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The Real Cause of Pasture-Associated Laminitis (PAL)

In a 2016 study, Menzies-Gow, et al., followed 446 animals on pasture over a period of three years. They found the most reliable indicator of risk of laminitis was basal insulin levels. Also significant were low adiponectin and high insulin response to dexamethasone. Fructan does not increase insulin. There was no indication of diarrhea or hind gut upset.
A 2019 study by de Laat, et al., looked at 301 cases of naturally occurring laminitis and found EMS and/or PPID in 94%. They were also careful to point out those that did not have elevated insulin at time of testing may have been reflecting their current diet, rather than their state at the time of acute laminitis. No diarrhea or other indication of hind gut distress was reported.
There are many other studies and they all come back to insulin. Very large doses of pure fructan by stomach tube can experimentally cause laminitis by resulting in extreme hind gut acidity, damage to the intestinal lining, and absorption of bacterial products, in the same way gorging on grain can. This hind gut upset is accompanied by diarrhea, septicemia, and fever. These horses are clearly sick. None of that happens with naturally occurring PAL.
Not only are there zero documented cases of high fructan in pasture causing laminitis, the levels of fructan naturally found in a whole day’s worth of eating pasture grasses almost never come even close to the amount needed to cause laminitis. Could laminitis prone horses be more sensitive to fructan?
Nope. Borer, et al., (2012) found virtually no insulin response to fructan in ponies whether predisposed to PAL or not.  Crawford, et al., (2007) fed a moderate fructan dose to normal and laminitis prone ponies and looked at the changes in fecal pH and fermentation products. They found pH and fermentation products did change but none of that was reflected in blood levels so wasn’t absorbed. There was also no difference in documented changes between normal and laminitis-prone ponies.
Only simple sugars — Ethanol Soluble Carbohydrates (ESC) on analysis — and starch, can increase insulin. Those two things should be less than 10% combined (ESC + Starch less than 10%) for at-risk horses.
The greatest danger in perpetuating the fructan myth is that owners will rely on supplements designed to control pH or alter hind gut fermentation to protect their horse or pony from PAL.  They won’t help if your animal is in the high risk group with endocrine disease that accounts for 94+ % of PAL cases. Not all horses or ponies at risk will develop obvious laminitis every year, but time is not on your side. Unlimited pasture access is Russian roulette.
If you suspect your horse is at risk, speak with your veterinarian and pursue testing. For further details, visit