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.

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.

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.