An experiment was conducted to investigate the effect of lemon verbena powder and vitamin C on performance
and immunity of broilers under heat stress. The experiment was carried out with a total of 160-day-old male Ross
308 broiler chickens in a completely randomized design. From 25 days of age, the birds were assigned to four
diets including control diet and treatment diets which were supplemented with 2 levels of lemon verbena (0.5%
and 1.0%) and one level of vitamin C (250 mg/kg) in 16-floor pens with 10 chickens each and reared to 42 days
of age. To induce chronic heat stress, birds were exposed to an ambient temperature of 35 2 °C for 8 h daily
(from 09:00 AM until 17:00 PM) between 25 and 42 days of age. At the end of experiment, one chick/pen was
randomly selected, and the performance and blood parameters were evaluated. Dietary supplementation of
1.0% lemon verbena increased (p < 0.05) average weight gain and feed intake by 5.81% and 3.29%, and
reduced feed conversion ratio by 2.59% respectively compared to control group. Birds fed diets containing 1.0%
lemon verbena had significantly higher relative weight of bursa of fabricius and breast (p < 0.05). LDL decreased
by 15.85% and 17.57%, for birds fed 0.5% and 1.0% lemon verbena respectively. The ratio of heterophyl to lymphocyte
was reduced (p < 0.05) by 20.68% via significant decrease in heterophyl by 15.55% and significant
increase in lymphocyte by 4.51% in birds fed lemon verbena at the rate of 1.0% compared to those fed the
control diet. 1.0% lemon verbena and vitamin C elevated (p = 0.0005) the level of glutathione peroxidase by
51.81% and 27.90%, respectively. In conclusion, lemon verbena and vitamin C improved some performance
data and blood metabolites which somehow suppressed the negative effects of heat stress.
