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Grass Founder

Older horses and ponies may be prone to grass founder (pasture-associated laminitis), particularly in the early spring when grasses contain a higher concentration of sugar. Horses suffering from equine metabolic syndrome (EMS) or Cushing's disease (also known as pituitary pars intermedia dysfunction, or PPID) are especially susceptible.

Pastures high in Non-Structural Carbohydrates (NSCs) are more likely to provoke laminitis. NSCs include fructan, sugar and starch. Fructan is the most commonly-implicated NSC with regard to inducing laminitis, although similar environmental conditions can create high concentrations of all carbohydrate forms.

Structural carbohydrates, which are digested differently from NSCs and not directly linked to laminitis, are the fibrous parts of the cell wall that give the plant rigidity.


NSC production depends on photosynthesis and therefore occurs during hours of direct sunlight. The more intense the sunlight, the greater the production of sugars within the plant.


When conditions are favorable for growth and photosynthesis can occur (e.g. during a warm day when the sun is out), the plant's concentration of NSC remains relatively constant as its size increases. When conditions are not favorable for growth during hours of direct sunlight, however, continued photosynthesis results in an increase in NSC concentration within the plant (which is not significantly changing in size). As previously mentioned, plants with a high NSC concentration are more likely to precipitate laminitis.


When conditions are not favorable for growth during hours of direct sunlight, continued photosynthesis results in an increase in NSC concentration within the plant (which is not significantly changing in size).
When conditions are favorable for growth and photosynthesis can occur (e.g. during a warm day when the sun is out), the plant's concentration of NSC remains relatively constant as its size increases.


Grass Comparison


There are several factors that can deleteriously affect a plant's ability to grow in the face of direct sunlight:

TEMPERATURE is the most common factor retarding plant growth during daylight hours (and therefore promoting an increase in NSC concentration). Very little photosynthesis occurs in temperatures consistently less than 20 degrees, and enzymatic activity required for plant growth is compromised below 40 degrees. Consequently, temperatures between 20- 40 degrees can encourage increased NSC concentration within the plant. Since these conditions most commonly exists during the spring and fall months, pasture-related laminitis is also more likely to occur during these time periods.

POOR FERTILIZATION. Lack of nutrition inhibits the plant's ability to assimilate sugars being produced via photosynthesis. Rather than being used for growth, sugars accumulate within the plant thereby increasing NSC concentration. Accordingly, soils deficient in nutrients (most notably nitrogen) create an environment which amplifies the plant's ability to contribute to the development of laminitis.

Click HERE to review proper fertilization techniques for your horse pasture.

DROUGHT. Lack of water not only inhibits the plant's ability to assimilate sugars and generate size, but may also stimulate the conversion of cool-season grass fructan to sugar, thereby promoting an increased risk towards the development of metabolically-driven laminitis.

PLANT STRESS. Stresses (of any sort) to the plant may slow its growth rate more than its rate of photosynthesis; in these instances carbohydrates will accumulate.

MATURE GRASS. Seed heads have a very high concentration of sugar and are therefore very sweet and palatable to horses. Their elevated sugar content also increases the consumer's risk for developing laminitis. Consequently, it is important to continually mow the grass before it "goes to seed".

WEEDS. Certain varieties of weeds may contain a higher NSC concentration than grass within the same pasture. Dandelion, plantain and thistle are particularly high in sugar.


Important Points to Remember

A thick, healthy stand of grass is the best defense against invasion of weeds and clover. LEARN MORE.

Many clients assume that dead grass has no nutritional value if it's brown. Remember... sugar is not green. Chlorophyll and protein may be no longer be present within the plant, but the sugar may remain.

The neck of a horse consuming grass excessively high in sugars may become enlarged or excessively firm.

Fructan is a carbohydrate composed of fructose and is generally found in cool season grasses.




Consider the use of a MUZZLE. While proper fertilization can decrease sugar concentration per mouthful of grass, there may be more sugar per acre. In this scenario, the use of a muzzle and/ or limited turnout may be necessary to discourage the development of laminitis.

SOAK HAY. Soaking hay for a couple of hours will encourage water-soluble sugars to leach-out of the plant, thereby significantly lower its NSC concentration. This technique may not work as well in starch-accumulating plants since starch is less soluble than sugars. Protein content should not be affected by soaking in water if hay is fed promptly post-treatment.

Fescue grass leaves have a waxy coating which impedes leaching and therefore bear a higher concentration of NSC for longer periods of time (especially during the winter and summer months).

LIMIT TURNOUT. Limiting your horse's access to grass (and therefore NSCs) is the most effective way to avert an episode of pasture-related laminitis.

Spring Turnout Guidelines



There are several basic principles of plant physiology important to consider when managing your horse's forages. They include:

  • Sugars are the substrates for all plant growth and therefore are vital to plant growth and development.

  • Sugars are produced by photosynthesis during daylight.

  • At night plants use energy from sugars generated during photosynthesis to grow.

  • Whenever the rate of photosynthesis exceeds the plant's growth rate, carbohydrates will accumulate.

  • Younger (more tender) light green grass generally carries a higher concentration of carbohydrates than older (more firm) dark green grass. It is for this reason that you might observe your horses congregating in the "less grassy" portions of the pasture.

  • Dry hay is lower in carbohydrates than the fresh plant material from whence it came because plant tissue continues to respire and process sugars during the drying process.

  • The faster harvested forage dries, the greater the amount of carbohydrates that are left in the hay.


Analyzing Your Hay

Average grass hay contains between 12-30% NSCs on a dry matter basis. High-risk animals should not be exposed to grass or hay containing more than 11% NSCs.

To test your grass or hay's sugar content, send a few handfuls of brown grass to Equi-Analytical Laboratories [, the equine division of Dairy One Cooperative Inc.] and have it analyzed. The test is only accurate if the grass is completely dead.

For a list of other National Forage Testing Association certified labs, please click HERE.


Strategies for Pasture Management

  • Plant grass varieties that tend to be lower in carbohydrates. Some native species of grass are lower in carbohydrates than cultivated species (such as brome, ryegrass or fescue).

  • Limit grazing time to the early morning hours. Carbohydrates are often lowest from 3 am to 10 am.

  • Choose grazing areas that are shaded for a portion of the day. Low sunlight limits the amount of sugars produced by green plants.

  • Decrease grazing time or stop grazing completely when grass is under stress from cool temperatures or frost.

  • Do not overgraze pastures. The bottom few inches of grass stems often serve as a plant carbohydrate reservoir and contain high concentrations of NSCs. Although intake may be limited on an overgrazed pasture, horses may still ingest too much carbohydrate due to the high carbohydrate concentrations in stem bases, especially in late fall or during the winter in areas where grasses do not go completely dormant.

  • Establish a system of rotational grazing. Graze regrowth to a height of 4-6 inches, and then move on to another section.

  • Sugar intolerant horses should not graze grass that is starting to go to seed. Many horses selectively graze seed heads and the concentrations of carbohydrates in seed heads are generally much higher than in leaves.

  • Save some areas of the pasture for standing hay to be grazed in winter when it is completely dead and brown; carbohydrates tend to be lower in such grasses.

  • Manage pastures for adequate, but not excessive growth. Determine fertilizer application rates from analyses of soil samples. Irrigate as needed to minimize plant stress without leaching fertilizer.


If you have any questions regarding Pasture-Related Laminitis (Grass Founder) in horses please call our office at (678) 867-2577. We look forward to serving you!
THE ATLANTA EQUINE CLINIC: 1665 Ward Road, Hoschton, Georgia 30548 - ph. 678-867-2577

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