Location: Forage-animal Production ResearchTitle: Effects of inulin chain length on fermentation by equine fecal bacteria and Streptococcus bovis Author
Submitted to: Journal of Equine Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2015
Publication Date: 12/11/2015
Citation: Harlow, B.E., Kagan, I., Lawrence, L.M., Flythe, M.D. 2015. Effects of inulin chain length on fermentation by equine fecal bacteria and Streptococcus bovis. Journal of Equine Veterinary Science. 48:113-120. Interpretive Summary: Horses are grazing animals, but modern pastures sometimes contain too much easily digestible carbohydrate. Fructans are one type of carbohydrate that can be a problem in lush, spring pastures. If horses consume too much fructan, the excess fructan will reach the hindgut and be fermented by the normal hindgut bacteria. The bacteria convert the fructan to acids, and acidosis, colic or even lameness can ensue. Cool season grasses and other plants produce many types of fructans. All the fructans are polymers, repeating units or “chains”, primarily made of the sugar, fructose. However, these fructose building-blocks can be assembled in different ways to make fructan chains of different lengths and other conformations. We should not assume that the horse hindgut bacteria convert all fructans to acid as readily or in the same way. These experiments were initiated to determine if horse hindgut bacteria would use a long-chain fructan and a short-chain fructan in the same way. Mixed bacteria were extracted from horse feces. The bacteria converted the short-chain fructan to acid more readily than the long-chain. A pure culture of a known acid-producing bacterium, Streptococcus bovis, grew better on short-chain fructan. Strept. bovis also caused a greater increase in acidity when grown on short-chain fructan. It is important to note that these results do not show that short- or long-chain fructans are better or worse for horses, only that a horse’s bacteria can respond to different degrees when presented with structurally different fructans. The impact of this research is knowledge that not all fructans are equal in terms of the horse’s hindgut bacteria, and that further research into grass fructans and their effects on equine microbiology and health are justified.
Technical Abstract: Fructans from pasture can be fermented by Gram-positive bacteria (e.g., Streptococcus bovis) in the equine hindgut, increasing production of lactic acid and decreasing pH. The degree of polymerization (DP) of fructans has been suggested to influence fermentation rates. The objective of the current study was to determine how DP impacts fermentation by equine fecal bacteria and a model S. bovis. Fecal microbes from 3 mares were harvested by differential centrifugation, washed, and re-suspended in anaerobic media containing short-chain (SC; DP = 10) or long-chain (LC) inulin (DP = 23) from 0-2% w/v. After 24 h of incubation (37 ºC), samples were collected for pH. Data were analyzed using the GLM procedure testing for the effect of treatment, concentration, and treatment × concentration (SAS v. 9.3). At all concentrations, the pH was lower in SC fermentations than in LC (P < 0.0001, in all cases). To determine the effect of DP on S. bovis, cultures were incubated (39 ºC) for 9 h with 0.1, 0.5, or 1.3% SC or LC inulin. Optical density (OD600) was determined by spectrophotometry. Maximum specific growth rates (µ) were determined by linear regression (2-5 h). Data were analyzed using the one-way ANOVA procedure (SAS v. 9.3). The final OD600, µ and yield were higher with SC than with LC fermentation (P < 0.05). These results indicate that SC inulin may be more available for fermentation than LC inulin by equine fecal bacteria and S. bovis, specifically.