الفهرس 
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Abstract
This work was conducted at the poultry farm of the Faculty of Agriculture ”Norfa project” Minufiya university, shebin El-kom. The aim of the investigation was to study the effect of some genetic and environmental factors on the performance the chickens during the brooding period. A total number of 276 chicks of Norfa and Fayoumi strains were used from 4 weeks of age until 32 weeks of age. At 4 weeks, birds were classified into two comparable groups. The first was exposed to heat stress (35-37 c°) for six hours, 1 time weekly, the second was exposed to the natural ambient temperature (control). Climatic chamber was used for the adjustment of temperature and relative humidity 65% and the treatment were continued up to 20 weeks. Studied traits were determined for each treatment at both growing and laying periods. Body weight, growth rate, age at sexual maturity and egg number, weight and mass during the first 3 months after sexual maturity and egg quality were recorded. Also, rectal temperature, respiratory rate and immune response to heat stress at the end of experiment were determined. The results and conclusions can be summarized as follows. : 1- Body weight of either Norfa or Fayoumi of control group at different ages during brooding period were higher than that of treated group.