Good vs. Bad Fiber in Horse Diets

We hear about fiber all the time when speaking about feeding our horses. Yet, most of us are not aware of just how important fiber can be to a horse’s health, wellbeing, and even performance. Not only is the amount of fiber you give your horse important, but even more critical is the quality of that fiber. Horses are always better off and are better performers when fed high quality fiber.

Why is Fiber Important to My Horse?

Horses have a unique digestive system that has evolved to efficiently extract nutrients from fibrous plant material. This has allowed them to thrive on a diet of grass and/or hay. Their digestive system consists of a large hindgut population of millions of beneficial bacteria that help break down fibrous plant material into volatile fatty-acids (VFAs). This happens through the fermentation of high-quality and digestible fiber.  

The VFAs important to horses include acetate, butyrate, and propriate. All are important energy sources for your horses and are crucial to maintaining their overall health and well-being. Some of the ways VFAs are important to horses include:

  • Energy source: VFAs are the primary energy source for most horses. Once the fibrous material is broken down by the microbes, the resulting VFAs are absorbed and transported to various tissues as an energy source.
  • Immune function: VFAs are thought to help boost the immune system and protect horses from infection and disease.
  • Gut motility: VFAs help stimulate the horse’s gut and limit digestive disorders, such as impaction colic.

The breakdown of fiber in the hindgut also helps produce B-vitamins and some beneficial amino acids. Higher fiber diets also help in preventing metabolic disorders by helping to regulate insulin and glucose levels in the blood. It is for these reasons that fiber and the quality of that fiber are so critical to your horses.

Good and Bad Sources of Fiber for Horses

The quality of the fiber you feed your horses is extremely important because of the horse’s complex digestion process of breaking down fibrous plants and extracting nutrients. Some types of fiber are indigestible and do very little for the horses. Other sources of digestible fiber are now being called “super fibers”, which are extremely digestible.

Equine nutritionists consider good sources of fiber to be those that are high in digestible fiber (hemicellulose, cellulose) and help provide the necessary nutrients for a balanced diet. Some examples of good sources of fiber include:

  • A well-maintained pasture is an excellent source of fiber for horses. Pastures are generally high in digestible fiber, while also providing critical nutrients to a horse’s health and wellbeing.
  • Hay: grass, legume, and mixed hays are usually great sources of fiber for a horse. Much will depend on the hay quality; however, high quality hays are an excellent choice.
  • Super fibers: this is a common term for fiber sources such as beet pulp and soybean hulls. These super fibers are high in pectin, which is a soluble fiber and more easily digested than other fiber types.

Poor quality fiber sources are those that are less digestible. Many are higher in the indigestible fiber called lignin. Because of its structure, lignin is not able to be digested by either the horse or the microbes in its hindgut. Some examples of poor-quality fibers include:

  • Very high in lignin and provides little nutritional value to horses.
  • Low quality hay or forage: hay or pasture plants that are more mature (i.e., seed heads on grass hays), are higher in indigestible fiber (lignin) and less beneficial to horses.
  • Corn stalks: very high in fiber but cannot be digested by the horse. Additionally, they can be contaminated with molds or toxins, which can be extremely harmful to a horse.
  • Horse feeds with rice, oat, or peanut hulls as a fiber source: often used to balance fiber levels in a lower quality horse feed and are typically high in indigestible fiber.
  • High-NSC horse feeds: horse feeds that are high in sugars and starches can disrupt the beneficial hindgut microbes and lead to digestive disorders, such as colic or laminitis.

How Can I Evaluate the Quality of my Horse’s Fiber?

Fiber quality can vary widely across all sorts of feeds we give our horses. Thankfully, there are a few ways you can analyze what you are feeding your horses and judge its quality. Since most of the fiber in a horse’s diet is from hay, it is highly recommended to get a hay (or forage) test.

Briefly, a hay test will help evaluate the quality of fiber in that sample by giving you values of NDF (neutral detergent fiber) and ADF (acid detergent fiber). The NDF value represents the hemicellulose, cellulose, and lignin in the hay. Whereas the ADF value represents the age and maturity of the hay. More mature forages are less digestible and even less palatable to the horse.  The following table indicates the quality values of both NDF and ADF seen in hay tests.


High Quality

Moderate Quality

Low Quality




> 60%




> 40%


Another way to evaluate your hay without a hay test is just a simple visual examination of the hay. This is another acceptable quick evaluation of fiber quality in a hay.

  • High quality hay: seen as fresh, soft with a lack of “stalkiness” or “pokiness.” Alfalfa hay should have a higher proportion of leaves compared to stems. Stems should be limited and fine or less dense. For grass varieties, there should be no seed heads.
  • Low quality hay: can be comparable to straw, with heavy stems and a low leaf-to-stem ratio. The hay appears to be brittle, is pokey and stemmy.

The other source of fiber for many horses is in their horse feed. Here, the quality of fiber can be very important. As mentioned above, some manufacturers will use rice, oat, or peanut hulls to increase and/or balance the fiber levels in the horse feed. Some companies may try to mask lower quality fiber sources by using the terms “fiber” or “roughage” or products on their feed tags, and not list the actual ingredients. This could indicate a feed high in poor or indigestible fiber.

Take Home Message

To answer, “is the quality of fiber important to my horse,” it is a resounding yes! The quality of the fiber in your horse’s diet can impact so many essential biological processes that directly impact your horse’s health, wellbeing, and performance. If you are having trouble evaluating the fiber in your horse’s diet or need general nutritional advice, please feel free to contact us for a free consultation.
Article By: Chris Mortensen, Ph.D.
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