Carbohydrates are an important part of every horse's diet. They are found in almost all the food your horse eats, including forages, grains, and by-products of forage and grain.
Ideally your horse's diet will be composed mostly of forage, in which case fiber, or the complex carbs of cellulose, hemicellulose, and lignin, will comprise most of his carb intake. Forages also provide him with some simple carbs as well, such as starch and sugar.
The grains in his diet will provide more starch and simple sugars, which provide high amounts of energy.
Carbohydrates are often discussed by their structure:
Monosaccharides are composed of one sugar unit. Common monosaccharides include glucose, fructose, and galactose. In your horse's diet these monosaccharides are often found as part of a larger sugar molecule.
Here is what a glucose molecule looks like:
Disaccharides are two sugar units linked together. The most important ones in the horse diet are lactose (important in the diet of the nursing foal) and maltose.
Maltose is pictured below...you can see that it is more complex than glucose.
Oligosaccharides are units of 3-10 sugar units linked together. Examples of oligosaccharides that would be found in your horse's diet are raffinose and fructans (sometimes called fructoligosaccharides...but that's a mouthful!)
Polysaccharides are chains of sugar molecules that contain more than 10 sugar units. In the horse diet, the most important ones are starch and cellulose, but hemicellulose and pectin are also polysaccharides.
Below is a picture of just one small part of a starch molecule:
All these different types of carbs contain about the same amount of energy. However, when they are broken down by your horse's digestive system, they provide him with different amounts of energy for his use.
This difference in usable energy (known as net energy) results because some energy is lost or used during the process of metabolism (breaking down nutrients). Energy that is lost includes energy used to produce heat, energy that is excreted through urine and fecal matter, and energy that is used by the microbes.
The carbs that are broken down and absorbed as monosaccharides in the small intestine are going to provide the most energy. It is these carbohydrates that can cause a horse to become "hot" on certain feeds.
For the oligosaccharides and polysaccharides, where they are digested depends on how the molecules are linked together.
If the molecules are linked by what is referred to as an alpha-1,6 bond or an alpha-1,4 bond, they can be broken down and absorbed in the small intestine, yielding a fair amount of energy.
However, if they are linked by a beta-1,4 linkage, they cannot be broken down by enzymes in the stomach, so they must be digested by the microbes in the large intestine. The carbs that have beta-1,4 linkages are cellulose and hemicellulose.
This has been a broad overview of carbs. To learn more about carbs in your horse's diet, please check out the following pages:
Carbohydrate Digestion and VFA's
Now that you understand how carbohydrates work and are classified, you'll better understand what they do for your horse.