Understanding Fructan's Role in Horse LaminitisBy Kentucky Equine Research Staff · May 13, 2016
Most horse owners likely already know that consumption of lush pastures puts some horses at risk of developing pasture-associated laminitis (PAL), a potentially life-threatening condition. Is it merely the ingestion of high concentration of water-soluble carbohydrates, like simple sugars? Does a horse’s reduced sensitivity to insulin also impact PAL? Is it a combination of these factors or even something completely different? Without an improved understanding of the underlying events leading up to PAL, controlling this condition remains challenging.
One theory is that a specific type of water-soluble carbohydrate, called fructan, can lead to PAL. Fructans are chains of fructose sugar molecules; they are configured much like starch, which is made glucose molecules linked together. Unlike starch, ingested fructans are minimally digested in the small intestine before entering the large intestine. Once in the hindgut, fructans are fermented by bacteria, primarily Streptococcus spp., to produce lactic acid. While the horse may eventually use lactic acid for energy, this is much different than the fermentation of fiber, which produces short-chain fatty acids that provide energy for the horse without affecting the pH.
“An increase in lactic acid produced by fermenting fructans decreases the pH of the large intestine, causing hindgut acidosis. This makes the walls of the intestine leaky, allowing endotoxins produced by bacteria, amines, and proteinases to be absorbed into the bloodstream and circulate to the hoof, potentially causing laminitis,” explained Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research (KER).
There are several types of fructans, and it is not clear if all fructans are fermented the same and are equally dangerous. To better understand the impact of fructans on PAL, researchers* created a model of the large intestine to measure the fermentation of a specific type of fructan called inulin. More specifically, the research group collected fecal microbes from mares and created cultures of Streptococcus bovis, a prominent bacterium in the equine hindgut suspected of fermenting fructans. Both short-chain inulin (with less than 10 fructose molecules making up the inulin) and long-chain inulin (with more than 23 fructose molecules) were incubated with the fecal microbes and S. bovis.
Short-chain inulin was more readily fermented than long-chain inulin in these models, but S. bovis was perfectly capable of making “copious amounts of lactic acid” from either inulin type. This research contributes to our understanding of PAL, a complex and multifactorial condition.
“To protect horses against deleterious pH changes in the large intestine, KER offers EquiShure, a time-released hindgut buffer that helps maintain a stable hindgut environment,” shared Crandell.
*Harlow, B.E., I.A. Kagan, L.M. Lawrence, et al. Effects on inulin chain length on fermentation by equine fecal bacteria and Streptococcus bovis. Journal of Equine Veterinary Science. In press.