الفهرس 
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Abstract
A total of 225 one-d old Cobb-500, Hubbard-classic, and Ross-308 chicks (75 each) were obtained from El-Dakahlia, El-Tokhy and El-Watania companies, Egypt, respectively were used in this study. Chicks were raised as separate strains with five replicate pens of 15 individuals per strain. The experiment was conducted till the chicks were of 42 days of age, and repeated under various seasonal conditions and this study aims to investigate the impact of breed (Cobb, Hubbard, and Ross) and/or season (winter, spring, summer, and autumn) on the productive and economic performance of broiler chickens and evaluate productive and economic performance as a function of the marketing age and determine the optimum marketing age for each strain under different environmental conditions.
The Cobb broiler birds exhibited the greatest final body weight, body weight gain, and total feed intake compared to Ross and Hubbard ones. The significant seasonal effect was found in FBW, BWG, TFI, and PEF, which was significantly higher in the winter season compared to spring, summer, and autumn seasons. There was an effect of interaction between breeds and seasons exhibited improved in FBW, BWG, and FCR in the winter season for Cobb, Ross, and Hubbard breeds. However, no significant differences were detected concerning IBW, TFI, and PEF, while the summer season was the lowest season for Ross and Hubbard breeds and spring season was the lowest for Cobb breed. This indicated that the most preferred season of rearing in three broiler breeds is winter season.