Winter Hay and Pasture Testing for Horses
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Winter Hay and Pasture Testing for Horses: What Actually Matters
By Dr Duncan Houston
Winter feeding is where many laminitis and metabolic problems quietly start.
When pasture quality drops, hay becomes the primary forage. That shift matters more than most owners realise, especially for horses with insulin resistance, PPID, or a history of laminitis. Not all hay is the same, and the variation in sugar and starch content can be large enough to change a horse’s risk profile completely.
This is where testing becomes important.
Because without testing, you are guessing.
Quick Answer
Hay and pasture testing in winter helps identify nonstructural carbohydrate levels, which directly affect horses prone to laminitis, insulin resistance, or PPID. For at-risk horses, total NSC is generally best kept below around 10%, and testing is the only reliable way to know whether a forage is safe.
Quick Decision Guide
Horse has no metabolic issues and maintains weight well → testing is helpful but not critical
Horse has insulin resistance, PPID, or laminitis history → testing is strongly recommended
Hay source is unknown or variable → testing becomes more important
Horse is gaining weight, footy, or less comfortable → forage sugar may be too high
No testing and feeding high-risk horse → unnecessary risk
Why Winter Forage Testing Matters
Winter changes the feeding system.
Pasture intake drops, hay intake increases, and the horse becomes more dependent on whatever forage you provide. The problem is that hay can vary widely in sugar and starch content.
In practice, that means two bales that look identical can have completely different effects on the same horse.
What This Usually Turns Out To Be
When forage causes problems in winter, the situation is usually one of these:
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hay is higher in sugar than expected
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pasture still contains significant carbohydrates despite looking dormant
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the horse’s metabolic condition is not fully controlled
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feeding decisions are based on appearance rather than analysis
The mistake I see most often is assuming hay is “safe enough” without actually knowing.
What Is NSC and Why It Matters
Nonstructural carbohydrates include:
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water-soluble carbohydrates
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ethanol-soluble carbohydrates
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starch
These are the components that influence blood glucose and insulin response.
For horses with metabolic conditions, high NSC forage can:
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trigger laminitis
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worsen insulin dysregulation
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increase metabolic instability
Decision Checkpoint
If a horse is metabolically sensitive, forage sugar matters more than almost anything else in the diet.
What Levels Are Considered Safer
For most horses with metabolic concerns:
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NSC below 10% is generally considered safer
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higher levels increase risk, especially in laminitic horses
This is not an absolute rule for every horse, but it is a practical working target in most cases.
The key point is not the exact number.
It is knowing the number.
Why You Cannot Judge Hay by Eye
Hay quality is often judged by:
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colour
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smell
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texture
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leafiness
These are useful indicators of general quality, but they do not reliably tell you sugar content.
A visually “nice” hay can still be too high in NSC for a sensitive horse.
That is why testing matters.
What to Ask Your Hay Supplier
If you are buying hay, ask:
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has this hay been tested
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can you provide a forage analysis
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what are the WSC and starch values
If they do not know, that does not automatically mean the hay is bad.
But it does mean you are feeding without data.
How to Take a Proper Hay Sample
A representative sample is essential.
That means:
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sampling multiple bales, not just one
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collecting from the center of the bale
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combining samples into a composite
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labelling clearly
The goal is to represent what the horse is actually eating, not just one section of one bale.
How to Sample Pasture
Even in winter, pasture can still contain carbohydrates.
Sampling should include:
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multiple areas of the paddock
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the height the horse is actually grazing
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consistent clipping method
Pasture testing is often overlooked, but it can be just as important as hay testing in some environments.
Where to Send Samples
Use a reputable forage lab.
The key is to request the correct panel.
For metabolic management, you need:
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water-soluble carbohydrates
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starch
This allows you to calculate NSC properly.
How to Read the Results
The most important number is:
WSC + starch = NSC
Interpretation depends on the horse.
What Vets Care About Most
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does the NSC level match the horse’s risk
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does the diet need adjusting
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is soaking or dilution needed
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is the hay appropriate for long-term feeding
Testing is only useful if the result leads to a decision.
What to Do if NSC Is Too High
If forage is too high in sugar:
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switch to a lower NSC hay if possible
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soak hay to reduce water-soluble carbohydrates
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dilute with lower NSC forage
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adjust the overall diet
Soaking can help, but it is not perfect.
It reduces sugars more than starch and results can vary depending on the hay.
Why Soaking Needs Care
Soaking can reduce sugar content, but it also:
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removes some nutrients
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changes palatability
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increases spoilage risk if handled poorly
Hay should not be left soaking for excessive periods, and feeding should follow promptly after draining.
Benefits of Testing Beyond Winter
Forage testing is not just a winter tool.
It helps with:
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consistent feeding plans
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performance management
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weight control
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supplement decisions
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avoiding unnecessary feed costs
The more predictable the forage, the more predictable the horse.
Severity Framework
| Situation | What It Looks Like | What It May Mean | What To Do |
|---|---|---|---|
| Low concern | Healthy horse, stable weight, no metabolic issues | Lower risk | Testing optional but useful |
| Moderate concern | Slight weight gain, mild sensitivity, uncertain forage | Possible NSC issue | Test forage and adjust |
| High concern | Laminitis history, insulin resistance, PPID | High risk | Test and manage strictly |
| Urgent concern | Foot soreness, laminitis flare, sudden deterioration | Forage may be a trigger | Immediate dietary reassessment |
Common Mistakes Owners Make
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assuming all hay is similar
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not testing forage for high-risk horses
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relying on appearance alone
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ignoring pasture contribution
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overfeeding without understanding content
The biggest mistake is guessing instead of measuring.
What Should You Do Right Now?
If you are feeding hay this winter:
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Identify whether your horse is at metabolic risk
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Test hay if there is any uncertainty
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Review pasture contribution if applicable
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Adjust feeding based on actual data
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Monitor your horse’s condition closely
Simple checkpoint:
tested forage → informed feeding
untested forage → unnecessary risk
When Is This an Emergency?
It becomes urgent if your horse shows:
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laminitis signs
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foot soreness
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sudden reluctance to move
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metabolic instability
In these cases, forage needs to be reviewed immediately.
Frequently Asked Questions
Do all horses need low NSC hay?
No. Mainly those with metabolic risk.
Can hay vary that much?
Yes. NSC levels can vary widely between batches.
Is soaking always enough?
Not always. It helps, but it does not fix every problem.
Should pasture be tested too?
Yes, especially in high-risk horses.
Is testing expensive?
No. It is inexpensive compared to treating laminitis.
Final Thoughts
Winter feeding is where many problems are created or prevented.
Hay is not just background feed. It is the main driver of the horse’s diet during this time. If the numbers are wrong, the horse pays for it.
Testing removes guesswork.
And in horses with metabolic risk, removing guesswork is one of the most important things you can do.
If you need help interpreting forage results, deciding whether your hay is safe, or building a winter feeding plan for a sensitive horse, ASK A VET™ can help you work through the next step clearly and practically.