effect of various levels of protein in diet based on total and digestible amino acids on performance of cobb strain broilers

in order to study the effects of various levels of protein in diet based on total and digestible amino acids on performance and carcass traits of broilers, an experiment was conducted as a completely randomized design with 288 broiler chicks from cobb 500 strain in 6 treatments, each treatment consist of 3 replicates with 16 chicks per replicate. treatments were the diets as follow: 1) diet formulated based on digestible amino acids which has 1% less crude protein (cp) than cobb 500 recommendation (2006); 2) diet formulated based on digestible amino acids with cp similar to cobb 500 recommendation; 3) diet formulated based on digestible amino acids with 1% higher cp than cobb 500 recommendation; 4) diet formulated with total amino acids with one level lower than suggested protein level in cobb 500 recommendation; 5) diet formulated with total amino acids with suggested protein level in cobb 500 recommendation and 6) diet formulated with total amino acids with one level lower than suggested protein level in cobb 500 recommendation. the metabolizable energy was considered constant and diets were fed to birds during 42 days of experiment. daily weight gain, feed consumption, feed conversion ratio, breast meat yield and abdominal fat content were measured. at the end of experiment, 4 chickens (2 males and 2 females) from each treatment was randomly selected and killed and their carcasses were analyzed. results indicated that formulating ration`s protein based on total amino acids for cobb 500 broilers shows better performances than digestible amino acids.