By Eleanor Kellon, VMD
In 2006, van Eps and Pollitt reported the induction of laminitis by administering a bolus of pure chicory root oligofructose (a fructan) by stomach tube. The amount required was 7.5 g/kg BW to induce laminitis in one foot; 10 to 12.5 g/kg for a systemic reaction and multifoot laminitis. This is a huge amount. At the lower end it equates to an 8.25 pound bolus of pure fructan for a 500 kg horse. For a horse to take in that much, even over a 24 hour period of grazing, would require a pasture with 37.5% fructan on a dry matter basis. 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 close. The average difference between WSC (sugars + fructans) and ESC (sugars) is only 2% in the Dairy One database. https://dairyone.com/.../forage.../feed-composition-library/ .
Crawford et al., 2007 fed 3 g/kg chickory fructan to ponies with and without a history of pasture laminitis. Despite a moderate drop in fecal pH from 6.89 to 6.18, there was no evidence of illness or laminitis, no increase in blood levels of fecal amines or D-lactate (bacterial) which would indicate a compromised colonic barrier. They concluded there is a threshold for fructan to have negative effects. For a pasture to reach that level of no effect the horse would have to consume a 15% fructan (dry matter basis) pasture for 24 hours. As above, that would be very high and is not the same thing as a pure bolus of chickory root fructan by stomach tube.
In 2006, Trieber et al., reported following a herd of 160 ponies on pasture and found a prelaminitic metabolic profile was defined on the basis of body condition, plasma triglyceride concentration, RISQI, and MIRG. (RISQI and MIRG are proxies for insulin sensitivity.) Meeting > or = 3 of these criteria differentiated prelaminitic from never-laminitic group ponies with a total predictive power of 78%. Onset of spring laminitis in the ponies at risk coincided with a flush of clover and increased pasture starch, not fructan.
Coleman et al., 2018 did a large epidemiological study of horses in North America and identified obesity, regional adiposity, and pre-existing endocrinopathy as risk factors. Menzies-Gow et al., 2017 followed 446 animals for a period of 3 years and monitored multiple factors to identify those which would be predictive of laminitis developing at pasture. They concluded: “Risk factors for future laminitis prior to disease occurrence include low plasma adiponectin and high serum basal insulin or insulin post-dexamethasone concentrations. “
Fructan-induced laminitis is a carbohydrate overload model with SIRS, endotoxemia, fever and diarrhea – none of which are seen with pasture laminitis. There is no question endocrinopathic laminitis is behind pasture laminitis. If fructan was the issue, all horses would be at risk; not only those identified as endocrinopathic.
Borer et al., 2016 demonstrated chicory fructan produces minimal changes in glucose or insulin which is not surprising considering fructan is not a sugar, and not absorbed. It is a storage form of carbohydrate composed of fructose chains but is no more a sugar than cellulose, which is a chain of glucose molecules. Mammalian digestive enzymes cannot break down these compounds, but bacteria in the hind gut can ferment them. They use the sugars they liberate for their own energy systems and produce volatile fatty acids or lactate as the end products.
It has been suggested that warm season grasses or legumes like alfalfa or clover would be safe since they do not contain fructan. This is not correct. In addition to Trieber's 2006 study documenting the starch in clover pasture as a trigger (not fructan), Kagan et al., 2020 compared red and white clover samples collected in the morning and afternoon and found significant diurnal variation in starch content from morning to afternoon; red clover 13-51 g/kg; white clover 24-52 g/kg freeze-dried weight. At 10 kg/day dry matter intake, this represents a range of 130 to 520 grams of starch intake alone. This, combined with the WSC fraction which, given the lack of fructan, would be comprised of simple sugars, led the authors to conclude that grazing clover is not recommended for horses at risk of endocrinopathic (insulin-induced) laminitis.
For further in-depth discussion of fructan see Dr. Gustafson’s presentation from the 2021 NO Laminitis Conference, available to download free here https://www.e-junkie.com/ecom/gb.php?&i=1740628&cl=276648&c=cart&ejc=2&custom=card .
Borer KE, Bailey SR, Menzies-Gow NJ, Harris PA, Elliott J. Effect of feeding glucose, fructose, and inulin on blood glucose and insulin concentrations in normal ponies and those predisposed to laminitis. J Anim Sci. 2012 Sep;90(9):3003-11. doi: 10.2527/jas.2011-4236. PMID: 22966077.
Coleman MC, Belknap JK, Eades SC, Galantino-Homer HL, Hunt RJ, Geor RJ, McCue ME, McIlwraith CW, Moore RM, Peroni JF, Townsend HG, White NA, Cummings KJ, Ivanek-Miojevic R, Cohen ND. Case-control study of risk factors for pasture-and endocrinopathy-associated laminitis in North American horses. J Am Vet Med Assoc. 2018 Aug 15;253(4):470-478. doi:2460/javma.253.4.470. PMID: 30058970.
Crawford C, Sepulveda MF, Elliott J, Harris PA, Bailey SR. Dietary fructan carbohydrate increases amine production in the equine large intestine: implications for pasture-associated laminitis. J Anim Sci. 2007 Nov;85(11):2949-58. doi:10.2527/jas.2006-600. Epub 2007 Jun 25. PMID: 17591708.
Kagan IA, Anderson ML, Kramer KJ, Seman DH, Lawrence LM, Smith SR. Seasonal and Diurnal Variation in Water-Soluble Carbohydrate Concentrations of Repeatedly Defoliated Red and White Clovers in Central Kentucky. J Equine Vet Sci. 2020 Jan;84:102858. doi: 10.1016/j.jevs.2019.102858. Epub 2019 Nov 14. PMID: 31864464.
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 Vet J. 2017 May;49(3):300-306. doi: 10.1111/evj.12606. Epub 2016 Aug 25. PMID: 27363591.
Treiber KH, Kronfeld DS, Hess TM, Byrd BM, Splan RK, Staniar WB. Evaluation of genetic and metabolic predispositions and nutritional risk factors for pasture-associated laminitis in ponies. J Am Vet Med Assoc. 2006 May 15;228(10):1538-45. doi: 10.2460/javma.228.10.1538. PMID: 16677122.
van Eps AW, Pollitt CC. Equine laminitis induced with oligofructose. Equine Vet J. 2006 May;38(3):203-8. doi:10.2746/042516406776866327. PMID: 16706272