چكيده لاتين :
Introduction Antibiotic feed additives have long been used as growth promoters in poultry nutrition. However, concern has been expressed about the potential development of antibiotic resistant bacteria (25). Consequently, the animal feed industry, exposed to increasing consumer pressure to reduce the use of antibiotic growth promoters in poultry diets, has to find alternative feed additives. Marjoram (Origonum vulgar) is a very popular and a common medicinal plant. The main chemical components of marjoram oil are carvacrol, thymol, myrsene, p-cymene, terpinene and pinene (29). The plant is reported to possess antibacterial and antioxidant activities (2, 36).
The present study was carried out to investigate the effect of adding different levels of marjoram leaves (powder and hydroalcoholic extract) into broiler diets on growth performance, blood metabolites, relative weight of internal organs, ileal microflora, jejunal histomorphology and meat quality of broiler chicks.
Materials and methods Two hundred and eighty eight one-day old Ross 308 broiler chicks (male) were obtained from a commercial local source and used in this study. The experiment was conducted in a completely randomized design with 8 treatments, 3 replicates and 12 birds in each replicate. Experimental treatments consisted of control diet (without any additives), antibiotic virginiamycin (100 mg/kg), Origanum vulgare leaves powder (1, 2 and 3%) and Origanum vulgare extract (150, 250 and 350 mg/kg). The experimental period lasted up to the 42 d of age. The rearing and management conditions were equal for all groups. Experimental diets were formulated to meet the nutrients requirements of the Ross broiler chicks (3). Chicks had full access to feed and water during the experimental period. Live body weight and feed intake were recorded at 10, 24 and 42 d of age for each replicate. At the end of the experiment, the blood samples (from one chick per replicate) were collected to determine hematological parameters, then the chicks were slaughtered and ileum contents were removed for bacterial counts and also jejunum were immediately removed for histological studies.
Results and Discussion Based on the results, in 1-10 d period, supplementing the broiler diet with virginiamycin increased significantly feed intake (P <0.01). Also in 11-24 d period, supplementing the broiler diet with virginiamycin increased significantly feed intake compared to the birds fed 2 and 3 percent origanum vulgar powder and 350 mg/kg extract (P <0.05). The lowest feed intake and weight gain were observed in birds fed diet supplemented with 3 percent origanum vulgar powder. In 1- 42 d period, weight gain of the chicks fed 1 and 2 percent powder and 350 mg/kg extract was improved significantly compared to control (P <0.01) and also feed conversion ratio of the chicks fed control and 3 percent powder were increased significantly compared to the other treatments (P <0.01). Essential oils have long been recognized because of their anti-microbial activity and their ability to improve digestion (13, 18, 29). The effect of essential oils on feed: gain ratio could relate to increased efficiency of feed utilization and/or altered carcass composition (29). Also, supplementing broiler diets with origanum vulgar powder at 3 percent or higher levels are not recommended because of its adverse effect on feed intake and weight gain..
Blood metabolites (glucose, triglyceride, cholesterol, HDL, LDL, alkaline phosphatase, albumin) and the relative weight of carcass components (heart, liver, breast, thighs, gizzard) were not significantly affected by the treatments. Our findings are in agreement with Hernandes et al. (23) and Kirkpinar et al. (27). It seems that supplementing broiler diets with different levels of origanum vulgar have no detrimental effect on blood metabolites and carcass components.
Using 1 and 2 percent powder and 350 mg/kg extract reduced coliform bacteria population in the small intestine in comparison with the control, because essential oils in origanum vulgar have anti-microbial activity (22, 28, 35). Supplementing diet with 150 mg/kg extract significantly increased villus height and crypt depth in comparison with the control and virginiamycin. Villus height: crypt depth ratio in chicks fed virginiamycin and 350 mg/kg extract were significantly higher than chicks received 1 and 2 percent powder (P <0.01). There are conflicting reports regarding the effect of phytogenic plants on villus height and crypt depth (16, 21, 26, 39). According to Perlic et al. (39), adding medicinal plants to broiler diets can significantly decrease villus height: crypt depth ratio. Hashemipour et al. (21) in agreement to our finding, reported thymol and carvacrol can increase villus height and have no effect on villus width. But according to Jia- chi et al. (26) few medicinal plants had no effect on villus height and depth.
The effect of different dietary treatments on drip loss and malondialdehyde value (TBA) of meat were significant (P <0.01). Supplementing diets with 1 or 2 percent powder and different levels of the extract significantly reduced TBA. Our findings are in agreement with few reports (7, 28, 37, 46). Origanum vulgare essential oil contains mainly carvacrol, thymol and their precursors and it possesses antioxidant properties. It was suggested that the high antioxidant activity of thymol is due to the presence of phenolic OH groups which act as hydrogen donors to the proxy radicals produced during lipid oxidation, thus retarding the hydroxyl peroxide formation (29).
Conclusion In conclusion, Origanum vulgare extract (at 350 mg/kg) can be used as a good replacement for antibiotics. Also, supplementing broiler diets with 3 percent Origanum vulgare leaves powder significantly decreased feed intake and subsequently weight gain. So, adding the powder to broiler diets is not recommended more than 2 percent.
