A NEW LOOK AT FIBER IN HORSE FEEDS
The Fiber-To-Energy Relationship
In the past, horse-feed concentrates were selected for high digestible energy (DE) and low fiber content (Table 1), because grains were the only feeds available which provided more energy per pound than hays. And, grains with the least fiber provided the most energy. This traditional fiber-to-energy relationship is based on the fact that corn (2% fiber), and most other cereal grains (barley, 5-6%; rye, 2%; wheat, 3%) contain very little fiber. Oats (12%) are the only cereal grain with even a reasonable amount of fiber. It's not surprising that oats are the safest of the cereal grains for horses.
The Fiber-to-Energy table actually reflects the starch content of the feed, since starch was the most energy-dense nutrient available when the table was developed. And, the more starch a feed contained, the less room there was in the feed for fiber, or anything else, for that matter. The newest version of the table (shown here) has a column for added fat feeds, but does not address the issues of digestible fiber and starch digestibility in horses.
The Fiber-to Energy table is now obsolete, due to new knowledge about feed digestibility and digestive processes in horses. The previously used DE values for cereal grains were determined in a calorimeter, which fully burns the feed. Horses' digestive processes are not able to liberate all of the DE in feeds in useable form. In fact, digestibility of feeds in horses varies greatly, and depends on the type of grain used and the processing method of the feed (See Equine Nutrition in the 21st Century, Part Two).
This new information on foregut digestibility of grains proves that we cannot use the older values for DE with horses. For instance, a recent article presented at the Thoroughbred International Conference and Exposition, in Lexington, Kentucky, concludes that corn-starch fermented in the hindgut of horses produces only about 75% or less of the DE of corn-starch digested in the foregut. And, starch in the hindgut also affects fiber digestibility, further reducing the useable DE of the total ration.
Fiber and Digestive Processes
Horses are designed to process forage and are very efficient at taking small amounts of fat, sugar, starch and protein out of large amounts of fibrous feed (forage) as the feed passes through the small intestine. However, feed progresses through the foregut of horses without much mixing. Feed often remains in the stomach for less than 1 hour, so the grain fed at 7 AM doesn't mix well with the hay your horse eats from 7:30 to 9:00 AM. Therefore, all of the feed your horse eats, including the grain or concentrate portion, should contain sufficient fiber to move it along the tract normally.
We can increase the amount of fat, starch and protein in a small amount of concentrate (1-2 pounds) within certain limits and still have good absorption of nutrients. However, when the fiber content of a feed falls below a certain amount, or we feed a lot of low-fiber concentrate (over 3 pounds per meal), the starch and other nutrients can become less digestible in the foregut. Feeds with less than 6% fiber seem to be more likely to cause colic, founder and other digestive disorders, while those with 12-14% fiber or more seem to reduce the risks of digestive disorders in horses.
In modern horse feeds, crude fiber content no longer accurately predicts DE. We can use fats for concentrated energy and fermentable fibers, like soybean hulls and beet pulp, to increase the fiber content of horse feeds, making them safer for horses, yet powerful enough to fuel even the most elite athletes. Of course, indigestible fibers like oat hulls, peanut hulls, rice hulls and straw provide fiber, which helps keep the foregut functioning properly. But, they do not 'feed' the hind-gut bacteria or provide energy for the horse. Be sure to check the feed label or call your feed company if you are concerned about the amount and type of fiber in your horse's feed.
It is time to retire the old fiber and DE table and start feeding our horses like the grazing, fiber-digesters they are. I recommend concentrates made with digestible fiber, which are available in all desired energy levels for horses. There is now a high-fiber feed available for every horse, from the 'easy keeper' to the race or endurance horse.
1. Forage provides significant energy to horses
2. Horse feeds should contain at least 12% crude fiber to reduce digestive disorders
3. High-fiber feeds come in all energy levels
4. Soybean hulls, beet pulp and immature alfalfa are highly-digestible energy sources for horses
5. Rice hulls, oat hulls, peanut hulls and straw are low in digestible fiber for horses
Equine Nutrition in the 21st Century
Part Five - Forages for Horses