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 withnormal 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 42days 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. Thecontrol diet was formulated according to the NRC of poultry (1994) and the other six dietsfed three different levels of low energy diets (2900, 2700 & 2500 kcal/kg; one level for each 2groups). The first three tested groups named ''normal calorie-protein ratio” groups in whichthe CP decreased in proportion to the decrease in ME, keeping the normal NRC ratio. In thesecond three tested groups, termed “narrow calorie-protein ratio” groups, the dietaryprotein was kept at the NRC levels leading to ratios narrower than that of the NRC. Resultsshowed that chicks fed low ME diets with normal energy to protein ratio had lower bodyweight and feed utilization efficiency than the chicks fed the control diets. While, birds fedthe low ME diets with normal protein NRC-levels and narrow ratios had nearly equal weightand feed conversion to the control. The body composition and carcass characteristics werenot affected by the dietary treatments. Moreover, the blood parameters had no significantvariations among the groups, except for total protein, ALT and AST which had an increasedresponse to decreased dietary energy density. In conclusion, decreasing the dietary ME levelwithout decreasing the crude protein level was more efficient economically and had no anyadverse effect on the performance. However, decreasing of dietary ME with normal ME:CPratio resulted in decreased performance and low economic efficiency.