Effect of Dietary Starch Source and Concentration on Equine Fecal Microbiota.
Authors: Harlow Brittany E, Lawrence Laurie M, Hayes Susan H, Crum Andrea, Flythe Michael D
Journal: PloS one
Summary
Starch digestibility varies considerably between grain sources in horses, with corn starch proving largely resistant to small intestinal breakdown and therefore reaching the hindgut where microbial fermentation occurs, whereas oat starch is more readily absorbed prior to this point. Researchers fed thirty horses six different dietary treatments—a forage-only control, high and low concentrations of corn, oats, or wheat middlings (with starch levels of 2 or 1 g/kg bodyweight respectively)—whilst monitoring faecal microbial populations across a two-week adaptation period using quantitative analysis of key bacterial groups including amylolytics, cellulolytics, lactobacilli and lactate-utilisers. Corn and wheat middlings diets produced marked shifts towards amylolytic bacteria (particularly *Enterococcus faecalis*) with simultaneous suppression of cellulolytic populations, whilst oat-based feeding drove increased lactobacilli and decreased Gram-positive cocci; notably, the low-oats group showed minimal microbial changes overall. These differential responses matter considerably for practitioners formulating diets, as selecting starch source will predictably alter hindgut fermentation dynamics—a factor that influences not only nutrient availability but also metabolic acidosis risk, hindgut health, and potentially performance-related issues such as colic or stereotypic behaviour. Given that individual grain sources produce distinctly different microbial communities rather than simply dose-dependent effects, farriers, veterinarians and nutritionists should recognise grain selection as a targeted tool for manipulating equine gut ecology rather than treating all starch as functionally equivalent.
Read the full abstract on PubMed
Practical Takeaways
- •Choose starch source carefully when feeding concentrates—oats may be safer for hindgut health than corn, as they promote beneficial lactobacilli rather than potentially pathogenic Enterococcus species
- •Gradual introduction of starch (reaching full amount by day 11) is important for monitoring individual horse responses, particularly when using corn or wheat-based feeds
- •Monitor fecal consistency and behavior when switching starch sources, as corn and wheat middlings produce more dramatic microbiota shifts than oats
Key Findings
- •Corn and wheat middlings increased amylolytic bacteria and decreased cellulolytic bacteria more than oats (P < 0.05)
- •Oat-fed horses showed increased lactobacilli and decreased Group D Gram-positive cocci, while corn had opposite effects (P < 0.05)
- •Enterococcus faecalis was the predominant amylolytic isolate in corn and wheat middlings groups but not in oat-fed horses
- •Starch source produces differential effects on equine fecal microbiota composition independent of starch concentration