Fructan in the grass, insulin in the horse: what laminitis research has actually measured

The fructan model: what was actually administered in the experiment

The idea that fructan in grass triggers laminitis does not come from pasture observation but from the laboratory. In 2006, twelve horses received oligofructose, an industrially produced form of fructan, as a single dose by nasogastric tube; six comparison animals were given a sham treatment. All twelve treated horses developed laminitis within 48 hours, detectable both clinically and in the tissue, and none of the comparison animals did. The closing sentence of that paper explicitly drew a link between cases seen in practice and the fructan content of pastures. Yet nothing had been measured on any pasture: the study had not watched a single horse graze.

Two years earlier the same question had been examined through a dose series. Three pairs of healthy horses received 7.5, 10 and 12.5 grams of oligofructose per kilogram of bodyweight, again as a single dose by tube. All developed laminitis after 48 hours, and as the dose rose the cells of the hoof lamellae increasingly lost their anchoring structures. That is the traceable origin of the figure of 7.5 grams per kilogram, which has circulated for years on manufacturers' pages without an author, without a year and without a reference, presented as a pasture risk.

Are 7.5 grams per kilogram a limit value for pasture?

No. It is the lowest dose tested in that series, given all at once through a tube. A lower value was never tested, so a minimum dose is unknown. The figure describes what reliably triggered laminitis in the experiment, not the point at which a pasture becomes dangerous.

How little robust the model is at its lower end was shown by a randomised trial from 2009. Three groups of eight horses there received endotoxin, oligofructose or both in sequence. With five grams of oligofructose per kilogram alone, only two of eight horses became laminitic; with the combination, five of eight; with endotoxin alone, none. Below the high doses, the model therefore no longer reliably triggers what it is meant to trigger.

The induction dose, translated into kilograms of grass

These doses can be converted into feed as soon as a measured fructan content is placed alongside them. A British methods paper determined the fructan content of four pasture grasses between April and November using high-performance liquid chromatography. The values lay between 83 and 299 grams per kilogram of dry matter, with a mean of 154.

For a 500 kilogram horse, the lowest induction dose means 3.75 kilograms of pure fructan at once. At the highest content ever measured, that corresponds to roughly 12.5 kilograms of dry matter; at the mean content, to roughly 24 kilograms. For comparison: in a grazing trial, ponies with immediate access to the whole area took in on average 2.33 per cent of their bodyweight as dry matter per day, which is just under twelve kilograms for an animal of 500 kilograms. The arithmetic comes out the same across all bodyweights: at the mean content, the single dose would be about twice what an animal eats in a whole day.

Two objections belong with this. First, the widely used colorimetric method measures too low: on the same samples its mean was 82 rather than 154 grams per kilogram. Part of the publicly quoted fructan values therefore underestimates the true content by an unknown margin. Second, arithmetic says nothing about smaller amounts. That 3.75 kilograms at once trigger laminitis does not mean that a tenth of that remains without consequence. The calculation shows only how far the model stands from a pasture.

The finding that shifted the centre of gravity

Alongside the fructan model, a second series of experiments tested something else: insulin on its own. In 2007, five healthy ponies with no history of laminitis received a continuous infusion that kept insulin high while blood glucose was deliberately held within the normal range; four randomly allocated comparison ponies did not receive it. All five treated animals developed laminitis in all four feet in less than 72 hours, on average after a good 55 hours. None of the comparison ponies fell ill. Digestive signs or indications of general illness were entirely absent.

In 2010 the same approach was repeated in sport horses. Four of four treated Standardbred trotters developed laminitis in less than 48 hours, none of the four comparison animals. All treated animals had a calculated insulin sensitivity in the normal range before the trial. The route is therefore not confined to ponies with disturbed metabolism.

Does that mean high insulin alone is enough?

In the experiment yes, but with an important qualification: the insulin values reached lay about 66 times above the animals' baseline and far above what a pony reaches at pasture. The experiments show that this route exists, not that it is taken in this form under pasture conditions.

A 2023 review sorts the findings. It separates three forms of laminitis: the endocrine form, the form accompanying severe general illness, and the form of the overloaded supporting limb. As a shared core process the authors propose stress of the basal cells of the hoof lamellae, which comes about differently in each of the three forms. For pasture laminitis they note that many affected ponies show the pattern of disturbed insulin regulation. That is a proposal by the authors, explicitly framed as a hypothesis, not a proven unifying theory.

Fructan or glucose: what moves insulin

If insulin is the lever, the question is which sugar pulls it. A randomised crossover trial in twelve ponies examined this directly, in spring and in autumn. Glucose, fructose and inulin, the commercially available form of fructan, were each fed in addition at one gram per kilogram of bodyweight per day. Inulin changed blood glucose and insulin only slightly, fructose distinctly less than glucose, and ponies with and without a history of laminitis separated most clearly after glucose. In autumn the insulin peaks were higher and more irregular than in spring.

An earlier paper reached a different result. There, insulin in laminitis-prone ponies rose to 5.5 times its starting value after inulin was fed, and those animals were not even overweight. The difference between the two papers probably lies in the amount: the earlier one used three grams per kilogram per day, three times as much as the later one. Taken together, both studies suggest that fructan could move insulin, but that this requires amounts far above the lower dose tested.

A further finding complicates the simple account in which fructan reaches the large intestine undigested and sends fermentation off the rails. A study of the stomach contents of 23 horses found the fructan concentration reduced by 84 per cent in grazing horses and by 54 per cent in hay-fed horses, above all in the non-glandular part of the stomach. In horses on a high-starch ration this breakdown was absent. A large part of the fructan therefore disappears before the large intestine, and how much depends on what the horse otherwise eats.

How widely the sugar content of grass varies

The practical question is usually: when is the sugar content highest? A 2022 review examined the available measurement series. Water-soluble carbohydrates mostly rise from morning to evening over the course of the day, but the measured range of that rise runs from minus 20 to plus 74 grams per kilogram of dry matter. There are therefore series in which the content was lower in the evening than in the morning. That is exactly where the mutually contradictory pieces of advice on this subject come from.

• Time of day: mostly a rise from morning to evening, but the reverse in individual measurement series
• Temperature: higher contents under cool conditions and in cold seasons
• Grazing and cutting: frequent defoliation lowers water-soluble carbohydrates and fructan
• Nitrogen fertilisation: higher or lower contents depending on the amount and the grass variety
• Drought stress: no uniform effect across the papers reviewed

The author explicitly concludes that several factors must be considered together before an effect is attributed to any single measure. On top of that comes the measurement problem: fructan is only one part of the water-soluble carbohydrates, and the cheap colorimetric determination underestimates it, because the enzymes used do not fully break down the fructan of pasture grasses. The authors of that methods paper note that it cannot replace chromatography. Anyone reading a fructan value for a pasture is reading a figure with considerable uncertainty attached.

Is pasture more dangerous after a frosty night?

This cannot be answered robustly. The review states only that water-soluble carbohydrate contents tend to be higher at cool temperatures and in cold seasons. A study linking frosty nights to laminitis cases could not be found in this search. The advice therefore rests on plausibility, not on a measurement in horses.

The risk sits in the horse, not only in the grass

Who falls ill can currently be described better than when. At a Finnish university clinic, 36 horses presented for laminitis were examined over sixteen months. In 89 per cent, indications of an underlying hormonal disorder were found. One third of those had pituitary dysfunction, two thirds a raised fasting insulin without a conspicuous coat. Among the animals with high insulin, 95 per cent showed outward features of being overweight. This is a snapshot from a single clinic, so it describes the make-up of the caseload, not a risk.

Prospective measurement was carried out in 446 British ponies aged seven and over, free of laminitis at entry and followed for three years. Low adiponectin and high insulin went together with the later occurrence of laminitis. After one year, laminitis had been diagnosed by a vet in 4.0 per cent of the animals, after two years in 6.7 and after three years in 9.9 per cent. At the start, 72.2 per cent of the ponies were overweight or obese. The markers were therefore measurable before the first episode, although each value was determined only once.

Pituitary dysfunction is more common than was long assumed. A systematic review from 2018 gives as its most robust estimates 21.2 per cent in horses and ponies aged fifteen and over and 2.9 per cent in the overall population. Laminitis is among the most frequently reported signs there, alongside coat changes and muscle loss over the back. Increasing age remained the only established risk factor.

Conversely, the epidemiology of naturally occurring laminitis is thin. A systematic review screened 17 publications and rated six as the most reliable. Only the association between increasing age and chronic laminitis rested on good evidence; for sex, breed and bodyweight the results remained contradictory.

How much a horse actually eats at pasture

One quantity is missing from almost every discussion of pasture and sugar: the amount taken in. A trial in twelve ponies over 28 days put a number on it. The individual plots were sized to yield 1.5 per cent of bodyweight as dry matter per day. The ponies with immediate access to the whole area took in a calculated 2.33 per cent, distinctly more than intended, and gained 4.82 per cent of their weight in four weeks.

In the two groups given the area in portions behind an electric fence, the values were 1.59 and 1.82 per cent, and weight gain 1.16 and 1.54 per cent. Body condition score and the assessment of the neck crest rose only in the group with immediate full access. Laminitis was not an endpoint in this trial, and intake was calculated from the growth of the plot rather than measured in the individual animal.

What does not follow from all this

The chain running from rapidly fermentable carbohydrates through acidification of the gut to laminitis has also been studied in cattle, where rumen acidosis has been centre stage for decades. A systematic review from 2023 included sixteen papers out of 339 screened. Fifteen of them confirmed the occurrence of rumen acidosis, yet in two papers that used oligofructose for the purpose not a single clinical sign of laminitis appeared. The chain is therefore not automatic even where it has been studied longest.

The inflammatory side also carries less weight than was long assumed. In one trial, twelve of 22 ponies received a ration with around 42 per cent non-structural carbohydrates for seven days, against around seven per cent in the comparison ration. In the hoof lamellae none of the pro-inflammatory messengers measured rose, and white blood cells did not migrate in. Only one particular enzyme was read out in greater amounts. The authors conclude from this that the marked lamellar inflammation of the sepsis models may play no central role in pasture laminitis.

Finally, nobody knows exactly how common laminitis is. A systematic review appraised 69 publications, kept ten as the most reliable and found frequencies between 1.5 and 34 per cent. The authors judge the quality of the papers to be predominantly poor and consider comparison of these figures with one another explicitly inadmissible, because the studies look at different causes of laminitis. Anyone reading a percentage for the frequency of pasture laminitis is reading a figure without a secure basis.

What the induction dose of the fructan model means in kilograms of pasture grass

Original analysis

Limitations and uncertainty

• The two insulin experiments rest on five and four treated animals, and the insulin values reached lay about 66 times above baseline. They establish a route of action, not a pasture condition, and the animals were put down once a predefined severity grade was reached, so nothing is known about the further course.
• The two feeding trials on fructan contradict one another, their doses differ threefold, and both used inulin, whose structure and chain length differ from the fructan of temperate pasture grasses. In addition the sugar was added to the ration rather than grazed.
• The fructan contents come from British grasses of a single harvest year, and the widely used colorimetric determination underestimates them. Measurement series for Swiss pastures could not be found in this search.
• There is no study that measured the fructan content of a pasture and then followed the horses grazing it for laminitis. The link between content and disease remains an assumption.
• The epidemiological basis is thin: one systematic review found only the association with increasing age well supported, a second found frequencies between 1.5 and 34 per cent with predominantly poor study quality. Both searches closed in 2010 and are therefore older than the cohort used here.
• Two of the core papers are reviews without a systematic procedure, the induction experiments work with four to twelve animals per group, and no meta-analysis on this subject exists. About half of the sources used here reach the level of systematic review or randomised trial, and the field offers no more than that.

Open questions

• From what amount of fructan, below the five grams per kilogram tested, does anything measurable change in the horse at all?
• How much fructan actually reaches the large intestine in grazing horses, if a large part already disappears in the stomach?
• Can insulin and adiponectin be condensed into a usable risk assessment if they are determined repeatedly rather than only once?
• Are there pasture conditions under which insulin in at-risk horses reaches values close to those of the experiments?

Frequently asked questions

When is the fructan content of grass highest?

The data point to no generally valid time of day. A 2022 review summarises that water-soluble carbohydrates mostly rise from morning to evening over the course of the day, but that the measured range of that rise runs from minus 20 to plus 74 grams per kilogram of dry matter. In individual measurement series the content was therefore lower in the evening than in the morning. Higher contents go together with cool temperatures and cold seasons, frequent grazing lowers them, and nitrogen fertilisation and drought stress act inconsistently. The author therefore explicitly advises against deriving a rule from any single factor.

How many grams of fructan are dangerous for a horse?

That figure is not known, and the number in circulation answers a different question. It comes from a dose series in which healthy horses received 7.5, 10 or 12.5 grams of oligofructose per kilogram of bodyweight once by nasogastric tube, in order to trigger laminitis deliberately. A lower step was never tested, so a minimum dose is unknown. In another experiment, five grams per kilogram were enough in only two of eight horses. These are experimental doses used to trigger the disease, not a limit value for a pasture.

Does fructan from grass trigger laminitis or not?

It is established that very high single doses by tube trigger laminitis; it is not established that grazed grass does the same. For a 500 kilogram horse, the lowest experimental dose would correspond to roughly 12.5 kilograms of dry matter of the most fructan-rich grass ever measured, all at once, which is more than one measured daily intake. On top of that, the fructan concentration in the stomach of grazing horses was reduced by 84 per cent in one study. The focus of research has shifted to insulin accordingly. A cleanly measured link between pasture content and disease is still missing.

Is turnout after a frosty night risky?

This cannot be answered with the available data. The review of sugar contents states that these tend to be higher at cool temperatures and in cold seasons. A study linking frosty nights to actual laminitis cases could not be found in this search. The widespread advice therefore rests on a plausible chain, not on a measurement in horses. For a horse whose metabolic situation is known, the attending veterinary practice is the right point of contact, because on current data the risk sits more in the animal than in the grass.

How long should I turn my horse out in spring?

There is no established figure for this, and this article deliberately names none. The specialist literature contains no trial that compared different spring turnout plans and measured laminitis as an endpoint. Something else was measured: in a trial of twelve ponies over four weeks, the animals with immediate access to the whole area took in 2.33 per cent of their bodyweight as dry matter per day instead of the intended 1.5 per cent, and 1.59 to 1.82 per cent where the area was allocated in portions. How an individual horse is managed is decided by the attending veterinary practice.

My pony is not fat, can it still be affected?

Yes, being overweight is neither a precondition nor a proof. In one feeding trial, ponies that were explicitly not overweight but prone to laminitis showed distinctly reduced insulin sensitivity, which only became apparent when the metabolism was challenged. Conversely, in a Finnish clinical series 95 per cent of the horses with raised insulin showed outward features of being overweight, and in a British cohort 72.2 per cent of the ponies were overweight or obese at entry. Being overweight is therefore common, but not necessary. Whether a particular animal is affected can only be established by a veterinary examination.

Sources

1. Elliott J, Bailey SR. A review of cellular and molecular mechanisms in endocrinopathic, sepsis-related and supporting limb equine laminitis. Equine Veterinary Journal, 2023 (Other | Horse)DOI 10.1111/evj.13933
   Narrative review that separates three forms of laminitis and proposes stress of the basal cells as a shared core process, explicitly as a hypothesis, noting that many ponies with pasture laminitis show the pattern of disturbed insulin regulation.
2. Asplin KE, Sillence MN, Pollitt CC, McGowan CM. Induction of laminitis by prolonged hyperinsulinaemia in clinically normal ponies. The Veterinary Journal, 2007 (Randomised trial | Horse)DOI 10.1016/j.tvjl.2007.07.003
   In nine healthy ponies with no history of laminitis, all five animals treated with insulin developed laminitis in all four feet after a mean of 55.4 hours with blood glucose held normal, none of the four comparison animals did, and no digestive or general signs appeared.
3. de Laat MA, McGowan CM, Sillence MN, Pollitt CC. Equine laminitis: induced by 48 h hyperinsulinaemia in Standardbred horses. Equine Veterinary Journal, 2010 (Randomised trial | Horse)DOI 10.2746/042516409X475779
   Four of four Standardbred trotters treated with insulin developed laminitis in less than 48 hours and none of the four comparison animals did, even though all treated animals had a calculated insulin sensitivity in the normal range beforehand.
4. Borer KE, Bailey SR, Menzies-Gow NJ, Harris PA. Effect of feeding glucose, fructose, and inulin on blood glucose and insulin concentrations in normal ponies and those predisposed to laminitis. Journal of Animal Science, 2012 (Randomised trial | Horse)DOI 10.2527/jas.2011-4236
   In a crossover trial in twelve ponies at one gram per kilogram per day, inulin changed blood glucose and insulin only slightly and fructose distinctly less than glucose, while laminitis-prone and normal ponies separated most clearly after glucose.
5. Bailey SR, Menzies-Gow NJ, Harris PA, Habershon-Butcher JL. Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis. Journal of the American Veterinary Medical Association, 2007 (Controlled trial | Horse)DOI 10.2460/javma.231.9.1365
   In 21 ponies that were not overweight, a compensated insulin resistance could be made visible in the laminitis-prone animals, whose insulin rose to 5.5 times its value after three grams of inulin per kilogram per day were fed, while the change from pasture to hay lowered it.
6. Toth F, Frank N, Chameroy KA, Boston RC. Effects of endotoxaemia and carbohydrate overload on glucose and insulin dynamics and the development of laminitis in horses. Equine Veterinary Journal, 2009 (Randomised trial | Horse)DOI 10.2746/042516409x479027
   In groups of eight horses, five grams of oligofructose per kilogram alone made only two animals laminitic, preceding endotoxin made five, and endotoxin alone none, while both stimuli lowered insulin sensitivity without reinforcing one another.
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   Founding paper of the fructan model: all twelve horses treated with oligofructose developed clinical and histological laminitis and none of the six comparison animals did, and the link to the fructan content of pastures is a conclusion of the authors, not a measured result.
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   Traceable origin of the figure of 7.5 grams per kilogram: three pairs of horses received 7.5, 10 and 12.5 grams of oligofructose per kilogram once by nasogastric tube, all became laminitic after 48 hours, and the loss of anchoring structures increased with the dose.
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   Carried out in 18 horses in three groups, this paper documents the model: oligofructose doses regarded as triggering still produced measurable lamellar damage seven days later, which 72 hours of limb cooling reduced markedly.
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    In the stomach contents of 23 horses the fructan concentration was reduced by 84 per cent in grazing horses and by 54 per cent in hay-fed horses, above all in the non-glandular part of the stomach, while this breakdown was absent on a high-starch ration.
11. Kagan IA. Water- and Ethanol-Soluble Carbohydrates of Temperate Grass Pastures: a Review of Factors Affecting Concentration and Composition. Journal of Equine Veterinary Science, 2022 (Other | Species-independent)DOI 10.1016/j.jevs.2022.103866
    Review of the variability of water-soluble carbohydrates: across the measurement series the rise from morning to evening runs from minus 20 to plus 74 grams per kilogram of dry matter, and the author explicitly advises against deriving a rule from any single factor.
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    In four pasture grasses, chromatography gave 83 to 299 grams of fructan per kilogram of dry matter (mean 154) and the cheap colorimetric method only 5 to 238 on the same samples (mean 82): it underestimates the content and cannot replace chromatography.
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    Twelve ponies on plots sized for 1.5 per cent of bodyweight took in a calculated 2.33 per cent with immediate full access and gained 4.82 per cent in weight, against 1.59 to 1.82 per cent and 1.16 to 1.54 per cent where the area was allocated in portions.
14. Burns TA, Watts MR, Weber PS, McCutcheon LJ. Laminar inflammatory events in lean and obese ponies subjected to high carbohydrate feeding: Implications for pasture-associated laminitis. Equine Veterinary Journal, 2015 (Controlled trial | Horse)DOI 10.1111/evj.12314
    Seven days at around 42 per cent non-structural carbohydrates raised none of the pro-inflammatory messengers measured in the hoof lamellae of twelve of 22 ponies and led to no migration of white blood cells, so the lamellar inflammation of the sepsis models may not be central to pasture laminitis.
15. Karikoski NP, Horn I, McGowan TW, McGowan CM. The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital. Domestic Animal Endocrinology, 2011 (Cross-sectional study | Horse)DOI 10.1016/j.domaniend.2011.05.004
    In 89 per cent of 36 horses presented for laminitis, indications of a hormonal disorder were found, in one third of them pituitary dysfunction and in two thirds a raised fasting insulin without any coat change.
16. Menzies-Gow NJ, Harris PA, Elliott J. Prospective cohort study evaluating risk factors for the development of pasture-associated laminitis in the United Kingdom. Equine Veterinary Journal, 2017 (Cohort study | Horse)DOI 10.1111/evj.12606
    In 446 ponies aged seven and over that were free of laminitis at the outset, low adiponectin and high insulin went together with the later occurrence of laminitis, which was diagnosed after one, two and three years in 4.0, 6.7 and 9.9 per cent of the animals.
17. Ireland JL, McGowan CM. Epidemiology of pituitary pars intermedia dysfunction: A systematic literature review of clinical presentation, disease prevalence and risk factors. The Veterinary Journal, 2018 (Systematic review | Horse)DOI 10.1016/j.tvjl.2018.03.002
    The 29 publications included yield as the most robust estimates a prevalence of 21.2 per cent in horses aged fifteen and over and 2.9 per cent in the overall population, with laminitis among the most frequent signs and age the only established risk factor.
18. Wylie CE, Collins SN, Verheyen KLP, Newton JR. Risk factors for equine laminitis: a systematic review with quality appraisal of published evidence. The Veterinary Journal, 2012 (Systematic review | Horse)DOI 10.1016/j.tvjl.2011.10.020
    Of 17 fully appraised publications, six were rated the most reliable, and only the association between increasing age and chronic laminitis rested on good evidence, while sex, breed and bodyweight remained contradictory.
19. Wylie CE, Collins SN, Verheyen KLP, Newton JR. Frequency of equine laminitis: a systematic review with quality appraisal of published evidence. The Veterinary Journal, 2011 (Systematic review | Horse)DOI 10.1016/j.tvjl.2011.04.014
    Of 69 appraised publications, ten remained as the most reliable, with frequency estimates between 1.5 and 34 per cent against predominantly poor quality, and the authors consider comparison of these figures with one another explicitly inadmissible.
20. Passos LT, Bettencourt AF, Ritt LA, Canozzi MEA. Systematic review of the relationship between rumen acidosis and laminitis in cattle. Research in Veterinary Science, 2023 (Systematic review | Other animal species)DOI 10.1016/j.rvsc.2023.06.001
    Sixteen papers were included out of 339 screened, fifteen of which confirmed rumen acidosis, while no clinical sign of laminitis appeared in two papers using oligofructose: the chain from fermentable carbohydrates to laminitis is not automatic in cattle either.