Sugars and Starches in Horse Diets: They’re Not All Bad!

Although owners are frequently warned against the consequences of feeding these carbs, horses need them in their diets.

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Sugars and Starches in Horse Diets
Grass pasture contributes the greatest amount of sugar to a horse's diet. | Photo: iStock

Although we frequently warn against the consequences of feeding these carbohydrates, horses do need them in their diets.

Owners are more carb-conscious than ever—and with good reason. It’s a fact that carbohydrates, particularly sugar and starch, can exacerbate equine muscle conditions such as polysaccharide storage myopathy, which is commonly known as tying-up. And scientists have linked dietary sugar and starch with colic and the hoof disease laminitis—especially when a horse consumes large quantities in a single meal. Excess carbohydrate intake can lead to other conditions, as well, including obesity and insulin resistance, where cells become resistant to the hormone insulin and require more to signal glucose uptake from the blood after a meal. Some horses even experience a “sugar rush” post-carb consumption that can lead to undesirable behaviors.  

Like it or not, horses do need sugar and starch in their diets and cannot thrive without them. How can you make peace with these carbs and find room for them in your horse’s feed bucket? Let’s take a closer look at sugar and starch and uncover how they help keep your horse healthy.

What They Are

Carbohydrates—these sugars and starches—are the largest source of energy in a horse’s diet. They are named based on the number of sugar molecules chained together: monosaccharides, disaccharides, oligosaccharides, or polysaccharides (see Table 1). Monosaccharides, or simple sugars, are the basic carbohydrate unit on which all others are built.

Table 1

Carbohydrate Classes (chain length) Examples
Monosaccharides (1 molecule) Glucose, fructose, galactose, mannose, arabinose, xylose
Disaccharides (2 molecules) Lactose, maltose
Oligosaccharides (3-10 molecules) Raffinose, stachyose, fructooligosaccharides
Polysaccharides (>10 molecules) Starch, cellulose, hemicellulose, pectin

In the horse’s daily diet are two groups of carbohydrates: nonstructural and structural. Structural carbs are the fibrous portion of plants and include the polysaccharides cellulose and hemicellulose. Hay constitutes the greatest percentage of structural carbs in a horse’s diet, but grains with hulls, such as oats, might also contribute to the total amount. Equids are not capable of digesting structural carbohydrates without the help of billions of microorganisms that reside in the hindgut (large intestine and colon). Microbial fermentation here breaks down fiber into a usable form of energy known as volatile fatty acids.

The nonstructural carbohydrates (NSC), also known as the nonfibrous carbs, include all of the monosaccharides, disaccharides, and oligosaccharides, along with the polysaccharide starch. Grains by far contribute the most NSCs to a horse’s diet, although all plants contain some. Digestive enzymes in the foregut (small intestine) break NSCs down to their simplest form, which the intestinal wall then absorbs. The horse can use this absorbed glucose immediately for energy needs such as digestion, for fat synthesis when in excess (which can result in obesity over time), or as stored glycogen in the muscle and liver.

Why They’re Important

Horses need energy to perform two types of work: aerobic, which basically means working for long periods, such as in endurance riding, and anaerobic, which involves speed-type activities such as racing and cutting. They meet those requirements by metabolizing carbohydrates and fats, among other nutrients.  

They store most of their fat in adipose tissue and tuck a very small amount away in muscle as triglycerides. Although fat produces about twice as much energy as carbohydrates, the body cannot use it without the presence of oxygen—the aerobic work described. That leaves carbohydrates—in particular, sugar and starch stored as glycogen—as the source of immediately available energy, for anaerobic work, when the body can’t use fat.

Metabolically speaking, using glycogen is the quickest and most efficient way to fuel muscle contraction, and blood glucose is the quickest energy for all nonmuscular energy needs, such as respiration, nutrient digestion, and brain function. More importantly, the body doesn’t require oxygen to use glycogen for energy.

Performance horses can’t meet their high energy requirements with forage alone; they also need to consume some carbohydrate-containing grains. As their exercise intensity increases, so does their bodies’ need for sugar and starch.  

“Horses exercising intensely are more dependent upon having a relatively available source of carbohydrates as an energy source since, when working anaerobically, energy demands are met through the utilization of carbohydrates,” says Brian Nielsen, PhD, professor of equine exercise physiology at Michigan State University.  

Sugar and starch are just as important after exercise in replenishing muscle glycogen, especially during events that take place over consecutive days. Research results have shown that muscle glycogen repletion occurs faster when a horse consumes hay and grain versus just hay after exercise.  

Where Can They Be Found?

Central to increasing or decreasing the sugar and starch in a horse’s diet is knowing what feedstuffs supply these carbs. Cereal grains contribute the most starch to equine rations. “Corn consists of approximately 70% starch, while oats consist of approximately 44% starch on a dry matter basis,” says Bridgett McIntosh, PhD, extension equine specialist at Virginia Tech.

Forages, including cool- and warm-season grasses, as well as legumes, typically contain less than 3% starch on a dry matter basis (the nutrient breakdown of a feed with the water fraction removed). Grass pasture contributes the most sugar to equine rations.  

“The sugar content of grasses varies depending on stage of plant growth, environmental conditions, geographic region, and plant species,” says McIntosh. Most grasses’ sugar content hovers around 7% to 15% dry matter, but can become elevated to as high as 30% dry matter under favorable conditions such as cooler temperatures and moisture.  

As far as commercial grain mixes, additives such as molasses contribute very little to a ration’s overall sugar content. It is important to keep in mind that the amount of sugar and starch in a horse’s ration is relative to how much of the particular ingredient or feedstuff he’s consuming, McIntosh adds.

How do you determine the sugar and starch content of a horse’s diet? The best way is to have a commercial laboratory such as Equi-analytical Laboratories ( analyze your hay and grain. McIntosh suggests using your local Extension office as a resource to assist with forage and feed testing.  

A basic nutrient analysis typically costs around $20, while a more comprehensive test can cost up to $80, says McIntosh. Not all forage and feed tests include sugar and starch, so make sure the analytical package you select includes these nutrients.  

To increase the amount of starch in your horse’s diet, pick feeds that contain greater amounts of cereal grains based on   the ingredients listed on the feed tag or by visual inspection. Some manufacturers will include the percent of sugar and starch in the feed label’s guaranteed analysis (usually as percent NSC).  

“Be sure to select feeds that are fortified and balanced by the manufacturer, because adding cereal grains alone can cause other nutrient imbalances, such as the calcium to phosphorus ratio,” says McIntosh.  

On the other hand, to reduce the amount of starch in your horse’s ration, select low-starch feeds that utilize fat and fiber as the primary calorie source. Perform forage testing to determine the amount of sugar and starch your hay provides. Hay that is mature and cut early in the day, with a long drying period, is typically lower in sugar than immature hay cut in the afternoon that dries rapidly.  

As for what your horse eats during turnout, “Pasture forages can be analyzed for sugar and starch content, but carbohydrates vary greatly throughout the day depending on environmental conditions, so it is usually neither appropriate nor cost-effective for most horse owners,” says McIntosh.

How Much Do Horses Need?

It’s clear that horses need at least some NSCs to be able to perform normal physiological functions, and we know it would be impossible to remove all sugar and starch from a horse’s diet completely, even without feeding grain. Conversely, the digestive system’s physiology seems to put some type of limit on the amount of NSCs a horse can ingest safely. If not digested and absorbed in the small intestine, these NSCs enter the hindgut where they undergo microbial fermentation, as the structural carbohydrates in forage would. But, unlike forage fermentation, that of sugar and starch produces lactic acid and decreases the hindgut’s pH, potentially leading to digestive disturbances such as colic.  

We also know too few carbs will negatively affect exercising horses’ performance. “When adequate sugar and starch is not available, the risk is that a horse will not be able to perform maximally for an extended period as they may have lower glycogen availability,” explains Nielsen. “Glycogen is like the gas for your car: If your tank isn’t full, you won’t go as long before you begin to slow down and eventually stop.”  

Performance horses get some nonstructural carbohydrates from their hay or pasture; whether it’s enough to allow them to perform at their best depends on the type of work they are expected to do. “That is the reason many athletic horses performing intensely can benefit by having grain as part of their diet,” Nielsen says.

Unfortunately, we’ve yet to determine a minimum value for starch and sugar. “While limiting it may be advisable for the easy keeper or the horse that has obesity issues, it usually is much less of a concern for most equine athletes,” says Nielsen.

For those concerned with their horse’s NSC intake, remember that removing high sugar and starch ingredients also removes other essential nutrients. So be sure to maintain a balance of all nutrients when calculating a horse’s ration, and consider specific ingredients secondary.

How to Avoid Trouble

What can you do to reduce the chances of digestive disturbances caused by sugar and starch? Let’s take a look:

  • Never allow horses free-choice access to feeds high in nonfibrous carbohydrates;  
  • Feed by weight, not by volume;  
  • Limit grain meals to 0.5-0.6% of body weight in starch or 150-200 grams per 100 kilograms of body weight per meal. That would be close to 5 to 6 pounds of feed per meal for a typical 1,100-pound horse on a grain mix considered to be “high NSC” (>30% NSC). Note: If horses are prone to digestive upset, consider reducing meals to provide no more than 2 to 4 pounds of feed per meal.
  • Feed processed grains (cracked, pelleted, extruded, etc.) to improve starch digestibility;  
  • Feed small meals frequently; and
  • Make feed adjustments gradually in a stepwise fashion.

Take-Home Message

Sugar and starch are important energy sources in all horses’ diets, particularly performance horses. While minimizing their inclusion might be necessary for horses with certain metabolic conditions, they serve as a vital energy reserve for proper brain and muscle function for all types of horses, whether competing in the show ring or simply living on pasture.  


Written by:

Kristen M. Janicki, a lifelong horsewoman, was born and raised in the suburbs of Chicago. She received her Bachelor of Science degree in Animal Sciences from the University of Illinois at Urbana-Champaign and later attended graduate school at the University of Kentucky, studying under Dr. Laurie Lawrence in the area of Equine Nutrition. Kristen has been a performance horse nutritionist for an industry feed manufacturer for more than a decade. Her job entails evaluating and improving the performance of the sport horse through proper nutrition.

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