By: Dr Rosie Alcorn BVSc PG Cert VPS Cert AVP MRCVS
Feeding the modern racehorse requires balancing energy to support elite athletic performance while protecting the digestive system. The challenge lies in the association between high-starch diets, often used to provide rapid-release energy, and the significant detrimental effects that starch overload can have on the hindgut.
Starch, primarily derived from concentrates, has long been a cornerstone of racehorse nutrition because it provides rapid, readily available energy. This article explores how starch works in the equine body, where the dangers lie, and what evidence supports the use of alternative energy sources. With this understanding, trainers and nutritionists can fuel horses safely and effectively.
While fibre is the most natural and beneficial energy source for horses, its breakdown is slow. Horses in intense training or competition may therefore require an additional, quicker source of energy to refuel between sessions. In such cases, higher-starch diets can play a valuable role.
Consider a racehorse in hard training. Even with ad-lib haylage, much of its day is occupied with exercise, the walker, veterinary care, physiotherapy, farriery, swimming and grooming. If the horse also tends to eat less when people are around, it may struggle to meet its energy demands. A higher-starch ration, fed in multiple small meals, can help replenish its energy stores efficiently.
Despite its benefits, starch can pose risks under certain conditions. As a quick-release energy source, it can cause undesirable fluctuations in blood glucose and insulin levels. Starch is designed to be digested in the small intestine; however, if consumption exceeds the horse’s digestive capacity, undigested starch can pass into the hindgut. This can lead to hindgut acidosis and significant disruption of the microbiome.
Horses prone to tying-up often have glycogen-storage irregularities. For these horses, maintaining stable glucose and insulin levels is especially important, which is why low-starch diets are typically recommended. Glucose is also able to cross the blood–brain barrier; therefore, high-starch diets may exacerbate excitability in horses that are already prone to becoming over-keen or difficult to settle in training or racing.
Energy Without the Risk
Modern feeding programmes aim to provide ample energy while reducing the starch load. Key strategies include:
Forage should provide at least 1.5–2% of bodyweight per day. Its benefits include:
A stable hindgut environment
A continuous energy supply via fibre fermentation
Reduced risk of gastric ulcers
Fats are calorie-dense and slow-burning, providing stamina without spiking glucose levels. Omega-3 fatty acids also offer benefits for joint and respiratory health. Recent studies show that high-fat diets can perform as well as high-starch diets, with no apparent disadvantages. However, as with any dietary change in horses, a gradual transition is essential.
Fat adaptation can improve endurance and reduce reliance on glycogen during training.
Rather than removing starch entirely, the goal is strategic moderation:
Keep total dietary starch below 1 g/kg bodyweight per meal where possible
Use grains processed for improved small-intestinal digestion (steam-flaked, micronised, extruded)
Split rations into multiple small meals throughout the day
Meeting energy needs while keeping starch intake moderate also requires support for:
Muscle recovery (lysine, threonine)
Hydration and nerve function (electrolytes)
Red blood cell production (B-vitamins, copper, iron, cobalt)
These nutrients help maintain fitness and health without excessive caloric intake.
A high-performance, lower-starch feeding plan might include:
Free-choice hay or generous amounts of high-quality forage
1–2 kg/day of a high-fat, high-fibre performance feed
200–500 mL/day of added oil (depending on bodyweight)
Pink mash as fibre support
Targeted supplements for ulcers, electrolytes or muscle support
Each horse responds differently, so diets should be tailored and monitored regularly.
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Conclusion
Starch remains a valuable energy source for racehorses, but the era of grain-heavy diets is fading. By prioritising forage, making greater use of fat and fibre, and feeding starch in controlled, digestible forms, trainers can fuel horses both safely and sustainably. This balanced approach supports peak performance on the track and promotes long-term digestive health, temperament and recovery, vital ingredients for a successful racing career.
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