Fructans
Fructans are long-chain sugar molecules that plants form as short-term energy stores. Up to 90 percent of the energy in grasses can be stored as fructans, with the remainder stored as starch.
The fructan content in grass depends on the grass variety, as well as on external factors such as hours of sunshine, temperature and moisture. As a simplified rule of thumb, fructans are formed and stored in larger quantities whenever the plant is carrying out photosynthesis (forming sugar in the presence of sunlight, CO2, and water) but is unable to grow at the same time (when it is too cold or too dry).
The fructan concentration is particularly high in the vegetative cone, i.e. in the base of the plant. This means that grass that has been closely grazed, following cold, frosty nights or during dry summer periods, has a high sugar content.
Fructan is regarded as one trigger of feeding-related laminitis. Horses whose breed was originally adapted to sparse vegetation are particularly at risk. Horses with metabolic disorders such as EMS are also particularly at risk.