The objective of the present experiment was to investigate the effects of dietary vitamin C (VC), vitamin E (VE), and betaine (BT) supplementations on productive performance, egg quality, relative organ weights, liver visual characteristics, antioxidant status, immune response, and stress indicator in laying hens raised under heat stress conditions. A total of 280 47-wk-old Hy-Line Brown laying hens were allotted to 1 of 4 dietary treatments with 7 replicates in a completely randomized design. Each replicate had 10 birds per cage. The basal diet was formulated to meet or exceed the requirement estimates for Hy-Line Brown laying hens. Three additional diets were prepared by adding 250 mg/kg VC, 250 mg/kg VE, or 3,000 mg/kg BT to the basal diet. The experimental diets and water were provided to hens on an ad libitum basis for 8 wk. Average daily room temperature and relative humidity were 30.7±1.41℃ and 72.5±11.61%, respectively. Results indicated that hens fed diets containing 250 mg/kg VE had a less (p<0.05) egg production rate than other dietary treatments. For egg quality, hens fed diets containing 3,000 mg/kg BT had a less (p<0.05) eggshell thickness than those fed the diets containing 250 mg/kg VC or 250 mg/kg VE. For antioxidant status, there was a tendency (p=0.09) for the least malondialdehyde (MDA) concentrations in the liver for BT treatment. A tendency (p=0.05) was observed for less blood heterophil:lymphocyte ratio in BT treatment as compared to other treatments. In conclusion, dietary supplementation of 250 mg/kg VC, 250 mg/kg VE, and 3,000 mg/kg BT has no beneficial effects on productive performance, egg quality, relative organ weights, liver visual characteristics, and immune responses of laying hens raised under the current heat stress conditions. However, dietary supplementation of 3,000 mg/kg BT alleviates antioxidant status and stress response of laying hens exposed to heat stress.

Abstract
Introduction
Materials and Methods
    1. Animals, diets, and experimental design
    2. Sample collection and analysis
    3. Statistical analysis
Results and Discussion
    1. Productive performance
    2. Egg quality
    3. Relative organ weight and liver visualcharacteristics
    4. Antioxidant status
    5. Immune and stress responses
Acknowledgement
References

• Gi Ppeum Han(Department of Animal Science and Technology, College of Biotechnology & Natural Resource, Chung-Ang University,)
• Sung Hoon Kwon(Department of Animal Science and Technology, College of Biotechnology & Natural Resource, Chung-Ang University)
• Chan Ho Kwon(Department of Animal Science and Technology, College of Biotechnology & Natural Resource, Chung-Ang University)
• Deok Yun Kim(Department of Animal Science and Technology, College of Biotechnology & Natural Resource, Chung-Ang University)
• Dong Yong Kil(Department of Animal Science and Technology, College of Biotechnology & Natural Resource, Chung-Ang University) Corresponding author