This study was conducted to determine the effect of low or high protein
diets with constant ME on growth performance, carcass characteristics, digestibilities and
blood parameters of Cobb Avian 48 broilers from 1 to 34 d of age. A total number of 2080
one-day-old chicks were housed randomly in 16 pens and divided into two experimental
groups, each group divided into 8 replicates and each replicate has 130 birds/ pen. All birds
were fed pre-starter diet (CP, 23% and ME, 2950 kcal/kg) for 4 days then the birds were
divided into two experimental diets which were formulated to have 2 levels of CP
respectively, in each phase: 22 and 21% CP with 3050 kcal/kg in the starter phase (5 to 10
d); 20 and 19% CP with 3100 kcal/kg in the grower phase (11 to 25 d); and 19 and 18% CP
with 3180kcal/kg in the finisher phase (26 to 34 d). Digestible Lysine was maintained at
1.22, 1.12, and 0.96% of the diet in the starter, grower, and finisher periods, respectively.
Body weight gain, feed intake and feed conversion as well as thigh and liver weights were
not influenced by changing protein level in the diets. However, carcass weight and breast
muscle weight were increased significantly (P≤ 0.05). On the other hand, abdominal fat
weight was deceased (P≤ 0.05) by feeding low protein diet. Although, dry matter and crude
fat utilization were not affected, while, crude protein and crude fiber utilization were
improved by feeding low protein diets. Plasma GOT, GPT and total cholesterol were not
changed, while; plasma HDL was increased by feeding low protein diets. Furthermore, it
was observed a decrease in muscle and liver MDA by feeding low protein diets, indicating
the improving of the anti-oxidative activities by decreasing the protein content in broiler
diets. Economic efficiency was improved by feeding low protein diets compared to high
protein diets. In conclusion, feeding Cobb Avian 48 broilers on 1% lower protein diets than
the strain recommendation, at constant ME, with the same amino acids levels had not
adversely affected the growth performance, carcass parameters and liver functions, while;
dietary crude protein and crude fiber utilization were improved.