Effect of type of feed formulation and dietary protein levels on performance and carcass characters of broiler chickens

Effect of type of diet formulation (diet with corn and soybean or control diet، diet with wheat، barley and agricultural byproducts balanced for sulfur-containing amino acids، total lysine and threonine and a diet similar to second diet with balanced digestible amino acids) and different levels of dietary protein (recommended level of Cobb company، 10 and 20 percentages lower than the recommended level) were studied on performance and carcass characteristics of broilers within a 3×3 factorial experiment with four replicates and 360 broiler chicks. Effect of formulation type was significant (P<0. 05). Feed intake and body weight of chicks used diets with balanced amino acids were lower than those in control group (4272 g vs. 4445 g and 2156 g vs. 2254 g). Effect of crude protein level was significant on body weight and feed conversion ratio (P<0. 05). Body weight was decreased from 2357 g to 2025 g and feed conversion ratio was increased from 1. 9 to 2. 2 along with decrease in dietary protein level. Percentages of edible carcass parts and breast were greater in control (76 and 26%، respectively) than those for two other formulations (P<0. 05). Percentages of thigh، abdominal fat and giblet were lower in recommended protein level group (20. 6، 2. 1 and 3. 8، respectively) than other levels (P<0. 05). In general، the use of diet based on agricultural byproducts balanced for digestible amino acids was recommendable for improving performance، but decrease in dietary protein level could decline performance.