📊 Understanding Hay Terms: TDN, RFV, NDF, and What They Mean for You
🌾 Introduction
If you’ve ever looked at a hay test report and felt lost among the acronyms — you’re not alone. Terms like TDN, RFV, and NDF can seem technical, but they’re crucial for understanding hay quality and value.
Whether you’re feeding horses, cattle, or goats, learning what these numbers mean helps you choose the right hay for your animals’ needs — and avoid overpaying for the wrong kind.
📈 1. What Is TDN (Total Digestible Nutrients)?
TDN measures the total energy available in hay — how much of it your animals can actually digest and use.
- Higher TDN = higher energy (good for growing or lactating animals).
- Lower TDN = lower energy (good for maintenance diets).
Typical TDN values:
| Hay Type | TDN (%) | Energy Level |
|---|---|---|
| Alfalfa | 55–62% | High |
| Grass Hay | 48–55% | Medium |
| Straw | <45% | Low |
👉 External link: University of Nebraska – Understanding TDN in Forage
Pro Tip: TDN decreases as hay matures — so cutting earlier means more energy.
🌱 2. What Is RFV (Relative Feed Value)?
RFV combines digestibility and intake potential into one easy-to-compare score.
It helps buyers and sellers quickly assess overall hay quality.
| RFV Score | Quality Grade | Typical Use |
|---|---|---|
| 151+ | Premium | Dairy cattle, show animals |
| 125–150 | Good | Horses, growing livestock |
| 103–124 | Fair | Maintenance hay |
| <103 | Poor | Filler feed only |
RFV assumes alfalfa as a baseline (100 = average). Anything above 150 is high-quality hay.
👉 External link: Iowa State University – RFV Explained
🌾 3. What Is NDF (Neutral Detergent Fiber)?
NDF measures the fiber that limits how much an animal can eat.
As NDF increases, hay becomes bulkier — animals eat less, even if it’s nutritious.
| Hay Type | NDF (%) | Intake Impact |
|---|---|---|
| Alfalfa (early cut) | 38–45% | High intake |
| Grass Hay (mature) | 55–65% | Lower intake |
| Straw | >70% | Very low intake |
🌿 4. How These Numbers Work Together
Think of these hay metrics as a triangle of nutrition:
- TDN = energy
- RFV = overall quality
- NDF = bulkiness and intake
The best hay combines moderate NDF, high TDN, and RFV above 120 — especially for dairy or performance animals.
For maintenance feeding, slightly lower numbers can save money without affecting health.
🧮 5. How to Read a Hay Test Report
A standard hay analysis might include:
| Metric | Ideal Range | Meaning |
|---|---|---|
| Moisture | 10–15% | Storage safety |
| Crude Protein (CP) | 10–18% | Growth and milk support |
| TDN | 50–60% | Energy content |
| RFV | 100–150+ | Quality rating |
| NDF | <55% | Digestibility |
👉 External link: Dairy One Forage Lab – Sample Hay Report
🌾 6. Why These Terms Matter for You
Understanding hay analysis helps you:
- Choose the right hay for your livestock type.
- Compare bales by value, not just color or smell.
- Avoid feeding too much or too little energy.
- Build trust when buying or selling hay with data-backed transparency.
🧠 7. Quick Cheat Sheet
| Term | What It Means | Higher = Better? | Affects |
|---|---|---|---|
| TDN | Energy level | ✅ | Growth, milk, stamina |
| RFV | Overall feed value | ✅ | Market price & quality |
| NDF | Fiber bulk | ❌ | Feed intake |
🌿 Final Thoughts
Knowing the difference between TDN, RFV, and NDF takes the guesswork out of buying or selling hay.
Armed with these numbers, you can confidently choose hay that fits your animals’ needs and your farm’s budget — no more relying on looks alone.
At Premium Hay Supply, every bale is lab-tested and certified for moisture, protein, and energy — giving you total confidence in what you feed.
🌾 About Premium Hay Supply
At Premium Hay Supply, transparency is our promise. We include detailed hay test data (TDN, RFV, NDF, and protein) on every order so you always know exactly what’s inside each bale.
