Racehorses are often fed high-grain, high-starch diets to fuel speed and power. That approach has been standard for decades. But research now shows there is another way to support performance, one that works with the horse’s digestive system, not against it.
High-fibre diets can deliver the same usable energy as grain-heavy diets, while reducing the risk of gut issues and helping muscles cope better during intense work.
The Problem With High-Starch Feeding
Horses are hindgut fermenters. Their digestive system is built to process fibre first, not large amounts of starch and sugar.
When a diet relies too heavily on grain:
- Excess starch can spill into the hindgut
- Gut pH drops
- Microbial balance is disrupted
Research links high-starch diets to:
- Gastric ulcers
- Hindgut irritation and poor fibre digestion
- Muscle disorders
- Increased anxiety and reactive behaviour
In short, starch may deliver fast energy, but it also creates metabolic and digestive stress that can limit performance over time.
Fibre Can Provide The Same Energy
A common myth is that fibre equals “slow energy.” That’s outdated thinking.
Well-formulated high-fibre diets can match the digestible energy of high-starch diets. More importantly, they change how the horse produces energy during work.
Instead of relying heavily on glucose, fibre-fed horses produce more acetate, a volatile fatty acid made when fibre is fermented in the hindgut. Acetate is a powerful and efficient fuel for muscle contraction.
What The Research Found
TIn a French study, 10 race-fit trotters were followed over an eight-week training period.
- All horses received the same amount of hay
- One group was fed a traditional oat-based diet
- The other group had 75% of the oats replaced with dehydrated alfalfa
Both diets supplied nearly the same amount of digestible energy.
Performance Results
After eight weeks:
- Both groups improved fitness
- Peak speed and acceleration were the same
- Training response was equal
So fibre did not reduce performance.
But there was one key difference.
A Big Shift In Muscle Metabolism
Horses on the higher-fibre diet produced less carbon dioxide during exercise. That matters because carbon dioxide output is linked to how energy is being generated in the muscle.
Lower CO₂ suggests the horses were using a more efficient energy pathway.
Here’s why that’s important.
Fibre, Acetate, and Lactic Acid
During hard exercise, muscles burn either:
- Glucose (from starch and sugar), or
- Acetate (from fibre fermentation)
Muscles will always use the fuel that is most available.
High-fibre diets increase acetate availability. When acetate is used:
- Muscles rely less on glucose
- Glucose is spared
- Lactic acid builds up more slowly
Lactic acid accumulation is one of the main reasons horses fatigue, tie-up, or lose power late in a race.
By delaying lactic acid buildup, fibre-fed horses may maintain strength and efficiency for longer.
Why This Matters For Racing?
This research shows that performance nutrition isn’t just about calories. It’s about fuel selection.
Feeding fibre:
- Supports gut health and microbial diversity
- Produces stable, usable energy
- Reduces metabolic stress
- Helps muscles cope better under pressure
The takeaway is clear:
Covering energy needs is essential, but how that energy is supplied matters just as much.
Our feed delivers high fibre, high-quality protein, low sugar and starch with zero rancid oils, fillers, or contamination, just pure fresh ingredients for your horse’s gut health. For a Free Diet Analysis please book at the CEN Nutrition website – https://cennutrition.com.au/horses/free-diet-analysis/
Written By Bryan Meggitt (BMedSc. PGCrtMedSc.)
Blood Scientist and Co-founder of CEN Horse Nutrition
References:
- Martin A, Lepers R, Vasseur M, Julliand S. Effect of high-starch or high-fibre diets on the energy metabolism and physical performance of horses during an 8-week training period. Front Physiol. 2023 Sep 8;14:1213032. doi: 10.3389/fphys.2023.1213032. PMID: 37745248; PMCID: PMC10514361.
- Bulmer L., McBride S., Williams K., Murray J.-A. (2015). The effects of a high-starch or high-fibre diet on equine reactivity and handling behaviour. Appl. Animal Behav. Sci. 165, 95–102. doi:10.1016/j.applanim.2015.01.008