Carbohydrate classification can be one of the harder parts of horse nutrition to wrap your brain around. However, it is also one of the most important...
It is especially important for owners of horses with metabolic diseases, as understanding the various language that goes with carbohydrate classification is vital to understanding how your horse is affected by them.
So, let's jump right in...
The most common way to classify carbohydrates is by a method developed in the 1960's by a man named Van Soest. Under his classification, carbohydrates were separated as follows:
Because non-structural carbohydrates (NSC) in a feed were hard to measure at the time, if not impossible, NSC was calculated using the following formula, where the 100 represents 100% of the dry matter of a feed:
NSC = 100 - (NDF + Crude Protein + Fat + Ash)
More and more today, the term nonfibrous carbohydrates (NFC) is used to refer to this difference. NSC is used to refer to a chemically analyzed result, since methods for analyzing those parts of a carbohydrate have since been developed.
NFC is all the carbohydrates in a feed that are not part of the NDF, and the NSC is a small part of the NFC.
NSC components include the following:
Still today not many labs that analyze feed completely break down the carbohydrate. Therefore, many times NSC is roughly calculated by the following equation:
NSC = Starch + WSC
where WSC stands for water-soluble carbohydrates. WSC is made up of compounds that are soluble in water or the gastrointestinal contents. These compounds include:
The difference between NSC and NFC can range from very small to very large.
Originally the practice of separating carbohydrates into NFC and NDF was developed for use in ruminant nutrition. However, it is also useful for equine nutrition due to similarities in the digestion of carbohydrates in the ruminant and horse tracts.
In 2001, Hoffman, et al.* proposed a classification system that would be more useful for equine nutrition.
This classification system has 3 parts:
Hydrolyzable Carbohydrates These carbohydrates can be digested in the small intestine and would include hexoses (molecules with a backbone of 6 carbon atoms), disaccharides, some of the oligosaccharides, as well as the nonresistant starches (starches that can be broken down by enzymes in the stomach). The energy yield from these compounds is very high, because they are broken down into monosaccharides.
Rapidly Fermented Carbohydrates These carbohydrates are easy for microbes in the large intestine to digest. They include pectin, fructan, and the oligosaccharides that are not digested in the small intestine.
Slowly Fermented Carbohydrates These carbohydrates include cellulose and hemicellulose that is broken down slowly by the microbes in the large intestine. These carbohydrates are an important source of acetate, a fatty acid.
This classification system would allow a better understanding of exactly how various carbohydrate components are used, as it separates carbohydrates that are broken down to glucose from those that are used to produce volatile fatty acids.
*Hoffman, R. M., J.A. Wilson, D. S. Kronfeld, W.L.Cooper, L.A. Lawrence, D. Sklan, and P.A. Harris. 2001. Hydrolyzable carbohydrates in pasture, hay and horse feeds: direct assay and seasonal variation. J. Anim. Sci. 79:500-506.