Cassava leaves as protein source for pigs in Central Vietnam

Abstract

The aim of the studies described in this thesis was to evaluate the use of cassava leaves as protein sources for pigs when used at high levels in the diet, either in fresh form or with simplified methods of processing. In twenty cassava varieties taken from the upper part of the plant at the root harvesting, the crude protein varied from 23.7 to 29.5 % in DM and the HCN from 610 to 1840 mg/kg DM. Chopping, washing and wilting the leaves are simple ways to process the. There was a 58% reduction in the HCN content of the cassava leaves after wilting 24 hours in the shade. Washing alone or washing after chopping the leaves reduced slightly (by 16 and 21%) the HCN level. The pink colour in the pig's urine observed when fresh cassava leaves were fed, was no longer visible when the leaves were washed prior to feeding. Wilting for 24 hours after chopping and washing reduced the HCN 82%. The intake of cassava leaves accounted for over 30% of the total DM intake resulting in intakes of HCN of 373 and 337 mg/day with washed and chopped / washed leaves, compared with 146 mg/day for the wilted leaves. Reported toxic levels of HCN (mg/kg live weight) for pigs range from 1.4 and 4.4 mg/kg. In the present study the HCN intakes were much higher (from 6.0 to 15 mg/kg live weight) yet no signs of toxicity were observed. That factors other than HCN, were the limitations of cassava leaves as a protein source for growing pigs was evident in an experiment where ensiled cassava leaves replaced fish meal in a diet. The apparent digestibility of the crude protein and the nitrogen retention showed a linear decrease as the ensiled cassava leaves replaced the fish meal. The ileal and total tract digestibility of cassava leaves compared with duckweed, sweet potato vines and stylosanthes leaves. There were negative relationships between crude fiber levels in the diets and total tract and ileal digestion of organic matter, crude protein and crude fibre. Effect of different levels of DL-methionine (0, 0.1 or 0.2% in diet DM) on growth performance of pigs given diets with fresh or ensiled cassava leaves. Growth rates were higher, and DM and crude protein conversion rates tended to be better, for fresh compared with ensiled cassava leaves. With both sources of leaves, live weight gains and DM conversion improved linearly with level of DL-methionine. The overall conclusions from the studies reported in this thesis are that the limiting factors in cassava leaves as protein sources for pigs are not the cyanogenic glucosides, but other factors which result in decreased availability, and/or biological value of the protein component