Assessing Fiber Quality in Horse Feed

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Assessing Fiber Quality in Horse Feed

Crude fiber, ADF, and NDF values all can be generated by doing a lab analysis of your feed, a service most feed companies and many universities provide.

Photo: Thinkstock

Not all fiber is created equal. Depending on its origins, it can vary widely in terms of quality and digestibility.

Fiber consists of three main substances: cellulose, hemicellulose, and lignin. Lignin is the very tough stuff that gives plant material its rigidity. It is 100% indigestible by either horses or the bacteria they harbor in their digestive tracts. However, cellulose and, to a certain extent, hemicellulose are digestible, and it’s from these materials that horses derive digestible.

Cellulose and hemicellulose are polysaccharide molecules, fairly complex chemical arrangements that need to be broken into smaller units to be absorbed through the gut wall.

Breaking the “beta bonds” holding the individual monosaccharide molecules together allows their conversion to volatile fatty acids, or VFAs. Cellulose and hemicellulose, which stem from the non-seed and non-fruit portions of a plant, such as the leaves, stems, and hulls, also are known as insoluble fiber.

Soluble fiber is fiber stemming from the “liquid” portions of a plant: the resin, sap, pectins, and mucilages. All plant eaters use nearly all of the soluble fiber they ingest. But the degree of insoluble fiber that horses use varies. The sooner the bacteria go to work breaking the beta bonds, the greater the percentage of the fiber used by the horse.

But even undigested insoluble fiber has its place in the equine diet. It helps maintain gut motility and function as well as prevent the too-quick consumption of carbohydrates, which are readily digested and which sometimes cause digestive upset if not “cushioned” by fiber in the colon.

In practice, it’s not terribly important to know how much of the fiber provided by a plant is soluble. An enzymatic test does exist, but it’s rarely used because the differences are not significant from a feeding point of view. There are, however, a few ways of defining the fiber content of a feed—each with its own pros and cons.

“Crude fiber,” or CF, is the value most of us are used to seeing on feed labels or tags. It’s an estimate of the total fiber in a feed. The calculation that results in a crude fiber value can overestimate the non-fiber carbohydrate content of a feed and underestimate the cellulose portion. This can also lead to an overestimation of the feed’s caloric content and, thus, its feeding value.

Another value commonly used to express the fiber content of a feed is the NDF, or neutral detergent fiber. Unlike the CF, an NDF value includes almost all of the cellulose in a feed sample and more than 50% of the hemicellulose, but it can also erroneously includes a high percentage of digestible starches in its calculations.

Acid detergent fiber, or ADF, is another way of expressing fiber percentages. This measure not only removes starches from consideration but also removes most of the hemicellulose. Because horses use most of the hemicellulose in a feed, ADF analysis ends up being a measure of the cellulose plus the lignin and, therefore, results in an underestimation of the feed’s insoluble fiber content and an overestimation of its energy content and feeding value.

Crude fiber, ADF, and NDF values all can be generated by doing a lab analysis of your feed, a service most feed companies and many universities provide.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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