امید علی اسماعیلی پور

Heat stress is one of the most serious problems in hot conditions, that negatively affects the production performance of poultry. Several researchers tried to reduce the negative effects of heat stress on poultry through using diet supplementation with feed additives such as antioxidants and herbal plants [2]. This study was conducted to investigate the effects of different levels of Mentha piperita (PP) and Melissa officinalis (MP) powder on performance and relative weight of internal organs of heat stressed broilers. A total of 200, one-day-old male broiler chickens (Ross 308) were randomly allocated to 5 treatments with 4 replicates and 10 chicks each, as a completely randomized design. The dietary treatments consisted of: basal diet (BD), BD+0.5% PP, BD+1% PP, BD+0.2 % MP, BD+0.4 % MP. The experiment was conducted from 25 to 42 day of age, before that, all the chicks were fed the same diet. During the experiment the birds were kept at 34°C±2 (9.00 to 17.00; for 8 hours). At the end of the experiment feed intake (FI) and body weight gain (BWG) were measured and feed canvertion ratio (FCR) was calculated. The results indicated that dietary supplementation with Mentha piperita and Melissa officinalis powder did not affect the FI and relative weights of the gizzard, liver, pancreas and spleen (P>0.05). Dietary supplementation with PP and MP significantly increased BWG and decreased FCR compared to the basal diet (P<0.05). The highest BWG and the lowest FCR were observed in the birds supplemented with 1% diet PP. These results was in agreement with the previous finding who observed that adding PP to the broiler diets improved performance and feed canvertion ratio [1]. In conclusion, the results of this experiment showed that using 1% of Mentha piperita powder in the diet improved broiler performance under heat stress.