Effects of low dietary energy, with low and normal protein levels, on broiler performance and production characteristics

The study was conducted to investigate the effect of low metabolizable energy diets with normal or narrow metabolizable energy to crude protein ratios (ME:CP) on performance, carcass characteristics, body composition and blood parameters in broilers fed from 1 to 42 days of age. The chicks were divided into 7 groups. The birds were fed starter & grower diets. Seven experimental diets were formulated in each phase; one control and 6 tested diets. The control diet was formulated according to the NRC of poultry (1994) and the other six diets fed three different levels of low energy diets (2900, 2700 & 2500 kcal/kg; one level for each 2 groups). The first three tested groups named ''normal calorie-protein ratio” groups in which the CP decreased in proportion to the decrease in ME, keeping the normal NRC ratio. In the second three tested groups, termed “narrow calorie-protein ratio” groups, the dietary protein was kept at the NRC levels leading to ratios narrower than that of the NRC. Results showed that chicks fed low ME diets with normal energy to protein ratio had lower body weight and feed utilization efficiency than the chicks fed the control diets. While, birds fed the low ME diets with normal protein NRC-levels and narrow ratios had nearly equal weight and feed conversion to the control. The body composition and carcass characteristics were not affected by the dietary treatments. Moreover, the blood parameters had no significant variations among the groups, except for total protein, ALT and AST which had an increased response to decreased dietary energy density. In conclusion, decreasing the dietary ME level without decreasing the crude protein level was more efficient economically and had no any adverse effect on the performance. However, decreasing of dietary ME with normal ME:CP ratio resulted in decreased performance and low economic efficiency.