Dietary fructan carbohydrate increases amine production in the equine large intestine: implications for pasture-associated laminitis

Abstract

Pasture-induced laminitis in the horse is associated with the overconsumption of fermentable carbohydrate, in the form of simple sugars, fructans, or starch. The fermentation of carbohydrate in the cecum and large intestine results in the production of lactic acid and other toxins or "laminitis trigger factors." Vasoactive amines have been suggested as possible initiating factors. The aim of this study was to feed a commercially available form of fructan carbohydrate (inulin, 3 g/kg of BW per day) to normal ponies and to ponies predisposed to laminitis, to mimic a change from a basal hay diet to lush spring-summer pasture. Five normal and 6 laminitis-prone, native-breed ponies were acclimated to a basal hay diet before the inclusion of inulin and chopped dried grass. Blood samples, fecal samples, and foot temperature measurements were taken throughout the study. Amines were measured in the feces and plasma by HPLC and liquid chromatography-mass spectrometry, respectively. The pH of the fecal samples decreased from 6.89 +/- 0.11 on the hay diet to a minimum of 6.18 +/- 0.11 with the addition of inulin (P <0.05). An increase was observed in the fecal concentrations of a number of amines, including tryptamine (2.5-fold increase, P <0.05) and tyramine (2-fold increase, P <0.05). No changes were noted in plasma amine concentrations or plasma D- or L-lactate, indicating that there may be a threshold of hindgut pH change before mucosal damage can result in the release of these factors into the circulation. No differences in pH or any of the measured compounds were observed between the group of normal ponies and those predisposed to laminitis. This indicates that differences in the intestinal microflora do not account for this predisposition. However, the results from this study indicate that moderate increases in dietary fructan carbohydrate can produce increases in bacterial fermentation products and other compounds in the large intestine, which may be relevant to the pathogenesis of acute laminitis in ponies on pasture.