The aim of present study was to investigate the effect of feeding fennel and ajwain essential oils on improving the damages caused by oxidative stress in rat as a mammalian model. For this purpose, 40 adult male Wistar rats with 294 ± 31g average body weight were used in a completely randomized design with 5 treatments and 8 replications each. The experimental groups were: 1- Control group without stress and supplementation (CON), 2- Stress group without supplementation (STR), 3- Stress group fed fennel essential oil (STR+FE), 4- Stress group fed ajwain essential oil (STR+AE), 5- Stress group fed mixed essential oils of fennel and ajwain (STR+FE+AE). The induction of stress was done by daily i.m. injection of dexamethasone (1 mg/kg BW/d). Essential oils of fennel, ajwain and their mixture were fed using the gastric gavage (100 mg / kg BW) in a 21 d period. Results showed that body mass index, body weight and feed intake in stressed groups decreased (P 0.05) compared to the CON group. However, feeding the essential oils improved these condition, so that in the fifth group (STR+FE+AE) the body mass index and body weight had highest increase. The group fed ajwain had the highest (P 0.05) feed intake than those the others. Relative weight of liver had significantly difference (P 0.05) between the experimental groups, so that in STR group liver had the highest relative weight. The results of blood metabolites showed that serum albumin in the stressed group was higher (P 0.05) than the control group and the groups treated with essential oils. However, malondialdehyde and alkaline phosphatase were not affected by the treatments. The activity of alanine amino transferase (ALT) and aspartate amino transferase (AST) enzymes increased (P 0.05) in the STR group compared to the CON group, and feeding essentiol oil could significantly decrease (P 0.05) the level of these enzymes. Moreover, the superoxide dismutase and glutathione peroxidase enzymes decreased (P 0.05) in the STR group. On the other hand, feeding essential oils increased (P 0.05) the serum superoxide dismutase enzyme. Feeding fennel essential oil increased (P 0.05) glutathione peroxidase in blood serum compared to STR group. The results of histology showed that feeding fennel essential oil improved liver damage in general. It was concluded that fennel and ajwain essential oils had potential to improve the damage induced by oxidative stress in rats. Therfore, feeding these essential oils in dairy cows’ nutrition, which are sensitive to metabolic stress in early lactation, could have positive effects. Key words: Oxidative stress, fennel and ajwain essential oils, blood metabolites, histology, rat
