Understanding Grass Sugars
A HØØF Knowledge Hub article
Understanding how grass produces and stores sugars helps horse owners make informed decisions about grazing management, particularly for horses prone to laminitis, obesity or insulin dysregulation.
Understanding Grass Sugars
Grass is often described as either “good” or “bad” for horses, but the reality is far more complex.
The nutritional value of grass changes continuously in response to weather, sunlight, temperature, rainfall, soil conditions and growth. One of the most important components is Water Soluble Carbohydrates (WSC), commonly referred to as grass sugars.
These naturally occurring sugars provide the energy a plant needs to grow, but they can also present challenges for some horses when consumed in excessive amounts.
Understanding how these sugars are produced and why they fluctuate helps separate scientific evidence from long-standing myths.
What Are Water Soluble Carbohydrates (WSC)?
Water soluble carbohydrates are sugars and fructans produced by grass during photosynthesis.
They serve two important functions:
• Providing energy for plant growth.
• Acting as energy reserves when growth slows.
When grass is actively growing, much of the sugar produced each day is immediately used to produce new leaves and stems.
When growth slows but photosynthesis continues, these sugars begin to accumulate within the plant.
This is why weather and growing conditions often have a greater influence on sugar levels than simply the season itself.
Why Do Sugar Levels Change?
Grass sugar concentrations are constantly changing.
Factors influencing WSC include:
• Hours of sunlight.
• Air temperature.
• Soil moisture.
• Grass species.
• Stage of growth.
• Grazing pressure.
• Fertiliser use.
Bright sunny days increase sugar production through photosynthesis.
Warm nights allow the plant to use those sugars to continue growing.
Cold nights slow growth, meaning sugars produced during the day remain stored within the plant instead of being used.
This explains why there is no single “safe” season or time of day that applies to every pasture.
Common Misconceptions
Myth: “Spring grass is always the most dangerous.”
Spring grass is frequently associated with laminitis because rapid growth coincides with increased grazing opportunities.
However, rapidly growing grass is also using large amounts of sugar to produce new tissue.
Bright sunny days followed by cold nights, drought stress or conditions where growth slows can sometimes lead to greater sugar accumulation outside of spring.
Risk depends upon the interaction between weather, plant growth and the individual horse rather than simply the calendar.
Myth: “Short grass is safer.”
This is one of the most common misconceptions in horse management.
A closely grazed paddock is not automatically low in sugars.
Heavily grazed grass is often under considerable stress. Like many plants, stressed grass attempts to survive by storing energy for regrowth.
The growing point of many grass species remains close to the ground. The short stems and leaf bases left behind after repeated grazing can therefore contain concentrated stores of water soluble carbohydrates.
At the same time, horses grazing sparse pasture often spend longer searching for every remaining blade, increasing grazing time and potentially increasing total sugar intake despite there appearing to be very little grass available.
A short paddock should never automatically be assumed to be a low-risk paddock.
Myth: “Brown grass contains no sugars.”
Grass that appears dry, brown or dormant may still contain significant stores of water soluble carbohydrates.
Appearance alone tells us very little about its nutritional composition.
Soaking Hay
For horses requiring dietary sugar restriction, soaking hay is commonly recommended.
Research has shown that soaking can reduce water soluble carbohydrate content, but the amount removed varies considerably between different batches of hay.
The reduction depends upon:
• The individual hay crop.
• Initial sugar concentration.
• Water temperature.
• Soaking duration.
• Hay type.
When hay is soaked, sugars dissolve into the surrounding water.
As soaking continues, the difference in sugar concentration between the hay and the water becomes progressively smaller, meaning sugars leave the hay more slowly. Eventually, extending the soaking time produces diminishing returns, with progressively smaller reductions in sugar.
At the same time, prolonged soaking removes increasing amounts of other water-soluble nutrients and minerals and may reduce palatability through fermentation and changes in smell and taste.
Current evidence suggests that approximately 15–30 minutes of soaking in clean water provides a useful reduction in sugars for many types of hay while limiting unnecessary nutrient loss. Longer soaking may remove additional sugars in some hays, but the benefits become increasingly variable and are not guaranteed.
For this reason, soaking should be viewed as one management tool rather than a precise method of achieving a specific sugar level.
Myth: “If some soaking is good, soaking overnight must be better.”
Not necessarily.
While longer soaking periods may continue to remove sugars from some hays, the additional benefit becomes progressively smaller and less predictable.
Extended soaking also increases the loss of valuable nutrients and, particularly during warmer weather, may encourage fermentation if the hay is left standing in water for prolonged periods.
Soaked hay should always be fed promptly and the soaking water discarded.
Managing Horses at Risk
Successful management rarely depends upon one single intervention.
Instead, it usually involves combining several strategies, including:
• Maintaining an appropriate body condition.
• Careful grazing management where necessary.
• Selecting suitable forage.
• Veterinary diagnosis where indicated.
• Appropriate exercise where possible.
• Regular farriery.
• Ongoing monitoring of the individual horse.
Every horse responds differently, and management should always be tailored to the individual rather than relying upon simple rules.
When to Seek Professional Advice
If your horse has previously suffered laminitis, has been diagnosed with Equine Metabolic Syndrome (EMS) or insulin dysregulation, or you are concerned about body condition or grazing management, seek advice from your veterinary surgeon.
Dietary changes should always form part of an overall management plan rather than being considered in isolation.
Key Takeaways
• Water soluble carbohydrates are naturally produced by grass through photosynthesis.
• Sugar levels change continually in response to weather and growing conditions.
• There is no universally “safe” season or time of day for grazing.
• Short, heavily grazed pasture should not automatically be assumed to be low in sugars.
• Soaking hay can reduce water soluble carbohydrates, but the amount removed varies considerably.
• Longer soaking does not necessarily mean significantly lower sugar levels.
• Successful management depends upon understanding the individual horse rather than relying on simple rules.
Take Home Message
Grass is a living plant, not a fixed feed. Its nutritional value changes from day to day, and sometimes from hour to hour, depending upon growing conditions.
Simple rules such as “short grass is safe” or “soak hay overnight” rarely reflect the complexity of the science. A better understanding of how grass grows, how sugars are stored and how forage management influences intake allows owners to make more informed decisions for each individual horse.
As with many aspects of equine management, there is rarely a single “magic” answer. Good outcomes are usually achieved by combining sound nutrition, appropriate grazing management, regular farriery and veterinary guidance where required. Understanding the principles behind these decisions is far more valuable than relying on fixed rules.
About the HØØF Knowledge Hub
The HØØF Knowledge Hub provides practical, evidence-based information to help horse owners better understand hoof health, equine management and related veterinary topics.
Our aim is to explain complex subjects clearly and accurately while supporting informed decision-making.
The Knowledge Hub is intended for educational purposes and does not replace advice from your veterinary surgeon, farrier or other qualified equine professional.
© HØØF Equine Hoof Care 2026
Article Information
Article Number: HKH021
Author: Paul Conroy BSc (Hons) AWCF
Organisation: HØØF Equine Hoof Care
Category: Nutrition & Pasture Management
First Published: July 2026
Last Reviewed: July 2026