Abstract
The aim of this study was to expose chicks during the early ages to heat stress for acclimating them with high temperature environment during the following days. In this experiment 400 broiler chicks were divided into two groups each of 200 chicks . The first group was grown under normal conditions , while the second exposed to heat stress (39±25C)during 6,12,18 and 24 day of ages for 6 hour/day. At the end of 28 days of age the two groups of chicks were exposed to cycling heat (25-36-25)5C from 1000 to 1800 o'clock until 56 days of age and they were fed ad liblitum with continuous supply of water and light, Each group was assigned to replication six each of 30 chicks where feed and water were available. Statistic analysis of data showed significant ((P ≤ 0.05) increase in weekly weight gain in acclimated birds at seven and eight weeks , water consumption , blood pH , red blood cells at eight week , Hemoglobin concentration , glycogen concentration in liver and heart and heat tolerance for acclimated birds . Significant decrease((P ≤ 0.05) for acclimated birds in food consumption in eight week of age , food conversion ratio in seven and eight week of age , blood glucose and decrease in body temperature in six and eight weeks at the three period of measurement .No significant differences in live body weight , packed cells volume and slightly decrease in acclimated birds mortality .
