الفهرس 
Introduction
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Abstract
The different experiments carried out during this study were reported in different chapters as follows:
Chapter One:
included two experiments:
The first experiment was carried out to evaluate the effect of energy level on
growth performance and carcass variables of broilers at 42 days of age under
hermoneutral or heal stress conditions. At 3 weeks of age three groups were fed
Three experimental diets as follows:
- Diet 1 contained 3000 KcaI ME I Kg
- Diet 2 diet contained 3150 Kcal ME / Kg
- Diet 3 diet contained 3300 Kcal ME I Kg
The three diets were equal in their calorie: protein ratios. At 3 - S weeks of age, rds of each group were devided in two subgrdups: one was kept under cyclic heat ress (HSI 24-35°C) and the other was kept under thermoneutral (TN, 24°C)
ditions. The results indicated that:
1- Body weight body weight gain feed efficiency and survivability were significantly (P<0.O5) decreased under HS conditions.
2- Increasing the energy level from 3000 to 3150 Kcal MEl Kg significantly increased body weight under MS conditions. No significant differences were detected in body weight between TN and HS birds.
3- Feed efficiency of MS birds fed diet contained 3300 Kcal ME! Kg was significantly improved compared to the birds fed 3000 Kcal under TN conditions.
4- No significant differences were proved for survivability, between TN or HS birds under all dietary treatments.
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5- High ambient temperature significantly increased fat pad and carcass fat content, however, it decreased carcass weight, breast percent and dressing percent.