Evaluation of an in vitro system to simulate equine foregut digestion and the influence of acidity on protein and fructan degradation in the horse's stomach.
Authors: Strauch S, Wichert B, Greef J M, Hillegeist D, Zeyner A, Liesegang A
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Strauch *et al.* (2017) sought to refine an in vitro model of equine foregut digestion to better understand how different forages are broken down in the stomach and upper small intestine, whilst investigating the poorly understood mechanism of fructan degradation across varying pH conditions. Their system simulated peptic and pancreatic digestion of six forage types (including perennial ryegrass, tall fescue, clover and lucerne) without incorporating microbial fermentation, producing results consistent with published in vivo data for crude protein and monosaccharide breakdown; notably, they observed substantial fructan losses in ryegrass and cow grass mixtures (from approximately 4–4.4% to 0–0.6% dry matter) despite fructans being considered resistant to mammalian digestive enzymes. A secondary experimental series manipulating gastric pH (2, 3 and 4) revealed counterintuitive findings: whilst protein degradation followed expected patterns (highest at pH 2), fructan degradation paradoxically peaked at pH 4, suggesting that plant-derived enzymes rather than simple acid hydrolysis drive fructan breakdown in the acidic stomach environment. These results have important implications for practitioners formulating diets for horses prone to gastric upset or metabolic sensitivity, indicating that high-fructan grasses may be partially degraded during gastric transit—a mechanism that may influence both nutrient availability and hindgut fermentation patterns.
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Practical Takeaways
- •Fructan content in pasture grasses (particularly ryegrass) may be partially degraded in the horse's stomach through acidic and enzymatic processes, potentially reducing the risk of fructan-related digestive upsets compared to previously assumed
- •pH variations in the equine stomach significantly influence both protein and fructan digestion; understanding these dynamics helps explain individual horse responses to different forage types
- •When selecting forages for horses with digestive sensitivities, consider that high-fructan grasses like ryegrass undergo measurable breakdown in the foregut, which may make them more suitable than traditional avoidance protocols suggest
Key Findings
- •An in vitro foregut digestion system using pepsin and pancreatin produced results consistent with in vivo studies, showing degradation of crude protein and monosaccharides with relative increase in fibres
- •Unexpected fructan loss occurred during simulated foregut digestion in English perennial ryegrass and grass mixture for cows (4.1-4.4% DM reduced to 0.0-0.59% DM)
- •Acidic hydrolysis alone does not explain fructan degradation, as highest fructan loss occurred at pH 4 rather than pH 2, suggesting plant enzymes contribute to fructan breakdown
- •Protein degradation was highest at lowest pH (pH 2: 6.11-8.28% DM versus pH 4: 7.73-10.64% DM in the two grass types tested)