or bale textures
• 💬 Get feedback on feeding safety or supplementation

Download the Ask A Vet app today and protect your herd from poor-quality forage. 🧪🌾

🏁 Final Thoughts: Don’t Guess—Test Your Hay

Rain-damaged hay might still be usable—but only if you know what’s in it. By understanding how rainfall affects nutrition and dry matter, you can make smarter feeding decisions. ✅

Whether you’re feeding a high-performance horse or a commercial cow-calf herd, always:

• 🧪 Test questionable hay
• 📉 Be aware of nutrient loss
• 🚫 Avoid mold risks

🐾 Need help evaluating rain-damaged forage? Visit AskAVet.com or download the Ask A Vet app for expert advice from veterinarians like Dr Duncan Houston. Your livestock deserve forage that feeds—not fails. 🐎🐄💙