What to Look for in a Hay Test (And Why It Matters More Than You Think)
When people say “forage-only didn’t work for my horse,” the problem is rarely forage itself. It’s almost always that they didn’t know what they were feeding.
Hay is not just “hay.” Two bales can look green, soft, and leafy, but produce completely different results in your horse’s body. If you’re not looking at a hay test, you’re guessing, and when it comes to performance, weight, and overall health, guessing doesn’t work.
Where Do Horses Actually Get Calories from Hay?
Most people think calories come from fat or starch but horses are designed differently.
The majority of a horse’s energy comes from fermentable fiber.
When your horse eats hay:
- Fiber is fermented in the hindgut
- This produces volatile fatty acids (VFAs)
- VFAs are absorbed and used as the horse’s primary fuel source
This fuels:
- Daily metabolism
- Endurance
- Muscle function
- Recovery
There is also small, natural starch in hay, which is digested and stored as glycogen for short bursts of energy.
So yes, horses can get all their calories and energy from forage…but only if the forage is actually providing it.
The Two Most Important Numbers on Your Hay Test
Everyone looks at protein but protein alone tells you very little.
The two numbers that matter most are:
1️⃣ RFV (Relative Feed Value)
RFV tells you how digestible the hay is and how much your horse can actually consume and utilize.
It’s based on fiber levels:
- Lower fiber = higher digestibility
- Higher digestibility = more usable nutrients
Higher RFV = better quality, more usable forage
Why this matters:
If hay is not digestible, your horse cannot extract nutrients—even if it “looks nice.”
2️⃣ DE (Digestible Energy)
DE tells you how many usable calories your horse is actually absorbing.
Not what’s in the hay…What the horse can actually use.
This is the number that determines:
- Weight gain or loss
- Performance output
- Stamina
- Recovery
How RFV and DE Work Together
RFV and DE are closely connected.
- Higher RFV → more digestible fiber
- More digestible fiber → more fermentation
- More fermentation → more VFAs
- More VFAs → more energy
Higher RFV almost always means higher DE
If RFV is low:
- Digestibility drops
- VFA production drops
- Energy availability drops
Even if the horse is eating plenty.
Why “Green and Leafy” Isn’t Enough
This is where many people go wrong.
They choose hay based on:
✔ Green color
✔ Soft texture
✔ Leafiness
✔ Protein %
But none of those guarantee:
- Digestibility
- Energy output
- Caloric intake
You can have:
- “Beautiful” hay
- Good protein
- And still have a horse losing weight or lacking energy
Because the DE is too low.
What to Look for Based on Your Horse
Performance Horses
Performance horses need higher energy availability.
Look for:
- RFV: ~140–180+
- DE: ~0.95–1.10+ Mcal/lb
This supports:
- Strong VFA production
- Adequate glycogen storage
- Stamina and repeatable performance
- Faster recovery
Without enough DE, performance horses will:
- Feel flat
- Struggle with stamina
- Lose condition
Easy Keepers / Metabolic Horses
Easy keepers don’t need high calorie density.
Look for:
- Moderate RFV: ~100–140
- Lower to moderate DE
This helps:
- Control calorie intake
- Reduce excess energy storage
- Support metabolic balance
Too high DE (even from “clean” hay like alfalfa) can:
- Lead to weight gain
- Contribute to metabolic stress
- Increase laminitis risk
Why Forage-Only Diets “Don’t Work”
Forage-only diets work extremely well…When the forage actually meets the horse’s needs.
They fail when:
- DE is too low → not enough calories
- RFV is too low → poor digestibility
- Intake is limited → not enough total energy
This is when people say: “My horse needs grain.” But what’s really happening is: The forage isn’t supplying enough usable energy. So grain is added to compensate.
The Bottom Line
If you don’t know your hay:
- You don’t know your calories
- You don’t know your energy output
- You don’t know if your horse’s needs are being met
And everything else becomes guesswork.
Final Takeaway
- Horses get energy primarily from fiber → VFAs
- RFV tells you how digestible your hay is
- DE tells you how much usable energy your horse gets
- Protein alone does not determine performance or weight
Good feeding starts with good forage and good forage starts with a hay test.
