The most important indigestible fraction of feed is derived from fiber. Among the fibers, the main source of indigestible fraction is the insoluble fiber; it can stay intact as it passes through the upper part of the intestinal tract, thereby locking in the nutrients (proteins, fat, phosphorus, etc…) present within the cell walls.
The insoluble fiber consists in a complex structural layer made up of pectin, hemi-cellulose, cellulose and lignin, for which animals lack the endogenous enzymes to digest them.
