The present study was conducted to investigate the effects of two plant extracts as alternatives to dietary antibiotics in broiler chickens exposed to low ambient temperature. A total of 300 one-day-old male broiler chickens were randomly assigned four dietary treatments (5 replicate pens; 15 broiler chickens each) which consisted of starter (d 0 to 10), and grower (d 10 to 28) diets. Dietary treatments included a basal diet (negative control, NC) and three similar diets that were each supplemented with 200 mg/kg of Prosopis farcta extract (PFE), Rhus coriaria L. extract (RCE) and an antibiotic premix containing oxytetracycline at a concentration of 20% (positive control, PC), respectively. In order to simulate low ambient temperature, the following protocol was employed: room temperature was maintained at 32°C during the first 3 d of the trial and afterwards, the temperature was gradually reduced by approximately 1.5°C each day to 14°C on d 21. PFE and PC treatments exerted a significant effect on body weight gain at d 28. The diet supplemented with PFE was effective in reducing mortality when compared with the NC (P < 0.05). Furthermore, PFE-incorporated diets caused increases in ileal gross energy, dry matter and organic matter digestibilities of broiler chickens when compared with the NC (P < 0.05). PFE and PC groups managed to decrease coliforms, total aerobic bacteria and total anaerobic bacteria loads in the caeca when compared with the NC (P < 0.05). Moreover, the addition of PFE to the diet improved villous height in all small intestinal segments as well as villous height:crypt depth in the duodenum when compared with the NC (P < 0.05). The results indicated that PFE is not only a valid alternative to oxytetracycline under cold stress conditions, with no antibiotic resistance, but also has the potential to increase the resistance of broiler chickens (immunity) against ascites syndrome.
