Fructans are a storage form of carbohydrate and a component of the non-structural carbohydrates (NSC) found in cool-season grasses, such as tall fescue, timothy, orchardgrass, and perennial ryegrass.

Fructans are indigestible by horses, passing through the foregut to the hindgut where they are rapidly fermented by bacteria to supply energy to the horse. [1]

There is an ongoing debate about the effects of fructans on equine health. Some researchers suggest that diets high in fructans predispose horses to health conditions such as insulin resistance, laminitis, or leaky gut syndrome.

Other researchers argue that fructans do not cause laminitis because they do not trigger insulin secretion. Laminitis has only been triggered experimentally by administering very large doses of chickory root fructan by stomach tube, with the resultant syndrome the same as with grain overload in the hind gut.

Fructan concentrations in forage can vary anywhere between 3 – 50%, depending on the type of grass, time of year, weather, and growing conditions. [2] However, there has never been a documented case of laminitis linked to the fructan level of pasture or hay.

What are Fructans in Forage?

Fructans occur naturally in many plants, including grasses. They serve as an energy storage form for plant cells. [1]

Fructans are polysaccharides composed of short chains of fructose molecules terminating with a glucose molecule. The length of a fructan depends on the number of fructose molecules linked together. [3]

Cool-season grasses such as tall fescue and ryegrass tend to store excess energy in the form of fructans. In contrast, warm-season grasses and legumes do not produce fructans. Instead, they store excess energy as starch (a complex chain of glucose molecules).

There are three main categories of fructans: graminans, inulins, and levans. These fructans differ in the number of fructose molecules and by the bonds connecting them. Graminans and levans are the main forms of fructans found in forages. [4][5][6]

All fructans are types of non-structural carbohydrates, used primarily as energy storage for plants. NSCs also include simple sugars (glucose, sucrose, fructose) and starches.

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Fructans in the Equine Diet

Fructans are complex carbohydrates that are rapidly fermented in the horse’s hindgut. This process generates volatile fatty acids that are absorbed from the hindgut and used for energy by the horse. [1]

Depending on environmental conditions and plant species, fresh forages can contain anywhere from 32 – 439 g of fructans per kg of dry matter. [2] It is concentrated in the lower stems of the plant.

Assuming a 500 kg / 1100 lb horse consumes 10 kg of dry matter per day, high fructan pasture could result in over 4 kg / 9 lb of fructans consumed in a day. However, slow intake over a 24-hour period is not the same thing as a bolus by stomach tube. In those studies chickory fructan was used, which is not the same thing as the levan most predominant in grasses.

In addition, the Dairy One database of over 8,000 North American pasture grass samples shows a maximum fructan content of less than 20 grams per kg of dry matter. [36]

The very high pasture fructan levels are mainly found other parts of the world, such as the subarctic or regions that grow a lot of high-fructan ryegrass. In these grasses, the simple sugars (ESC) are also very high; well above the threshold for triggering laminitis in a horse with metabolic syndrome. [2]

The best way to determine the carbohydrate content of your horse’s forage is to submit a sample for analysis.

A hay analysis will provide levels of water-soluble carbohydrates (WSC), ethanol-soluble carbohydrates (ESC), and starch.

High fructan levels in grasses correlate with greater energy supply to the horse. [7] While forages with high digestible energy may be appropriate for horses in heavy exercise or with high-calorie requirements, they are not recommended for easy keepers or overweight or obese ho