“The horse’s digestive tract is designed to handle lots of fi ber and thrives best if it has a variety of fi ber types to feed the diff erent microbes in the gut.”
carbohydrates. The contents of the cell held in by the cell wall are mostly non- structural carbohydrates. The cell walls are called structural because they give the cell shape and strength, which keep the cells from looking like gelatin. Of the structural carbohydrates, certain
ones can be broken down by the microbes living in harmony in the digestive tract of the horse, mostly in the cecum and colon. These are “digestible” fi bers such as cel- lulose and hemicellulose. There are also “indigestible” fibers
found in the cell walls like lignocellulose, which are not broken down by the micro- bial population and have no nutritional value except to work like a laxative and help the progression of the digested mate- rial through the tract. In general, the stiffer or harder the plant component, the more indigestible fi ber is present. For example, the rigid stems of alfalfa plants are high in indigestible fi ber, while the soft, pliable leaves are rich in digestible fi ber. The amount of digestible fi ber found in
fresh forage and hay is generally between 30% and 50%. If food is 100% digestible fi ber, it causes stagnation problems in the tract and can lead to serious gastrointes- tinal disorders like enteritis or colic. The general term “fi ber” includes both digest- ible and indigestible fi bers and does not distinguish between how much energy a horse can get from it. Commercial horse feeds commonly
contain ingredients other than hay that are known to be high in fi ber. Some are excel- lent sources of digestible fi ber while oth- ers are not. Beet pulp and soy hulls have become staples in commercial horse feeds
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or as standalones in equine diets because they are high in digestible fi ber—between 75% and 80%. Uncommon fi ber products that are reasonably high in digestible fi - ber are sunfl ower hulls, almond hulls and citrus pulp, but palatability issues keep their use limited. Other feed ingredients that are high in fi ber but low in digestible fi ber are cottonseed hulls, peanut hulls, oat hulls and rice hulls. These have very little nutritional value.
WHY WOULD HIGH FIBER BE GOOD? Horses are grassland—grazing—ani-
mals. In order to be able to survive on grass, they have an interesting symbiotic relationship with microbes in their gastro- intestinal tract that digest plant material for the horse. Without the millions of bac- teria, protozoa and yeasts to break down cellulose molecules, horses would not derive any benefi t from eating fi ber. The key to maintaining an effi cient microbial population is a steady supply of ferment- able products. The horse’s digestive tract is designed to handle lots of fi ber and thrives best if it has a variety of fi ber types to feed the different microbes in the gut. When feed is digested by microbes it
is called fermentation, and the result of this process is volatile fatty acids, or VFAs. These short-chain fatty acids are easily absorbed into the bloodstream and are used as readily available energy to fuel various body processes. The VFAs pro- duced are primarily acetate, propionate and butyrate. VFAs are handled like other
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