Assessing Carbohydrates in Horse Feed

Directly measuring the amount of sugar in the horse’s ration used to be difficult to do and could be quite expensive, and therefore was usually indirectly estimated by calculation. However, chemical assays are now widely available to measure the amounts of starch and other soluble carbohydrates in horse feeds and forages.

Assays commonly used to determine NSC content of feedstuffs include starch, water soluble carbohydrates (WSC) and ethanol soluble carbohydrates (ESC). NSC is typically defined as starch + WSC, which will include most forms of soluble carbohydrates in the feed including simple sugars, starch and other nonstructural carbs such as fructans. In some situations, ESC may be substituted for WSC in the calculation of NSC to more closely estimate the contribution of feed components that are absorbed as simple sugars in the horse’s digestive tract (the ESC assay does not capture all the fructans as does WSC, and much of the dietary fructan component escapes digestion in the small intestine and will not be absorbed as simple sugars).

There is a wide range in digestible energy (DE) and NSC among common horse feeds. Typically, the NSC content is lowest in straw and mature hays. Legume hays are usually higher in NSC than grass hays and cereal grains have the highest concentration of NSC. Molasses is also high in NSC, containing a level between corn and barley, but its overall DE content is lower because it contains 25% water.

As a rule, the lower the cell wall content of a feed, the higher the NSC and energy density. This is because horses digest over 95% of the NSC and typically only about 40 to 50% of the cell wall. There are certain feedstuffs, however, that contain much more digestible cell wall such as beet pulp and soy hulls. These “super fibers” have digestible energy values that are intermediate between hays and cereal grains.