What Causes Fizzy Behavior?

Hyperactive, hot, fizzy.

There are numerous ways to describe a horse that has too much energy and is being difficult to manage. Worse yet, this behavior generally occurs at the most inopportune times, such as at an event or outing, when you want the horse to behave the most. What causes this and how can horsemen effectively manage the horse and its diet to avoid it? To answer this question, a closer look at the different energy sources available to the horse and the energy response each causes is necessary.

Horses derive energy from three primary sources: carbohydrates, fats, and to a lesser degree, protein. Carbohydrates are the predominant energy source and consist of two groups, structural and nonstructural. Structural carbohydrates should be the largest part of the diet. These include forage sources such as pasture, hay, and chaff, as well as super fibers like beet pulp and soy hulls. Not only do horses derive most of their energy from structural carbohydrates, but they are crucial to digestive health. Structural carbohydrates are digested through fermentation in the hindgut by the billions of bacteria that reside there, which in turn creates energy. Inadequate amounts of fiber can lead to digestive problems such as gastric ulcers and hindgut acidosis, both of which contribute to a multitude of symptoms, including behavioral problems.

While structural carbohydrates produce cool energy, are digested in the hindgut, and are vital to digestive health, nonstructural carbohydrates are quite different. This group of carbohydrates includes starch and sugars, which are found in feedstuffs such as grains and rich pasture. Nonstructural carbohydrates are digested in the small intestine and stomach, and are released rapidly into the bloodstream as glucose. Any blood glucose that is not used immediately for muscle activity is stored as glycogen for later use. Because starch and sugars are digested rapidly, they can contribute to hyperactive or hot behavior through peaks in blood glucose, similar to giving a child a bag of candy! Large amounts of grain, particularly when fed in one meal, can also contribute to digestive upset.

Fat as an energy source is utilized during periods of long, slow work and is released slowly over time. There are numerous benefits to including fat in the diets of performance horses, especially ones that are prone to being reactive. The slow-release energy that fat produces can improve undesirable behavior in many horses. Fat has an additional benefit: if fed over a long period of time, horses can switch to utilizing it as their predominant energy source and adopt glycogen-sparing properties, which means horses will use glycogen stores last and have a larger energy reservoir. For horses working over long periods of time, such as endurance or eventers, this is an invaluable tool. To fully utilize this mechanism, 8-10% of the diets of performance horses should consist of a fat source such as oil or stabilized rice bran.

Despite being a relatively inefficient energy source, protein does contribute to energy supply in most horses. It has a more important role in muscle repair and integrity and can work to increase the temperature of the horse when converted to energy, which is not desirable, especially in warmer climates. Protein is commonly blamed for causing hyperactive behavior in horses; however, its inefficiency as an energy source makes this improbable, and nonstructural carbohydrates are far more likely to be the cause.

Don’t jump to the wrong conclusion, however. Nonstructural carbohydrates are not all bad, and they certainly belong in the diets of certain horses. Hard-working performance horses cannot meet their energy requirements through forage alone, and therefore grains are often needed to fill this energy deficit and provide much-needed energy for competing and weight management. However, certain horses prone to becoming hyperactive are often classified as being sensitive, or intolerant, to grain. In these instances, it is necessary to reduce their reliance on non-structural carbohydrates as an energy source and replace these calories with fiber sources such as beet pulp and soy hulls, and fat sources such as vegetable oil or stabilized rice bran.

Despite dietary adjustments to reduce the starch and sugar in equine diets, the numerous factors that contribute to behavior mean that this is often only one aspect of calming fizzy behavior. Environment contributes significantly to how a horse is feeling and how it reacts, which is why behavioral problems often occur when environment changes, such as during outings or events. Low-starch diets should be adopted along with experience and training, which also play an important role in improving hyperactive or nervous behavior.