Characterisation of microbial metabolite profiles across the gastrointestinal tract of horses fed on pasture, hay or oat-supplemented rations.

Overview

• This study investigated how different diets—pasture, hay, or oat-supplemented hay—affect microbial metabolite production throughout the gastrointestinal tract of horses.
• The researchers measured various metabolites and chemical parameters in different gut sections to understand diet-driven changes in microbial fermentation and metabolism.

Introduction and Study Purpose

• The gastrointestinal (GI) tract of horses hosts microbial communities that ferment feed and produce metabolites beneficial for health.
• However, these metabolites can also contribute to gastrointestinal disorders.
• Different feeding strategies, particularly starch supplementation, might change where and how microbes produce these metabolites along the GI tract, but this is not well understood in horses.
• This study aimed to characterize and compare the profiles of microbial metabolites throughout the GI tract in horses fed three different diets: pasture 24 h/day, hay ad libitum, and hay with two levels of oat (starch) supplementation.

Study Design and Methods

• Four groups of horses were fed different diets:
  • PST: Pasture 24 hours/day (n=4)
  • HAY: Hay ad libitum (n=8)
  • OS1: Hay ad libitum + oats at 1 g starch/kg body weight/meal (n=6)
  • OS2: Hay ad libitum + oats at 2 g starch/kg body weight/meal (n=6)
• After the feeding period, horses were euthanised for sample collection.
• Digesta (intestinal contents) samples were collected from multiple sections of the GI tract, spanning foregut and hindgut.
• Parameters analyzed included:
  • Dry matter content
  • pH level
  • Short chain fatty acids (SCFAs) such as n-butyrate, n-valerate, iso-SCFAs
  • Ammonia concentration
  • Lactate concentration
• Statistical analyses tested for differences between gut sections, diets, and interactions between diet and section.

Key Findings: Gastrointestinal Tract Differences

• Significant differences in dry matter, pH, SCFAs, ammonia, and lactate were found between GI tract sections (P < 0.001).
• Clear separation was observed between:
  • Foregut (stomach and small intestine) and hindgut (cecum and colon)
  • Proximal and distal sections within the hindgut
• These differences reflect the diverse microbial activities and environments in different parts of the gut.

Key Findings: Diet-Driven Effects on Microbial Metabolites

• Diet significantly affected:
  • Dry matter content (P < 0.001)
  • Total SCFA concentration (P = 0.011)
  • n-Butyrate (P = 0.015)
  • n-Valerate (P = 0.045)
  • Iso-SCFA levels (P = 0.017)
• There were significant interactions between diet and GI tract section affecting dry matter, n-butyrate, n-valerate, iso-SCFAs, and ammonia (all P ≤ 0.012), meaning diet effects varied along the gut.

Interpreting the Metabolite Patterns

• Pasture-fed horses (PST group) had:
  • Higher total SCFA concentrations in digesta, suggesting more intense microbial fermentation activity.
  • Elevated levels of n-valerate, iso-SCFAs, and ammonia in distal hindgut sections, indicating increased microbial fermentation of amino acids and altered microbial protein metabolism.
• Hay-only and oat-supplemented groups had distinct metabolite profiles:
  • Oat supplementation notably influenced metabolites primarily in the stomach region of the foregut.
  • This suggests increased proteolytic (protein-degrading) microbial activities possibly due to the starch in oats.

Conclusions and Implications

• The type of diet significantly changes microbial metabolism along the equine GI tract, both in the foregut and hindgut.
• Pasture feeding promotes robust microbial fermentation and amino acid breakdown in the hindgut, which could have beneficial or detrimental effects depending on context.
• Starch supplementation with oats alters stomach microbial metabolism, possibly increasing protein degradation.
• Understanding these differences helps in managing equine diets to optimize gut health and reduce risk of gastrointestinal disorders related to microbial metabolite imbalances.