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Manihot esculentaCassava, manioc, tapioca, Brazilian arrowroot, yucaUseful reference: 90 Herbaceous shrub or small tree up to 4 m high with fingerlike leaves. Cultivated widely in the tropics and subtropics for its edible roots. One of the highest yielders of starch found in the tropics. TOXICITY Cassava roots must be processed very carefully as they contain a glucoside, linimarin, which is acted upon by an enzyme to liberate prussic acid. The peeled roots contain much less prussic acid than unpeeled roots because most of the prussic acid is in the skin.
2. Sweet varieties with roots containing less than 0.01% prussic acid. These can be used raw for feeding. Most commercial varieties belong to this group. The prussic acid content depends not only on the variety, but also, and possibly even more, on soil conditions. Usually the bitter varieties have longer and thicker roots than the sweet varieties, but there is no simple safe method to judge the level of prussic acid in the roots. The Indians of South America place the ground cassava roots intended for human consumption in nets, and wash and squeeze them 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. Cassava root meal is not attacked by insects; the same is true, of feed concentrates to which 15% cassava root meal has been added. USE OF ROOTS Both fresh and dried cassava roots are consumed by ruminants in different forms (sliced, chopped, ground). Dried cassava roots have given satisfactory, results as the principal energy source for dairy cattle, intensive beef fattening and lamb growth. Cassava can replace almost all of the grain in the diets with little reduction in performance. Inclusion levels of up to 65%, preferably pelleted, do not seem to affect health, carcass quality or overall performance when the diets are carefully balanced. Palatability can be enhanced by the addition of molasses if pelleting is not possible. Complete replacement of grain by cassava root meal in layer feed has yielded similar egg production, although egg weight was significantly reduced (a sign of methionine deficiency). Supplementation with methionine has yielded similar results to grain controls. It should be noted that, besides methionine supplementation, careful control of energy-protein ratios is necessary for satisfactory results. The effect of methionine may be attributable to improvement of the protein quality as well as to the utilization of the methionine sulphur in the detoxication process. For unknown reasons cassava meal seems to cause health problems when included in turkey rations. LEAVES It is possible to obtain from cassava more than 6 tons of crude protein per hectare a year with the proper agronomic practices directed toward foliage harvesting. Cassava leaf and stem meal has been used at the 35% level in dairy cow concentrates to advantage. Cassava bushes can be harvested as forage when they are three to four months old. They are cut about 40 cm from the ground and chopped in small pieces by hand or in a stationary forage chopper. The forage has been used to provide by-pass protein to ruminants fed urea and molasses. The intake of cassava forage was about 5 kg per day, and about two months of adaptation was required before full production was obtained. In poultry rations the replacement of as little as 5% of the lucerne meal with cassava leaf meal significantly reduced broiler weight gains; however, the inclusion of methionine and vegetable oil additives in rations consisting of up to 20% cassava leaf meal practically eliminated the depression in response. SILAGE The whole cassava plant (including root and aerial part) can be chopped and ensiled in simple pit silos for dry-season feeding at the village level. Simple equipment is required both for harvest and preparation of the silage. The silage is fairly well balanced for ruminants. CASSAVA POMACE Often called cassava meal, pomace is the residue from the extraction of starch from cassava roots. Cassava roots yield approximately equal amounts of starch and pomace, which have less feed value than cassava root meal but can be included in rations for cattle. Starch and pomace are extensively used for pigs in Southeast Asia, where they are regarded as a valuable feed. Up to 10% has been used in poultry rations.
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