effect of essential oils of peppermint, lemon, thyme and ajwain on performance, blood metabolites and hepatic lipogenic gene expression of broilers

intoduction essential oils (eos) are important aromatic components of herbs and spices which are complex mixtures of secondary plant metabolites consisting of low-boiling-phenylpropenes and terpenes. their biological activities have been known and utilized since ancient times in perfumery, food preservation, flavoring, and medicine. some of their biological activities include antibacterial, antifungal, anti-oxidant and anti-inflammatory effects. the ban on the use of antibiotics as growth promoters has stimulated the search for alternative feed supplements in animal production. eos have received attention in recent years as potential ‘natural’ alternatives for replacing antibiotic growth promoters (agps) in animal diets due to their positive impact on growth performance and welfare. a number of studies have been carried out to investigate the effects of eos on broiler performance rather than the physiological effects, but the results have not been consistent (or constant). the purpose of this study was to investigate the effects of four essential oils (thymus vulgaris, mentha piperita, citrus lemon, carum copticom) on growth performance, some of the serum biochemistry parameters and lipogenic gene expression in broiler chickens. materials and methods a total of 312, 1-day-old broiler chicks were allocated in completely randomized design to 13 groups with 6 replicate cages per treatment. after 2-day adjustment with the basal diet, the birds were randomly assigned to the corresponding experimental diets supplemented with 0 (control), 50, 100 and 150 mg/kg diet essential oils extracted from crum capticum, thymus vulgaris, mentha piperita and cirtus lemon. the basal diet composed of maize–soybean meal prepared in our laboratory and all birds had free access to water for the entire period. food intake and bw were recorded to determine growth performance and feed: gain ratio. at the end of the experiment (42 day) blood samples (6 samples per treatment) were taken for measuring biochemical analysis including total protein, triglyceride, total cholesterol, hdl-c and ldl-c by commercial kits. samples of the liver were collected on day 42 after slaughter (6 samples per treatment) and the hepatic expression of the genes encoding malic enzyme (me), fatty acid synthase (fas) were determined with reverse transcription-polymerase chain reaction (rt-pcr) using sybr green as a flourophore monitored in a real time mode. results and discussion the results showed that the body weight, feed intake and feed conversion ratio of broilers at day 42 were not affected by supplementing eos to the basal diet. however, daily body weight gain of broilers at 21 day decreased significantly (p<0.05) by dietary supplementation of 150 ppm mentha piperita essential oil compared to control and some of the treatment groups. in the previous studies, variable effects of eos on performance have been reported. the variability in the efficacy of eos on animal performance could be attributed to the composition of the basal diet (less digestible diet), level of feed intake, hygienic standards and environmental conditions. other factors that could affect the results of in vivo experiments are: harvesting time and state of maturity of plants, extraction methods of plants, method and duration of conservation and storing and possible synergistic or antagonistic effect of the bioactive compounds. the concentrations of serum cholesterol, total protein, triglyceride, total cholesterol, hdl-c and ldl-c were not affected by treatments. the absence of hypochlosrtrolemic and hypolipidemic effects of applied essential oils in the present study may be attributed to rapid urinary excretion of essential oil metabolites and composition of the basal feed. treatments had no significant effect on the expression of mrna for fatty acid synthase compared to control. in chicks fed the diet supplemented with 150 ppm mint essential oil, malic enzyme mrna expression was significantly (p≤0.05) enhanced compared with chicks fed the basal diet. the reason for this effect is unknown, but it may be attributed to stress-induced metabolic or metabolic stress inducing by upper dose of mint eo that may predispose broilers to hepatic steatosis.in general, results of the present study propose a possible role for some herbal essential oils in the regulation of broiler metabolism. however, contrary to our previous assumption, this role may not be antilypogenic. moreover, according to the results it could be claimed that eos may have differential and dose response effects on lipid metabolism in broilers. in conclusion, supplementation of mint eo at upper levels (150 ppm) in not recommended as feed additive in broiler diets.