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Ensiling or sun-drying of cassava leaves has been considered to
be essential, before using the leaves as a protein source for pigs,
in order to reduce the risk of HCN toxicity due to the presence of
cyanogenic glucosides. However, even after processing the leaves
and reducing the HCN levels it has been found that growth
performance and feed conversion ratio deteriorate when the level of
the leaves exceeded 10 to 15% of the diet on DM basis.
The hypothesis underlying a series of experiments carried out by
the authors was that factors other than HCN toxicity were limiting
pig performance with high levels of cassava leaves in the diet. In
the first experiment, eighteen crossbred castrated male pigs (11 to
14 kg initial weight) were fed a basal diet of broken rice
supplemented with fresh cassava leaves, water spinach, or a mixture
[50:50 on a fresh weight basis] of the two. The growth and
conversion ratios were 50% better for the diets with water spinach
alone, and in the mixture with fresh cassava leaves, compared with
fresh cassava leaves alone. On all diets the foliages supplied
between 65 and 75% of the total protein. On the diet with the 50:50
mixture of fresh cassava leaves and water spinach, intakes of HCN
were 4.96mg/kg live weight which is more than was considered to be
the lethal dose in pigs (from 1.5 to 4.4mg/kg live weight). However,
daily gains rates on the 50: 50 diet were the same as on the diet
without cassava leaves.
In the second experiment, 10 to 30% of fresh cassava leaves were
replaced by water spinach. At all levels the intake of HCN was
within the range reported to be toxic, yet no toxicity symptoms
were observed. However, the same positive synergistic effects from
combining the two sources of protein-rich leaves as supplements to
a low protein basal diet for growing pigs were observed. It is
concluded: (i) that factors other than the content of cyanogenic
glucosides are the limiting factors in the use of cassava leaves as
a protein supplement for growing pigs; and (ii) fresh cassava
leaves can be fed with no risk of toxicity even at levels
equivalent to 50% of the diet DM.