A measurement of fibre content. Also known as Weende cellulose, crude fibre is the insoluble residue of an acid hydrolysis followed by an alkaline one. This residue contains true cellulose and insoluble lignin. It is also used to assess hair, hoof or feather residues in animal by-products. Even though the more accurate Van Soest analysis has superseded it since the 1970s, the analysis of crude fibre remains common in feed laboratories.