How much starch does a race horse need?

Traditionally, racehorse diets have comprised of large quantities of cereal grains (oats, corn and barley). However, as we learn more about the equine digestive system, we understand that starch is not the ideal feed source for a horse.

Why is starch bad for the horse?

Starch in the stomach

The horse's stomach actually contains a microbial population. This is not as substantial as what exists in the hindgut and does not have the same function, but it does exist. When a horse consumes starch, a portion of this is fermented in the horse’s stomach. This has been linked with an increased risk of Equine Gastric Ulcer Syndrome (EGUS) - which is highly prevalent in racing horses.

(Images above: Squamous ulceration (left) and glandular ulceration (right) in a horse’s stomach provided by the University of Adelaide)

Starch in the hindgut

Starch (polysaccharide) is comprised of long, branched chains of sugar. The chains are broken down into their individual sugar units (monosaccharide) by enzymes – think biological scissors – in the small intestine. However, the horse has a finite number of enzymes which can break down starch. If a horse is provided with a high starch diet the enzyme capacity in the small intestine is overwhelmed = undigested starch leaks into the hindgut.

(Image above: Representation of different types of sugar including starch (polysaccharide) and glucose (monosaccharide).

When starch enters the hindgut, it is rapidly fermented which creates gas, lactic acid and heat. This disrupts the microbial ecosystem which can lead to microbial death. This may lead to:

• Reduced feed efficiency = horse not extracting as much energy from the feed as it could
• Increased risk of pathogens inhabiting the hindgut such as salmonella
• Increased inflammatory markers
• Diarrhoea
• Gas colic
• Laminitis – if a large microbial death event occurs

All of which impact overall health and performance.

Why do we add starch to the horse’s diet?

Starch breaks down into units of sugar. This can be rapidly transformed into energy for the horse. This fast release energy can be beneficial for racing horses but also helps with maintaining the horse's condition.

How much starch is too much?

There are various suggested ‘safety’ levels of starch depending on the risk you are trying to mitigate. When considering the horses hindgut, research suggested providing less than 2g/kg bwt/meal to avoid starch leaking into the hindgut. 

This quantity puts the horse’s digestive system at risk. This could be reduced by splitting the meal into three rather than two feeds or by selecting an option which is lower in starch.

If the digestive system is protected by controlling starch intake, is the horse provided with enough energy to race?

Yes! More does not always equal better and this is true for the case of starch. Fast release energy (sugar) is stored in the muscles as glycogen. The muscle has a finite storage capacity of glycogen. Once this is met, no more can be stored. Research has demonstrated that providing oral glucose or increasing levels of grain does not enhance muscle glycogen replenishment in horses (Jose-Cunilleras et al., 2006, Varasteh et al., 2024). This is likely because of the finite capacity of the small intestine to breakdown the starch mentioned earlier.

It has also been shown that horses provided diets using high fibre feeds in place of high starch diets have no difference in their performance (Martin et al., 2023, Orme et al., 1997, Lindberg et al., 2006, Gurbuz and Coskun, 2011, Jansson and Lindberg, 2012, Phillips et al., 2017). This is because horses are able to switch the metabolic (energy producing) pathway they are using.

So, not only does a reduced starch diet protect the horse’s digestive system, but it also provides them with enough energy to fuel their performance.  

(Image above: Thoroughbred horses racing)

The perfect balance of energy for the racing horse

Hygain®’s latest innovation is a cumulation of top racing trainer feedback and equine nutrition research. Hygain Edge® provide the ideal combination of controlled starch and high fat to provide racing horses with the perfect balance of energy. This helps to protect the digestive tract whilst providing enough fast release energy to fuel performance.

Want to learn more about the research behind Hygain Edge®? Download the whitepaper here.

References

GURBUZ, E. & COSKUN, B. 2011. Effect of Dried Sugar Beet Pulp on Some Blood Parameters and Heart Rate in Exercised Horses. Kafkas Universitesi Veteriner Fakultesi Dergisi, 17, 191-195.

JANSSON, A. & LINDBERG, J. E. 2012. A forage-only diet alters the metabolic response of horses in training. Animal, 6, 1939-1946.

JOSE-CUNILLERAS, E., HINCHCLIFF, K. W., LACOMBE, V. A., SAMS, R. A., KOHN, C. W., TAYLOR, L. E. & DEVOR, S. T. 2006. Ingestion of starch-rich meals after exercise increases glucose kinetics but fails to enhance muscle glycogen replenishment in horses. The veterinary journal (1997), 171, 468-477.

LINDBERG, J. E., ESSEN-GUSTAVSSON, B., DAHLBORN, K., GOTTLIEB-VEDI, M. & JANSSON, A. 2006. Exercise response, metabolism at rest and digestibility in athletic horses fed high-fat oats. Equine veterinary journal. Supplement, 626-30.

MARTIN, A., LEPERS, R., VASSEUR, M. & JULLIAND, S. 2023. Effect of high-starch or high-fibre diets on the energy metabolism and physical performance of horses during an 8-week training period. Frontiers in Physiology, 14.

ORME, C. E., HARRIS, R. C., MARLIN, D. J. & HURLEY, J. 1997. Metabolic adaptation to a fat-supplemented diet by the thoroughbred horse. British journal of nutrition, 78, 443-458.

PHILLIPS, C. A., CAVINDER, C. A., SIGLER, D. H. & FLUCKEY, J. D. 2017. Effect of various levels of dietary starch on glycogen replenishment in the light working horse. Professional Animal Scientist, 33, 729-738.

VARASTEH, F., EBRAHIMI, S. H., NASERIAN, A. A., ZEREHDARAN, S. & HEIDARIAN MIRI, V. 2024. Effect of micronization and meal size of corn grain on glycemic response and in vitro hindgut acidosis potential in horses. Journal of equine veterinary science, 132, 104982-104982.