📊 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.

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📈 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.

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🌱 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.

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🧮 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.

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🧠 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.

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🌾 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.