Two hundred day-old unsexed broiler (Cobb 500) chicks were
randomly distributed to four groups. The first (control) group was fed
on starter (22% CP, 3100 Kcal/kg ME, 1.10% Lysine, and 0.48%
Methionine) and finisher (20% CP, 3200 Kcal/Kg ME, 0.90% Lysine,
and 0.35% Methionine) diets. The other three groups were fed on
three starter and finisher isocaloric isonitrogenou diets with 2% lower
protein content than the diets of control group with addition of graded
levels of L-lysine HCl and DL-methionine to give 120%, 140%, and
160% of the NRC (2000), At the end of starting period, the increased
Lysine and Methionine content of the low-protein starter's rations
didn't affect body weight and gain but increased the feed consumption
and decreased the feed conversion ratio of the birds. At the end of
finishing period, body weight, body gain, feed intake, and breast meat
yield increased significantly with the increasing of synthetic amino
acids in the diets, while the best feed conversion ratio was obtained
with 120% amino acids level. Plasma uric acid level increased with feeding broiler on low protein diets and with increasing of synthetic
amino acids supplementation to the diets. Plasma Creatinine
increased in the birds fed on low-protein diet supplemented with the
highest synthetic amino acids level (160%). Plasma Calcium wasn't
affected by the treatment while phosphorus increased in the birds fed
on low-protein, DL-Methionine and L-lysine supplemented diets
compared with the control group, which might be as indicator for
enhanced growth of these groups. It could be concluded that the
minimum levels of protein (20% and 18% for starting and finishing
periods, respectively) in the broiler's diets supplemented with 120% of
NRC requirements for Lysine and Methionine requirements ensure an
optimum body weights, body gains, and feed conversion ratios with
reduced plasma level of Uric acid but were inadequate to produce the
highest breast meat yield.