Carbohydrate Evaluations in Animal Diets
If it seems like you need a graduate degree to make sense of the many types of carbohydrates, don’t worry – we’ve put together a guide to the carbohydrate types you’re most likely to see on a feed/forage analysis report.
We’ll give you the carbohydrate name, description, and nutritional significance for horses:
- NDF (Neutral Detergent Fiber): Total plant cell wall carbohydrates, including ADF (see below) and Hemicellulose; often considered an indicator of forage quality and intake potential (lower NDF = easier to digest fiber = higher quality and higher intake/day).
- ADF (Acid Detergent Fiber): Less digestible carbohydrates in plant cell walls, including cellulose and lignin; higher ADF = lower digestibility and is less palatable.
- NFC (Non-Fiber Carbohydrates): A calculated estimate of carbohydrates composed of starch, simple sugars, fructan, soluble fiber, and fermentation acids; calculation may vary, but generally equals 100% minus (CP +NDF + Fat + Ash). A rough estimate of carbohydrate value (high NFC) generally indicates more digestible carbohydrates than indigestible fiber types.
- NSC (Non-Structural Carbohydrates): Intended to describe easily digestible carbohydrate components of a feed more accurately than those in NFC; usually calculated as WSC + Starch or ESC + Starch.
- Starch: A polysaccharide composed of many linked glucose molecules found mainly in cereal grains where they are broken down and absorbed as glucose (simple sugar). Some starches are resistant to small intestine digestion and are fermented in the large intestine; a typical analysis does not differentiate between the two types. Low starch content generally means little glucose will be absorbed in the small intestine (low glycemic response). This is good for horses that can’t handle large blood sugar changes (e.g., insulin-resistant horses). High starch generally means a high glycemic response.
- WSC (Water-Soluble Carbohydrates): Carbohydrates solubilized and extracted with water, including simple sugars and fructans (see below); sometimes called “sugar” on analysis reports. Interpretation of WSC is dependent upon the relative proportions of simple sugars and fructan as they are metabolized at different sites in the gastrointestinal tract. High WSC might indicate high fructan levels in grasses or high simple sugars in cereal grains.
- ESC (Ethanol-Soluble Carbohydrates): Carbohydrates that dissolve in 80% ethanol solution; these carbohydrates are a subset of WSC that are primarily digested in the small intestine and give a true glycemic (blood sugar) response. However, some fructans can be included in this fraction. High ESC generally means a feed will generate a high glycemic response (unless there is a high level of fructans in this fraction). This might be helpful for hardworking horses that need lots of energy, but not very good for horses that are sensitive to large blood sugar changes (e.g., insulin-resistant horses). However, low ESC does not necessarily mean the feed will have a low glycemic response because the starch could still keep it high.
- Fructans: Compounds made up of many large fructose molecules (complex sugars); fermented and only digested in the large intestine. Occasionally, it is analyzed separately from WSC. Primarily present in “cool season” grass forages. Not found in “warm season” grasses or in legumes. Therefore, adding a legume with a cool season grass would be beneficial when feeding horses with special needs, especially horses with laminitis.
Richard Ten Eyck is the Oregon Department of Agriculture feed specialist and chair of the Carbohydrate Working Group of the Feed Labeling Committee for the Association of Animal Feed Control Officials (AAFCO).
- Cereal Grains: Corn, Wheat, Barley, Rice, Oats, etc.
- Cool season grasses: Timothy, Bluegrass, Orchard-grass, Fescue, Brome, Prairie Hay, etc.
- Warm season grasses: Bahia, Tiftin-44, Coastal Bermuda, etc.
- Legumes: Alfalfa, Clover, Lespedeza, Peanut Hay, etc.
- NSC: Currently listed as: Starch + Sugar + Fructans, but when laboratories become uniform it will become: WSC + Starch or ESC + Starch.
- Forages: Hay (dried) and Pasture (fresh) and Haylage (preserved by fermentation).
- Glycemic Response: Will vary according to individual size of the horse, pounds of feed fed at one time, daily activity level of the horse, etc.