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

By Dr Duncan Houston, BVSc

Winter weather brings big changes to your horse’s diet. As pasture quality declines, hay becomes the primary forage source. But not all hay—or pasture—is equal. For horses with insulin resistance, PPID (Cushing’s), or a history of laminitis, carbohydrate content in forage can make or break their health. 🧬🐎

In this 2025 winter feeding guide, Dr Duncan Houston explains how to test your hay and pasture, what results to look for, and why starch and sugar levels matter more than ever this season. ❄️🔬

1. Why Winter Testing Matters 🧪

As pasture becomes dormant in winter, horses rely heavily on hay. But recent research shows that nonstructural carbohydrate (NSC) content in hay can range from 5% to 35%—a wide swing that can cause issues for sugar-sensitive horses. 📈

High-NSC forage may trigger:

• 🍬 Blood sugar spikes
• 🐾 Laminitis flare-ups
• 🧠 Hormonal imbalances in PPID horses

That’s why it’s essential to test your hay and pasture—or ask your supplier to do it. ✅

2. What Is NSC and Why It Matters 🍭

Nonstructural carbohydrates (NSCs) include:

• 🔹 Water-soluble carbohydrates (WSC)
• 🔹 Ethanol-soluble carbohydrates (ESC)
• 🔹 Starch

Horses with insulin resistance or PPID should be fed hay with NSC levels below 10%. Laminitic horses may need even lower values. 🔍

3. What to Ask Your Hay Supplier 🛒

If you’re buying hay, don’t be afraid to ask:

• 📦 “Has this hay been tested for NSC content?”
• 📋 “Can you provide a forage analysis?”

If they haven’t tested it, you can request a starch panel or do your own testing. Hay dealers serious about horse owners’ needs should expect these questions. 🧾

4. How to Collect a Hay Sample 🧰

To test your hay:

🔧 Tools Needed:

• 📌 Hay probe
• 🔋 Electric drill
• 🛍️ 1-quart ziplock bag

📦 Sampling Process:

• Sample 10–20 random bales
• Drill into the center of the bale using the hay probe
• Collect enough to fill a quart bag with ~1 lb of hay
• Seal and label the bag with date, location, and batch

Mix all samples into one “composite” for accurate representation. 🧪

5. How to Sample Pasture Grass 🌿

To test pasture, follow these steps:

• ✂️ Use scissors to clip the top ~6 inches of grass
• 🌱 Take ~20 samples from various grazing areas
• ❌ Avoid cutting down to the dirt unless horses are grazing it that short
• ✂️ Cut grass into ~2-inch pieces and mix thoroughly

Freeze or refrigerate until shipping, and always ship samples promptly. ❄️📦

6. Where to Send Hay and Grass Samples 🧪📬

Reputable forage labs include:

• 🔬 Equi-Analytical
• 🧪 Dairy One
• 🧬 Midwest Laboratories

Cost: ~$20–$50 depending on the panel. Ask for the WSC + starch panel to calculate NSC. 💸

7. Reading Your Forage Report 📊

Key values for sugar-sensitive horses:

• 📉 WSC + starch < 10% = Safe for most IR and PPID horses
• 📈 >12% = Consider soaking hay or choosing another batch

Compare forage nutrient levels with your horse’s needs. Work with a vet or equine nutritionist for best results. 🧠

8. What to Do if Your Hay Tests Too High 💧

Soaking hay can reduce WSC (but not much starch):

• 💧 Soak 30–60 minutes in cold water (more in warm climates)
• 🧽 Drain well before feeding
• ⚠️ Don’t soak hay for >2 hours to avoid fermentation

This method may reduce NSC by up to 30%, depending on hay type. Test soaked hay for accurate results. 🧪

9. Hay Testing Benefits Beyond Winter 🌱❄️

Testing isn’t just for winter—benefits include:

• 🧾 Know exactly what nutrients your horse is getting
• 📉 Prevent laminitis and metabolic flare-ups
• 🧠 Customize feed and supplement plans
• 📦 Build trust with hay suppliers

Smart feeding starts with smart forage choices. 🎯

10. Summary Table: Winter Forage Testing Checklist ✅

11. Final Thoughts from Dr Duncan Houston 💬

Hay is not just hay—especially in winter. For horses with metabolic conditions, testing forage is a simple, affordable way to safeguard against dangerous spikes in sugar and starch. Feed smart, plan ahead, and protect your horse’s health all winter long. 🐴❄️

Need help interpreting your forage analysis or building a winter diet plan? Visit AskAVet.com or download the Ask A Vet app 📲 for personalized veterinary advice from equine nutrition experts.

— Dr Duncan Houston, BVSc