مشخصات پژوهش

This study was conducted to find out the effects of drinking water containing lemon juice and thyme sup-plemented diet on growth performance, serum concentration of cholesterol and triglycerides, heterophils (H), lymphocytes (L), H/L ratio and enzyme activity of glutathione peroxidase (GPX) in broilers under heat stress condition. The experiment was carried out as a 2 × 3 factorial arrangement with 2 levels of lemon juice (0 and 2 mL/L of drinking water) and 3 levels of thyme (0, 0.5 and 1 % of diet). Each dietary treat-ment consisted of 4 replicate pens (9 birds/pen). The birds were kept at 34 °C ± 2 (9.00 to 17.00) from 25 to 42 d of age. Feed intake (FI), body weight gain (BWG), feed conversion ratio (FCR), H/L ratio and GPX activity and serum cholesterol concentration were not affected (P>0.05) by individual addition of lemon juice or thyme; whereas, combination effect of the two additives improved performance and reduced H/L ratio and serum triglycerides concentration (P≤0.05). Concurrent usage of 0.5 thyme and 2 mL/L of lemon juice increased FI and BWG by 229 and 165 g, respectively. Addition of 0.5 and 1% thyme to the diet and 2 mL/L lemon juice to drinking water reduced the serum triglycerides concentration by 9.8, 11.1 and 8.5 mg/dL, respectively (P≤0.05). It is concluded that the concurrent administration of 0.5% of thyme to diet and 2 mL/L lemon juice to drinking water provides a potential protective management strategy in prevent-ing heat-stress-related reduction in the performance of broiler chickens.