Fructans are storage polysaccharides (sugars) consisting of a chain of fructose molecules with a glucose molecule attached. They are generated in plants by photosynthesis and used to store energy. Their importance in horse nutrition is that they can build up to high levels in pasture grass and when consumed and digested by a horse, trigger a marked insulin response. In horses suffering from Insulin Resistance, Cushings Disease, or chronic Laminitis, high fructan content in pasture or hay may be sufficient to trigger an attack of Laminitis.
The fructan content of pasture forms part of the Non Structural Carbohydrate NSC as well as part of the Water Soluble Carbohydrate WSC and can only be determined by laboratory analysis. Fructan content can be estimated by subtracting the simple sugars as measured by the ESC level, from the WSC value.
Fructan levels tend to be higher after the plant has been exposed to sunlight and it accumulates throughout the day, so levels are highest in the afternoon. Levels are also higher in spring and autumn and following frost. For this reason, sensitive horses and ponies may best be grazed only at night or better still in the early morning when fructan levels in pasture are lower.