ABSTRACT: This study was carried out at the Research Poultry Farm, Faculty of
Agriculture, Sohag University,Egypt. It was designed to study the effect of betaine
supplementation on broilers performance under cyclic heat stress. A total number of 375 Ross, one day-old were equally divided into five groups (75 birds/group) with three replicates (25birds / replicat). In the first group, birds were fed a commercial ration produced with ALWADI Company without any betaine supplementation and served as control group. While, birds in the 2 nd , 3 rd , 4 th and 5 th groups were fed the same diet with supplemented betaine at different levels of 100, 150, 200 and 250% i.e. 2, 3, 4 and 5kg betaine/1000 kg diet, respectively compared to the company recommendations. All birds were daily exposed to cyclic heat stress (35◦
C) from 8 AM to 4 PM and then from 4 PM to 7 AM , they were exposed to natural ambient temperature. Chicks in all groups were housed in partitioned litter floor.
Each pen was used as a replicate (25chicks) of the treatment, provided with a feeder and one nipple for supplementing water. Feed and water were available ad-libitim throughout the experimental period. All chicks were exposed to traditional continuous lighting programs with 60 watt from incandescent lamb at the height of 2.4 m from the floor up to the marketing age.
The results showed that the BW and BWG significantly improved in treated groups. Feed consumption and feed conversion ratio significantly improved in treated groups. Recta temperature significantly increased at 42 days of age and respiration rate significantly increased at 14, 21 and 42 days of age in treated groups. Heart percentage significantly increased in treated groups compared to control group. Chemical composition of meat was no significantly affected with betaine levels compared to control group.