Horses, Grass, and Fructans

Grass is the most natural food for horses. It is easily grown in many areas of the world, appeals to horses, and can tolerate year-round grazing with minimal management. However, this forage holds a significant danger for some equines.

The factor that makes grass so tasty for horses is its sugar content. Kathleen Crandell, Ph.D., a nutritionist with Kentucky Equine Research, explains that in addition to glucose and fructose, sugars that are easily digested by horses, many grasses contain another form of sugar that can’t be broken down in the foregut. Fructans are formed when several fructose molecules are bonded together, creating chains that are resistant to the digestive enzymes in the stomach and small intestine. Passing into the hindgut, fructans skew the pH balance as lactic acid production rises. This severe disruption in acid level is followed by an inflammatory response that is a common trigger of colic and laminitis in pastured horses.

Fructans are more of a threat at some times of the year than others. Grasses have more available fructans during periods of rapid growth (springtime and also rainy fall days after hot summer weather) and times when grass is stressed (overgrazing, drought, high salinity in soil). Fructan level changes with time of day, generally being highest in late afternoon and evening and lowest in the very early morning hours.

The amount of fructan in grass also varies within the plant’s tissues. Sugar is produced by photosynthesis, and sugar levels rise in the leaves during the day. At night, the plant uses this energy to grow, storing any extra sugar in the lower part of its stem. However, cool nights don’t encourage growth and sugars may remain in the leaves where they can be ingested as horses graze.

If pastures offer taller grass, horses eat more of the plant tops, but overgrazed pastures may force horses to nip grass close to the ground’s surface, thus taking in the lower stems that tend to contain the largest amount of fructans.

Some horses are very sensitive to the digestive challenge presented by fructan consumption, while other horses grazing the same pasture won’t be affected. As a general rule, younger horses and those of light-horse breeding are less susceptible to problems than older horses of heavier-bodied breeds. Equines at increased risk include ponies, overweight horses, those with metabolic conditions like insulin resistance or equine metabolic syndrome, and any horse with a history of laminitis. These equines should have grazing eliminated or greatly restricted during times when fructan levels are highest.

To help horses avoid problems with hindgut acidosis caused by fructan consumption, owners may consider using a hindgut buffer such as EquiShure. This encapsulated digestive health supplement is formulated to support a stable hindgut environment, encouraging proper digestion and absorption of nutrients.