Grass Height and Laminitis Risk in Horses: What Actually Matters

By Dr Duncan Houston

If your horse is prone to laminitis, grass height alone will not keep them safe.

Many owners assume that shorter grass means lower risk. In reality, laminitis risk is driven by sugar intake, not just how long the grass looks.

This is where management often goes wrong. The pasture looks controlled, but the metabolic risk is still there.

Quick Answer

Shorter grass may reduce how much a horse eats, but it does not reliably reduce sugar content. Laminitis risk is driven by non-structural carbohydrates in grass, which fluctuate with time of day, weather, and plant stress. For high-risk horses, grass access often needs to be strictly controlled or avoided altogether.

Why Grass Triggers Laminitis

Grass contains non-structural carbohydrates, mainly sugars and starches.

When intake is high:

• blood glucose rises

• insulin levels increase

• the laminae are disrupted

In insulin-sensitive horses, this response can occur even with relatively small amounts of grazing.

This is why laminitis is often not about overfeeding, but about how the horse processes sugar.

The Real Question: Does Grass Height Change Risk?

Shorter grass does change one thing:

• horses tend to eat less per bite

However, it does not reliably change:

• sugar concentration

• metabolic response

In some cases, short or stressed grass can actually contain higher sugar levels.

This is the critical point most people miss.

What Research Suggests

Studies comparing taller and shorter pasture show:

• horses may consume less on shorter grass

• some weight loss may occur

• total intake can still meet daily needs

But importantly:

• these studies are usually done on healthy horses

• they do not reflect high-risk metabolic horses

In practice, what is “safe enough” for a normal horse is often not safe for a laminitis-prone horse.

Why Short Grass Can Still Be Dangerous

Grass sugar levels change constantly.

Higher risk conditions include:

• late afternoon and evening grazing

• sunny days with cool temperatures

• drought or overgrazed pasture

• stressed or slow-growing grass

Short grass is often under more stress, which can increase sugar concentration.

So while intake may drop, sugar exposure may not.

How Serious Is This?

Low Risk

• healthy horse

• no history of laminitis

• controlled pasture exposure

What this means: grass height has minor impact

Moderate Risk

• overweight horse

• early metabolic changes

What this means: pasture must be managed carefully

High Risk

• confirmed laminitis

• insulin dysregulation

• previous episodes

What this means: grass exposure is a major trigger

Critical

• active laminitis

• significant hoof pain

What this means: complete removal from pasture required

What Actually Works for High-Risk Horses

Dry Lot Management

This is the most reliable option.

• eliminates pasture sugar exposure

• allows full control of diet

Low-NSC Hay

• consistent

• measurable

• safer than pasture

Testing is ideal to confirm sugar levels.

Grazing Muzzles

These can:

• reduce intake significantly

• allow turnout and movement

They are useful but not foolproof.

Controlled Grazing Timing

If grazing is allowed:

• early morning is the lowest-risk window

• avoid afternoon and evening

Even then, risk remains in sensitive horses.

Weight Management

Reducing body fat:

• improves insulin sensitivity

• lowers laminitis risk

This is one of the most powerful long-term strategies.

What To Do Right Now

If your horse is at risk:

• do not rely on grass height alone

• assess total pasture exposure

• consider removing or limiting access

• switch to controlled forage feeding if needed

• monitor weight and hoof changes closely

If laminitis has occurred before, err on the side of caution.

When Is This an Emergency?

Treat as urgent if:

• your horse becomes foot sore

• shifts weight or resists movement

• heat or digital pulse increases

These are early laminitis signs and require immediate action.

Common Mistakes

• assuming short grass is safe

• relying on mowing as a prevention strategy

• underestimating sugar fluctuations

• allowing unrestricted grazing in high-risk horses

• ignoring weight gain

In practice, these are some of the most common reasons laminitis recurs.

Long-Term Prevention

Effective management focuses on:

• controlling sugar intake

• maintaining healthy body condition

• managing pasture access strategically

• monitoring seasonal changes

Laminitis prevention is about consistency, not quick fixes.

Frequently Asked Questions

Is short grass lower in sugar?
Not reliably. In some cases, it can be higher due to plant stress.

Can mowing prevent laminitis?
No. It may reduce intake slightly but does not eliminate risk.

Is pasture ever safe for laminitic horses?
Some may tolerate limited exposure, but many require strict control or removal.

What is safer, hay or grass?
Tested low-NSC hay is far more consistent and predictable.

Why does laminitis still occur on “managed” pasture?
Because sugar levels fluctuate independently of how the pasture looks.

Final Thoughts

Grass height is only one small part of the picture.

The real drivers of laminitis risk are:

• how much sugar is being consumed

• how the horse’s body responds to it

• how consistent management is over time

A pasture can look safe and still be risky.

Understanding that difference is what prevents repeat episodes.

If you are unsure whether your current grazing setup is safe or want help building a practical laminitis prevention plan, ASK A VET™ can guide you with clear, tailored advice based on your horse’s risk level.