الفهرس 
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Abstract
Aim of the work: The aim of the study was to investigate the possibility of alleviating the adverse effects of heat stress, to which laying hens are exposed during the summer season, by means of dietary supplementation with potassium chloride (KCl), vitamin E or their combinations. Birds and Experimental diets: Three hundred and sixty, 20-week-old Hy-Line W-36 pullets were assigned to twelve equal experimental groups of 5 replications of 6 birds each. All birds were kept in community battery cages (6 birds per cage), set up in an open-sided laying house, and exposed to a daily photoperiod of 16 hr and managed similarly. Twelve experimental diets were formulated and used. The criteria of response: These included the productive performance of laying hens (in terms of live body weight, change in body weight, feed intake, egg production rate and feed conversion efficiency), mortality rate, economic efficiency of egg production, egg quality traits, nutrient digestibility and some physiological changes including: relative weights of certain endocrine glands and lymphoid organs, immune response, and levels of some blood constituents, metabolites, electrolytes and activities of certain blood plasma enzymes. All criteria of response of laying hens were measured on a replicate group basis. Based on the present results (definitely on productive performance, mortality rate, egg quality and economic efficiency) it could be concluded that: 1-Dietary supplementation with KCl, vitamin E, either separately or in combination, can be used as an effective tool for alleviating the adverse effects of heat stress on productive performance, egg quality, and bird viability, economic efficiency of production and some other physiological responses of laying hens. 2-Either of the following three options could be recommended in order to ameliorate the effect of heat stress on laying hens: dietary supplementation with 1.6% KCl, with 300 mg/kg vitamin E/kg diet or with combination of 1.6% KCl + 150 mg vitamin E/kg diet. 3-Even though, dietary supplementation with 1.6% KCl in combination with 300 mg/kg diet, and with 2.4% KCl alone or in combination with 150 or 300 mg vitamin E/kg diet exerted significantly positive effects on the performance and physiological parameters of laying hens; similar to those of the recommended supplementary levels mentioned above, yet no extra benefits were not gained. 4-Dietary treatments, applied herein, during the summer season probably had carry-over effects that positively in flounced and the physiological parameters of laying hens to a certain extend, throughout the rest of egg production year. 5-It seems likely that some synergistic effects excited between supplemental KCl and vitamin E on some productive and physiological parameters of laying hens, under the conductions of the present study.