1. The study was conducted to determine the effects of dietary supplementation of enzyme and oregano essential oil at two levels, alone or together, on performance, digestive enzyme, nutrient digestibility, lipid metabolism and immune response of broilers fed on wheat-soybean meal based diets. 2. The following dietary treatments were used from d 0 to 21. Diet 1 (control, CONT): a commercial diet containing no enzyme or oregano essential oil, diet 2 (ENZY): supplemented with enzyme, diet 3 (EO250): supplemented with essential oil at 250 mg/kg feed, diet 4 (EO500): supplemented with essential oil at 500 mg/kg feed, diet 5 (ENZY + EO250): supplemented with enzyme and essential oil at 250 mg/kg, and diet 6 (ENZY + EO500): supplemented with enzyme and essential oil at 500 mg/kg. 3. Birds fed on diets containing ENZY, EO250 and ENZY + EO250 had significantly higher weight gain than those given CONT diet from d 0 to 7. No significant effects on feed intake, feed conversion ratio, mortality, organ weights except for jejunum weight and intestinal lengths was found with either enzyme or essential oil, alone or in combination, over the 21-d growth period. The supplementation of essential oil together with enzyme decreased jejunum weight compared with essential oil alone. 4. Supplementation with enzyme significantly decreased viscosity and increased dry matter of digesta, but did not alter pH of digesta. There was no effect of essential oil alone at either concentration on viscosity, dry matter or pH of digesta. A significant decrease in viscosity of digesta appeared when essential oil was used with together enzyme. 5. The supplementation of essential oil at both levels with or without enzyme significantly increased chymotrypsin activity in the digestive system, and improved crude protein digestibility. 6. The higher concentration of essential oil with and without enzyme significantly increased serum total cholesterol concentrations. No significant effect on immune response was found with either enzyme or essential oil, alone or together. 7. Enzymes and essential oil had different modes of actions. The supplementation of enzyme with essential oil in diets is likely more effective in view of performance, nutrient digestibility, enzyme activities and immune system.

________________________________________________________________________________ AbstractThe present study was conducted so that the possible effects of thermally-oxidised dietary oil and vitamin E supplementation could be determined on the performance, lipid peroxidation, antioxidant defence system and some blood and meat quality traits of broilers. Broilers were fed grower diets containing fresh or oxidised oil, supplemented with and without vitamin E (200 mg/kg) from four to six weeks of age. Neither oxidised dietary oil nor vitamin E supplementation had any adverse effect on weight gain, feed consumption or feed conversion ratio. However, the broilers that received oxidised oil had lower levels of plasma cholesterol and triglyceride compared to the control. The glucose level was neither influenced by oxidised oil nor by vitamin E supplementation. The plasma malondialdehyde level increased slightly in broilers fed oxidised oil, indicating increased lipid peroxidation. Higher glutathione peroxidise (GSH-P x ) activity observed in the broilers fed oxidised oil suggests greater oxidative stress. Vitamin E supplementation partly depressed GSH-P x activity in broilers fed oxidised oil. This depression in enzyme activity might be the result of homeostatic compensation. The uric acid concentration was not affected by oxidised oil and vitamin E supplementation. Feeding oxidised oil did not cause a marked discolouration in breast meat. Vitamin E supplementation had some beneficial effects on colour measurements.