Starch is a non-structural (or soluble) carbohydrate made up of chains of glucose molecules. Plants store starch as an energy source. Although grains contain a lot of starch, almost everything a horse eats—including forage, i.e., hay—adds to the total daily intake of starch. In the horse’s small intestine, starch is broken down mainly by the enzyme amylase, and the body absorbs glucose into the bloodstream. In healthy horses, the rise in blood sugar triggers the pancreas to release insulin, which allows glucose to move into insulin-sensitive cells such as muscle. All horses need some starch to support basic bodily functions and exercise.
The role of carbohydrates in feeding has been one of the key nutrition topics in recent years. The topic has also been studied extensively.
Starch and the horse’s gut health
Excessive starch intake can exceed the small intestine’s ability to digest it, meaning some starch passes into the large intestine. There, microbes begin to ferment it rapidly, producing lactic acid among other compounds. This can lead to a situation where the gut’s bacterial balance is disrupted—some bacteria multiply uncontrollably, and fiber-digesting bacteria may die off. The outcome may be digestive upset, colic, and in severe cases even the triggering of laminitis.
So how much starch is too much? Researchers agree that the amount of starch per meal should be kept below 2 g per kilogram of body weight (for example, a 500 kg horse should eat no more than about 2.2 kg of oats per meal). A more cautious approach is to halve that limit: under 1 g/kg/meal may also reduce the risk of gastric ulcers. For very sensitive horses and those at metabolic risk, the recommendation is under 0.3 g/kg/meal—this still allows, for example, 2.5 kg portions of low-starch concentrates.
Many starch amounts that leisure-horse owners perceive as “high” are, from a professional perspective, moderate. In healthy performance horses they can be beneficial when the goal is to support stamina at work and replenish muscle glycogen stores after heavy exercise to aid recovery.
Starch and the horse’s behaviour
There is less research evidence related to behaviour, and starch-related effects vary between individual horses. There is a physiological basis for the idea that soluble carbohydrates provide “faster” energy, while fat and fiber are “slower fuels.” However, this does not mean that sweet, sugary, or starch-containing feeds automatically “heat up” a horse, or that a high-fat feed will automatically make a horse calm.
The most significant factor in a horse’s “energy level” is total calorie intake. The more calories a horse receives beyond its actual needs, the more energy remains available for movement or weight gain—regardless of whether those calories come from carbohydrate or fat.
As a general guideline, if the goal is to increase alertness and sharpness, increasing carbohydrate intake may be helpful. If the aim is a calmer overall demeanour and behaviour, increasing fat can be a good option for meeting total energy needs.
Summary
Some horses with specific health issues benefit from a low- or very low-starch diet. Healthy performance horses, however, tolerate—and can benefit from—a moderate amount of starch in the diet. Today, thinking is moving away from extremes and increasingly toward a “golden middle path”: a moderate amount of soluble carbohydrate in the diet can be useful, and it is not automatically something that must be avoided.
Source: The Horse Magazine
