The Digestibility and Interrelationships of Various Carbohydrate Fractions of Pasture Herbage and a Resolution of the Components of Crude Fiber and Nitrogen-Free Extract

The system of proximate analysis which was introduced by Henneberg in 1863 involves the determination of crude protein, crude fiber, nitrogen-free extract, ether extract, and ash and is still used today in essentially the same form as that first introduced (2). Undoubtedly, the measurement of crude fiber and nitrogen-free extract was an attempt to divide the feed constituents into digestible and indigestible portions. Any portion of a feed-stuff that could not be extracted or dissolved by successive treatments with weak acid and weak alkaline solutions was intended to represent the indigestible portion. Actually the nitrogen-free extract fraction contains portions of relatively indigestible materials, such as lignin, and the crude fiber fraction is digested to a very considerable extent by ruminants. Crampton (5) pointed out that in pasture herbage the crude fiber may be just as digestible and, often, even more digestible than the nitrogen-free extract.