الخلاصة

Two stage-study was carried out at poultry station of Animal Resources Department, College of Agriculture at Kufa University from the 6th of September to the 20th of November 2010 as an attempt to reduce growth rate of birds in the early ages and release it later to get advantage of compensatory growth in comparison with supporting restricted diet of those birds with a mixture of vitamin C, salicylic acid and betaine and investigate the effect of these treatments on some productive and physiological characteristics of heat stressed broiler. Two hundred twenty five unsexed one-day-old chicks of Cobb breed with average weight of 40g were used in the study. Birds were reared on ground and were randomly allocated into 3 treatments with 25 chicks per each. The 1st stage of the study was extended for 9-19 days of age for birds of control treatment and were offered free feeding until the end of the this stage and the whole study (T1), while birds of treatment 2 and 3 were fastened for 10 hours a day from 8 a.m to 6 p.m until the end of this stage. The 2nd stage was extended for 20-35 days of age during which free feeding for birds in T2 and T3 was resumed and a mixture containing 100 mg of vitamin C and 50 mg of salicylic acid and 800 mg of betaine per 1 kg of feed was added to the diet of birds in T3only.Heat and humidity inside house as an average were 26-36 C° and 60-70% respectively. Results of the study were as follows: 1- Birds of T3 during 2-5 weeks of age achieved significantly (P<0.05) higher average body weight (BW) and average weight gain (WG) as compared with those of other treatments. 2- Feed intake by birds of T1during 2-5 weeks of age was significantly (P<0.05) higher as compared with those of T2 and no differences were observed between birds of T1vs. T3 and T2 vs. T3. 3- Feed conversion ratio (FCR) of birds in T2 and T3during 2-5 weeks of age was significantly (P<0.05) higher as compared with those in T1. 4- Dressing percentage (DP) of bird's carcasses in T3was significantly (P<0.05) higher as compared with that of birds in T1 and T2 with no differences among treatments in carcasses main cuts except wings. 5- Abdominal fat in carcasses of birds in T2 and T3 was significantly (P<0.05) lower as compared with that of T1birds and no difference was observed among treatments in interior eaten parts. 6- Lower (P<0.05) mortality rate was recorded in T3 as compared with other treatments. 7- Lymphocytes (L) ratio was significantly (P<0.05) increased, whereas, Heterophil (H) and H/L ratios