Understanding Non-structural and Structural Carbohydrates
Understanding the difference between non-structural carbohydrates (NSC) and structural carbohydrates, and how they are calculated, can be an important guide to maintaining healthy weight and a more balanced metabolism in easy keepers and metabolic horses.
There are two general categories of carbohydrates: non-structural and structural. Starches and sugars are known as non-structural carbohydrates. They are digested by enzymes and absorbed in the foregut. Although minimal carbohydrate digestion happens in the stomach, most of the digestion and absorption occurs in the small intestine.
Structural carbohydrates are fiber components like cellulose, pectin, fructan, and hemicellulose that are digested with the help of microorganisms in the hindgut.
Both structural carbohydrates and non-structural carbohydrates are energy sources for horses. Structural carbohydrates are digested slowly, and provide sustained energy. Non-structural carbohydrates are digested rapidly and energy is released quickly for a short burst of energy.
A word about fructans and laminitis:
Currently there are two basic theories of fructans and their relationship to laminitis in horses. 1. That fructans are a cause of pasture-associated laminitis in horses. 2. That pasture-associated laminitis is an endocrine disorder with an abnormal insulin response.
Researchers have categorized laminitis into 3 main categories:
- Systemic: inflammatory/intestinal events where the horse is systemically ill.
- Weight bearing
- Endocrine: metabolic/hormonal disturbances
A 2011 study on insulin-induced laminitis found that laminitis occurring in insulin-resistant horses is accompanied by the intake of large amounts of non-structural carbohydrate-rich pasture. Since fructans are structural carbohydrates this would support the theory that fructans do not cause pasture-associated laminitis.
However, an overload in the hindgut of fructans can cause changes in the hindgut microflora, which alters the bacterial populations in the hindgut and can cause a rapid rise of gram positive bacteria. The change in the hindgut bacteria may produce inflammation, a profound drop in pH and a rise in endotoxin. If laminitis resulted this would be a systemic form of laminitis.
Fructans are found in grasses, legumes, apples, garlic, rye, chickory, wheat, and barley. Oats do not have fructans.
Calculating Non-structural Carbohydrates (NSC):
There are two methods of calculating NSC. One method that is most commonly used by feed companies and some veterinarians is to take the ethanol soluble carbohydrates (ESC) analysis and add the starch analysis to get the NSC. The ESC is simple sugars only and does not include the fructans. Using this method, the NSC should be 10 or below for metabolic horses and easy keepers.
Plant scientists, some veterinarians and nutritionists take the Water Soluble Carbohydrates (WSC) number, which includes the fructans and the ESC, then add the starch number to get a total NSC. For metabolic horses this needs to be 14 or below.
For example, I went looking for the NSC percentage of SafeChoice. The ESC was 4.0% and the starch was 11.0% for a total of 15% NSC. But this calculation was made without WSC — so at 15% for the sugars and starch combined, this feed is significantly higher than the 10% or below recommended for the ESC plus starch calculations.
- Purina’s Wellsolve comes in at 7% starch and 4% sugar (ESC) for a total of 11% NSC. Just a tad over the 10% or less NSC that is recommended.
- Progressive Nutrition’s Premium Lo Carb Pellet comes in at 6% starch and 2.7% sugar(ESC) for 8.7% NSC.
- Standlee Alfalfa pellets use WSC plus starch to arrive at the NSC. For their alfalfa pellet it is: 7% WSC and 1% starch for a total of 8% NSC.
Testing for NSC:
Whether your horse is metabolic or an easy keeper, it is important in the overall management plan to test your hay and pastures. It is important to get a variety of samples from different parts of the pasture and different bales of hay. Some county extension offices will loan hay probes that are more reliable than handfuls of hay from several bales.
Dairy One or Equi-Analytical (a division of Dairy One) are popular labs for testing. The basic NSC test (WSC, ESC, Starch) is around $20.
Average sugar(ESC) and starch content of common feed ingredients:
- Rice Bran: 6.2% sugar, 17.7% starch = 21.2% NSC
- Oats: 4.8% sugar, 44.4% starch = 54.1% NSC
- Beet Pulp: 10.7% sugar, 1.4% starch = 12.3% NSC
- Soybean Hulls: 4.3% sugar, 1.9% starch = 6.3% NSC
- Soybean Meal: 14.3% sugar, 2.1% starch = 16.2% NSC
- Wheat Bran: 8.3% sugar, 22.8% starch = 31.1% NSC
- Wheat Middlings: 10.1% sugar, 26.2% starch = 32.0% NSC
(Values provided by Equi Analytical Laboratories)
BioStar’s Tri Dosha EQ provides 12.6% maximum NSC.
(Starch: 1.0%, WSC: 11.6%, ESC: 8.4%)
* These statements have not been evaluated by the Food and Drug Administration.
This information is not intended to diagnose, treat, cure, or prevent any disease.