Q: How does the starch content in commercial concentrates affect gut health and behavior in performance horses?

A: Starch is a nonstructural (or soluble) carbohydrate composed of chains of glucose molecules. Plants store starch to use as an energy source. While grains contain higher levels of starch, almost everything your horse eats, including forage, contributes to the total amount of starch consumed per day. The horse’s small intestine primarily breaks down starch using the enzyme amylase, and his body absorbs glucose into the bloodstream. In healthy horses this rise in blood glucose triggers the pancreas to release insulin, which enables glucose to enter insulin-sensitive cells, such as muscle. All horses need some starch to fuel essential body functions and exercise.

It seems the “carb issue” has become the defining nutritional debate of the past 20 years or so. Let’s review what the science tells us about the effects of starch on horse gut health and behavior.

Starch and Horse Gut Health

Too much dietary starch can overwhelm the small intestine’s digestive capacity, causing it to spill into the hindgut, where microbes rapidly ferment it, producing, among others, lactic acid. This can in turn create dysbiosis, where existing bacteria in the gut experience unexpected growth and fiber-digesters might die off. This can cause digestive upset, colic, and in severe cases, kick off the cascade of laminitis.

How much starch is too much? Researchers agree the amount of starch per meal should be limited to less than 2 grams/kilogram of body weight (BW) to avoid starch overload (for context, that would be equivalent to a 500-kg horse eating a 2.2-kg meal of oats). To take a more conservative approach and potentially reduce the risk for gastric ulceration, cut that recommendation in half to less than 1 g/kg BW/meal. For the most sensitive metabolic horses, reduce starch to less than 0.3 g/kg BW/meal (which still allows for 2.5-kg meals of low-starch concentrates). Levels horse owners might interpret as high starch would be considered by most equine nutritionists as moderate starch and could be beneficial for healthy performance horses when it comes to maintaining energy levels for work and for efficiently replenishing muscle glycogen after more intense exercise.

Starch and Horse Behavior

Turning our attention to the behavior part of the equation, less solid data exists, and the effects of starch on a horse’s behavior often differ between individual horses. There is a physiological basis to the generalization that soluble carbohydrates provide more readily available energy, and fats and fibers are cooler burning. However, that does not necessarily mean sweet feed will make a horse hot, and a high-fat feed will not. The main driver of how much “energy” a horse has is their total calorie intake. The more calories available beyond their needs, the more fuel for activity or weight gain, whether that comes from carbs or fat. If I am attempting to give a horse a bit more zip or inspiration, I might try shifting his fuel sources toward more carbohydrates with less reliance on fat, and vice versa if the goal is to help a horse be more relaxed.

Take-Home Message

Some horses with specific health issues, often benefit from low- or very low-starch diets. However, healthy performance horses can handle and might benefit from a moderate amount of starch in the diet. We might see a shift back toward the center, with more horse people acknowledging that a moderate amount of dietary soluble carbohydrate can be useful rather than something to be avoided at all costs.

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