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Ensiling or sun-drying of cassava leaves
have been considered to be essential steps, before using cassava
leaves as a major protein source for pigs, in order to reduce the
risk of HCN toxicity due to presence of cyanogenic glucosides.
However, even after processing the leaves to reduce the HCN levels
it has been found that growth performance and feed conversion rate
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 on 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 fresh basic basis] of the two). The growth and conversion rates were 50% better for the diets with water spinach alone, or as a 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 diets with 50:50 mixture of fresh cassava leaves and water spinach, intakes of HCN were 4.96% of live weight which is more than was considered to be the lethal dose in pigs (from 1.5 to 4.4% of live weight). Yet growth rates on the 50: 50 diet were the same as on the diet without cassava leaves.
In a second experiment, replacement of
fresh cassava leaves by water spinach was from 10 to 30%. 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
to 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 leaves equivalent to50% of the diet DM.