The aims of the studies were to evaluate the nutrient status of local and improved scavenging hens in different seasons and locations by crop content analysis (Paper I), and the effects of scavenging and supplementing energy, protein, lysine and methionine on feed intake, performance, carcass quality and economic efficiency of different breeds of growing chickens and laying hens (Paper II, III and IV). In Paper I, the nutrient, metabolisable energy (ME) and amino acid intakes of scavenging Ri (local) and Luongphuong (improved) hens from scavenging feed resources (SFR) were estimated to be about 50 % higher for the rainy season compared to the dry season, and significant differences were found between breeds and locations. In Paper II, III and IV, the nutrient intakes from SFR were estimated to be at least 12 and 31 % of the nutrient intakes of confined growing and laying chickens, respectively. Supplement feed conversion ratios (FCR) and feed cost (FCS) were reduced by 12 to 36 % for scavenging chickens compared to confined chickens, depending on production type. Feed intake, performance and economic efficiency of scavenging local and improved laying hens were not significantly different among diets with supplementation of energy (maize meal only) compared to the control diet. However, protein supplementation (soybean meal only) reduced feed intake and performance of both local and improved hens, which indicated that energy supplementation was more important than protein for scavenging hens in Northern Vietnam. Lysine and methionine supplementation of diets for growing chickens reduced the supplement FCR and FCS by 12 and 16 %, respectively, and improved performance and carcass quality. The production performance of scavenging pullets and laying hens was not affected by replacing soybean meal (SBM) with cassava leaf meal, and fish meal with SBM in the diets of scavenging chickens. It is concluded that scavenging chicken systems are sustainable and economical for both local and improved chicken breeds in Northern Vietnam. Economic benefits were 12 to 36 % higher compared to total confinement, and locally available feed resources such as cassava leaf meal can be used as supplements for scavenging chickens.
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