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How High-Starch Diets Affect Horse Behaviour via the Gut-Brain Axis

How High-Starch Diets Affect Horse Behaviour via the Gut-Brain Axis

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Gut-Brain Axis in Horses: How Diet Impacts Stress and Behaviour 

 The gut-brain axis refers to the two-way communication between the central nervous system and the enteric (gut) nervous system. This connection is widely recognised in both humans and animals, including horses. In recent years, researchers have linked gut microbiota, the community of microbes living in the digestive system, to stress-related conditions such as anxiety, depression, and irritable bowel syndrome. This study aimed to explore whether changes in gut microbiota, induced by diet, could influence stress-related behaviours in horses. 

Study Design

 Six fistulated horses were fed two different diets: 

  • High-Fibre Diet (H diet): 100% hay 
  • High-Starch Diet (HB diet): 56% hay and 44% barley 

The researchers examined the horses' colonic microbiota on each diet, measuring populations of anaerobic, cellulolytic, amylolytic, and lactate-utilising bacteria. Bacterial richness, diversity, and community structure were also analysed. 

To assess behaviour, horses underwent two standardised stress tests: 

  • Novelty Test – exposure to a new object 
  • Umbrella Test – exposure to a sudden, startling object 

Key Findings 

  • Horses on the high-starch (HB) diet had a reduced fibre-digesting (fibrolytic) capacity and an increased starch-digesting (amylolytic) capacity.
  • In the novelty test, horses on the HB diet showed a significantly higher frequency of blowing, a behaviour associated with anxiety. 
  • This behaviour correlated with increased levels of amylolytic bacteria and a higher presence of Succinivibrionaceae, a bacterial family linked to starch fermentation. 
  • In the umbrella test, while behavioural differences were not statistically significant, a lower colonic pH (a result of high-starch intake) was associated with more frequent startle responses. 

Conclusion 

This study highlights that changes in gut microbiota, driven by dietary starch levels, can influence behavioural responses in horses. A high-starch, low-fibre diet may increase signs of anxiety in horses by altering the microbial balance in the hindgut. 

This reinforces the importance of feeding horses a diet that supports gut health, primarily one rich in forage and low in rapidly fermentable carbohydrates. 

Practical Takeaway 

 For horse owners, trainers, and nutritionists: 

  • A high-starch diet (NSC >12%) can shift the gut microbiome and potentially increase stress or anxiety in horses.
  • Maintaining a high-fibre diet is not only beneficial for digestive health but may also help regulate behaviour in stressful situations.
  • Feed fat plus firbre plus balanced minerals and Vitamins

Stance Supplements


Scientific Articles hindgut stress microbiota horse gut health gut brain axis in horses high starch horse diet horse anxiety equine microbiota horse behaviour and diet horse stress response hindgut health high fibre diet for horses