الفهرس 
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Abstract
This study was conducted to evaluate the effect of the use of different ratio of lysine on the weight, feed conversion ratio, protein efficiency ratio, European production efficiency factor, some biochemical parameters and histological changes in broilers. 500 broilers (initial weight 160 g) 10 days, age were randomly divided into 5 groups (each one contained 100 chicks), each group subdivided into 4 replicate with 25 chicks.
At First Stage, the control group (group Control) has 23% CP with Lys. 1.44%; the second group (group 1) 23% CP with Lys. 1.54%; third group (group 2) 23% CP with Lys. 1.68%; forth group (group 3) 22% CP with Lys. 1.44%; fifth group (group 4) 21% CP with Lys. 1.44%.
While at Second Stage, the control group (group Control) has 21.5% CP with Lys. 1.29%; (group 1) 21.5% CP with Lys. 1.4%; (group 2) 21.5% CP with Lys. 1.53%; Gr3, 20.5% CP with Lys. 1.29%; (group 4) 19.5% CP with Lys. 1.29%
Then at Finishing Stage, the control group (group Control) has 19.5 % CP with Lys. 1.16%; (group 1) 19.5% CP with Lys. 1.3%; (group 2) 19.5% CP with Lys. 1.41%; (group 3) 18.5% CP with Lys. 1.16%; (group 4) 17.5% CP with Lys. 1.16%.
The results have shown that in the first period, the growth performance of the broilers was significantly improved with the groups (Gr4, Gr3 and Gr5) where it was 473.67, 471.33and 412.43 g, respectively.
While, the second and third periods, the productive performance in Table 4 showed that increasing the Lys concentration from 1.29% (group Control) to 1.4% (group 1) with standard requirement of methionine and CP in diet significantly improves the FCR and weight gain of the broilers was the best one, followed by group Control while group 2 (Lys 1.53%) came at the last in groups allotted with standard CP requirements, group 3 and group 4 with less CP and standard Lys content had less body weight gain than the other groups.
from the obtained results, broilers that had a lower level of CP consistently gave depressed BWG and FI, especially after 21-day-old chicks. As the weight of the broilers was significantly reduced in diets with reduced levels of lysine, and the effect of methionine is less evident on the growth performance of the broilers (Lee et al., 2020). Overall, Gr1 supplemented with additional lysine with the standard methionine level and CP diet gave the best results in terms of FCR.
In the present study supplementation with excess of Lys (20%, Gr2) resulted in depression in BW gain (P ≤ 0.05), while feed consumption remained unchanged and FCR increased.
Concerning serum biochemical parameters, excesses of Lys had no significant effect on total protein, urea and creatinine levels. This result showed that amino acid excesses had no significant effects on total protein and creatinine levels in broiler chicks.
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