California Riding Magazine • July, 2013

Equine Nutrition Update
Understanding fiber and its role in horse's health is important.

The importance of fiber in the human diet is a well-documented topic, but it's a newer subject in the equine world. When the opportunity to chat with an equine nutrition expert visiting from Europe arose recently, we asked about the role of fiber in the gastrointestinal health of our horses. The expert, Dr. D (David). A. van Doorn, MSc, is part of the Cavalor Equine Nutrition Research team, Secretary of the European Equine Health & Nutrition Congress and his work has been widely published.

Riding Magazine: What is fiber?
Dr. van Doorn:
Fiber is a unique and complex nutritional entity often defined as the indigestible or slowly fermenting components of feeds. Like humans, the horse is not able to digest fibers. However, horses have a bacterial population in the hindgut that is able to ferment a significant amount of fiber present in the feed. The fermentation of these fibers results in (slow-releasing) energy that the horse can use to meet its energy requirement.

Riding: Is there a difference between fiber and roughage?
Dr. van Doorn:
In dairy production, feedstuffs with a high fiber content are often referred to as "roughage." A feedstuff is considered roughage when it contributes to rumination (chewing feed until it's soft, as cows do) by its form and chemical composition and has a particle size of more than about 8 mm. Although the horse is not a ruminant, its original diet consisted of small meals of grasses that were often not highly digestible. As indicated, bacteria in the hindgut of horses are able to ferment these fibers. In contrast to ruminants, horses ferment fibers at the end of the digestive tract. From these perspectives some general characteristics of "roughage" for horses: can be derived:

  • It has high amount of (crude) fiber based on its chemical analysis
  • It is mainly digested by bacteria in the hindgut of the horse
  • The physical appearance of these feeds often increase the duration of intake (more chewing and more saliva production)

Thus, fiber refers to a chemical component of the feed while "roughage" refers to a feed with a high amount of fiber. Unfortunately, there are many definitions and different analytical procedures that can be used to classify and analyze the amount of fiber in feed.

Riding: Why is fiber important to horses?
Dr. van Doorn:
The natural diet of horses is grass, which is typically high in fiber and does not contain a high amount of calories. The digestive tract of the horse is adapted to such diet to be able to derive energy from fibrous plant materials. In practice, fiber can be present in grass or less diluted in roughages that are available to horses. Compared to pellets, roughages have, in general, a longer intake duration resulting in a lower risk of boredom. Providing multiple portions of roughage during the day seems to benefit the welfare of horses (preventing stereotype behavior). Due to the longer chewing activity on most roughage, a higher production of saliva is obtained. Roughage helps to maintain a good dental condition (chewing) and composition of the semi-fluid mass of partly digested feed (it helps to reduce obstructions). Roughages stimulate the gut's motility, important for proper function of the digestive tract. In comparison to concentrates, roughages and fiber-based diets influence in a different way the gastrointestinal tract fill, the pH (acidity) and the water balance in the hindgut of horses.

Riding: What feeds contain the most fiber?
Dr. van Doorn:
There are different sources of fiber and different fiber types and fiber content may differ between and within feedstuffs. This affects the nutritional value of the feed. Roughages are typical feeds for horses that contain a high fiber content. Grass and grass hay varieties, alfalfa (legume), straw and beet pulp are examples of feeds that have a higher fiber content. Although beet pulp does not have particles with a long stem, it is often considered roughage for horses. This is because beet pulp contains a relatively large amount of fibers that are fermented in the hindgut of the horse.
Roughages may vary in fiber content and type of fibers depending on grass variety, maturity of the plant at harvesting, etc. The type of fiber may also differ between roughages. Further, plants become less digestible when harvested in a mature state and the amount of indigestible fiber increases. A higher fiber content of a feed generally points to a lower digestibility (e.g. straw). This also implies that the amount of energy that the horse can derive from this feedstuff will be lower than that from, for example, grass hay.

Riding: Is there a fiber requirement?
Dr. van Doorn:
There have been no conclusive reports that have set a fiber requirement for horse diets. However, fibrous forages represent the diet of wild equids best. In addition, research suggests that a lack of roughage may lead to hindgut acidosis, colic, gastric ulcers, increased risk for crib-biting and wood-chewing and behavioral problems. A lower limit of feeding at least 1 kg of dry matter of hay per 100 kg of horse per day has been suggested. Generally, it is aimed to provide an amount of roughage (kg) in the total ration of horses that is about 1.5% on body weight basis. Thus, for a 500 kg horse 7.5 kg of roughage in the ration is indicated. It is not known how exercise affects the need for fiber. Clearly, as hay-only diets or an increased fiber content of the diet are prescribed for performance horses prone to or recovering from gastric ulcers, it seems likely that fiber in the diet of performance horses is also important to prevent or support horses with these problems. Generally it is important to maximize fiber intake. Especially, if your horse is considered an easy keeper.

Riding: Is it possible to get too much fiber? If so, what are the possible consequences?
Dr. van Doorn:
That is a complicated question to answer. The fiber in the diet should be of good quality to be digested. Too much fiber from low energy sources, like straw, is also undesired. Horses can only take up a certain amount of feedstuff per day. In animal nutrition this is referred to as "a maximum amount of dry matter that the horse can ingest per day." If you are feeding bulky fibrous low energy feeds to a (performance) horse, it is possible that these horses do not take in the amount of energy (and other nutrients) needed due to the low feed quality. Too bulky and fibrous feed may increase the risk of impaction, and thus, colic.

Riding: How is a horse's need for roughage affected by living in a pasture, versus being kept in a boarded/stall environment?
Dr. van Doorn:
Generally speaking, pasture contains fiber but its concentration is diluted due to the high water content of grass. Horses therefore need to take up more grass to take up the same amount of fiber (and other nutrients) compared to stabled horses that are often fed roughages subjected to some kind of drying, like hay and alfalfa.

Riding: Do you have a suggestion for older horses who have problems getting enough roughage because of dental problems?
Dr. van Doorn:
Older horses need fiber in their diet. This can be challenging when the horse suffers from dental problems. Longer feed particles or fibrous roughage can be difficult to take in for these horses. Sometimes these horses are only able to take in a limited amount of hay. A softer, early cut hay in combination with other fiber sources (like beet pulp) or special formulated diets for senior horses containing sufficient fiber and other nutrients may be used for these horses. It may be advised to contact an equine nutritionist to help formulate this horse's diet.

Riding: Do you have any general suggestions for feeding horses?
Dr. van Doorn:
Feed your horse sufficient fiber and provide multiple meals per day. Make sure that your horse has also roughage available during the evening/night. This prevents boredom and prevents long periods of fasting. This helps to maintain your horse happy and healthy. A ration calculation and/or nutrient analysis of the feed may be indicated to control your horse's nutrient intake. Especially, when the roughage quality differs considerably. As a consequence the intake of some nutrients may be too low. Also, as there is not much green pasture in California, the intake of essential fatty acids may be important.

Riding: Thank you!
Dr. van Doorn:
You are welcome!

Dr. David A. van Doorn obtained a bachelor's degree in Animal Husbandry, a master's degree in Animal Science from Wageningen University and Research Centre (WUR), and a Ph.D. from Utrecht University (NL). His Ph.D. thesis project was executed at the Nutrition Department of the Veterinary Faculty and entitled "Equine phosphorus absorption and excretion." Since 2001 David has represented Cavalor Equine Nutrition Research and is responsible for the organization of the European Equine Health and Nutrition Congress ( initiated and sponsored by Cavalor. Since 2010, David has been an assistant professor of equine nutrition on a weekly basis at the Nutrition Department of the Faculty of Veterinary Medicine of Utrecht University. In addition to equine nutrition, David has been involved in projects related to the preservation of the equine veterinary patrimony.