Starch Overload and Cecal Alkalinization: Impacts on the Intestinal Microbiota and Health of Horses.

Overview

• This study investigates how excessive starch intake affects the gut bacteria (microbiota) in horses and whether an intracecal buffering solution can protect against related negative health effects.
• The researchers found that the buffer did not prevent microbiota disruption but instead worsened intestinal and clinical issues after starch overload.

Research Context and Objectives

• Starch overload in horses is known to cause dysbiosis, a disruption of the normal balance of gut bacteria, largely due to a drop in the pH (increased acidity) in the cecum, a part of the large intestine.
• The study aimed to explore how starch overload affects cecal microbiota composition over time and whether an intracecal buffering solution could reduce these effects.
• The hypothesis was that alkalizing the cecal environment with a buffering solution would prevent or reduce changes in the intestinal microbiota and lessen clinical symptoms associated with starch overload.

Study Design

• Ten horses were randomly split into two groups, each receiving two different treatments:
  • Group I: saline solution with starch buffer (WSa and SB)
  • Group II: buffer-water and starch-saline (WB and SSa)
• Starch overload was administered via a nasogastric tube at a dose of 17.6 g/kg body weight to induce dysbiosis.
• Clinical assessments and cecal content samples were collected at six time points — before treatment (T0) and at 8, 12, 24, 48, and 72 hours after (T08 to T72).
• The V4 region of bacterial 16S rRNA genes was sequenced using Illumina technology to characterize the bacterial communities present.
• Bioinformatics analysis was performed using QIIME2 to process sequencing data.
• Statistical tests (ExpDes package and Tukey’s test in R) were used to analyze differences in bacterial richness, evenness, and the relative abundance of key bacterial groups.

Key Findings

• Diversity metrics:
  • Group I showed reduced bacterial richness (number of species) and evenness (balance of species abundance) after treatment, with signs as early as 8 hours post-starch overload in the starch buffer (SB) treatment.
• Microbial composition changes:
  • Certain bacterial taxa significantly increased in abundance between 8 and 24 hours in both the SB (starch + buffer) and SSa (starch + saline) treatments.
  • Simultaneously, other bacterial groups declined, indicating a shift in microbial balance consistent with dysbiosis.
• Clinical outcomes:
  • All horses exposed to starch overload treatments developed clinical signs (such as digestive disturbances), confirming the impact of starch overload on health.
  • The starch buffer (SB) group experienced more severe and longer-lasting clinical symptoms compared to other groups.
  • The administration of the intracecal buffer alongside starch overload paradoxically worsened both microbiota disruption and clinical health status.

Conclusions and Implications

• Contrary to the initial hypothesis, the intracecal buffering solution did not protect the intestinal microbiota or reduce clinical signs following starch overload in horses.
• Instead, the buffer exacerbated microbial imbalances and clinical symptoms, suggesting that cecal alkalinization in this context may be detrimental rather than beneficial.
• This finding warns against the routine use of buffering agents during starch overload events in horses without further research on their effects.
• The study highlights the complexity of manipulating intestinal pH and microbiota during dietary challenges and the need for careful management of starch intake in equine health.