Effect of dietary inclusion of peppermint essential oils on productive performance and immune response in laying hen imposed to dexamethasone-induced stress

This study was conducted to evaluate the effects of dietary inclusion of peppermint essential oils (PEO) on productive performance and immune response in laying hens imposed to dexamethasone-induced stress. The experiment was performed in a 2×3 factorial arrangement in a randomized complete block design with 90 Hy- Line (W36) laying hens in 6 treatments and 5 replicates of 3 birds in each. Peppermint essential oil was included into a basal (control) diet at 200 and 400 mg/kg. Dexamethasone was injected subcutaneously in two levels of 0 and 4 mg per bird/ week. Dexamethasone injection decreased egg production, egg mass and body weight gain while increased feed conversion ratio, eosinophil count and serum total protein concentration compared with control birds (P < 0.05). Egg yolk weight was greater in birds fed with diets containing 200 mg/ kg PEO compared with control birds (P < 0.05). Dexamethasone, peppermint essential oil as well their interaction exhibited no significant effect on antibody titer against Newcastle, Influenza and Gambro viruses (P > 0.05). In conclusion, dexamethasone-induced stress exhibited an adverse impact on feed conversion ratio and egg production in laying hens and inclusion of PEO at 200 mg/ kg modulated, in part, certain negative effects including egg weight of hens.