Fiber is one of the most important components in the equine diet, providing up to 70% of a horse’s energy needs.

Fiber in the equine diet predominantly originates from forages such as hay and pasture grass. Fiber can also be obtained from highly fermentable sources such as beet pulp and soy hulls.

While horses do not have a daily requirement for fiber, nutritionists recommend maximizing horse’s fiber intake by feeding a forage-based diet.

In horses, eating a diet rich in fiber supports gut health, enables foraging behaviors, and reduces the risk of stereotypic behaviors. Continue reading to learn more about the role of fiber in your horse’s diet.

Fiber in the Equine Diet

As grazing animals, horses evolved to thrive on a diet primarily composed of fibrous plant material.

Also referred to as structural carbohydrates, fiber comprises the structural components of cell walls that give plants their rigidity and form.

Structural carbohydrates differ from non-structural carbohydrates (NSC), like sugar and starch, which plants use primarily for energy and other functions.

Several different types of fiber can be found in the equine diet, but all structural carbohydrates share one common characteristic: they cannot be digested by enzymes that horse produces in their gastrointestinal tract. Instead, horses depend on microbes in the hindgut to break down these dietary components. [1]

Fiber undergoes microbial fermentation in the horse’s hindgut, particularly in the cecum and colon, where beneficial microorganisms break it down into volatile fatty acids (VFAs).

These VFAs serve as an energy source for horses providing up to 70% of the horse’s energy requirements.

Fiber consists of long chains of sugars, such as glucose, linked together with beta linkages. The horse produces digestive enzymes in the small intestine and pancreas that can break alpha linkages (such as those in starch) but cannot break beta linkages in structural carbohydrates.

This is why starch can be digested in the horse’s small intestine, but fiber cannot. Instead, fiber passes undigested into the hindgut where microbes produce enzymes that can break beta linkages and release sugar.

Types of Fiber

In order to understand how fiber contributes to a horse’s diet, it is important to differentiate between types of fiber in forages and feedstuff.

Different fibers vary in terms of their chemical composition, physical structure, digestibility and energy content.

Some fibers are highly fermentable and easily broken down by microbes in the hindgut. Others are indigestible and remain largely unchanged as they pass through the digestive tract.

The following are descriptions of the different classifications of fiber typically reported on forage and feed analyses for horses.

Horse Feed Tag Fibre Content

Crude Fiber

Crude fiber is one of the oldest methods of estimating the fiber content in animal feeds. This value represents the portion of plant carbohydrates in a feed that are not digestible by the horse but can undergo fermentation in the hindgut.

Crude fiber is measured by chemically mimicking gastric digestion of feeds with solutions consisting of acids and bases. [1] This chemical digestion breaks down feed components, leaving behind fibrous material, which is then measured.

However, this analysis of crude fiber results in some loss of fibrous components such as cellulose, hemicellulose, and lignin, underestimating the fiber content of the feed. [1] For this reason, more advanced analytical methods are preferred to estimate fiber content.

Total Dietary Fiber

Total dietary fiber is defined as the sum of all the indigestible components of a horse’s diet, including both soluble and insoluble fibers.

While total dietary fiber provides a reasonable approximation of fiber in equine diets, it is used more commonly in human nutrition. [1]

Total dietary fiber represents the combined content of various fibers, including: [1]

  • Cellulose
  • Hemicellulose
  • Lignin
  • Pectin
  • Other soluble fibers such as gums and mucilages

Cellulose

Cellulose is a polysaccharide made up of long chains of glucose that are held together with beta-1,4 linkages. [2] Cellulose makes up a large percent of plant mass, with cool season grass pasture containing around 50 – 60% cellulose on a dry matter basis. [3]

Cellulose is an insoluble fiber, which means it doesn’t dissolve in water and isn’t directly digestible by the horse. Instead, cellulose adds bulk to the digestive contents, aiding in the movement of food through the digestive tract.

Hemicellulose

Hemicellulose is a polysaccharide with mixed alpha and beta linkages. Hemicellulose may consist of various simple sugar units, including glucose, xylose, mannose and arabinose. [2]

Like cellulose, hemicellulose makes up a large proportion of plants, with cool season grass pasture containing approximately 30 – 50% hemicellulose on a dry matter basis. [3] Hemicellulose is also an insoluble fiber.

Lignin

Lignin is a portion of the plant cell wall that has a phenolic (ring-like) structure that inhibits the digestion of polysaccharides. This makes it indigestible for both horses and microbes. [2]

Lignin can bind to cellulose and hemicellulose, forming lignocellulose, which is less digestible by microbes compared to cellulose and hemicellulose. [2][4]

Lignin is less abundant in plants than cellulose and hemicellulose, with cool-season grass pasture containing roughly five percent lignin on a dry matter basis. [3]

Pectins

Pectins are structural carbohydrates that help to bind plant cells together. They are made of simple sugar units including galacturonic acid, arabinose, and galactose. [2] Pectins are soluble fibers and are therefore quickly fermented in the hindgut. [2]

Pectins are less abundant in plants compared to cellulose and hemicellulose, with pasture typically containing about 2 – 4% pectin.