While developing the detergent system of fiber analyses in forages, Van Soest observed that materials dried at high temperatures resulted in high fiber values and the fiber contained nitrogen which was difficult to remove with detergent or pepsin. From this observation, he developed the concept that detergent could be used to partition protein into fractions that vary in their digestibility and availability in the rumen. This naturally occurring ADIN probably is the truly indigestible protein in feeds. Van Soest suggests that the difference between NDIN and ADIN represents the protein that is slowly degraded in the rumen but is digested in the intestines. It should be recognized that heating can have both positive and negative effects on protein utilization by the animal.
Heating generally results in lowered digestibility of protein.
The following equations are applicable for the estimation of energy in forages for ruminants. Prediction of energy availability from laboratory analyses usually requires specific equations for each type of feed. The accuracy of energy predictions is a function of the accuracy of laboratory analyses and the accuracy of the animal experimentation used to develop the prediction equation. Digestibility and energy value can be measured under a variety of conditions that influence the values that are obtained. Compared to cattle, sheep will obtain different digestibilities for the same feed.