Effects of Origanum syriacum essential oil added in different levels to the diet of broilers under heat stress on performance and intestinal histology

This study compared the effects on performance parameters, intestinal microflora and histology of adding Origanum syriacum (OS) essential oil and an antibiotic (Avilamycin) to the rations of broilers fed under heat stress conditions. The 42-day study used 500 day-old male broilers (Ross-308) divided into 10 groups of 50 animals each. Then, each of these groups was further divided into 5 groups of 10 each. Groups were either kept at 22 degrees C (stress-free) or at 36 degrees C (heat stressed). Birds were fed with 5 experimental diets: control (basic feed (BF) without feed additive), antibiotic (BF + 100 mg/kg Avilamycin), OS 100 (BF + 100 mg/kg OS), OS 300 (BF + 300 mg/kg OS, OS 600 (BF + 600 mg/kg OS). At the end of the study period, some performance parameters, including feed intake, feed-conversion ratio, body weight, average daily weight gain, ileum crypt depth, villus height and microflora, decreased in groups under heat stress without additives (P < 0.01). However, comparison with the control group and the antibiotic group showed that adding OS essential oil provided a benefit close to that of the antibiotic, yet still inadequate, even at the 600 mg/kg dose.