High fructan concentrations in horse pastures can be a potential precursor to laminitis in susceptible equine.
Much attention is now being paid to the type of carbohydrates present in forage since more horses are being diagnosed as insulin-resistant. In particular, easy keeping light horse breeds like Morgans, Paso Finos and Tennessee Walker, mustangs, ponies, and miniature donkeys, are targets for this condition, especially if they are allowed to be obese. Ingestion of water-soluble carbohydrates (glucose, fructose, sucrose, and fructan) found in rich spring grasses may trigger laminitis in some horses as a result of the rapid fermentation of the sugars in the hindgut (similar to a high-starch diet). While fructan content in hay and pastures is currently receiving the most attention since it is a potential trigger for laminitis in susceptible horses, all sugars and starches should be considered potential triggers.
Fructan concentrations can vary greatly according to the growing season, weather conditions, and time of day. Fructans are found in the largest quantities in cool season grasses. Early spring pastures are highest in sugar content with mid-summer pastures being lowest and early fall/autumn pastures being intermediate in sugar content. In addition, as a result of photosynthesis reaction, sugars begin to accumulate in grasses during the early morning and reach their peak by the afternoon.