Vet Advice: Winter Hay and Pasture Testing for Horses 2025 ❄️🌾🐴

By Dr Duncan Houston, BVSc

As fall fades into winter, pasture grass loses its nutritional value, and hay becomes the primary forage for most horses. But not all hay is the same—and for horses with PPID (Cushing’s disease) or equine metabolic syndrome (EMS), what's in that hay can make or break their health. 🌾🧠

In this 2025 winter feeding guide, Dr Duncan Houston explains how and why to test your hay and pasture, especially if you have insulin-resistant horses. Testing isn’t just smart—it’s essential. ❄️🐎

1. Why Test Your Hay and Pasture? 🧪

Research shows that nonstructural carbohydrate (NSC) content in hay can vary widely:

• 📊 NSC can range from 5% to 35% in grass hay alone
• ⚠️ Horses with metabolic issues need hay under 10% NSC

Feeding high-sugar hay to a horse with EMS or PPID may trigger laminitis, weight gain, or worsening insulin resistance. Knowing what’s in your forage helps prevent this. 🩺

2. What Is NSC? 🍭

Nonstructural carbohydrates (NSC) include sugars, starches, and fructans—components of the plant that spike insulin levels. It’s calculated as:

NSC = Water-Soluble Carbohydrates (WSC) + Starch

For horses with metabolic concerns, target NSC <10%. For very sensitive horses, lower is better. 🔍

3. What to Ask Your Hay Dealer 🛒

• 🧾 Has this hay been tested?
• 📄 Can I see the full forage analysis?
• 💬 If not tested, can you submit it—or allow me to sample it?

If you're buying hay for multiple horses, especially those with medical needs, insist on testing. Reliable hay producers will understand. 🧠

4. How to Collect a Hay Sample 📦

🔧 What You’ll Need:

• 🔩 Hay probe + electric drill
• 📦 1-quart plastic bag
• 🧺 Sample at least 10 random bales

🧪 Instructions:

• Drill into the center of each bale with the hay probe
• Collect ~1 pound total from all bales combined
• Mix samples, seal bag, and label with date and batch info

Ship or drop off at a forage lab promptly. ❄️📬

5. Sampling Pasture Grass 🌱

Even in winter, pasture testing is helpful if your horses still graze. Use scissors to:

• ✂️ Cut the part of the plant that your horse is actually eating (don’t clip near the ground if they aren’t grazing that short)
• 📍 Take 20+ samples from various grazing areas
• 🪵 Chop into 2-inch pieces and mix thoroughly

Refrigerate the sample and send to a lab ASAP. 📦

6. What to Test For 🧬

Full analysis is great, but if you’re focused on metabolic conditions, ask for:

• 🔍 WSC
• 🔍 Starch

Labs like Equi-Analytical offer cost-effective “carbohydrate or starch panels” for this purpose. Expect to pay $20–$50. 💸

7. For Hay Producers and Barn Managers 🧱

If you produce hay or manage multiple horses, routine testing helps with:

• ✅ Matching forage to horses’ nutritional needs
• 📉 Reducing health risks
• 📊 Planning feed purchases and supplements more precisely

Testing once per cutting is ideal. If hay changes sources, re-test. 🔁

8. Summary Table: Winter Forage Testing Guide 📋✅

9. Final Thoughts from Dr Duncan Houston 💬

In winter, forage is everything. For horses with insulin resistance or PPID, even a “normal” hay could pose a hidden danger. Testing your hay and pasture isn’t just smart—it’s lifesaving. Protect your horse’s health by knowing what’s in their diet. 🧠🐴🌿

Need help interpreting a forage report or finding a testing lab? Visit AskAVet.com or download the Ask A Vet app 📲 for feed planning and metabolic condition support from trusted equine nutrition experts.

— Dr Duncan Houston, BVSc