It’s Time to Put the Fructan Theory to Rest

Despite the fact there is absolutely no proof that the level of grass fructan (levan) found in horse pastures and hays has ever caused laminitis, fructan continues to be touted as the cause of pasture laminitis.  Any mention of fructan is steadily disappearing from the scientific literature but it continues to surface regularly in other locations, including the web pages and newsletters of companies selling supplements that claim to control alleged hind gut acidosis caused by fructans.


No Evidence that Pasture Fructan Levels are Dangerous

It’s true that artificially loading a horse with the chickory root fructan inulin by giving over 8 pounds of pure inulin by stomach tube (500 kg horse) can cause hind gut upset that mimics overeating grain and can cause laminitis.  However, let’s look at some facts.

The fructan found in grasses is primarily levan, which is fermented in the hind gut at a much slower rate than inulin.

No one has produced laminitis in horses by tubing them with levan.  No one has proven than pasture grasses can cause the same damage to the hind gut, toxemia and laminitis that tubing with inulin can.

Laminitis caused by inulin is a dose dependent effect.  The lowest dose of inulin by stomach tube that has been shown to reliably produce laminitis is 7.5 g/kg of body weight, or 3750 grams for a 500 kg horse.  A 500 kg horse on pasture will consume about 10 kg of dry matter (grass with the water removed) a day.  To take in that much fructan (levan in the case of grass), the grass would have to be 37.5% fructan.  Perennial ryegrass improved varieties growing under extreme conditions in areas of the world that are cool and rainy might have the potential to reach that level, at least transiently, but no grass in North America comes even close.

In addition to the grasses not having a high enough level of fructan to meet the amount in the experimental model, it’s important to remember that experimentally the fructan was dumped into the horses all at once in pure form while when grazing we are talking about total intake over a 24 hour period with a lot of dilution by fiber, protein, water, etc. and a type of fructan that is fermented much slower.

Another very misleading claim that frightens people is that fructan is a sugar and therefore a threat to horses with insulin resistance/metabolic syndrome.  Fructan is NOT a sugar.  It is a long chain polysaccharide made of repeating units of the sugar fructose but that does not make it a sugar.  Cellulose, the long chain polysaccharide fiber that is high in wood and straw, is made of repeating units of glucose but that doesn’t make cellulose a sugar either.  Starch is also made up of chains of glucose but you can’t put corn starch in your sugar bowl.

The only sugars that are of concern for an IR horse are those that can be digested and cause an insulin spike.  This is limited to the short chain, one or two sugar unit, sugars such a glucose and sucrose.  Fructan is not digested or otherwise broken down into simple sugar.

The next time you hear or read about fructan being the cause of pasture laminitis, please remember that was a theory that has never been proven.  The real reason that ponies and horses with IR/EMS are prone to pasture laminitis is the simple sugar and starch levels in the grass.

Eleanor Kellon,VMD

About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions,, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition.
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10 Responses to It’s Time to Put the Fructan Theory to Rest

  1. Clare Jackson says:

    I seeded a small area in spring with a special grass mix for horses and have been mowing it over the summer, I was wondering if I should still leave it unmunched on by the horses until next spring? Is it too soon to put them on it. I was leaving it so it formed a good thatch and wouldn’t get too trashed over winter. My mare has Cushings which is treated with prascend and the other horse is a haffy, so both good doers and potential for laminitis. Any suggestions? Usually I just give them last year’s hay, steamed, and very, very little feed at all and they do fine!

    • Dr. Kellon says:

      In terms of getting the grasses well established you should check with the company that developed the mix. As far as laminitis potential, when the nights get very cool the grasses do not use much sugar overnight. When cold enough to stress the grass, the sugars really go up. There’s just no way to say for sure a pasture is going to be safe. The other side of that equation is how insulin resistant the horse is. To know that you will have to do the lab work.

  2. jgerlJanet says:

    I swear the average person hasn’t a chance in understanding this information. God forbid you should read more than one article ……. I grazed my EMS horse on winter pasture (I.e. Winter pasture in this case means pasture that was neither cut nor eaten the entire growing season. He did GREAT! This was northeastern WI, FROZEN TUNDRA. Winter means September thru March. Now it is August and he get NO pasture April thru August. So I send in pasture sample of Ungrazed, Uncut pasture on Augusf 1st. ECS Is 6.5. Better than my winter grass hay. Is it safe for him to begin grazing?.. One would think so…..until reading this commentary/article……now the answer would be no. If the ESC IS LOWER THAn safe WINTER SUPPLY OF HAY then why is this a game with Russian Roulette??

    • uckeleequine says:

      It’s risky for two reasons. One is that pasture samples have to be flash frozen in liquid nitrogen in the field to guarantee there is no loss of carbohydrate. The second reason is that live grass is changing constantly. Simple carbohydrate levels will vary widely over the course of a day, as well as from day to day. That said, grasses that have been allowed to grow to full natural height and go to seed, that are not being stressed by drought, are likely the safest to graze of the growing season but there are still no guarantees.

  3. Fiona says:

    Thank you for a helpful article. Can we expect or is there already an equally informative article by Dr. Kellen about “The next time you hear or read about fructan being the cause of pasture laminitis, please remember that was a theory that has never been proven. The real reason that ponies and horses with IR/EMS are prone to pasture laminitis is the simple sugar and starch levels in the grass.” In other words, please discuss what IR/EMS equids’ owners should be aware of in terms of prevention and treatment regarding simple sugar and starch levels in grass.

    • uckeleequine says:

      The early spring growths of grass are most dangerous, much less so when they reach full height and have gone to seed. However, stressors such as extreme heat, drought and cold can cause sugar levels to rise at any time. Grazing an IR horse is Russian roulette. It can be tolerated for a while, maybe a year or more, but sooner or later the odds are the horse is going to get laminitic.

  4. Melanie says:

    I get this, but does it make a difference that fructans are fermented not enzymatically digested? So theoretically a lower glycemic index? Warm season grasses do not have fructans but don’t they use starch as a storage molecule? So it seems like warm season grasses would have a higher glycemic index. So this is interesting theoretically but really doesn’t matter to horse owner. If they have a IR/EMS they still have to be careful with grass. Thank you.

    • uckeleequine says:

      Yes,being fermented rather than digested to simple sugars is why fructans are not a threat to IR horses per se. Warm season grasses are also problematic but you’re right that the bottom line is that any grass can pose problems for an IR horse.

  5. LuAnn Placeres says:

    What if all we have is green pasture grass; is there anyway to help a horse who grazes on green grass not get laminitis? Or how do you treat the horse when it does get laminitis by just eating green grass?

    • uckeleequine says:

      If you have an insulin resistant horse getting laminitis on pasture the only way to prevent or treat it is to keep the horse off pasture. There is no such thing as a “safe” pasture although IR feral horses avoided problems by exercising as much as 20 miles per day and likewise endurance horses that have trouble when not working will often be OK on pasture when in training and competition. Early growths in the spring are most dangerous but dangerous conditions can develop at any time.

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