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.
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.