Effect of replacing soybean protein with cassava leaf protein in cassava root meal based diets for growing pigs on digestibility and N retention

The nutrient and HCN contents of cassava leaves from six varieties of cassava growing in south Viet Nam were analysed and three balance experiments were performed with growing pigs to evaluate the digestibility and nitrogen utilisation of cassava root meal based diets with increasing levels of replacement of the protein from soybean meal (SBM) by the protein of cassava leaves. In Experiment 1 cassava leaf meal (CLM) replaced SBM in the proportions 0, 0.35, 0.70 and 1.00 of the crude protein (CP); in Experiment 2 ensiled cassava leaves (ECL) replaced SBM in the proportions 0, 0.15, 0.30 and 0.45 of CP and in Experiment 3 CLM replaced SBM in the proportions 0, 0.15, 0.30 and 0.45 of the CP. contents of the cassava leaves ranged from 240 to 350 g/kg, and the crude fibre (CF) contents from 100 to 150 g/kg on a dry matter (DM) basis. The HCN content was markedly reduced by both sun-drying and ensiling, with the reduction being higher after sun-drying. parent digestibilities of organic matter (OM), CP, ether extract and CF decreased linearly (P<0.001) with increasing levels of inclusion of cassava leaves in the diet. The amount (g/day) of total nitrogen retained and the proportion of nitrogen utilised (proportion of N digested) decreased (P<0.001) with increasing levels of inclusion of cassava leaves in the diet. The digestibility coefficients of OM, CP and CF were calculated to be 0.49, 0.51 and 0.44 and 0.52, 0.51 and 0.59 in CLM and ECL, respectively.