Q: What role do carbohydrates play in horse feed? I often hear about carbohydrates in a negative context because they can be harmful to horses with metabolic problems, but what groups of horses might need more carbohydrates and what sources should they be getting them from?

A: Thank you for asking this question because this is an important but often misunderstood concept in equine nutrition. With the increased awareness of and ability to diagnose horses with carbohydrate sensitivities (i.e., insulin dysregulation, equine metabolic syndrome) and the rise in popularity of low-carb rations for horses, it’s understandable how some horse owners might be unaware there are many benefits of feeding nonstructural carbohydrates (NSCs) to horses.

Nonstructural carbohydrates are the simple sugars (i.e., glucose and fructose) and starches in feeds readily digested and absorbed in the horse’s small intestine. This results in a rise in blood glucose and, subsequently, blood insulin levels following a meal. If horses have been diagnosed with a carbohydrate sensitivity by a veterinarian, then this discussion does not apply to them since minimizing the rise in glucose and insulin following a meal is an important nutritional strategy for managing those horses. However, horses with normal glucose and insulin metabolism can safely and effectively digest and utilize dietary NSCs, and they serve as an important source of fuel for exercise. Grain ingredients such as oats, barley, and corn have the highest NSC content by weight and typically contribute the biggest NSC proportion in feeds, but even lower-NSC ingredients such as grass hay and beet pulp still contribute some NSCs to the overall ration. In general, the most efficient way to increase NSC content of the ration is including grain-based ingredients in the diet.

Glucose and muscle glycogen (the storage form of dietary carbohydrates) derived from NSC digestion both serve as important fuel sources for exercise, especially for performance horses. In fact, glycogen is the primary fuel source horses need for anaerobic metabolism, which occurs during shorter bursts of intense work such as sprinting and jumping. Once that glycogen depletes during an exercise bout, fatigue occurs. The only way to efficiently build and replenish glycogen stores in the muscle is through dietary NSCs. Dietary fat and structural carbohydrates (fiber) cannot replenish glycogen. In other words, the lower the NSC content of the ration, the longer it takes to replenish muscle glycogen.

Horses training and competing in disciplines involving speed and/or intensity, such as racehorses, jumpers, eventers, cutters, barrel racers, and even dressage horses, can utilize and benefit from some NSCs in the diet. If concentrate meals are kept at an appropriate size, horses digest and utilize NSCs quite efficiently. A good general rule of thumb is to keep concentrate meals to 0.5% of the horse’s body weight or less to ensure he can completely digest NSCs in the small intestine (this applies to feeding straight grains, too). If a horse consumes an excessive amount of NSCs in a meal (such as when a horse gets into the feed room and gorges himself), the small intestine can become overwhelmed, and his body will transfer NSCs to the hindgut. Horse owners should avoid this situation at all costs because excessive NSCs in the hindgut can lead to major problems such as hindgut acidosis, colic, and laminitis.

Modern performance horse feeds come in many formulations, and most contain a blend of fuel sources that include a certain percentage of NSCs, fat, and fiber. The concentration of these three fuel sources varies widely between products, allowing horse owners to try different formulations to see how their horses perform with different NSC concentrations. If horses struggle with lower energy levels and fatigue during and after exercise, higher NSC levels in their diets might be just the thing they need to help put more fuel in the tank. Horse owners should not shy away from feeding the right fuels to help their horses feel and perform their best when doing the jobs we ask of them.

Do you have an equine nutrition question?