ABSTRACT: This experiment aimed to study the effect of supplementation excessive level of vitamin E (1000 mg/kg diet) on growth performance of broiler chickens under heat stress conditions. One hundred and fifty Cobb broiler chicks, 14 days old, were divided into three equal groups. Chicks in the 1st group were fed on the commercial basal diet; while those in the 2nd and 3rd groups were fed the same diet
with adding 200 and 1000 mg Vit. E/kg diet, respectively. Broilers had free access to feed and fresh tap water. Broilers were raised under 32 and 30°C during the first and second weeks, respectively, while the broilers were reared under natural ambient temperatures from 2-5 weeks of age. The broilers in the different groups were daily exposed to continuous lighting program.
The obtained results showed that the broilers in the 2nd group tended to have higher daily weight gain (p=0.056) in addition they significantly improved feed conversion ratio (FCR; p<0.01) compared to the other groups during the period 28-35 days of age. At 35 days of age, broilers in the 2nd group had heavier live body weights (p<0.05) compared to control.
Broilers in the 2nd group (200mg/kg diet) significantly enhanced (p<0.05) plasma total antioxidant capacity (p<0.05) compared to the other groups. Plasma malondialdehyde concentrations for broilers in the 2nd and 3rd groups were decreased compared to control group. The higher antibody titers against Newcastle Disease Virus in the serum were observed at 30 days of age in the 200 mg Vit. E/kg group compared to the other treatment groups. H/L ratio, plasma cholesterol, and glucose concentrations
were insignificantly differed among treatment groups.
In general, it could be concluded that the excessive vitamin E supplementation during summer reduces its effect for maximum performance, while the better antioxidant capacity and higher antibody titers were achieved by adding the lower level (200 mg Vit. E/kg diet).