3. Effect of variety and wilting on HCN content of cassava leaves and on intake, digestibility and N retention by growing pigs
Authors: Chhay Ty, T R Preston* and Khieu Borin
*UTA (Colombia), AA #48, Socorro, Santander, Colombia
Abstract: Two experiments were carried out to study the effect of duration of wilting (0, 24 or 48 h) on HCN content of leaves from "sweet" and "bitter" varieties of cassava and on their nutritive value for pigs as measured by digestibility and N balance. In the first experiment, the duration of wilting was 0, 24 or 48 h. In the second experiment, the leaves from the bitter and sweet varieties were fed to pigs, either fresh or after 24 h wilting, as the only supplementary source of protein in diets based in broken rice and sugar palm juice.
The bitter variety was higher in DM, N and HCN than the sweet variety. However, there were significant interactions between variety and time of wilting. DM increased and HCN decreased at a faster rate in the bitter than in the sweet variety. Wilting cassava leaves for up to 48 h reduced HCN content to minimal values, the rate of decrease being more pronounced in the bitter than in the sweet variety, with no differences between varieties after 48 h. There were no differences in the nutritive value for pigs, between bitter and sweet varieties, nor were there benefits from wilting for 24 hours, as measured by apparent digestibilities of DM, crude protein and crude fibre, and by N retention. The fresh cassava leaves provided about 20% of the diet DM, which resulted in HCN intakes of from.
3.08 to 3.19 mg/kg LW for the diets with fresh cassava leaves, and from 1.85 to 2.16 when the leaves were wilted 24 h.
It is concluded that amino acid imbalance, levels of cell wall constituents and condensed tannins are more important than HCN levels in limiting the usefulness of cassava leaves for pigs.