What Is Fructan? Simply Explained

Anyone looking into laminitis quickly comes across the word fructan. It is one of the most important risk factors on pasture – but what exactly is it?

Fructan is a storage sugar

During the day grasses carry out photosynthesis: using sunlight they convert CO₂ and water into sugar. They need this sugar as energy to grow. When they produce more than they currently use, they store the surplus as a reserve – in our pasture grasses mainly as fructan, a chain of many fruit-sugar units.

Why do grasses store sugar?

Fructan is the plant's energy reserve – a store for growth spurts, cold nights or dry spells. For the grass this is a clever survival mechanism. It only becomes a problem when a laminitis-prone horse eats large amounts of it.

C3 and C4 grasses

The typical pasture grasses in our regions are C3 grasses – they store sugar as fructan and are therefore potentially problematic. Tropical C4 grasses use other storage forms and play hardly any role here.

When is the fructan content high?

In short: whenever the grass produces a lot of sugar but grows little – for example in sun and cold, during frost or drought. Which weather situations are critical and when the best grazing time is are explained in Fructan in Grass: When Is the Risk Highest?.

Why is fructan dangerous for horses?

Large amounts of fructan reach the hindgut undigested and disrupt the bacterial flora there. This can cause metabolic imbalances that trigger laminitis – especially in horses with EMS, Cushing's or obesity.

You do not have to estimate the fructan content yourself: the fructan traffic light calculates the risk from the weather for your location. Note: This article does not replace veterinary advice.