Comparative effects of Mentha piperita extract, vitamin E, vitamin C, probiotic and antibiotic on performance and immune response of broilers under heat stress

 This experiment was performed to evaluate the effects of peppermint extract, vitamins C, vitamin E, probiotics and antibiotics on performance, biochemical parameters and immune system of broilers under heat stress conditions. Peppermint (Mentha piperita) is considered as one of these medical plants and belongs to the Lamiaceae family. The essential oils and extracts of this plant are mainly made up of menthone, menthol and methyl acetate. Peppermint is traditionally used as an antiseptic, antispasmodic, mild tonic, antimicrobial.

 A total of 240 one-day-old broilers (Ross 308) were distributed to 8 treatments with 5 replications/treatment based on a randomized block design. Experimental diets consisted of base diet without feed additive and under standard temperature conditions (negative control), base diet without feed additive and under heat stress conditions (positive control), positive control supplemented with 28 mg/kg virginiamycin, 28 mg/kg probiotic protexin, 1 g/kg vitamin C, 1 g/kg vitamin E, 250 and 500 mg/kg peppermint extract, respectively. House temperature was initially set at 28°C for the second week and then reduced by 0.5°C per day until a temperature of 22°C was achieved at the end of the fourth week and then maintained constant thereafter. To induce heat stress, room temperature was raised to 34◦C during 10 AM to 16 PM from 15 to 42 days of age. A 23:1h light to darkness lightening regimen was followed throughout the experimentation period. Body weight gain and feed intake were recorded for days 10, 24 and 42 of age and data were used to calculate feed conversion ratio (FCR). At the end of the experiment (day 42), two birds from each replication with a body weight close to cage mean were selected and killed. Individual blood samples were collected form the slaughtered birds and centrifuged at 1800× g for 15 min. The collected sera samples stored at -20°C pending biochemical assessments. Concentrations of serum glucose, triglyceride, total cholesterol and low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), very- low-density lipoprotein cholesterol (VLDL-C), white blood cells (WBC), red blood cells (RBC), Hematocrit and Hemoglobin were determined by different recommended procedures. To assay the primary and secondary antibody responses against SRBC, 2 birds/replicate were immunized intramuscularly with 0.5 mL 10% SRBC in. Blood samples (1.5 mL/bird) were obtained from the brachial vein at 7d following each injection.

 The results showed that the highest feed intake and feed conversion ratio were observed in chickens fed with negative control diets (P <0.05). The greatest body weight was observed in the birds fed with the negative control and diets supplemented with probiotics and vitamin E (P <0.05). Broilers fed with diets containing antibiotics as same as positive control group could increase abdominal fat percentage and serum triglycerides concentration than other treatments (P <0.05). The broilers fed with diets supplemented with all feed additives decreased the heterophils to lymphocytes ratio compared to the positive control group (P <0.05). The probiotics and 500 mg peppermint extract-supplemented diets improved the antibody titer against Newcastle, Gumburo and influenza diseases, as well as anti-SRBC titer, compared to the positive control group (P <0.05). The results of this study are supported by other studies, indicating that the dietary supplementation of probiotic could improve physiological responses and immune system and thus performance of heat-stressed birds. Dietary supplementation of vitamin C is an effective strategy to reduce the harmful effects of heat stress in poultry. The results of previous studies have demonstrated that the antioxidant and inflammatory properties of peppermint contributes to the prevention and treatment of diseases associated with oxidative stress, through removing free radical. Medicinal plants with secondary metabolites have also reported to possess the positive effects on growth performance and thus increasing the immune function. The positive effects of peppermint could be due to its active ingredients such as carvacrol, flavonoids and menthol. Flavonoids with antioxidant effects have protective properties against free radicals. The mucous membrane of the gastrointestinal tract plays an important role in preventing antigens and harmful microorganisms from entering the organ and eliminating them, while also being effective in selective nutrient absorption. The results of the present experiment and the other reports also indicate that dietary supplementation of probiotic and vitamin E and C and peppermint extract improve the immune response and growth performance of broilers and could be account as an alternative to antibiotics.

 In conclusion, a high dose of peppermint (500 mg/kg) was as effective as probiotic, vitamin E and C in alleviating the negative effects of heat stress on growth performance, health and immune function.