Low-NSC Diets: Not for Every Horse

From Kentucky Equine Research:

When it comes to feeding horses, carbohydrates get a lot of attention. After all, they are the main energy source used by horses to fuel countless body processes.

A “carbohydrate” is a general term that includes simple sugars (one or two molecule sugars such as glucose and sucrose) and polysaccharides (long chains of sugar molecules such as starches, fructans, and fibers). Sugars, starches, and fructans are also referred to as nonstructural carbohydrates, commonly abbreviated NSC.

One NSC, glucose, is stored in the liver and muscle in the form of glycogen. Glycogen can be recruited quickly when energy is needed without waiting for oxygen, so the energy boost is fast but short-lived. Once the stored glycogen is diminished after vigorous exercise, NSC must be fed for “refueling” muscles so they are ready for the next bout of work. Research has suggested that diets low in NSC may inhibit or slow recovery from strenuous exercise.^*

Glycogen replenishment in horses can take 72 hours or more, depending on the diet. Researchers fed Standardbred horses a high-, medium- (control), or low-glycemic diet found that horses on higher glycemic diets had more muscle glycogen restored compared to horses on a moderate- or low-glycemic diet after three days.^** High-glycemic diets contain more NSC compared to low- or medium-glycemic diets and will subsequently result in a greater spike in blood sugar. In other words, there is glucose available to be converted to glycogen and stored in the muscles and liver. Consequently, after a race, competition, or other strenuous activity, the horse on a low-glycemic diet may need more time to replenish the energy stores in the muscle.

This does not mean that horses should be “carb loaded,” suddenly offered a large amount of NSC just prior to or just after exercise. Carb loading is something human athletes do by consuming a diet high in carbohydrates, such as a pasta meal, the day before strenuous athletic effort. Suddenly adding a bolus of NSC to a horse’s diet without acclimation can cause digestive upset, so this must be done slowly and according to the individual horse’s needs. Humans can store glycogen quickly, often within 24 hours, but the process in horses is slower and may take three days or more.^** Consequently, a horse competing in multiday competitions may not be working on a full tank of fuel by the second or third day. A horse on a low-NSC diet may take even longer to fully replenish energy stores after strenuous exercise.

“As a guide, a horse should consume no more than 0.5% of its body weight in grain or concentrate in any single meal. So, for an 1,100-lb (500-kg) horse, this is a maximum of 5.5 lb or 2.5 kg,” according to Catherine Whitehouse, M.S., a nutritionist at Kentucky Equine Research.

Some performance horses require more concentrate (and therefore calories) than others to maintain their weight and energy for work. For others, though, feeding large concentrate meals is not appropriate. The type of feed being fed should be selected based on the horse’s individual needs, body condition, and health status.

There are unquestionably situations in which NSC should be limited in a horse’s diet, particularly when endocrine disorders such as insulin dysregulation (ID) or equine metabolic syndrome (EMS) are present. These disorders do not discriminate based on breed, age, or even body condition. Simply put, horses with ID/EMS have an abnormally high insulin response when nonstructural carbohydrates are ingested, which puts them at risk for health concerns such as laminitis. Most horses, however, do not have ID or EMS. Horses without endocrine disorders that are also in moderate to heavy training may have slower recovery if they consume a diet very low in NSC.

There are many factors to consider when designing a diet for an individual horse. Breed, health status, current body condition, and activity level are usually the starting points for evaluating a proper diet. A Kentucky Equine Research nutritionist can help you navigate the complexities of creating a diet with sufficient sources of energy and nutrients to support your horse’s optimal performance.

^*Mesquita, V.S., J.D. Pagan, S.J. Valberg, B.M. Waldridge, and C. Whitehouse. 2014. Effect of nonstructural carbohydrate, fat and fiber intake on glycogen repletion following intense exercise. Equine Veterinary Journal 64(S46):33.

 ^**Lacombe, V., K.W. Hinchcliff, C.W. Kohn, S.T. Devor, and L.E. Taylor. 2003. Effects of feeding meals with various soluble-carbohydrate content on muscle glycogen synthesis after exercise in horses. American Journal of Veterinary Research 65(7).