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Pig production in Vietnam is an important part of small farming systems, and the main feeds for pigs are rice bran, maize, cassava meal and vegetables, which are rich in energy but low in protein and essential amino acids. The conventional protein supplements in the region are soybean meal, groundnut cake and fishmeal, but they are relatively expensive and not available in village conditions. It is very important to identify local protein resources especially those that can be produced on the small farm. Cassava (Manihot esculenta Crantz) is the second most important food crop, and new high-yielding varietie, such as KM60, KM94 and KM98, and more sustainable production practices have increased the economic effectiveness of cassava production, especially in the Central region. Cassava leaves have been used as a protein source for monogastric animals, but the high cyanide content can limit their use. Making silage is an appropriate method to preserve cassava leaves and reduce the toxicity of HCN, and is also easy to apply under village conditions, especially during the wet season. Additives used in ensiling process, such as rice bran, cassava root meal are available in village conditions. It was found that the inclusion of rice bran or cassava root meal at levels 5 or 10 % produced good quality silage that could be stored for at least five months. The HCN content of ensiled cassava (KM94) leaves decreased very quickly during the first 30 days, and the HCN content was only from 10.4 - 13.2 % of the initial level at 90 days after ensiling. The inclusion of 15 % (as DM) ensiled cassava leaves (ECL) in diets for growing pigs improved daily gains and the feed conversion ratio (FCR) and reduced the feed cost by 25 %. In Huong Van commune the inclusion of 16 % ensiled cassava leaves (ECL) or dry cassava leaf meal (CLM) in the diet of growing pigs (as DM) had no statistically significant effect on live weight gain (LWG) or feed conversion ratio (FCR), but reduced feed cost by 12 - 16 % as compared to pigs fed a diet containing 16 % ensiled sweet potato vines (ESP). Another experiment was carried out in Huong Van commune to evaluate the effect of supplementation with synthetic amino acids (L- Lysine and DL – methionine) of a diet containing ensiled cassava leaves. Supplementation with L- lysine and DL - methionine significantly improved LWG, feed intake and FCR in diets containing CLM and ECL. The diet including15 % ECL (DM basis) with supplementation of 0.2 % lysine and 0.1 % DL – methionine, and 0.1 % lysine and 0.05 % DL - methionine at the 20-50 kg and 50 -90 kg growth stages, respectively, resulted in the highest economic efficiency and can be recommended for crossbred pigs. An experiment was conducted on farm in Huong Van village to determine the effect of different levels of ECL (KM94) in the diet on the performance of growing pigs. The four experimental diets included ECL (KM94) in the diets at 0 %,10 %, 15% and 20 % of DM. It was concluded that, 10 % to 20 % (of DM) of ECL (KM94) could be included in diets for growing pigs without affecting the animal's health or overall performance and carcass quality, and resulted in 8.0 - 13.8 % reduction in feed cost.
In conclusion, cassava leaves can be used as a protein supplement for feeding pigs, and ensiled cassava leaves in diet results in higher benefits to pig farmers in Central Vietnam. Ensiling is the best method for preserving cassava when the harvest of cassava coincides with the rainy season; the technique is simple, cheap and suitable for small farm conditions in central Vietnam.