الفهرس 
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Abstract
Two experimental feeding trials were conducted to visualize the impact of practical application of reduced levels of CP (experiment 1) and/or metabolizable energy (ME) levels (experiment 2) in diets formulated on ideal amino acid profile basis on performance parameters egg weight ( EW ), Average weight gain (AWG), hen day egg production % (HDEP %) and egg mass (EM)), egg quality traits, health status and immunity as well as the economic efficiency of these diets in Bovans - Brown laying hens during the first phase of production. In the first trial, a total of 480 laying hens (22 up to 40 weeks of age) were randomly assigned in to 3 groups (CG18, G16 and G14) each of 8 replicates (20 bird / replicate) in a random block design. Birds received diets of 18, 16 and 14% dietary CP levels, respectively. Results revealed that there were no significant differences (P > 0.05) among dietary treatments in most of performance parameters (HDEP%, EW) as well as EM (g/hens), egg quality traits (shell thickness (ST), albumin height (AH), albumin weight (AW) and Haugh unit as well as antibody titer against Newcastle disease virus (NDV). It was also observed that reduced CP – amino acid balanced diets (16% & 14%) were more cost effective than commercially available diet (18% CP). In the second trial, a total of 480 commercial Bovans – Brown laying hens were used during the first phase 1 of egg production (24-40 weeks of age).Based on a 3×2 factorial arrangement, birds were randomly assigned to one of six dietary treatments (CG18, G18, G16, G16L, G14, and G14L) in a random block design. Each group consisted of 4 replicates (20 bird / replicate).Experimental diets consisted of 2 intakes of dietary ME levels (2810 and 2710 Kcal/kg)) and 3 intakes of dietary crude protein levels (18%, 16% and 14%). Results revealed that no significant differences (P > 0.05) were observed among dietary treatments in most of performance parameters (AWG, EW as well as EM) and egg quality traits (egg specific gravity (ESG), AW, albumin index (AI) and yolk weight (YW)). Moreover, the least cost diet with the highest net revenue and economic efficiency % was achieved for the reduced CP diet that contained 14% CP and 2810 Kcal/Kg ME. In conclusion, reduced crude protein – amino acid balanced diets may be used as a reliable tool in egg production industry and may have beneficial effects if applied probably in laying hens nutrition.