High environmental temperature is one of the important stressors faced by laying hens usually in summer months. In a hot environment, hens exert extra effort to maintain their body temperature within a normal range. This challenge is associated with behavioural, physiological, hormonal and molecular responses. Hens in stressful environments decrease their rate of ovulation and also produce lower antibody response to a variety of antigens. Vitamin E and selenium have important roles in the antioxidant system and they have an influence on the immune system. Dietary supplementation with Vitamin E facilitates release of vitellogenine necessary for yolk formation which reduces its release in heat stress (Bollengier-Lee et al., 1998). Also, Chickens provided with organic selenium are more resistant to thermal stress than chickens fed inorganic sodium selenite (Mahmoud and Edens, 2003).

This study was conducted to determine the effect of dietary vitamin E and selenium, as well as comparison of organic and inorganic selenium, on performance, egg quality and antibody response to sheep red blood cells (SRBC) in laying hens exposed to high environmental temperature.