Effects of different levels of dietary metabolizable energy and protein on growth performance, energy and protein efficiency ratios and immunity system response of Ross 308 broilers

In order to investigate the effects of different levels of dietary metabolizable energy (ME) and protein (CP) on growth performance, energy efficiency ratio (EER), protein efficiency ratio (PER), and immunity system response of broilers, a total of 640 Ross 308 broilers were used in a 2×2×2 factorial arrangement with completely randomized design including 8 treatments, 4 replication and 20 chicks in each replication. The increasing of ME with lower level of CP (22%) decreased ME and CP intakes up to 21 day of age and then the rising of CP level (24%) increased ME and CP intakes up to 42 day of age. The FCR of males improved inconsiderably by increasing of dietary ME level but the ME and CP intakes were slightly higher and females had higher EER and PER at 35 day of age. The antibody titer against SRBC enhanced by increasing of dietary ME level. The concentration of HDL and heart weight were higher in males. Enhancing of ME led to an increase in nitrogen excretion and higher protein level (24%) caused decrease in intestine weight. Therefore, the increasing of ME and CP up to the 3rd week and then the decreasing of CP up to the end of production period is recommended to optimize ME and CP intakes and improving EER and PER.