Winter Hay and Pasture Testing for Horses

Winter Hay and Pasture Testing for Horses

By Dr Duncan Houston

Once winter arrives, most horses rely far more heavily on hay and far less on fresh pasture. That shift matters because forage is no longer just part of the diet. It becomes the diet. For many horses, that is manageable. For horses with Equine Metabolic Syndrome, PPID, insulin dysregulation, obesity risk, or a history of laminitis, it can become one of the most important management decisions of the season.

The problem is that hay is not nutritionally predictable just because it looks green, smells fresh, or came from a familiar supplier. Sugar and starch levels can vary dramatically between cuttings, farms, fields, and even batches. That means feeding “normal hay” without testing can be a genuine risk in the wrong horse. Winter forage testing is not overkill. In higher-risk horses, it is one of the smartest preventive steps you can take.

Quick Answer

Winter hay and pasture testing matters because non-structural carbohydrate levels can vary widely, and visually assessing forage tells you very little about whether it is safe for a horse with PPID, Equine Metabolic Syndrome, insulin dysregulation, or laminitis risk. For these horses, forage often needs to stay under about 10 percent NSC, depending on the case. The safest approach is to test the actual hay or pasture being fed rather than guessing based on type, color, or supplier reputation.

Why Winter Forage Testing Matters

In winter, horses often move from variable pasture intake to a much more concentrated reliance on hay. That can be good or bad depending on what the hay contains.

Testing matters because forage affects:

• blood insulin response

• laminitis risk

• calorie intake

• body condition

• need for soaking or restriction

• how safely a horse with metabolic disease can be managed

In practice, owners often spend a lot of time worrying about treats, grain, and supplements while the biggest sugar source in the diet is sitting in the hay net.

That is the real issue. Forage is usually the largest part of the ration, so it is the part that needs the most respect.

What Is NSC and Why Does It Matter?

NSC stands for non-structural carbohydrates. In practical equine feeding terms, this is the part of the forage most relevant to insulin response and laminitis risk.

It usually includes:

• sugars

• starches

• some rapidly available plant carbohydrates depending on how the lab reports them

A useful practical definition in many horse-feeding contexts is:

NSC = water-soluble carbohydrates plus starch

For horses with:

• Equine Metabolic Syndrome

• insulin dysregulation

• PPID with metabolic instability

• a history of laminitis

forage NSC becomes one of the most important numbers on the whole feed plan.

Many higher-risk horses are managed best on forage around or below 10 percent NSC, though the exact safe target depends on the individual case.

Which Horses Need Forage Testing Most?

Some horses can tolerate moderate variation in forage with few consequences. Others cannot.

Testing becomes especially important for:

• horses with Equine Metabolic Syndrome

• horses with insulin resistance or insulin dysregulation

• horses with PPID

• horses with a history of laminitis

• easy keepers and obese horses

• ponies and hardy breeds with strong metabolic tendencies

• barns feeding one hay source to mixed-risk horses

Decision checkpoint

If your horse has had laminitis before, or your vet has raised concern about insulin or metabolic disease, forage testing should be considered a core management tool, not an optional extra.

Why You Cannot Judge Hay by Eye

Owners often try to judge hay by:

• color

• smell

• softness

• species label

• what the supplier says

None of those reliably tells you the sugar level.

Hay that looks beautiful can still be unsuitable for a laminitis-prone horse. Hay that looks coarse can sometimes be safer. The only way to know the carbohydrate profile with confidence is to test it.

This is one of the biggest mistakes I see. Owners assume they are choosing “safe hay” because it looks mature or because the seller says it is low sugar. That is not enough.

How Much Can Hay Vary?

Quite a lot.

Hay NSC can vary widely based on:

• grass species

• cutting time

• maturity at harvest

• weather

• fertilization

• drought or stress

• storage conditions

• field variation

That is exactly why two bales that look similar may not behave similarly in a metabolic horse.

The more vulnerable the horse, the less acceptable that guesswork becomes.

How Worried Should You Be?

Low risk

• healthy horse

• no metabolic history

• normal body condition

• no laminitis history

Action: Testing is still useful, but not always urgent.

Moderate risk

• easy keeper

• overweight horse

• mild regional fat pads

• older horse with suspected metabolic change

Action: Hay testing is sensible and often worthwhile.

High risk

• diagnosed Equine Metabolic Syndrome

• insulin dysregulation

• PPID with metabolic concerns

• past laminitis episode

Action: Forage testing is strongly recommended.

Critical risk

• active laminitis

• recent laminitis flare

• severe metabolic instability

• repeated flare-ups triggered by diet changes

Action: This is not the time to guess. Testing and strict forage control matter urgently.

What Should You Ask a Hay Supplier?

If you are buying hay, ask directly:

• Has this hay been tested?

• Can I see the forage analysis?

• Which cutting is this?

• Is this analysis from this batch or a different one?

• If it has not been tested, can I sample it?

A good supplier may not always have a test, but a reliable supplier should at least understand why it matters.

If a horse has serious metabolic risk, it is reasonable to insist on knowing what you are feeding rather than just accepting reassurance.

How To Sample Hay Properly

A poor sample gives poor results, so the sampling method matters.

A practical hay sampling approach usually includes:

• using a hay probe

• sampling at least 10 bales from the batch

• taking cores from the center of each bale

• combining the material into one mixed sample

• labeling clearly by batch and date

• sending it promptly to the laboratory

If you only grab a handful off the outside of one bale, the result is much less useful.

The point is to represent the batch the horse will actually eat.

How To Sample Pasture Properly

Pasture testing is less commonly done than hay testing, but it can still be very useful, especially if horses continue to graze during winter or seasonal transition periods.

A practical pasture sample should:

• come from the areas horses are actually grazing

• reflect the height the horse is eating

• include multiple small cuts from different parts of the paddock

• be mixed together

• be kept cool and sent quickly

Do not cut random lush patches the horse never touches. The goal is to test the intake, not the appearance of the field.

What Should You Test For?

If your main concern is metabolic safety, the most useful values usually include:

• water-soluble carbohydrates

• starch

From there, NSC can be interpreted based on the reporting method.

A fuller forage analysis can also be helpful because it may show:

• protein

• fiber

• mineral balance

• digestibility

• energy profile

That matters especially if you are feeding multiple horses with different needs, or if you are trying to build a complete ration rather than only assess sugar risk.

What Results Are You Usually Looking For?

For horses with laminitis or metabolic risk, many feeding plans aim for forage around or below 10 percent NSC.

That is not a universal law, but it is a very common practical target.

Some horses can tolerate a little more. Some need tighter control. The right interpretation depends on:

• the horse’s insulin status

• whether laminitis is active or historical

• body condition

• overall calorie intake

• what else is in the ration

Decision checkpoint

If the horse has a strong metabolic history, do not interpret the report in isolation. Interpret it in the context of the actual horse.

What If the Hay Tests Too High?

If the forage is higher in NSC than is safe for the horse, options may include:

• sourcing a different hay

• soaking the hay where appropriate

• blending only if it is truly safe to do so

• tightening grazing access

• reviewing the whole ration

• working with your vet or nutritionist on a safer plan

The biggest mistake is continuing to feed unsuitable hay because “it is what we have.” In a high-risk horse, that can become very expensive very quickly if it leads to laminitis.

Is Pasture Still a Winter Risk?

Yes, sometimes.

Owners often assume winter pasture is automatically safe because growth is slower or the field looks sparse. That is not always true.

Risk depends on:

• species present

• weather pattern

• frost

• sunlight

• drought stress

• grazing pressure

• plant regrowth dynamics

This is why some horses still flare on pasture in cooler months. Winter does not guarantee metabolic safety.

Common Mistakes Owners Make

Assuming hay is safe because it is mature-looking

Appearance is not enough.

Testing one batch and assuming all future hay is the same

Each batch can differ.

Ignoring pasture because hay is the main focus

Both can matter in winter.

Waiting until after a laminitis flare to test

Testing works best as prevention.

Using general breed advice instead of the actual horse’s risk

One pony may cope well. Another may not.

Thinking “a little bit won’t matter”

In a high-risk horse, small repeated dietary errors do matter.

A Practical Winter Forage Testing Plan

When Is This an Emergency-Level Concern?

Forage testing itself is not the emergency. The horse can be.

Treat the situation urgently if a horse with suspected dietary risk develops:

• foot pain

• reluctance to move

• heat in the feet

• bounding digital pulses

• rocked-back stance

• sudden worsening in comfort after forage change

At that point, this is no longer just a feeding question. It is a laminitis risk and needs prompt veterinary attention.

What To Do Right Now

1. Identify whether your horse is metabolically high risk

2. Check whether the current hay has ever actually been tested

3. Sample the forage properly if it has not

4. Test winter pasture too if grazing still matters

5. Do not rely on appearance, smell, or supplier reassurance alone

6. Reassess every time the hay batch changes

That sequence will prevent far more problems than trying to fix a bad forage decision after the horse is already sore.

FAQs

Do I really need to test hay every winter?

If your horse has PPID, insulin dysregulation, Equine Metabolic Syndrome, or a history of laminitis, it is strongly worth doing.

Is all grass hay safe for metabolic horses?

No. Grass hay can vary widely in NSC.

What is the most important number on the forage report?

For many metabolic horses, NSC is the key number, usually interpreted from WSC and starch.

Can winter pasture still be too sugary?

Yes. Cooler seasons do not automatically make pasture safe.

What if my hay is too high in NSC?

You may need to source different hay, soak it where appropriate, or change the feeding plan with veterinary or nutrition support.

Final Thoughts

Winter forage is where a lot of good or bad metabolic management happens. Once pasture quality changes and hay becomes the main feed, the horse’s safety often depends on numbers that cannot be seen just by opening a bale.

For low-risk horses, testing is useful. For high-risk horses, it can be the difference between a stable winter and a laminitis flare. That is why winter hay and pasture testing should be thought of as a core preventive tool, not a luxury.

If you are unsure how to interpret a forage report or whether your horse’s hay is appropriate for PPID, insulin dysregulation, or laminitis risk, ASK A VET™ can help you think through the next step clearly.