High-starch diets are common in modern horse management, particularly for performance horses, but they may come with hidden risks. While horses are designed to digest fibre almost continuously, excess starch can reach the hindgut and disrupt the delicate microbial balance.
A recent scientific study investigated exactly this, examining how sudden starch overload affects the equine hindgut microbiota and whether buffering could reduce the damage. Understanding these effects is important because disruptions to the gut microbiome have been linked to several health conditions.
Aim of the Study
This study aimed to investigate the effects of starch overload on the equine gut microbiota, and to determine whether alkalinising (buffering) the cecum could reduce any resulting damage.
Why Does This Matter?
Horses are naturally adapted to consume fibre-rich diets, grazing for long periods throughout the day. However, modern feeding practices often include high levels of starch, particularly in concentrate feeds.
When excess starch reaches the hindgut, it can disrupt the microbial balance (known as dysbiosis), which has been associated with serious health issues such as colic and laminitis. This imbalance means that the bacteria responsible for fibre digestion are reduced, while less desirable bacteria increase which can further alter gut function.
This is a particularly important study for horse owners due to many feeding practices unintentionally increasing starch intake, while potentially putting horses at risk of digestive disturbances.
The Study Design
Horses were divided into three groups:
- A starch overload group
- A starch + alkaline buffer (cecal infusion) group
- A control group
What Was Measured?
Researchers assessed:
- The gut microbiota (bacteria present in the cecum)
- Clinical signs, including lameness and discomfort
These measurements were taken over a period of up to 72 hours.
Key Findings
1. Starch Overload Disrupted the Microbiota
Starch overload led to a clear disruption of the hindgut microbiota. This was characterised by:
- Reduced bacterial diversity
- A significant imbalance in microbial populations
Diverse microbiota is essential for gut health, this indicates a negative impact on the horse’s digestive system.
2. Shift in Bacterial Populations
Horses experiencing starch overload showed:
- An increase in starch-digesting bacteria
- A decrease in fibre-digesting bacteria
This shift is particularly concerning, as horses rely heavily on fibre fermentation. A reduction in fibre-digesting bacteria may impair gut function and overall digestive health.
3. Cecal Alkalinisation Did Not Prevent Damage
Buffering the cecum did not prevent microbiota disruption. In some cases, it appeared to worsen dysbiosis and increase clinical signs.
This suggests that simply altering pH is not sufficient to restore microbial balance once disruption has occurred.
Clinical Signs Observed
Horses showed:
- Increased heart rate (from 8 hours post-starch overload)
- Fever in some horses
- Soft/pasty faeces (all horses)
- Dehydration and reduced appetite (starch-only group)
- Signs of abdominal discomfort
- Increased movement/stepping (indicative of discomfort)
- Lameness (Obel grades 2–4), consistent with laminitis risk
What Does Microbiota Imbalance Lead To?
Disruption of the gut microbiota can result in:
- Toxin production
- Inflammation
- Wider systemic effects throughout the body
Overall, this study reinforces the importance of appropriate dietary management in horses. Excessive starch intake can significantly disrupt gut health, and interventions such as buffering appear insufficient to prevent these effects.
The key takeaway: preventing starch overload through careful feeding practices remains the most effective way to support equine gut health.
