The cassava plant contains 2 glycosides, linamarin (80% of total glycoside) and lotaustralin (20%), which are acted upon by a cell-wall enzyme to liberate hydrogen cyanide (HCN), which is lethal to animals. HCN concentrations depend on cultivar, environmental conditions, plant age, number of harvest (for the foliage) and on the organ considered. While there is a continuous gradient of HCN content between varieties (Peroni et al., 2007), cassava varieties are usually divided into two groups:
Bitter varieties have roots containing 0.02-0.03% HCN (DM basis) and fresh leaves containing up to 0.2% HCN (DM basis) (Murugesrawi et al., 2006). Values up to 0.22% DM have been reported in fresh roots (Smith, 1988). These varieties have to be processed before being fed to animals.
Sweet varieties have roots containing less than 0.01% HCN and fresh leaves containing about 0.1% HCN (DM basis)(Murugesrawi et al., 2006). These varieties can be fed raw. Most commercial varieties belong to this group.
Bitter varieties often have longer and thicker roots than the sweet varieties, but there is no simple and safe method to assess HCN content.
Intensive use of cassava in animal feeding is possible after removal of the cyanogenic glucosides. It is generally assumed that roots containing less than 0.01% (100 mg/kg) of HCN in the DM are safe for use in animal diets (Buitrago et al., 2002b). Hydrogen cyanide is easily destroyed by simple treatments and many detoxification processes have been tested. Drying or ensiling cassava roots are the main processes for detoxification and storage (Gomez et al., 1988b; Tewe, 1992). In South America, ground cassava roots are put in nets, and then washed and squeezed until the toxic substance is eliminated. The toxic elements can also be removed by cooking, or by drying slices of the roots for about two weeks. Sun-drying appeared to be more efficient than oven-drying (60°C) (Panigrahi et al., 1992; Tewe, 1992).
The presence of HCN makes cassava products insect-resistant and easy to store. Adding 15% cassava root meal to a concentrate feed also improves its resistance to pests (Göhl, 1982).