When we think about laminitis, most of us picture lush, green spring paddocks.
But many horse owners are surprised to learn that winter pasture can be just as risky for horses with Equine Metabolic Syndrome (EMS), insulin resistance or PPID (Cushing's disease).

While winter grass often looks brown, dry or dormant, appearances can be deceiving. Under the right conditions, winter pasture can contain surprisingly high levels of sugars that can trigger dangerous insulin spikes in susceptible horses.

Grass Doesn't Stop Making Sugar

Like all plants, pasture grasses use sunlight to make energy through photosynthesis. During this process, they convert sunlight, carbon dioxide and water into sugars that fuel growth and survival.

Throughout spring and summer, these sugars are quickly used to produce new leaves, stems and roots.

However, winter changes everything.

Once temperatures fall below around 8–10°C, grass growth slows dramatically or stops altogether. But as long as temperatures remain above freezing and the sun is shining, the plant can continue producing sugars through photosynthesis.

Because the grass is no longer actively growing, those sugars aren't used—they're stored within the plant instead.

Why Cold Weather Increases Sugar Levels

Winter grasses have another clever survival strategy.

Grass contains a large amount of water, making it vulnerable to freezing. To protect itself from frost damage, the plant stores soluble sugars—particularly sucrose—which act as a natural antifreeze.

These sugars help prevent ice crystals from forming inside the plant's cells, allowing the grass to survive cold weather and bounce back when conditions improve.
This means cold, frosty weather can actually increase the amount of sugar stored within pasture grasses.

Sunny Days and Cold Nights Are the Perfect Storm

One of the highest-risk situations occurs after bright, sunny winter days followed by cold or frosty nights.

During the day, sunlight allows the grass to manufacture sugars through photosynthesis.
At night, the cold temperatures slow growth, so those sugars aren't used by the plant and instead continue to accumulate.

This is why pasture that looks brown, short or dormant may still contain significant amounts of sugar.

Why This Matters for Metabolic Horses

For horses with insulin dysregulation, consuming high-sugar pasture can trigger excessive insulin responses.

Research has shown that elevated insulin levels play a key role in the development of endocrinopathic laminitis.

Because sugar levels can remain elevated throughout winter, metabolic horses are not necessarily "safe" simply because the grass has stopped growing.

In fact, winter pasture management is just as important as spring management.

Managing Winter Grazing

If your horse has EMS, insulin resistance or PPID, don't assume winter pasture is low-risk simply because it looks dormant.

Instead:

• Monitor overnight temperatures and sunny winter days.
• Be particularly cautious following frosts.
• Restrict grazing when pasture conditions favour high sugar accumulation.
• Feed a balanced, low-sugar forage diet.
• Ensure the diet is correctly balanced with appropriate vitamins and minerals.
• Maintain regular exercise where appropriate.

The Take-Home Message

Brown doesn't always mean low sugar.

Winter pasture may appear dormant, but cool-season grasses can continue producing and storing sugars throughout the colder months. Combined with the increased risk of reduced hoof circulation during cold weather, winter can be a surprisingly high-risk time for horses with metabolic disease.

By understanding how pasture behaves during winter, horse owners can make more informed grazing decisions and help reduce the risk of winter laminitis.