🌧️🍃 Hay Damaged by Rain for Horses & Cattle: A Vet’s 2025 Guide

Dr Duncan Houston, BVSc

In 2025, hay remains a backbone of winter and drought-year nutrition for horses and cattle. But when cut hay gets rained on before baling, quality drops fast—and that affects your herd’s health. As your veterinarian, I want you to understand exactly what happens, and how to manage rain‑damaged hay safely.

🔍 Four Main Ways Rain Damages Hay

Dr Brian Pugh (Oklahoma State) outlines four key ways moisture reduces hay value:

1. Leaching: Soluble carbohydrates, vitamins & minerals wash away—especially if the hay was partially dry.
2. Respiration: High moisture (>30%) allows plants to continue metabolizing—burning energy and lowering digestibility.
3. Leaf shatter: Wet hay requires more raking—losing fragile leaves rich in nutrients.
4. Microbial breakdown: Ground moisture promotes mold, bacteria—and dry matter loss (~5% per inch of rain).

📉 How Much Nutrient Loss to Expect?

Studies show losing **5% of dry matter per inch of rain**—so a 2″ shower might reduce yield by 10%, with much of that being protein-rich leaf material. That’s a big nutritional hit your animals will notice.

🧪 When & How to Test Rain‑Damaged Hay

Always send rained-on or exposed hay for analysis. A basic lab test should include: moisture, crude protein, fiber, energy content, and fungal count. Compare results to your target levels:

• 💧 Moisture content: ≤13% for baled hay
• 📈 Crude protein & energy suitable for lactating horses or gestating cows
• 🧫 Low mold & yeast counts

Lab results tell you whether the hay can be used directly or needs supplementation or discarding.

🐄 Feeding Rain‑Damaged Hay Safely

For Cattle

• Mix low-quality hay with better forage to maintain Body Condition Score (BCS)
• Supplement with protein blocks or distillers grains
• Monitor condition monthly; adjust as needed

For Horses

• Supplement with alfalfa or commercial hay cubes to meet protein/energy targets
• Check for mold (musty smell, dust, dark spots); *no moldy hay for horses*
• Introduce gradually to monitor palatability and digestion

🔧 Best Management Practices Post-Rain

• Reshed hay quickly to <30% moisture if possible
• Minimize extra raking to retain leaves
• Store any exposed bales under cover ASAP
• Protect from wildlife and microbes by elevating off soil

💰 Economic Impact & Your Budget

Lost dry matter = lost income. If a ton of hay costs $150, a 10% loss cuts it to $135—and nutritional deficiencies may cost more in supplements or lost field condition. Routine testing and smart feeding strategies can save hundreds per herd annually.

🧾 Record‑Keeping Tips

• Note rain events and affected lots in your feed log
• Record lab test results by bale lot
• Track herd BCS monthly during feeding period
• Note supplement amounts added due to low hay quality

🧠 Vet’s Final Thoughts for 2025

Rain-damaged hay doesn’t need to become your liability—but you must treat it like variable forage. Testing, smart feeding, and good barn management make all the difference. As **Dr Duncan Houston**, I recommend a proactive plan every hay season: test early, store wisely, and monitor your herd carefully.

📣 AskAVet® Support

Need help interpreting hay test results, planning rained-on hay feeding, or adjusting your nutrition plan? Visit AskAVet.com or download the Ask A Vet App for expert advice to protect your horses and cattle this year. 🐾💡

© 2025 Dr Duncan Houston, BVSc | Proudly brought to you by Ask A Vet Blog