Effect of chopping and wilting on HCN content Determinations were made of dry matter (DM), crude protein and HCN according to AOAC (1990) procedures. Samples of leaves were taken at the time of root harvest (180 days) from the tender green leaves at the top of the stem. Cattle manure was applied at 800 kg/ha prior to planting. Cassava stem cuttings were used as planting material at 50*30 cm spacing between rows and cuttings. The experimental design was a randomized block with plots of 2*5 m and three replications of each variety. Twenty varieties of cassava were grown under the same condition in the research garden of the Crop Production faculty in Hue university. Materials and Methods Effect of age of leaves on chemical composition The use of simpler methods of processing the fresh leaves, such as chopping, washing and / or wilting would facilitate the use of cassava leaves as animal feed. However, sun-drying is difficult when cassava leaves are harvested in the wet season and ensiling is labour-intensive. Many researches have demonstrated that the HCN content in leaves can be reduced by sun-drying (Bui Van Chinh and Le Viet Ly 2001) and ensiling (Ly and RodrÃguez 2001). The cyanide levels in leaves are influenced by genetic, physiological, edaphic and climatic differences with the stage of maturity being perhaps the major source of variation (Ravindran 1995). The main limiting factor to the use of cassava leaves as animal feed is the presence of cyanogenic glucosides, which give rise to hydrocyanic acid (HCN) when the plant tissue is broken down by processing or during ingestion by animals. In recent years, attention has been focused on the leaves as feed for ruminants (Preston 2001 Wanapat 2001) and pigs (Bui Huy Nhu Phuc et al 2001). Traditionally the crop is grown for the roots, which are used as human and animal food and industrially as a source of starch. Cassava (Manihot esculenta, Crant) is cultivated in Viet Nam in an area exceeding 250,000 ha (Bui van Chinh and Le Viet Ly 2001).
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