This experiment was focused on determining the potential outcomes of feeding varying levels of CP and net energy (NE) on live performance and carcass traits during the finisher phase (31–41d) in Cobb 500 broilers. The NE formulation in poultry may provide better accuracy in terms of energy values of ingredients. In NE equations, heat increment is utilized, and thus positive results may be achieved, such as better energy efficiency and utilization, in addition to avoiding dietary energy misuse. Amino acid formulations at proper levels are known in poultry for improving muscle growth, performance, and reducing environmental damage. Cobb 500 fast feathered broilers(2,304) were vent-sexed and randomly allocate to a tunnel- ventilated house containing 96 pens (6 x 8 feet). Each pen had 24 birds (12 per sex) which were fed to 12 different experimental diets. Primary breeder recommendations for management of lighting, ventilation, and temperature, were strictly followed, while water and feed were provided ad libitum. A 3×4 factorial arrangement was designed and the 12 experimental diets (8 replications each) were: 1) 2,250 kcal/kg NE, 16% CP; 2) 2,300 kcal/kg NE, 16% CP; 3) 2,350 kcal/kg, 16% CP; 4) 2,400 kcal/kg, 16% CP; 5) 2,250 kcal/kg NE, 18% CP; 6) 2,300 kcal/kg, 18% CP; 7) 2,350 kcal/kg, 18% CP; 8) 2,400 kcal/kg, 18% CP; 9) 2,250 kcal/kg, 20% CP; 10) 2,300 kcal/kg, 20% CP; 11) 2,350 kcal/kg, 20% CP; and 12) 2,400 kcal/kg, 20% CP. All data were analyzed using a two-way ANOVA and a mixed model design, and the dietary treatments were set to pens in a randomized complete block design, whereas the location of the pens was the blocking factor. Pen was used as the experimental unit. No CP x NE interactions (P > 0.05) occurred on any live performance parameter (32–41d) or carcass trait (42d). Furthermore, increasing the dietary energy above 2,250 kcal/kg NE did not ameliorate carcass characteristics. However, birds fed increased NE obtained improved feed conversion ratio (FCR), and reduced feed intake (FI) (P<0.05). Broilers fed increased CP had improved FCR, and breast meat yield; additionally, they had decreased FI and abdominal fat deposition (P<0.05).
Therefore, more research must be done to assess NE responses and energy needs on modern broilers, in order to comprehend the relationship between formulation on NE basis and CP.