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Cassava leaves collected from a high-yielding variety after 60 days of growth and at root harvest (180 days) were wilted for 24 hours for determination of changes in the DM and HCN content. The HCN level was reduced by 58% after 24 hours with no difference between the two sources of leaves.In a comparison of three processing methods (washing, wilting and ensiling) the HCN level in cassava leaves from a high-yielding variety was reduced by 19% by washing, 74% by wilting for 24 hours and 76% by ensiling for 21 days.
Three simple methods to reduce HCN content of cassava leaves before feeding (washing, chopping and washing; and chopping, washing and wilting) were compared in a feeding trial with 6 pigs of 25 kg mean live weight (3 Mong Cai and 3 F1 [Large White X Mong Cai]) in a double Latin square arrangement (2[3*3]) with 21-day periods. The leaves were offered ad libitum in one feed trough with a mixture of ensiled cassava roots and rice bran (2:1 fresh basis) at 80% of ad libitum level in a separate trough.
The fresh cassava leaves were readily consumed, providing 38% of the dietary DM and over 70% of the dietary protein, with no effect of processing method on total DM intake, which ranged from 27 to 31 g/kg live weight. Levels of HCN were reduced slightly (16%) by washing and substantially (82%) by wilting, resulting in intakes of HCN between 6.0 and 15 mg/kg live weight, levels considerably higher than previously reported as safe to avoid toxicity (1.4 to 4.4 mg/kg live weight). There were no apparent symptoms of HCN toxicity.
12 crossbred (Large White x Mong Cai) pigs with an average initial weight 27.2 kg ± 2.71 kg were allocated to 4 treatments in a random design with one pig per pen. Three test diets (with 0, 0.1 and 0.2% DL-methionine) contained fresh cassava leaves (20% in DM) replacing fishmeal on equal protein basis. The control diet contained 15% fish meal. After 80 days the live weight gain on the treatment with cassava leaves and 0.2% DL methionine was higher and feed conversion better, than for other levels of DL-methionine, and similar to the control.
It is concluded that fresh cassava leaves, chopped and washed before feeding, can be included in ensiled cassava root / rice bran diets for growing pigs at levels of up to 40% of the diet DM, and as the sole source of supplementary protein. Adding 0.2% methionine to a diet with 50% cassava leaves improved the live weight gain and feed conversion ratio.