الفهرس 
2.1. System approachOnly 14 pages are availabe for public view
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Abstract
This study was conducted to evaluate the productive and economical performance of three commercial layer strains (Hy-Line Brown, Lohman Brown and Bovans Brown) kept under two different production systems (semi-closed and closed) in AL-Sharkia and AL-Gharbia governorates. Productive data were weekly obtained all over the production periods and analyzed to 52 weeks of production and also at the end of production cycles for each farm. While, economical data were measured and analyzed at the end of production cycles after sealing the flocks. Under semi-closed system, results indicated that Bovans Brown and Hy-Line Brown layers had significantly better age (day) at 50% of production, mortality percentages, feed conversion (g /egg), hen day egg production percentages (HD), hen housed egg production percentages (HH) and numbers and finally production efficiency coefficient compared to Lohman Brown layers to 52 weeks and the end of production cycles. On the other hand, Lohman Brown layers kept under closed system recorded the best age (day) at 50% of production, mortality percentage, hen day percentage, hen housed egg number, and of course production efficiency coefficient value all over the production period whencompared with others under semi-closed system in AL-Sharkia governorate. Under closed system age (day) at 50% of production, feed conversion (g /egg), hen day percentages, and production efficiency coefficient for Bovans Brownlayers were significantly affected by different pad cooling systems to 52 weeks and the end of production cycles. Moreover, egg production (HD %) was significantly affected by different ambient temperature degrees of house’s parts and pad cooling systems. Results showed that HD % for Hy-Line Brown layers was significantly affected by season of the year, house’s parts and even battery liens location inside the semi-closed houses in AL-Gharbia governorate. Hy-Line layer’s production performance was not significantly differed between AL-Sharkia and AL-Gharbia semi-closed system farms. Whereas, Bovans strain of AL-Gharbia governorate showed better egg production performance than Lohman strain of AL-Sharkia governorate under closed system. Egg production performance of layers kept under the same conditions was significantly affected by layer’s strain. Economical results confirmed that Bovans Brown layers had better hen’s revenue, net profit, gross margin, revenue attributed to variable costs, revenue attributed to total costs, followed by Hy-Line and Lohman layers under semi-closed system. Lohman Brown layers under closed system showed better economical performance than others under semi-closed system in AL-Sharkia governorate. It could be noticed that Hy-Line layers of AL-Gharbia governorate were more economically efficient when compared with others in AL-Sharkia governorate under semi-closed system. The same trend was found when comparing Bovans Brown layers under closed system in AL-Gharbia governorate with others under semi-closed system in AL-Sharkia governorate. Generally, commercial table egg production layers of Brown strains (Hy-Line, Lohman and Bovans) showed more productive and economical efficiency when kept under closed system farms than semi-closed system farms under Egyptian conditions.