An in vitro investigation into the effects of postbiotic supplementation on stabilising equine hindgut pH.

Overview

• This study investigated how supplementing with a postbiotic derived from Saccharomyces cerevisiae affects the acidity (pH) and fermentation products in the equine hindgut when exposed to different carbohydrate levels.
• The research aimed to determine if postbiotic addition could stabilize pH and reduce harmful lactate accumulation, which are key factors in preventing hindgut acidosis in horses.

Background and Rationale

• Hindgut acidosis in horses is caused by dysbiosis—an imbalance in the gut microbial population—which can result from dietary changes, particularly increased levels of easily fermentable carbohydrates.
• The microbial community diversity and fermentation profile in the hindgut are crucial for maintaining gut health; disturbances can lead to a drop in pH and harmful metabolite accumulation such as lactate.
• Postbiotics, which are bioactive compounds produced by beneficial microbes (in this case, from yeast Saccharomyces cerevisiae), might modulate fermentation processes and help maintain a healthier microbial environment.

Objective and Hypothesis

• The study tested whether including a yeast-derived postbiotic in in vitro fermentation would reduce the extent of pH drop and lactate accumulation during fermentation, potentially stabilizing hindgut conditions.

Methods

• In vitro batch cultures were prepared using faecal inoculum from horses to simulate hindgut fermentation.
• Two substrates were used to imitate different dietary conditions:
  • Low starch (LS) – representing normal fermentation and healthier conditions.
  • High glucose (G) – representing high fermentable carbohydrate ingestion that can cause acidic fermentation conditions.
• Two concentrations of Saccharomyces cerevisiae postbiotic were tested:
  • T1: 280 μg – equivalent to the recommended daily dose for a 500 kg horse adjusted for dry matter.
  • T2: 560 μg – double the recommended dose.
• Incubations lasted 48 hours to track fermentation changes over time.
• Measured parameters included:
  • pH changes over time to assess acidity trends.
  • Gas production as an indicator of fermentation activity.
  • Volatile fatty acid (VFA) concentrations (propionic, acetic, butyric acids), which serve as key energy sources and indicators of fermentation products.
  • Ammonia (NH₃) levels, relevant for nitrogen metabolism and microbial activity.
  • D-lactate concentrations, an organic acid that can accumulate under acidic conditions and contribute to acidosis.

Key Results

• The high glucose (G) substrate caused a faster and more significant decline in pH compared to the low starch (LS) substrate at 6 and 12 hours—confirming the acidic fermentation condition model.
• A positive linear relationship was found between the postbiotic concentration and pH in the high glucose substrate:
  • T1 postbiotic dose improved pH at 6 h.
  • T2 dose improved pH at both 6 and 12 h.
• Postbiotic supplementation increased production of key VFAs:
  • Propionic and acetic acids were significantly increased at 12 and 36 hours.
  • Butyric acid was higher at 36 hours with postbiotic addition.
• D-lactate production was:
  • Higher in the high glucose substrate at 12 h, indicating acidotic risk.
  • Lower at 36 h, indicating possible metabolic shifts over time.
  • Postbiotic reduced d-lactate accumulation at 12 and 36 h in the low starch substrate.
• Gas and ammonia levels were measured but specifics were not highlighted as significant in the abstract.

Conclusions

• Postbiotic supplementation from Saccharomyces cerevisiae can help moderate the decline in hindgut pH under high non-structural carbohydrate (high glucose) conditions, suggesting it may reduce the severity of hindgut acidification.
• It also positively influences production of beneficial volatile fatty acids, which are important for gut health and energy supply to the host animal.
• Despite these benefits, the postbiotic did not completely prevent acidosis in vitro, indicating that while it may reduce risk or severity, it is not a standalone solution to hindgut acidosis.
• Overall, postbiotic supplementation shows promise as a strategy to enhance hindgut microbial stability and fermentation profiles, but further in vivo studies are warranted to evaluate practical effects in live horses.