Nutrition Terms to Know When Managing Metabolic Horses

An equine nutritionist breaks down nutrition terms and acronyms, including NSC, WSC, and ESC. Understanding these concepts can help you manage horses with metabolic problems.
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Carbohydrates serve as the primary energy source for horses. | Getty images

Q: I have two ponies with metabolic problems. I’ve been researching the best ways to feed them, but there are several terms I don’t understand. I see terms such as nonstructural carbohydrates, hydrolysable carbohydrates, and so many more, but I can’t make sense of them. Help!

A: Carbohydrates serve as the primary energy source for horses and can be divided into two broad categories: structural and nonstructural. The equine gastrointestinal tract is designed to handle large amounts of structural carbohydrates, which are abundant in forages. Sugars are nonstructural carbohydrates (NSCs) and a key concern for owners managing horses with metabolic or digestive disorders.

An important factor when classifying carbohydrates is where in the gastrointestinal tract they are digested. For example, those digested and absorbed in the small intestine provide more energy to the horse than those digested by microbial action in the hindgut, which includes the cecum and large colon (or large intestine). When enzymes break down carbohydrates in the small intestine, the resulting sugars are absorbed into the bloodstream as glucose, stimulating an insulin response.

Common Equine Nutrition Terms

You’ll likely come across a variety of terms when reading about equine nutrition, especially if you research how to manage your metabolic horse’s diet. You’ll likely see the common term NSC, but you might also read about starch, fructans, water-soluble carbohydrates (WSCs), ethanol-soluble carbohydrates (ESCs), and hydrolysable carbohydrates (HCs).

Feed manufacturers use these terms in a variety of places, from educational articles to hay analyses and feed labels, so it’s valuable to understand what they mean and how to navigate the terminology. The authors of Nutrient Requirements of Horses, 2007, propose a three-prong partitioning system for carbohydrates in the equine diet: slowly fermentable carbohydrates, rapidly fermentable carbohydrates, and hydrolysable carbohydrates.

  1. Slowly Fermentable Carbohydrates: The horse’s gastrointestinal tract has evolved to consume large amounts of slowly fermentable carbohydrates. These complex molecules are not digested by enzymes in the horse’s foregut (stomach and small intestine). Instead, they are fermented in the hindgut to produce volatile fatty acids (VFAs) as an energy source. Examples include cellulose and hemicellulose.
  1. Rapidly Fermentable Carbohydrates: These carbohydrates cannot be broken down by enzymes in the horse’s foregut but take less time to be fermented in the hindgut than fiber, for example. The fermentation process produces both VFAs and lactic acid. Examples include fructans, oligosaccharides, and resistant starch.
  1. Hydrolysable Carbohydrates (HCs): Hydrolyzable carbohydrates are made up of the simple sugars and starch that can be digested by enzymes in the horse’s foregut. The body absorbs these molecules as glucose, and they have a direct impact on blood insulin levels. Examples include glucose, sucrose, and fructose. The calculation for HC is ESC + starch.
  1. Ethanol-soluble carbohydrates (ESCs): ESCs are the simple sugars (mono- and disaccharides) digested by enzymes in the foregut. Glucose is an example of an ESC.
  1. Nonstructural Carbohydrates (NSCs): Nonstructural carbohydrates are calculated values composed of both the hydrolysable and rapidly fermentable carbohydrates. The calculation is WSC + starch.
  1. Water-soluble carbohydrates (WSCs): Water-soluble carbohydrates are a subsection of NSC and include the simple sugars and fructans.
  1. Fructans: Fructans are a type of nonstructural, or rapidly fermentable carbohydrates. They cannot be digested by enzymes in the foregut and, therefore, pass on to ferment in the horse’s hindgut.

Take-Home Message

Although carbohydrates in horses’ diets occasionally get a bad reputation, they serve as the primary energy source for horses and are critical to balanced nutrition. Understanding the different carbohydrate terms can help you ensure that your horses are on a safe nutrition program if they are sensitive to excess starch and sugar.

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Written by:

Madeline Boast, MSc completed her master’s in Equine Nutrition at the University of Guelph and started an independent nutrition company known as Balanced Bay. She has worked with a variety of equids—from Miniature Ponies to competing Thoroughbreds. Boast designs customized balanced nutrition plans that prioritize equine well-being, both for optimal performance and solving complex nutritional issues and everything between. 

2 Responses

  1. Hay needs to be tested and the ESC+Starch needs to be under 10% for it to be considered *safe* for insulin resistant or Cushings horses. Starch preferably under 4%. Not only are there zero documented cases of high fructan in pasture causing laminitis, the levels of fructan naturally found in a whole day’s worth of eating pasture grasses almost never come even close to the amount needed to cause laminitis.

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