Effects of adding essential oils of rosemary, dill and chicory extract to diets on performance, egg quality and some blood parameters of laying hens subjected to heat stress

To determine the effects of adding essential oils of rosemary, dill and chicory extract to diets on performance, egg quality and enzyme activity of laying hens subjected to heat stress, a total of 240 laying hens were used and based on a 2 × 2 × 2 factorial, eight diets, with five replicates, including basal diet with two levels of rosemary essential oil (0, 20 ml/100 kg), two levels of dill essential oil (0, 15 ml/100 kg) and two levels of chicory extract (0, 250 ml/100 kg) were fed to the experimental birds. Dietary dill had a significant effect on egg index under heat stress condition. The birds given rosemary, dill and chicory alone exhibited lower serum cholesterol and triglycerides concentration under thermoneutral and heat stress condition compared to those fed the basal diet (P < 0.05). Synergistic effects between dietary rosemary, dill and chicory significantly increased plasma glutathione peroxidase activity compared to those that received only rosemary, dill or chicory, which has been never reported (P < 0.05). In conclusion, the addition of single or combination of rosemary, dill and chicory can improve at least some production performance and antioxidant enzyme activity (glutathione peroxidase) in heat-stressed laying hens