The Real Cause of PAL – Pasture-Associated Laminitis

It isn’t fructan.  It isn’t hind gut acidosis.  Here’s the science.

The AAEP’s Laminitis Working Group did a four year study with the goal of identifying laminitis risks. Other than diet, EMS pattern obesity, known EMS or PPID and use of corticosteroids within 30 days were identified. All relate to equine metabolic syndrome [EMS] and elevated insulin.

A 2006 field study performed by a group from Virginia Polytechnic followed a herd of 106 mixed breed ponies on pasture for a year, performing pasture analyses and monitoring the ponies using proxies of insulin resistance they had developed from the results of intravenous testing. They found both prior laminitis and development of acute laminitis correlated well with indicators of insulin resistance. There was no increase of  fructan in the pasture when laminitis cases appeared, no indication of diarrhea or hind gut upset.

In a 2016 study, Menzies-Gow at al followed 446 animals on pasture over a period of 3 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 (ESC fraction 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.

Eleanor Kellon, VMD

About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions, www.drkellon.com, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition.
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4 Responses to The Real Cause of PAL – Pasture-Associated Laminitis

  1. Kathy Ward says:

    So to determine whether a horse who has had laminitus should be allowed back on pasture, an insulin test should be undertaken ?
    My horse had laminitus for the first time when he was 20 years old, he was diagnosed ppid at the same time. Through medication and diet his levels came back as normal earlier this year, so if his insulin was checked as normal it would be safe to put him back on grass ? Or have I got that wrong ?

    • Dr. Kellon says:

      Yes, you have it right. If his ACTH and insulin are now normal, he’s not at risk but you have to realize his insulin reflects his diet so if he wasn’t on pasture when he tested normal he might still be at risk. He’s also high risk in the Fall unless his ACTH remains controlled during the seasonal rise.

  2. Dr. Kellon says:

    It’s high insulin from the simple sugar and starch content of the grass. Fructan is not a sugar. It doesn’t increase insulin levels.

  3. Cathie says:

    So fructans don’t cause laminitis. What is it about unlimited grass access that does cause laminitis? Please clarify this.

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