What are Fructans?

  • Fructans are chains of sugar molecules (known as fructose) which fall into the category of non-structural carbohydrates (NSC).

  • Grass stores these sugars as fructans for later use. This is a mechanism of survival for the plant (grass) when conditions are poor. It means the grass can survive by drawing on the stored fructan sugars. However, this type of sugar being different to the normal grass sugars, can cause havoc with a horse’s digestive system.

  • Most sugar molecules produced by photosynthesis and starch are digested by enzymes in the small intestine. Fructans, however are sugars that cannot be digested enzymatically by horses in the small intestine.

  • Fructans, instead, pass into the hindgut (cecum & colon) of the horse, where they are rapidly fermented by microbes.

How do Fructans Affect Horse Health?

  1. Rapid Fermentation: When fructans reach the hindgut, they are quickly fermented by bacteria producing lactic acid.

  2. Hindgut Acidosis: The subsequent lactic acid produced, in turn, lowers gut pH, disrupting the microbial balance. This sets off a chain reaction killing off good fibre-fermenting bacteria and triggering a release of endotoxins.

  3. Laminitis Trigger: These endotoxins are absorbed into the blood stream which cause metabolic changes and may trigger systemic inflammation, altered blood flow to the hoof, and also a bout of laminitis.

KEY POINT: Horses or ponies prone to laminitis, EMS (equine metabolic syndrome), or PPID (Cushing’s disease) therefore need careful management of fructan intake.

 What Grasses Contain Fructans ?

Fructan levels vary by grass species, season, sunlight, and stress factors such as over grazing, drought or frost.

  • High-fructan cool-season grasses (in New Zealand):

    • Ryegrass (especially perennial ryegrass)

    • Timothy

    • Fescues

    • Cocksfoot

  • Low-fructan grasses (in New Zealand):

    • Kikuyu

KEY POINT: Cool-season (temperate) grasses are the main cause of concern and laminitis risk.

 Research Evidence Linking Fructans to Laminitis

Below are some controlled studies which support the link between fructans and laminitis.

1. Garner et al., 1975 (Cornell University)

One of the earliest studies to experimentally induce laminitis in ponies using fructan-rich extracts.

2. Pollitt et al., 2001 (University of Queensland)

In this study horses were given a large oral dose of fructans. These horses developed acute laminitis within 48 hours.

This study demonstrated clearly the direct cause-and-effect relationship with fructans and laminitis in horses.

3. Van Eps & Pollitt, 2006 (Equine Vet J.)

This study describes the mechanisms caused from fructan ingestion such as hindgut acidosis, bacterial death, endotoxin release and how these lead to laminar damage.

4. Bailey et al., 2007 (Vet J.)

This study shows how seasonal fructan accumulation in pasture is linked to pasture-associated laminitis cases.

KEY POINT: Not every laminitis case is caused by fructans (endocrinopathic laminitis from insulin dysregulation is even more common), but fructan overload is a well-proven experimental model for inducing laminitis.

5 KEY POINTS TO REMEMBER:

  1. Fructans are indigestible sugars in many cool-season grasses.

  2. They ferment in the hindgut, leading to toxins that are absorbed into bloodstream – a potential trigger for laminitis.

  3. Ryegrass, timothy, fescue (In New Zealand) are high-risk grasses to watch for when the conditions favour fructans.

  4. Multiple studies (Pollitt, van Eps, Garner, Bailey) confirm fructans cause laminitis experimentally and explain why spring/autumn pastures are dangerous for susceptible horses and ponies.

  5. Safe grazing is knowing when to graze and when risk conditions are high, to take steps to alleviate ingestion.
🌱 Practical Guide: When Fructan Levels in Grass Are Highest

Fructan levels in grass aren’t static; they fluctuate with time of day, weather, and season, which directly impacts as a laminitis risk. Here’s a practical guide you can use:

1.Time of Day, under normal conditions:

  • Highest: Afternoon (midday–late afternoon) on sunny days.

  • Photosynthesis produces sugars (including fructans), and plants haven’t yet used them up for overnight growth.

  • Lowest: Early morning (just before sunrise).

  • Plants use stored sugars overnight for growth, so fructan levels drop.

👉 Safer turnout: early morning, before the sun has had hours to drive sugar production.

2.Weather Conditions; high risk:

  • Bright, sunny days with cool nights (less than 5–10°C) → sugar made in the day but not used at night = accumulation.
  • Frosty mornings → very dangerous: grass looks “safe,” but fructans are high.
  • Drought or stressed grass → plant stores sugars in the base, making it highly concentrated.

Weather Conditions: low risk:

  • Warm, overcast, or rainy weather → more sugar used for growth, less accumulation.

  • Long, warm nights (less than 10–12°C) → plants use up stored sugars overnight.

3. Seasonal risk:

Spring & Autumn = Highest risk

Cool nights, sunny days, and rapid growth = fructan spikes.

Summer = Moderate

Risk lower in hot climates unless grass is stressed by drought.

Winter = Variable

Dormant grasses in cold climates can still accumulate high fructan during sunny but frosty days.

4. Grass Types in New Zealand

  • High-fructan grasses: ryegrass, timothy, fescue

  • Lower-fructan grasses: warm-season species like Kikuyu

✅ Safe Grazing Tips

  • Turn out early morning (before 10am) when nights are warm (greater than 10°C).

  • Avoid turnout on sunny frosty mornings or after drought stress.

  • Use a grazing muzzle (if grass is long) or track system to limit intake.

  • Test pasture NSC if managing a laminitis-prone horse (lab forage analysis).

  • Bulk out feeding with lower sugar (or older hay) instead of unrestricted pasture if risk is high.

  • Supplement with Opti-mize which contains a digestive aid, toxin binder, magnesium and key minerals helpful for spring grazing. This helpful supplement assists dietary management as well as behaviour. Click here for more information Opti-Mize | Grass affected Horses

 

👉 This guide is based on research from Pollitt (2001), Longland & Byrd (2006), and Bailey et al. (2007), all of which link pasture fructan levels to laminitis risk.