Essential oils can be used in feed as appetite stimulant, stimulant of saliva production, gastric and pancreatic juices production enhancer, and antimicrobial and antioxidant to improve broiler performance. Antimicrobial effects of essential oils are well documented. Essential oils due to their potent nature should be used as low as possible levels in animal nutrition. Otherwise, they can lead to feed intake reduction, gastrointestinal (GIT) microflora disturbance, or accumulation in animal tissues and products. Odor and taste of essential oils may contribute to feed refusal; however, encapsulation of essential oils could solve this problem (Gauthier, 2005).
Generally, Gram-positive bacteria are considered more sensitive to essential oils than Gramnegative bacteria because of their less complex membrane structure (Lis-Balchin, 2003).
Carvacrol, the main constituent of oregano oils, is a powerful antimicrobial agent (Baser, 2008). It asserts its effect through the biological membranes of bacteria. It acts through inducing a sharp reduction of the intercellular ATP pool through the reduction of ATP synthesis and increased hydrolysis. Reduction of the membrane potential (transmembrane electrical potential), which is the driving force of ATP synthesis, makes the membrane more permeable to protons. A high level of carvacrol (1 mM) decreases the internal pH of bacteria from 7.1 to 5.8 related to ion gradients across the cell membrane. 1 mM of carvacrol reduces the internal potassium (K) level of bacteria from 12 mmol/mg of cell protein to 0.99 mmol/mg in 5 min. K plays a role in the activation of cytoplasmic enzymes and in maintaining osmotic pressure and in the regulation of cytoplasmic pH. K efflux is a solid indication of membrane damage (Ultee et al., 1999).
It has been shown that the mode of action of oregano oils is related to an impairment of a variety of enzyme systems, mainly involved in the production of energy and the synthesis of structural components. Leakage of ions, ATP, and amino acids also explain the mode of action. Potassium and phosphate ion concentrations are affected at levels below the MIC concentration (Lambert et al., 2001).
A recent review compiled information on botanicals including essential oils used in ruminant health and productivity (Rochfort et al., 2008). Unfortunately, there are few reports on the effects of essential oils and natural aromachemicals on ruminants. It was demonstrated that the consumption of terpene volatiles such as camphor and a-pinene in "tarbush" (Flourencia cernua) effected feed intake in sheep (Estell et al., 1998). In vitro and in vivo antimicrobial activities of essential oils have been demonstrated in ruminants (Cardozo, 2005; Elgayyar et al., 2001; Moreira et al., 2005; Wallace et al., 2002). Synergistic antinematodal effects of essential oils and lipids were demonstrated (Ghisalberti, 2002). Other nematocidal volatiles reported are as follows: benzyl isothiocyanate (goat), ascaridole (goat and sheep) (Githiori et al., 2006; Ghisalberti, 2002), geraniol, eugenol (Githiori et al., 2006; Chitwood, 2002), and menthol, 1,8-cineole (Chitwood, 2002).
Methylsalicylate, the main component of the essential oil of Gaultheria procumbens (Wintergreen), is topically used as emulsion in cattle, horses, sheep, goats, and poultry in the treatment of muscular and articular pain. The recommended dose is 600 mg/kg bw twice a day. The duration of treatment is usually less than 1 week (EMEA, 1999). It is included in Annex II of
Council Regulation (EEC) N. 2377/90 as a substance that does not need an MRL level. Gaultheria procumbens should not to be used as flavoring in pet food since salicylates are toxic to dogs and cats. As cats metabolize salicylates much more slowly than other species, they are more likely to be overdosed. Use of methylsalicylate in combination with anticoagulants such as warfarin can result in adverse interactions and bleedings (Chow et al., 1989; Ramanathan, 1995; Tam et al., 1995; Yip et al., 1990).
The essential oil of Lavandula angustifolia (Lavandulae aetheroleum) is used in veterinary medicinal products for topical use together with other plant extracts or essential oils for antiseptic and healing purposes. The product is used in horses, cattle, sheep, goats, rabbits, and poultry. It is included in Annex II of Council Regulation (EEC) N. 2377/90 as a substance that does not need an MRL level (EMEA, 1999; Franz et al., 2005).
The outcomes of in vitro studies investigating the potential of Pimpinella anisum essential oil as a feed additive to improve nutrient use in ruminants are inconclusive, and more and larger preferably in vivo studies are necessary for evaluation of efficacy (Franz et al., 2005).
Carvacrol, carvone, cinnamaldehyde, cinnamon oil, clove bud oil, eugenol, and oregano oil have resulted in a 30-50% reduction in ammonia N concentration in diluted ruminal fluid with a 50:50 forage concentrate diet during the 24-h incubation (Busquet et al., 2006).
Carvacrol has been suggested as a potential modulator of ruminal fermentation (Garcia et al., 2007).
Dietary addition of essential oils in a commercial blend (CRINA® Poultry) showed a decreased Escherichia coli population in ileo-cecal digesta of broiler chickens. Furthermore, in high doses, a significant increase in certain digestive enzyme activities of the pancreas and intestine was observed in broiler chickens (Jang et al., 2007).
In another study, CRINA Poultry was shown to control the colonization of the intestine of broilers with Clostridium perfringens and the stimulation of animal growth was put down to this development (Losa, 2001).
Commercial essential oil blends CRINA Poultry and CRINA Alternate were tested in broilers infected with viable oocysts of mixed Eimeria spp. It was concluded that these essential oil blends may serve as an alternative to antibiotics and/or ionophores in mixed Eimeria infections in non-cocci-vaccinated broilers, but no benefit of essential oil supplementation was observed for vaccinated broilers against coccidia (Oviedo-Rondon et al., 2006).
Supplementation of 200 ppm essential oil mixture (EOM) that included oregano, clove, and anise oils (no species name or composition given!) in broiler diets was said to significantly improve the daily live weight gain and feed conversion ratio (FCR) during a growing period of 5 weeks (Ertas et al., 2006). Similar results were obtained with 400 mg/kg anise oil (composition not known!) (Ciftci et al., 2005).
A total of 50 and 100 mg/kg of feed of oregano oil* were tested on broilers. No growth-promoting effect was observed. At 100 mg/kg of feed, antioxidant effect was detected on chicken tissues (Botsoglou et al., 2002a).
Positive results were also reported for oregano oil added in poultry feed (Bassett, 2000).
* Oregano essential oil was in the form of a powder called Orego-Stim. This product contains 5% oregano essential oil (Ecopharm Hellas, SA, Kilkis, Greece) and 95% natural feed grade inert carrier. The oil of Origanum vulgare subsp. hirtum used in this product contains 85% carvacrol + thymol.
Antioxidant activities of rosemary and sage oils on lipid oxidation of broiler meat have been shown. Following dietary administration of rosemary and sage oils to the live birds, a significant inhibition of lipid peroxidation was reported in chicken meat stored for 9 days (Lopez-Bote et al., 1998). A dietary supplementation of oregano essential oil (300 mg/kg) showed a positive effect on the performance of broiler chickens experimentally infected with Eimeria tenella. Throughout the experimental period of 42 days, oregano essential oil exerted an anticoccidial effect against Eimeria tenella, which was, however, lower than that exhibited by lasalocid. Supplementation with dietary oregano oil to Eimeria tenella-infected chickens resulted in body weight gains and feed conversion ratios not differing from the noninfected group, but higher than those of the infected control group and lower than those of chickens treated with the anticoccidial lasalocid (Giannenas et al., 2003).
Inclusion of oregano oil at 0.005% and 0.01% in chicken diets for 38 days resulted in a significant antioxidant effect in raw and cooked breast and thigh muscle stored up to 9 days in refrigerator (Botsoglou et al., 2002b).
Oregano oil (55% carvacrol) exhibited a strong bactericidal effect against lactobacilli and following the oral administration of the oil MIC values of amicain, apramycin, and streptomycinand neomyc against Escherichia coli strains increased (Horosova et al., 2006).
An in vitro assay measuring the antimicrobial activity of essential oils of Coridothymus capi-tatus, Satureja montana, Thymus mastichina, Thymus zygis, and Origanum vulgare was carried out against poultry origin strains of Escherichia coli, Salmonella enteritidis, and Salmonella essen, and pig origin strains of enterotoxigenic Escherichia coli (ETEC), Salmonella choleraesuis, and Salmonella typhimurium. Origanum vulgare (MIC < 1% v/v) oil showed the highest antimicrobial activity against the four strains of Salmonella. It was followed by Thymus zygis oil (MIC < 2% v/v). Thymus mastichina oil inhibited all the microorganisms at the highest concentration, 4% (v/v). Monoterpenic phenols carvacrol and thymol showed higher inhibitory capacity than the monoter-penic alcohol linalool. The results confirmed potential application of such oils in the treatment and prevention of poultry and pig diseases caused by salmonella (Penalver et al., 2005).
In another study, groups of male, 1-day-old Lohmann broilers were given maize-soya bean meal diets, with oils extracted from thyme, mace, and caraway or coriander, garlic, and onion (0, 20, 40, and 80 mg/kg) for 6 weeks. The average daily gain and FCR were not different between the broilers fed with the different oils; meat was not tainted with flavor or smell of the oils (Vogt and Rauch, 1991).
Essential oils from oregano herb (Origanum onites), laurel leaf (Laurus nobilis), sage leaf (Salvia fruticosa), fennel fruit (Foeniculum vulgare), myrtle leaf (Myrtus communis), and citrus peel (rich in limonene) were mixed and formulated as feed additive after encapsulation. It is marketed in Turkey as poultry feed under the name Herbromix®.
The following three in vivo experiments with this product were recently accomplished.
In this study, 1250 sexed 1-day-old broiler chicks obtained from a commercial hatchery were randomly divided into five treatment groups of 250 birds each (negative control, antibiotic, and essential oil combination (EOC) at three levels). Each treatment group was further subdivided into five replicates of 50 birds (25 males and 25 females) per replicate. Commercial EOC at three different levels (24, 48, and 72 mg) and antibiotic (10 mg avilamycin) per kg were added to the basal diet. There were significant effects of dietary treatments on body weight, feed intake (except at day 42), FCR, and carcass yield at 21 and 42 days. Body weights were significantly different between the treatments. Birds fed on diet containing 48 mg essential oil/kg being the highest and this treatment was followed by chicks fed on the diet containing 72 mg essential oil/kg, antibiotic, negative control, and 24 mg essential oil/kg at day 42.
Supplementation with 48 mg EOC/kg to the broiler diet significantly improved the body weight gain, FCR, and carcass yield compared to other dietary treatments on 42 days of age. EOC may be considered as a potential growth promoter in the future of the new era, which agrees with producer needs for increased performance and today's consumer demands for environment-friendly broiler production. The EOC can be used cost effectively when its cost is compared with antibiotics and other commercially available products in the market.
In this study, 1250 sexed 1-day-old broiler chicks were randomly divided into five treatment groups of 250 birds each (negative control, organic acid, probiotic, and EOC at two levels). Each treatment group was further subdivided into five replicates of 50 birds (25 males and 25 females) per replicate. The oils in the EOC were extracted from different herbs growing in Turkey. The organic acid at 2.5 g/kg diet, the probiotic at 1 g/kg diet, and the EOC at 36 and 48 mg/kg diet were added to the basal diet.
The results obtained from this study indicated that the inclusion of 48 mg EOC/kg broiler diet significantly improved the body weight gain, FCR, and carcass yield of broilers compared to organic acid and probiotic treatments after a growing period of 42 days. The EOC may be considered as a potential growth promoter like organic acids and probiotics for environment-friendly broiler production.
The aim of the present study was to examine the effect of essential oils and breeder age on growth performance and some internal organs weight of broilers. A total of 1008 unsexed 1-day-old broiler chicks (Ross-308) originating from young (30 weeks) and older (80 weeks) breeder flocks were randomly divided into three treatment groups of 336 birds each, consisting of control and two EOMs at a level of 24 and 48 mg/kg diet. There were no significant effects of dietary treatments on body weight gain of broilers at days 21 and 42.
On the other hand, there were significant differences on the feed intake at days 21 and 42. The addition of 24 or 48 mg/kg EOM to the diet reduced significantly the feed intake compared to the control. The groups fed with the added EOM had significantly better FCR than the control at days 21 and 42. Although, there was no significant effect of broiler breeder age on body weight gain at day 21, significant differences were observed on body weight gain at 42 days of age. Broilers originating from young breeder flock had significantly higher body weight gain than those originating from old breeder flock at 42 days of age. No difference was noticed for carcass yield, liver, pancreas, proventriculus, gizzard, and small intestine weight. Supplementation with EOM to the diet in both levels significantly decreased mortality at days 21 and 42.
The results indicated that the Herbromix may be considered as a potential growth promoter. However, more trials are needed to determine the effect of essential oil supplementation to diet on the performance of broilers with regard to variable management conditions including different stress factors, essential oils and their optimal dietary inclusion levels, active substances of oils, dietary ingredients, and nutrient density (Cabuk et al., 2006a, 2006b; Alcicek et al., 2003, 2004; Bozkurt and Baser, 2002a, 2002b).
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