If there is one part of the horse’s body that quietly determines everything – from behaviour to weight to overall health – it is the hindgut.
We talk a lot about feed, supplements, and calories, but at the end of the day, a horse is a hindgut fermenter. Their entire digestive system, behaviour, and even their mental wellbeing depend on one thing: a steady supply of fibre that ferments slowly and safely.
When horses don’t get enough fibre, or when the hindgut is overwhelmed by starch and sugar, the consequences ripple through the entire body. Colic, ulcers, weight issues, behavioural changes, and laminitis all have roots in how well the hindgut is functioning.
This article explains what really happens inside the hindgut, how fermentation works, why fibre is essential, and the practical steps you can take to support your horse’s digestive health every day.
Why the Hindgut Matters So Much
Unlike humans, horses are designed to extract most of their energy from fermenting fibre, not digesting grain. The hindgut – made up of the cecum, large colon, small colon, and rectum — is essentially a giant fermentation chamber housing billions of microbes.
These microbes break down fibre and produce:
- Volatile fatty acids (VFAs), the horse’s main energy source
- Heat, helping regulate body temperature
- B vitamins, aiding metabolism
- A healthy gut environment, preventing disease
When the hindgut is functioning well, horses are:
- Calm
- Comfortable
- Able to maintain weight
- Less prone to colic
- More resistant to stress
- More efficient at converting feed into usable energy
When it isn’t, everything becomes harder.
Case example:
A local veterinarian once worked with a mare who was bright, shiny, and energetic in spring but became anxious and girthy in autumn every year. The underlying issue wasn’t behavioural. When we adjusted her diet to increase fibre and reduce her starch load, her mood, manure consistency, and comfort improved dramatically.
How Fibre Fermentation Really Works
Fibre fermentation happens slowly and continuously. Horses evolved to graze up to 18 hours a day, providing a steady trickle of fibre that keeps the hindgut microbes stable.
When fibre enters the hindgut:
- Microbes attach to fibre particles
- They break the fibre down into VFAs
- VFAs are absorbed and used for energy
- Fermentation produces heat
- The gut remains full, hydrated, and active
This slow, steady process supports:
- Safe energy release
- Even blood sugar
- Calm temperament
- Improved gut motility
- A balanced microbiome
Fibre is not optional. It is the foundation of the entire digestive system.
What Happens When Fibre Is Lacking
Low fibre intake leads to:
- Dry, hard manure
- Increased risk of impaction colic
- Faster gut transit time
- Acid build-up in the stomach
- Disruption of the hindgut microbiome
- Reduced production of VFAs
- Increased risk of ulcers
- Behaviour changes
- Weakened immunity
Even short periods without fibre can trigger a cascade of problems. Horses should never go longer than 3 to 4 hours without forage.
Why Starch and Sugar Overload the Hindgut
The stomach and small intestine are designed to digest limited amounts of starch.
When a meal contains more starch than the small intestine can handle:
- Undigested starch spills into the hindgut
- The wrong microbes begin to ferment it
- Lactic acid is produced
- The gut pH drops
- Good microbes die
- Toxins may be released
- The gut lining becomes irritated
This process is called hindgut acidosis, and it can lead to:
- Colic
- Diarrhoea
- Laminitis
- Behavioural changes
- Poor coat quality
- Muscle soreness
- Reduced performance
Fibre protects the hindgut. Excess starch and sugar destabilise it.
The Role of Saliva in Supporting Fermentation
Chewing fibre produces large amounts of saliva. Saliva is the horse’s natural buffer.
It:
- Neutralises stomach acid
- Protects against ulcers
- Helps food slide through the gut
- Supports microbial health
Pellets, cubes, and grain require far less chewing, so they produce far less saliva. This is another reason fibre-based diets are gentler and safer.
Forage: The Non-Negotiable Foundation
Forage should make up at least 70 percent of a horse’s diet. Many thrive on even higher levels.
Good forage options include:
- Pasture
- Meadow hay
- Timothy or oaten hay
- Lucerne (alfalfa) in appropriate amounts
- Haylage (if suitable for the horse’s health needs)
- Soaked hay pellets
- Beet pulp
The best forage:
- Smells fresh
- Is free of dust and mould
- Has a soft, leafy feel
- Is appropriate for the horse’s metabolic needs
Some horses require low-sugar hay. Others benefit from lucerne as a buffer.
How to Feed for Healthy Fermentation
1. Provide Forage Continuously
Avoid long fasting periods. Use hay nets, slow feeders, or multiple small piles.
2. Choose Low-Starch Feeds
Look for feeds labelled “low starch” or “low NSC.”
3. Feed Small Meals, Often
Large grain meals overwhelm the small intestine.
4. Introduce New Feeds Slowly
Sudden changes disrupt the microbiome.
5. Keep Water Warm and Accessible
Hydration supports fermentation and gut motility.
6. Maintain Routine and Reduce Stress
Stress alters hormones and gut motility, affecting fermentation.
7. Support Chewing
Healthy teeth make fibre digestion possible. Routine dental care is essential.
Understanding Manure: Your Daily Diagnostic Tool
Manure tells a story. Healthy manure should be:
- Firm
- Moist
- Formed into balls
- Easy to break apart
- Consistent in colour
Warning signs of poor fermentation include:
- Very loose manure
- Very dry manure
- Undigested hay
- Grain in the droppings
- Strong or sour odour
- Sudden changes in consistency
Your horse’s manure provides extremely valuable daily insight into their digestive health.
Horses Who Need Extra Support
Some horses require more careful management:
- Seniors
- Horses with metabolic issues
- Horses on box rest
- High-performance athletes
- Horses recovering from colic
- Horses with ulcer history
- Miniature horses and ponies
These horses often benefit from:
- Soaked beet pulp
- Senior fibre blends
- Higher-quality hay
- Buffet-style forage feeding
- Strictly limited starch and sugar
When to Call Your Veterinarian
Contact your vet if your horse shows:
- Any signs of colic, even mild or early signs
- Sudden behaviour changes
- Diarrhoea or chronic loose manure
- Extreme gas build-up
- Lack of appetite
- Sudden weight loss
- Pain after eating
These signs may indicate underlying hindgut dysfunction.
The Takeaway
Your horse’s hindgut is a living, breathing ecosystem. When it is fed well, the entire horse thrives – physically, mentally, and behaviourally. When it isn’t, even small mistakes can create ripple effects that affect health and welfare.
Fibre is the foundation of every feeding decision. It fuels fermentation, supports mental calmness, protects the gut, and maintains long-term health.
Feeding for fermentation isn’t a trend. It is the way the horse’s body was designed to live.
Disclaimer
This article provides general information only and does not replace veterinary advice for your individual horse. If you’re concerned, contact your veterinarian promptly.