الفهرس 
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Abstract
The experimental work of the present study was conducted at the Poultry Farm; Station of Agricultural researches and experiments; Faculty of Agriculture, Mansoura University, Egypt. The experimental feeding trial of this study was carried out during June, July and August 2000.
The aim of the study was to investigate the possibility of alleviating the adverse effects of heat stress to which broiler chicks are exposed during the summer season by means of early-age feed restriction (EFR) and dietary supplementation with potassium chloride (KCl), either singly or in combination.
A total number of 360 one-day old, broiler-type Hubbared chicks were randomly divided into two halves, each of which was assigned to four treatments (T), and given isonitrgenous and isocaloric starter diets (21.6% CP and ME of 3000 KCal/kg) from 0 to 3 weeks of age and grower diets (19.6% CP with ME content of 2955 KCal/kg) between 3 to 6 weeks of age. Two feeding regimens were imposed on these birds. Chicks of the first half (treatment groups of T1, T2, T3 and T4) were full-fed (FF); on ad libitum basis, during the entire experimental period from 0 to 6 weeks of age, while feed of the other half (treatment groups of T5, T6, T7 and T8) was restricted; only during the first week to ME intake of 1.5 KCal X BW0.66, to meet their daily maintenance requirements for energy with a concomitant achievement of some growth, and thereafter had a free access to feed to the end of the experimental period.
Both starter and grower diets originally contained about 0.8% K. from 1 to 6 weeks of age, diets of chicks on both the two feeding regimens (FF and EFR) were either unsupplemented with KCl for those in T1 and T5 which served as controls, or supplemented with KCl at levels of 0.75, 1.5, and 2.25% of diets for chicks of T2 and T6, T3 and T7, or T4 and T8, respectively. Thus, in these diets, supplemental KCl plus basal K provided average dietary K levels of 0.8, 1.2, 1.6 or 2.0%, respectively.
The criteria of response included:
A. Performance of chicks for weight gain, feed intake, feed conversion, and carcass yield, and viability of experimental chicks, up to 6 weeks of age.
B. Some physiological responses and hematological changes assessed by:
a. Body temperature (rectal and skin temperatures) and panting rate of experimental chicks at the 5th and 6th weeks of age.
b. Blood sedimentation rate and hemoglobin level, activity of alkaline phosphatase, and concentrations of total protein, total lipids, glucose and cholesterol in plasma of 6-week old experimental chicks.
c. Blood acid-base balance in 6-week old experimental chicks; as assessed by blood pH value, and concentrations of plasma K, Na and Cl.