Advances in Animal and Veterinary Sciences
Review Article
Advances in Animal and Veterinary Sciences 2 (1): 1 – 7Essential Oils as a Feed Additive in Poultry Nutrition
Marappan Gopi1*, Kumaragurubaran Karthik2, Haranahalli Vasanthachar Manjunathachar3, Paramasivam Tamilmahan4, Manickam Kesavan5, Moorthy Dashprakash6, Bharemara Lingaraju Balaraju7, Manika Ragavan Purushothaman8
- Division of Animal Nutrition, IVRI, Izatnagar
- Division of Bacteriology and Mycology, IVRI, Izatnagar
- Division of Parasitology, IVRI, Izatnagar
- Division of Veterinary Surgery and Radiology, IVRI, Izatnagar
- Division of Veterinary Pharmacology and Toxicology, IVRI, Izatnagar
- Division of Veterinary Virology, IVRI, Izatnagar
- Division of Extension Education, IVRI, Izatnagar
- Department of Animal Nutrition, Veterinary College and Research Institute, Namakkal, India
*Corresponding author:getgopi72@gmail.com
ARTICLE CITATION:
Gopi M, Karthik K, Manjunathachar HV, Tamilmahan P, Kesavan M, Dashprakash M, Balaraju BL and Purushothaman MR (2014). Essential oils as a feed additive in poultry nutrition. Adv. Anim. Vet. Sci. 2 (1): 1 – 7.
Received: 2013–09–16, Revised: 2013–10–31, Accepted: 2013–10–31
The electronic version of this article is the complete one and can be found online at
(
http://dx.doi.org/10.14737/journal.aavs/2014.2.1.1.7
)
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
ABSTRACT
The increased awareness and concern over the antibiotic residues in animal and poultry products among the consumers made the hour a prime time to find an alternative to antibiotic growth promoters (AGPs) and it have increased a lot over the past decade. One such alternative is the essential oils (EOs) which are derived from various plants as secondary metabolites. Essential oil usage in animal feeding has been practiced for their role as antibacterial, antiviral, antifungal, antioxidant, digestive stimulant, immunomodulator, hypolipidemic agent and also heat stress alleviator. They had been successfully used as a dietary antibiotic replacer without residues. They not only act as an in vivo anti-oxidant for the animal but also exert its anti-oxidant action to prolong the shelf life of the feed in which it is incorporated and the meat which is obtained from the animal fed with essential oils. The lean meat produced by essential oil supplementation through the poultry diet reduces the risk of hyperlipidemia in the consumers. The results being favourable as an alternative to antibiotics, spur the researchers to exploit the role of essential oil mixtures as a feed additive. Nowadays, essential oils are used in the ruminant experiments as an agent to reduce the rate of methanogenesis thereby traffics the organic molecules for efficient energy synthesis. Hence, various studies have been carried out across the globe with possible combinations and cocktail of these oils or the crude extracts of their active principles to explore the multifaceted calibre of these feed additives. The expanding horizons in the research on essential oils are expected to pull the curtain down for the extensive use of antibiotics as feed additives. In the near future the role of essential oils in the poultry feeding will play a huge role in the industry development.
INTRODUCTION
The dietary use of antibiotics has been practised for decades in animal production especially in commercial poultry production as a growth promoter. The need for the use of antibiotics to decrease the spread of disease (Waldroup et al., 2003) and as a growth enhancer is increasing day by day to sustain the growth of poultry production (Roura et al., 1992). The opportunistic pathogens that are normally inhabitant of the intestinal tract may reduce the growth rate and is related with the microbial load of the chicken’s environment (Thomke and Elwinger, 1998). Antibiotics act on pathogenic intestinal bacteria that will produce toxins that harm the birds either in terms of livelihood or production performance. Antibiotics used in this way get accumulated in the tissues of birds leading to antibiotic resistance in human through food chain ultimately ending up in therapeutic failure (Levy and Marshall, 2004).
Many countries have banned the use of antibiotics in animal production as a feed additive. Hence the need of the hour is to find an alternative to antibiotics. Therefore, search for antibiotic alternatives have already been undergoing to control the enteric diseases (Fritts and Waldroup, 2003; Ayed et al., 2004) which is encouraged by the World Health Organization (Humphrey et al., 2002). The quest for the alternatives to antibiotics has been tried by many scientists like Langhout, (2000); Mellor, (2000); Wenk, (2000) and Humphrey et al., (2002). Humphrey et al. (2002) found that lactoferrin and lysozyme are having the antibacterial activity and can be used as an alternative to antibiotics in chickens as feed additive. Rectenly, Essential Oils (EOs) are found to have antibacterial property and also exhibiting antioxidant, antiinflammatory, anticarcinogenic, digestion–stimulating and hypolipidemic activities (Viuda–Martos et al., 2009, 2011). Considering the versatility of EOs, it can be used as growth promoters in animal production.
What are Essential Oils?
EOs are derived as a mixture of aromatic oily liquids obtained from plant materials such as flowers, buds, seeds, leaves, twigs, bark, herbs, wood, fruits and roots. They are fragrant volatile compounds, named after their origin (Oyen and Dung, 1999). The term ‘essential’ was proposed by Paracelsus in his theory of ‘quinta essentia’ who believed that this quintessence was the effective element in a medical preparation (Oyen and Dung 1999) but the term ‘volatile oil’ had been proposed in medieval pharmacy (Hay and Waterman, 1993). Essential oils were obtained by various methods like expression, fermentation or extraction but the method of steam distillation is the most commonly used method commercially. They are categorized as “generally recognized as safe” (GRAS), as endorsed by the Flavour and Extract Manufacturers Association (FEMA) and the Food and Drug Administration (FDA) from the U.S.A., and used in the food industry. The use of EOs in enhancing productivity gives promising results as growth and health promoter.
Classification of Essential Oils
EOs are basically comprises two classes of compounds: Terpenes and Phenylpropenes. Terpenes are sub–divided based on the 5–carbon isoprene unit (building block) into mono, sesqui and diterpenes where the numbers of isoprene units are 2, 3 and 4 respectively, while the phenylpropenes consist of 6–carbon aromatic ring with a 3–carbon side chain (C6–C3 compounds). More than 1000 monoterpenes and 3000 sesquiterpenes are identified until today (Clegg et al., 1980; Cooke et al., 1998).
Essential Oil Synthesis
The terpenes and phenylpropenes are synthesized by mevalonic and shikimic pathways, respectively. Mevalonic acid (six carbons) that is formed by condensation of three acetate units by HMG–CoA reductase, is converted to 5–carbon isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are the activated 5–carbon units of isoprene. IPP and DMAPP are then combined in a 1:1 molar ratio to generate 10–carbon geranyl pyrophosphate (GPP), the precursor of monoterpenes. The conversion of IPP to GPP produces the 15–carbon sesquiterpene compound, farnesyl pyrophosphate (FPP). Thymol and carvacrol are derived from GPP and classified as monoterpenoids or isoprenoids. β–ionone is derived from FPP and thus classified as either sesquiterpene or isoprenoid. Classification of essential oils is given in Figure 1.
The shikimic acid pathway produces the aromatic amino acid phenylalanine, the products of which are cinnamic acid and p–coumaric acid, occurring in trans–configuration (Seigler, 1998).
Among the important phenylpropene compounds are eugenol, trans–cinnamaldehyde, safrole and also the pungent principles, capsaicin and piperine. These are classified as phenylpropenoids. The synthetic pathways and the related compounds are reviewed in more detail elsewhere (Loza–Tavera, 1999).
Properties of Essential Oils
Essential oils possess the characteristic odours that are specific to that oil. They exist either in liquid or volatile form at the ambient temperature. They are readily soluble in common organic solvents like ether, benzene, acetone, etc. Most of the EOs are lighter than water with specific gravity between 0.8 and 1.17 but the clove and cinnamon oils are heavier.
Uses of Essential Oils in Poultry Feeding
The EOs have wide range of activities in system like anti–bacterial, antioxidant, digestive stimulant, hypolipidemic, growth promoter, immunomodulator, antimycotic, antiparasitic, antitoxigenic, antiviral and insecticidal. But the most important uses of EOs are reviewed here. Beneficial activities of essential oils are summarized in Figure 2
Antimicrobial Activity
The antimicrobial activities of EOs were exploited from the ancient period (Hammer et al., 1999). This property has kindled the interest of researchers to use it as an antibiotic alternative. The pure compounds have been shown to have antimicrobial effects in vitro (Cowan, 1999). Cinnamaldehyde derived from Cinnamon strongly inhibits Clostridium perfringens and Bacteroides fragilis and moderately inhibits Bifidobacterium longum and Lactobacillus acidophilus isolated from human faeces (Lee and Ahn, 1998). This property of selective inhibition of intestinal pathogenic bacteria can be exploited to balance the microbial population in the poultry intestine.
The antimicrobial properties of 29 essential oils were evaluated against 59 microorganisms (Deans and Ritchie, 1987) and this property differs with the family it belongs, like Lavandin, Tea tree and Peppermint oils have shown a little or no antimicrobial property but Cinnamon, Oregano, Thyme have shown great antimicrobial activity, while Juniper shows an antifungal activity (Dorman and Deans, 2000, Royo et al., 2010).
The exact mechanism of antimicrobial activity is poorly understood. The cell membrane is the main site of action. It may be due to the change in the permeability of cytoplasmic membrane to hydrogen (H+) and potassium (K+) ions (Deans and Ritchie, 1987). Their hydrophobic nature makes them more active against Gram positive bacteria and the small molecular weight of these oils makes them active against Gram negative bacteria too (Deans and Ritchie, 1987).
Antimicrobial Action of Individual Essential Oils
Carvacrol and thymol causes disintegration of the membrane of bacteria and hence leading to the release of membrane–associated material from the cells to the external medium.
Terpenoids and Phenylpropanoids can penetrate the membrane of the bacteria due to their lipophilicity and reach the inner part of the cell.
The antifungal activity of cinnamaldehyde (Kurita et al., 1979) due to its reaction with sulfhydryl groups which is necessary for the growth of the fungi. The formation of charge transfer complexes with electron donors in the fungal cell could lead to inhibition of cell division and thus interferes with cell metabolism.
It was also reported that cinnamaldehyde inhibits fungal cell wall synthesizing enzymes (Bang et al., 2000).
The combination of probiotics and essential oils inflicted a decrease of microbial load in the intestine.
Garlic oil has been shown to inhibit E. coli and Salmonella Typhimurium during in vitro studies (Ross et al., 2001).
Table 1 shows the In vitro studies on essential oils for its antimicrobial activity and minimum inhibitory concentration (mic,ppm).
Blends of EOs could be used to control Clostridium perfringens; Thymol can inhibit the growth of S. Typhimurium and E. coli (Helander et al., 1998).
Hernandez et al. (2003) showed, in a study with live chickens, that a blend of the EOs of cinnamon, pepper, and oregano improved digestibility in chickens receiving supplemental feed compared with chickens fed a control diet without the blend. Several studies indicated that the use of EOs improved broiler feed conversion ratio (Windisch et al., 2008).
Thyme essential oil (TEO) fed to Japanese quail reduced the ileal E. coli and increased the Lactobacillus count (Figure 3) on 35 days of feeding (Khaksar et al., 2012).
Essential oils in addition to its antimicrobial activity also possess various activities like antioxidant property (Krause and Ternes, 1999; Botsoglou et al., 2002a), hypocholesterolemic activity (Yu et al., 1994; Case et al., 1995; Craig, 1999), flavouring agent and also has digestive stimulant properties (Langhout, 2000; Williams and Losa, 2001).
Antioxidant Activity of Essential Oils in the Biological System
Essential oils have good antioxidant role in biological system. EOs acts as effective free radicals scavenger (Youdim and Deans, 1999 and 2000). EOs influences the in vivo antioxidant defense systems such as SOD, glutathione peroxidase and Vit E. Oregano essential oil possesses high antioxidant activity (Cervato et al., 2000; Dorman et al., 2003) and enhances oxidative stability of fat–containing animal products like meat and eggs by compensating the increased degree of unsaturation (Bauer et al., 2001; Botsoglou et al., 2002b)
In Vitro Studies
Economou et al. (1991) assessed the antioxidative properties of various extracts of plant oils like oregano, thyme, marjoram, spearmint, lavender and basil which was added to lard kept at 75 °C. He assessed the antioxidant property by their effectiveness in stabilizing the lard and found out that extract containing Oregano (Raza et al., 2009) was the most effective followed by thyme, dittany, marjoram and lavender. Studies of Schwarz et al. (1996) reported that compounds like β–cymene–2, 3–diol, thymol and carvacrol (Baratta et al., 1998) were found in thyme showed strong antioxidant properties.
Farag et al. (1989) carried out a study to find out the relationship between the antioxidant property of the essential oils and its chemical composition, and found that the high antioxidant activity of thymol is due to its phenolic OH groups acting as hydrogen donors to the peroxy radicals which are produced during the lipid oxidation and thereby reduce the hydroxyl peroxide formation.
In Vivo Studies
The antioxidant effect of essential oils in broiler chicken has been reported by the studies of Lopez–Bote et al. (1998); Botsoglou et al. (2002a, 2002b). Botsoglou et al. (2002b) found that Oregano essential oils exert its antioxidant property on the cell membrane of meat and abdominal fat. EOs acts as effective free radical scavengers and enhances the in vivo antioxidant systems – superoxide dismutase, glutathione peroxidase and vitamin E. Botsoglou et al. (1997) found that lower concentration of malonaldehyde in chicken egg yolk feed with thyme and related it to the transfer of antioxidant components but its effect disappeared soon after the stop of supplementation. Thymol and carvacrol have antioxidant activity on egg and chicken meat when supplemented in the feed (Lee and Marshall, 2004).
Phenols olive oil are effective non–tocopherol antioxidants (Baldioli et al., 1996), have antioxidative property (Papadopoulos and Boskou, 1991), free radical scavenging ability (Visioli et al., 1998), act as a specific antioxidant on bio-membranes (Saija et al., 1998) and inhibit the low density lipoprotein oxidation (Wiseman et al., 1996; Visioli et al., 1998).
Essential Oil as Flavouring Agent
Essential oils are used as flavouring agent in human foods. Carvacrol can be used in non alcoholic beverages up to the level of 26 ppm and in baked goods up to 120 ppm (Furia and Bellanca, 1975). Cinnamaldehyde can be used as low as 8 ppm in ice cream products and as high as 4900 ppm in chewing gum (Furia and Bellanca, 1975). Thymol and beta–ionone are also used as flavouring agents in foods. The characteristic flavour of essential oils can be used to standardize the diet so that there is no alteration in feed intake post weaning in piglets. Specific effects of flavours on chicken performance have not received much attention because poultry may not acutely respond to flavour when compared to pigs (Moran, 1982). With the limited literature, there is evidence (Deyoe et al., 1962) that flavours could affect feed intake. On the other hand, the effects of flavours on poultry performance are regarded as negligible (Moran, 1982). Hence the aspect of essential oil as flavouring agent in poultry nutrition needs to be assessed.
Essential Oils on Digestive Processes
There are studies that dietary essential oils addition could improve the digestion process (Mellor, 2000), the reason behind the use of spices and herbs (from which essential oils are derived) in food (Pradeep and Geervani, 1994). They enhance the trypsin and amylase enzyme activity (Jang et al., 2007). The pungent principles in essential oils like curcumin, capsaicin and piperine have been found to stimulate the digestive enzyme activities of both intestinal mucosa and also in pancreas (Platel and Srinivasan, 2000). Studies have shown that the spices or its active components increased the bile salt secretion (Sambaiah and Srinivasan, 1991). Cinnamaldehyde increased the bile secretion in the rat (Harada and Yano, 1975). The pungent principles capsaicin, piperine and cinnamaldehyde share their synthetic pathways (shikimic pathway). Lee et al. (2003) reported that cinnamaldehyde in diet had a role in the digestion process while thymol is not involved in these processes. Kreydiyyeh et al. (2000) observed that there was an increase in the absorption of glucose in the intestine of rats when they were fed with anise oil.
Role of Essential Oils in Lipid Metabolism
Craig (1999) reported that the herbs and its essential oils have a role in cholesterol lowering activity and by doing so they provide protection against cancer. The hypocholesterolemic effect of lemongrass oil is due to the inhibition of hepatic 3–hydroxy–3–methylglutaryl coenzyme A (HMG–CoA) reductase activity which is a key regulatory enzyme in cholesterol synthesis (Elson et al., 1989, Cooke et al., 1998, Crowell, 1999).
Case et al. (1995) reported in poultry, a 5% inhibition of HMC–CoA reductase activity will lead to lowered serum cholesterol by 2%. Qureshi et al. (1988) fed cockerels with limonene at 25 to 100 ppm for a period of 26 days and found that the hepatic HMG–CoA reductase activity as well as the serum cholesterol show a dose–dependent decrease, however, the hepatic fatty acid synthetase activity remained unaffected. Dietary essential oils like borneol, cineole, citral, geraniol, menthone, menthol, fenchone and β–ionone suppresses the hepatic HMG–CoA reductase activity (Yu et al., 1994). Middleton and Hui (1982) reported that the inhibitory action of essential oils on hepatic HMG–CoA reductase is independent of the diurnal cycle of the enzyme and of hormones like insulin, glucocorticoids, triiodothyronine and glucagon. Study by Gopi et al. (2012) reported a significant reduction in the serum cholesterol level of broiler fed with cinnamon powder at 250 and 500 ppm (97.43 and 94.87 mg/dl vs 116 mg/dl). The broilers showed a dose dependent reduction in serum cholesterol levels.
Essential Oils in Meat Type Chickens
The essential oils as single or mixture may be used as a growth promoter in broiler production. Many studies have shown positive effects of dietary essential oil on body weight. Supplementing the dietary essential oils (Cross et al., 2002, 2007; Bampidis et al., 2005) would stimulate the growth performance of broilers. Higher body weight gain was observed in broilers fed with peppermint diet (Lovkova et al., 2001). The essential oils act as digestibility enhancer, optimizing the gut microbial ecosystem, stimulates the secretions of digestive enzymes and improves the growth performance in poultry (Lovkova et al., 2001; Williams and Losa, 2001; Cross et al., 2007). Ocak et al. (2008) supplemented a mixture of herbal essential oils to broilers and found a significant reduction in feed intake which was also observed in the study performed by Lee et al. (2003). When broilers were fed with essential oil mixture at levels of 24 and 48 mg/kg diet there was better feed conversion ratio and the mortality was reduced when fed with 0.2% of peppermint and thyme diets separately than groups fed with control diets during the 42 days growth period (0.00 and 0.00 vs 2.88% respectively). Denli et al. (2004) observed improved feed efficiency when the broiler quails were fed with thyme essential oils. They reported that the improvement in feed efficiency and feed intake achieved with essential oil mixture could be due to its positive effects on nutrient digestibility as reported by Langhout (2000a); Alcicek et al. (2003); Hernandez et al. (2004); Lee et al. (2003) interpreted that essential oil and their mixture could positively affect the intestinal microflora and thus digestion. Fotea et al. (2004) observed best average body weight of 2484g at the age of 42 days and 4% improvement in feed efficiency when broilers fed with 1.0% Oregano oil. Essential oils mixture of 200 ppm of oregano, anise oil, clove, rosmarin and tumeric plant have shown improvement in the growth performance of live broilers (Jamroz and Kamel 2002; Al–Sultan Zhang et al., 2003). Gopi et al. (2012) reported that there was improvement in body weight gain in broilers fed with cinnamon powder at the rate of 500 ppm and 250 ppm (2109 and 1982 vs 1947 g). The feed efficiency was significantly better in supplemented group compared to control group (1.79 and 1.83 vs 2.03).
Thymol and carvacrol, from thyme and oregano respectively, have demonstrated biological properties such as antimicrobial, antioxidant and antiseptic activities (Lee and Ahn, 1998). Although evidence of the underlying mechanisms is still lacking by which dietary EO affect growth performance, dietary supplementation of EO has a beneficial effect on intestinal microflora (Helander et al., 1998) and digestive enzymes (Lee et al., 2003; Jang et al., 2007). Total and specific activities of trypsin in the pancreas were significantly (P<0.05) greater in blend EO at 50mg/kg. Total activity of maltase in the proximal region was much greater (P<0.05) in birds fed with 50 ppm of EO than those fed with basal diet or the diets containing antibiotics and 25 ppm of EO (Jang et al., 2007).
The efficacy of EO on growth performance in poultry is not consistent as it was supplemented to the diets at the levels of 20–200 mg EO/kg diet. Botsoglou et al. (2004) reported that supplementation of essential oils to diet had no beneficial effect on body weight. Similar observation was also made by Hernandez et al. (2004) who found that the addition of two plant extract to the diet had no effect on body weight and also Madrid et al. (2003) carried out studies on the blend of oregano, cinnamon and pepper essential oil on broiler performance. Hernandez et al. (2004) and Botsologlu et al. (2004) found that the addition of plant extracts to the diet had no beneficial effect on feed conversion ratio.
Cross et al. (2007) reported that dietary thyme had a different effect when used as herb or oil on weight gain and body mass. Essential oils or the main components of the essential oil did not affect the body weight gain or feed efficiency in broilers (Cross et al., 2002, 2007; Demir et al., 2003; Botsoglou et al., 2004; Hernandez et al., 2004; Bampidis et al., 2005).
The body weight of broilers fed with curcumin at the level of 0.1% was significantly (p<0.05) more (2273.39 ± 52.97) when compared to the control (1947.83 ± 41.39) and turmeric powder (2151.89 ± 55.16) fed groups (Mehala and Moorthy, 2008 and Moorthy and Edwin, 2010). The feed intake was significantly (p<0.05) more in curcumin (4504.76 ± 90.66) and turmeric powder (4256.65±93.04) supplemented groups than control (3954.22 ± 83.24). AL–Sultan (2003) observed improved feed consumption and increased average body weight in broilers fed with turmeric supplemented diets. Feed conversion ratio did not differ significantly.
The serum glutathione peroxidase (mg/ml) and ascorbic acid (mg/ml) contents were better in turmeric powder and curcumin fed groups compared to the control group. Chattopadhyay et al. (2004) and Holovska et al. (2003) observed increase in plasma antioxidant enzyme levels due to the supplementation of antioxidants in the diet of broilers. Rezaei–Moghadam et al. (2012) has also reported that supplementation of turmeric increases serum antioxidant levels. The immune status of the birds as assessed by RD titre values (log2) was found to be better in essential oil supplemented at 0.1% (7.0) and essential oil supplemented at 0.2% (6.75) groups as compared to control group (6.6). Madpouly et al. (2011) reported that turmeric powder in poultry rations enhances the immune response. Jamroz et al. (2005) also demonstrated increased pancreatic and intestinal lipase activity in broilers diets fed with added plant extract.
Essential Oils in Egg Laying Chickens
Supplementation of a diet with a mixture powder of garlic and thyme assisted in improving performance of laying hens and egg quality traits (Ghasemi et al., 2010). Plant extracts and spices as single compounds or as mixed preparations can play a role in supporting both performance and health status of animals (Alcicek et al., 2003;
2004; Cabuk et al., 2006). Essential oil addition significantly increased egg production than the addition of the antibiotic. Essential oils significantly reduced the incidence of broken/cracked eggs. An essential oil mixture was the only additive to significantly improve feed efficiency compared to the control. Dietary supplementation with essential oil mixture also improved (P < 0.01) feed efficiency. A similar result was observed by Ather (2000), who reported that the addition of essential oils of a polyherbal feed additive to a broiler breeder diet showed better average egg production compared to their control. Deying et al. (2005) found that a diet supplemented with herbal medicine (Ligustrum lucidum and Schisandra chinensis) significantly improved egg production and feed efficiency of laying hens. Botsoglou et al. (2005) was unable to find any significant effect on either on the egg production nor the feed efficiency on dietary addition of rosemary, oregano and saffron to the layers.
The performance of laying hens during the summer season can be maintained with dietary inclusions of essential oil mixtures. The results with essential oils during summer season have anti–heat stress effects (Liu–Fengtlua et al., 1998). Summer stress leads to drop in egg production, more egg breakage and mortality. To alleviate heat stress in poultry during summer season herbs such as tulsi, ashwagandha, amla, curry leaf, garlic and turmeric powder were evaluated in broiler chicken birds. Among the various herbal preparations screened, amla followed by ashwagandha (Withania somnifera) were found to increase the body weight, immune status, serum antioxidant levels and general health of the commercial broiler birds (Vasanthakumar et al., 2012a). The inclusion of essential oil mixture at the rate of 24 mg/kg diet significantly improved egg production, feed efficiency and reduced the percentage of cracked/broken eggs (Cabuk et al., 2006).
The preliminary findings by author with fenugreek seeds improved the semen quality in broiler breeder birds and thereby significant improvement in hatchability is expected. Further studies are in progress both in broilers and breeder hens to derive concrete results.
CONCLUSION
The antimicrobial activities of essential oils have been well documented while its toxicological effects are seen only at very high doses. The antioxidant and hypocholesterolemic effects have been studied in chickens. The characteristic flavour and stimulation of digestive process of essential oils might play role in poultry performance, however, it requires further studies. The hypolipidemic and immunomodulatory properties of these oils are gaining more interest among the poultry industrialists. The antioxidant property of these oils provides an effective protection against the drip loss during the prolonged low temperature storage which increases the acceptance among the consumers and reduces the loss for the meat processors. To conclude, the essential oils in the poultry diet could be used as an alternative to antibiotics, growth performance and value added products – low cholesterol meat, tenderness, green eggs, etc. Its role in improving the keeping quality and durability of raw as well as processed meat and nutraceutical property is also gaining importance. In the near future, it is expected that essential oils will play a huge role in the poultry industry development.
REFERENCES
Alcicek A, Bozkurt M and Cabuk M (2003). The effect an essential oil combination derived from selected herbs growing wild in Turkey on broiler performance. S. Afr. J. Anim. Sci. 33: 89–94.
http://dx.doi.org/10.4314/sajas.v33i2.3761
Alcicek A, Bozkurt M and Cabuk M (2004). The effect of a mixture of herbal essential oils, an organic acid or a probiotic on broiler performance. S. Afr. J. Anim. Sci. 34: 217–22.
Ali–Shtayeh MS, Al–Nuri MA, Yaghmour RMR and Faidi YR (1997). Antimicrobial activity Micromeria nervosa from the Palestinian area. J. Ethnopharm. 58: 143–147.
http://dx.doi.org/10.1016/S0378-8741(97)00088-3
AL–Sultan SI (2003). The effect of Curcuma longa (Turmeric) on overall performance of broiler chickens. Int. J. Poult. Sci. 2: 351–53.
http://dx.doi.org/10.3923/ijps.2003.351.353
Ather MAM (2000). Poly herbal additive proves effective against vertical transmission of IBD. World Poultry–Elsevier. 16 (11): 50–52.
Ayed MH, Laamari Z and Rekik B (2004). Effects of incorporating an antibiotic Avilamycin and a probiotic Activis in broiler diets. Western section ASAS, Am. Society Ani. Sci. Champaign, IL. 55: 237–240.
Baldioli M, Servili M, Perretti G and Montedoro GF (1996). Antioxidant activity of tocopherols and phenolic compounds of virgin olive oil. J. Am. Oil Chem. Soc. 73:1589.
http://dx.doi.org/10.1007/BF02523530
Bampidis VA, Christodoulou V, Florou–Paneri P, Christaki E, Chatzopoulou PS, Tsiligianni T and Spais AB (2005). Effect of dietary dried oregano leaves on growth performance, carcase characteristics and serum cholesterol of female early maturing turkeys. Br. Poult. Sci. 46: 595–601.
http://dx.doi.org/10.1080/00071660500256057
PMid:16359114
Bang KH, Lee DW, Park HM and Rhee YH (2000). Inhibition of fungal cell wall synthesizing enzymes by trans–cinnamaldehyde. Biosci. Biotech. Biochem. 64:1061–63.
http://dx.doi.org/10.1271/bbb.64.1061
PMid:10879482
Baratta MT, Dorman H JD, Deans SG, Biondi DM and Ruberto G (1998). Chemical composition, antimicrobial and antioxidative activity of laurel, sage, rosemary, oregano and coriander essential oils. J. Essential Oils Res. 10: 618–27.
http://dx.doi.org/10.1080/10412905.1998.9700989
Bauer K, Garbe D and Surburg H (2001). Common Fragrance and Flavor Materials: Preparation, Properties and Uses. Wiley–VCH, Weinheim. 293
http://dx.doi.org/10.1002/3527600205
Botsoglou NA, Christaki E, Florou–Paneri P, Giannenas I, Papageorgiou G and Spais AB (2004). The effect of a mixture of herbal essential oils or α–tocopheryl acetate on performance parameters and oxidation of body lipid in broilers. S. Afr. J. Anim. Sci. 34: 52–61.
http://dx.doi.org/10.4314/sajas.v34i1.4039
Botsoglou NA, Yannakopoulos AL, Fletouris DJ, Tserveni–Goussi AS andFortomaris PD (1997). Effect of dietary thyme on the oxidative stability of egg yolk. J. Agri. Food Chem. 45: 3711–16.
http://dx.doi.org/10.1021/jf9703009
Botsoglou NA, Florou–paner P, Christaki E, Fletouris DJ and Spais AB (2002a). Effect of dietary oregano essential oil on performance of chickens and on iron–induced lipid oxidation of breast, thigh and abdominal fat tissues. Br. Poult. Sci. 43: 223–30.
http://dx.doi.org/10.1080/00071660120121436
PMid:12047086
Botsoglou NA, Florou–Paner P, Christaki E, Fletouris DJ and Spais AB (2002b). Effect of dietary oregano essential oil on performance of chickens and on iron–induced lipid oxidation of breast, thigh and abdominal fat tissues. Br. Poult. Sci. 43: 223–30.
http://dx.doi.org/10.1080/00071660120121436
PMid:12047086
Botsoglou NA, Florou–Paneri P, Botsoglou E, Datos V, Giannenas I, Koidis A and Mitrakos P (2005). The effect of feeding rosemary, oregano, saffron and α–tocopheryl acetate on hen performance and oxidative stability of eggs. S. Afr. J. Anim. Sci. 35:143–51.
Burt S (2004). Essential oils: their antibacterial properties and potential applications in foods – a review. Inter. J. Food Micro. 94:223–53.
http://dx.doi.org/10.1016/j.ijfoodmicro.2004.03.022
PMid:15246235
Cabuk M, Bozkurt M, Alcicek A, Akbas Y and Kucukyılmaz K (2006). Effect of a herbal essential oil mixture on growth and internal organ weight of broilers from young and old breeder flocks. S. Afr. J. Anim. Sci. 36: 135–41.
http://dx.doi.org/10.4314/sajas.v36i2.3996
Case GL, He L, Mo H and Elson CE (1995). Induction of geranyl pyrophosphate pyrophosphatase activity by cholesterol–suppressive isoprenoids. Lipids, 30:357–59.
http://dx.doi.org/10.1007/BF02536045
PMid:7609605
Cervato G, Carabelli M, Gervasio S, Cittera A, Cazzola R and Cestaro B (2000). Antioxidant properties of oregano (Origanum vulgare) leaf extracts. J. Food Biochem. 24: 453–65.
http://dx.doi.org/10.1111/j.1745-4514.2000.tb00715.x
Chattopadhyay I, Biswas K, Bandyopadhyay U and Banerjee RK (2004). Turmeric and curcumin: Biological actions and medicinal applications. Current Science, 87:44–53.
Clegg RJ, Middleton B, Bell GD and White DA (1980). Inhibition of hepatic cholesterol synthesis and S–3–hydroxy–3–methylglutaryl–CoA reductase by mono and bicyclic monoterpenes administered in vivo. Biochemical Pharmacology, 29: 2125–27.
http://dx.doi.org/10.1016/0006-2952(80)90183-5
Cooke CJ, Nanjee MN, Dewey P, Cooper JA, Miller GJ and Miller NE (1998). Plant monoterpenes do not raise plasma high–density–lipoprotein concentrations in humans. Am. J. Cli. Nutri. 68: 1042–45.
PMid:9808220
Cosentino S, Tuberoso CIG, Pisano B, Satta M, Mascia V, Arzedi E and Plamas F (1999). Invitro antimicrobial activity and chemical composition of SardinianThymus essential oils. Letters in Applied Microbiology, 29: 130–135.
http://dx.doi.org/10.1046/j.1472-765X.1999.00605.x
PMid:10499301
Cowan M (1999). Plant products as antimicrobial agents. Cli. Microbio. Rev. 12: 564–582.
PMid:10515903 PMCid:PMC88925
Craig WJ (1999). Health promoting properties of common herbs. Am. J. Cli. Nutri. 70: 491–99.
Cross DE, McDevitt RM, Hillman K and Acamovic T (2007). The effect of herbs and their associated essential oils on performance, dietary digestibility and gut microflora in chickens from 7 to 28 days of age. Br. Poult. Sci. 48: 496–506.
http://dx.doi.org/10.1080/00071660701463221
PMid:17701503
Cross DE, Acamovic T, Deans SG and Cdevitt RM (2002). The effects of dietary inclusion of herbs and their volatile oils on the performance of growing chickens. Br. Poult. Sci. 43: 33–35.
http://dx.doi.org/10.1080/000716602762388536
Crowell PL (1999). Prevention and therapy of cancer by dietary monoterpenes. J. Nutri. 129: 775–78.
Deans SG and Ritchie G (1987). Antibacterial properties of plant essential oils. Int. J. Food Microbiol. 5: 165–80.
http://dx.doi.org/10.1016/0168-1605(87)90034-1
Demir E, Sarica S, Ozcan MA and Suicmez M (2003). The use of natural feed additives as alternatives for an Antibiotic growth promoter in broiler diets. Br. Poult. Sci. 44: 44–45.
http://dx.doi.org/10.1080/713655288
http://dx.doi.org/10.1080/00071660301944
Denli M, Okan F and Uluocak AM (2003). Effect of dietary supplementation of herb essential oils on the growth performance carcass and intestinal characteristics of quail (Coturnix coturnix japonica). South African J. Ani. Sci. 34:174–79.
Deying MA, Anshan–Shan, Zhihui–Chen, Juan–Du, Kaii–Song, Jianpıng–Li and Qiyou Xu (2005). Effect of Ligustrum lucidum and Schisandra chinensis on the egg production, antioxidant status and immunity of laying hens during heat stress. Arch. Anim. Nutr. 59: 439–47.
http://dx.doi.org/10.1080/17450390500353499
PMid:16429829
Deyoe CW, Davies RE, Krishnan R, Khaund R and Couch JR (1962). Studies on the taste preference of the chick. Poult. Sci. 41: 781–84.
http://dx.doi.org/10.3382/ps.0410781
Didry N, Dubreuil L and Pinkas M (1994). Activity of thymol, carvacrol, cinnamaldehyde and eugenol on oral bacteria. Pharmaceutica Acta Helvetiae, 69: 25–28.
http://dx.doi.org/10.1016/0031-6865(94)90027-2
Dorman HJD and Deans SG (2000). Antimicrobial agents from plants: antibacterial activity of plant volatile oils. J. Appl. Microbiol. 88: 308–16.
http://dx.doi.org/10.1046/j.1365-2672.2000.00969.x
PMid:10736000
Economou KD, Oreopoulou V and Thomopoulos CD (1991). Antioxidant activity of some plant extracts of the family Labiatae. J. Am. Oil Chem. Soc. 68(2): 109–13.
http://dx.doi.org/10.1007/BF02662329
Elson CE, Underbakke GL, Hanson P, Shrago E, Wainberg RH and Qureshi AA (1989). Impact of lemongrass oil, an essential oil, on serum cholesterol. Lipids, 24: 677 – 79.
http://dx.doi.org/10.1007/BF02535203
PMid:2586227
Farag RS, Badei AZMA, Hewedi FM and El–Baroty GSA (1989). Antioxidant activity of some spice essential oils on linoleic acid oxidation in aqueous media. J. Am. Oil Chem. Society, 66: 792–99.
http://dx.doi.org/10.1007/BF02653670
Ferhout H, Bohatier J, Guillot J and Chalchat JC (1999). Antifungal activity of selected essential oils, cinnamaldehyde and carvacrol against Malassezia furfur and Candida albicans. J. Essential Oil Res. 11: 119–29.
http://dx.doi.org/10.1080/10412905.1999.9701086
Fotea L, Costachescu E, Hoha G, Doina L (2004). The effect of oregano essential oil (Origanum vulgare L) on broiler performance. Lucrari stiintifice – vol. 53, seria zootehnie. 491–94.
Fritts CA and Waldroup PW (2003). Evaluation of bio–mos mannanoligosaccharide as a replacement for growth promoting antibiotics in diets for turkeys. Int. J. Poult. Sci. 2: 19–22.
http://dx.doi.org/10.3923/ijps.2003.19.22
Furia TE and Bellanca N (1975). Fenaroli's Handbook of Flavor Ingredients; CRC Press: Cleveland, OH, USA, 1975.
Ghasemi R, Zarei M and Torki M (2010). Adding medicinal herbs including Garlic (Allium sativum) and Thyme (Thymus vulgaris) to diet of laying hens and evaluating productive performance and egg quality characteristics. Am. J. Ani.Vet. Sci., 5 (2): 151–54.
http://dx.doi.org/10.3844/ajavsp.2010.151.154
Gopi M, Kathirvelan C, Premchander D, Vasanthakumar P, Pangayarselvi B, Sasikumar P and Chandrasekaran D (2012). Effect of cinnamon powder (Cinnamomum zeylanicum) supplementation on growth performance of broilers. Commercial and rural poultry production: Novel concepts and strategies to meet growing demand and changing consumer needs. 24th Annual Conference and National Symposium of Indian Poultry Science Association. 5–7th December. 35–36.
Hammer KA, Carson CF and Riley TV (1999). Antimicrobial activity of essential oils and other plant extracts. J. Appli. Microbiology, 86: 985–90.
http://dx.doi.org/10.1046/j.1365-2672.1999.00780.x
PMid:10438227
Harada M and Yano S (1975). Pharmacological studies on Chinese cinnamon. II. Effects of cinnamaldehyde on the cardiovascular and digestive system. Chemical and Pharmaceutical Bulletin, 23: 941–47.
http://dx.doi.org/10.1248/cpb.23.941
Hay RKM and Waterman PG (1993). Volatile oil crops: Their biology, biochemistry and production. Longman Scientific and Techival, Great Britain, Aron.
Helander IM, Alakomi HL, Latva–Kala K, Mattila–Sandholm T, Pol I, Smid E J, Gorris LGM and Von Wright A (1998). Characterization of the action of selected essential oil components on Gram–negative bacteria. J. Agri. Food Chem. 46: 3590–95.
http://dx.doi.org/10.1021/jf980154m
Hernandez F, Madrid J, Garcia V, Orengo J and Megias M D (2004). Influence of two plant extracts on broiler performance, digestibility, and digestive organ size. Poult. Sci. 83: 169–74
http://dx.doi.org/10.1093/ps/83.2.169
Hernandez T, Canales M, Avila JG, Duran A, Caballero J, Romo de Vivar A and Lira R (2003). Ethnobotany and antibacterial activity of some plants used in tradicional medicine of Zapotitlan de las Salinas, Puebla (Mexico).J. Ethnopharmacology, 88: 181– 88.
http://dx.doi.org/10.1016/S0378-8741(03)00213-7
Holovska K, Boldizarova K, Cekonova S, Lenartova V, Levkut M, Javorsky P and Leng L (2003). Antioxidant enzyme activities in liver tissues of chickens fed diets supplemented with various forms and amounts of selenium. J. Animal and Feed sci., 12: 143 – 52.
Humphrey B D, Huang N and Klasing K C (2002). Rice expressing lactoferrin and lysozyme has antibiotic–like properties when fed to chicks. J. Nutri. 132: 1214 –18.
PMid:12042436
Jamroz D, Wiliczkiewicz A, Wertelecki T, Orda J and Sukorupinska J (2005). Use of active substances of plant origininchicken diets based on maize and locally grown cereals. Br. Poult. Sci. 46: 485–93.
http://dx.doi.org/10.1080/00071660500191056
PMid:16268107
Jamroz D, Orda J, Kamel C, Wiliczkiewicz A, Wertelecki T and Skorupinska J (2003). The influence of phytogenetic extracts on performance, nutrient digestibility, carcass characteristics and gut microbial status in broiler chickens. J. Anim. Feed Sci. 12: 583–96.
Jang IS, Ko YH, Kang SY and Lee CY (2007). Effect of a commercial essential oil on growth performance, digestive enzyme activity and intestinal microflora population in broiler chickens. Ani. Feed Sci.Techn. 134: 304–15.
http://dx.doi.org/10.1016/j.anifeedsci.2006.06.009
Khaksar V, Krimpen MV, Hashemipour H and Pilevar M (2012). Effects of Thyme Essential Oil on Performance, Some Blood Parameters and Ileal Microflora of Japanese Quail. J. Poult. Sci. 25: 201–10.
Krause EL and Ternes W (2000). Bioavailability of the antioxidative Rosmarinus officinalis compound carnosic acid in egg. EUR FOOD RE. 210(3): 161–64.
http://dx.doi.org/10.1007/PL00005505
Kreydiyyeh SI, Usta J and Copti R (2000). Effect of cinnamon, clove and some of their constituents on the Na+– K+– ATPase activity and alanine absorption in the rat jejunum. Food and Chemical Toxicology, 38: 755–62.
http://dx.doi.org/10.1016/S0278-6915(00)00073-9
Kurita N, Miyaji M, Kurane R, Takahara Y and Ichimura K (1979). Antifungal activity and molecular orbital energies of aldehyde compounds from oils of higher plants. Agri. Bio. Chem. 43: 2365–71.
http://dx.doi.org/10.1271/bbb1961.43.2365
Langhout DJ, Schutte JB, deJong J, Sloetjes H, Verstegen MWA and Tamminga S (2000a). Effect of viscosity on digestion of nutrients in conventional and germ –free chicks. Br. J. Nutri. 83: 533–40.
PMid:10953678
Langhout P (2000b). New additives for broiler chickens. World poultry, 16: 22–27.
Lee KW, Everts H, Kappert HJ, Frehner M, Losa R and Beynen AC (2003). Effects of dietary essential oil components on growth performance, digestive enzymes and lipid metabolism in female broiler chickens. Br. Poult. Sci. 44: 450–57.
http://dx.doi.org/10.1080/0007166031000085508
PMid:12964629
Lee HS and Ahn YJ (1998). Growing–inhibiting effects of Cinnamomum cassia bark derived materials on human intestinal bacteria. J. Agric. Food. Chem. 46: 8–12.
http://dx.doi.org/10.1021/jf970548y
PMid:10554188
Lee K, Everest WJ, Kappert HJ, Yeom KH and Beynen AC (2003). Dietary Carvacrol lowers body weight gain but İmproves feed conversion in female broiler chickens. Appl. Poult. Res. 12:394–99.
http://dx.doi.org/10.1093/japr/12.4.394
Lee KW, Evert H, Kappert HJ, Frehner M, Losa R and Beynen AC (2003). Effects of dietary essential oil components on growth performance, digestive enzymes and lipid metabolism in female broiler chickens. Br. Poult. Sci. 44 (3): 450–57.
http://dx.doi.org/10.1080/0007166031000085508
PMid:12964629
Levy SB and Marshall B (2004). Antibacterial resistance worldwide: causes, challenges and responses. Nat. Med. 10: 122–29.
http://dx.doi.org/10.1038/nm1145
PMid:15577930
Liu–Fengtlua, Xıe–Zhon Quon, Sun–Chao Long, Qian–Zhi Pıng and Li–Chun Hua (1998). Study of anti–heat stress effect of some Chinese medicinal herbs. Chin. J. Ani. Sci.34: 28–30.
Lopez–Bote C J, Gray JG, Gomaa EA and Flegal CJ (1998). Effect of dietary administration of oil extracts from rosemary and sage on lipid oxidation in broiler meat. Br. Poult. Sci. 39: 235–40.
http://dx.doi.org/10.1080/00071669889402
http://dx.doi.org/10.1080/00071669889187
PMid:9649877
Lovkova MY, Buzuk GN, Sokolova SM and Klimenteva NI (2001). Chemical features of medicinal plants. Appl. Biochem. Microbiol. 37: 229–37.
http://dx.doi.org/10.1023/A:1010254131166
Loza–Tavera H (1999). Monoterpenes in essential oils: Biosynthesis and properties. Adv. Exp. Medi.Bio. 464: 49–62.
http://dx.doi.org/10.1007/978-1-4615-4729-7_5
PMid:10335385
Madpouly HM, Saif MA and Hussein AS (2011). Curcuma longa for protecting chicks against Newcastle disease virus infection and immunosuppressive effect of Marek's disease viral vaccine. Int. J. Virology, 7: 176–83.
http://dx.doi.org/10.3923/ijv.2011.176.183
Madrid J, Hernandez F, Garcia V, Orengo J, Magias D and Savilla V (2003). 14th European symposium on poultry nutrition. August 10–14, Norway.
Mehala C and Moorthy M (2008). Effect of Aloe vera and Curcuma longa (Turmeric) on carcass characteristics and biochemical parameters of broilers. Int. J. Poult. Sci. 7: 857–61.
http://dx.doi.org/10.3923/ijps.2008.857.861
Mellor S (2000). Nutraceuticals – alternatives to antibiotics. World Poultry, 16 (2): 30–33.
Middleton B and Hui KP (1982). Inhibition of hepatic S–3–hydroxy–3–methylglutaryl–CoA reductase and in vivo rates of lipogenesis by a mixture of pure cyclic monoterpenes. Biochemical Pharmacology, 31: 2897–01.
http://dx.doi.org/10.1016/0006-2952(82)90261-1
Moorthy M and Edwin SC (2010). Aloe vera in White Leghorn layer diet Indian.J. Poult. Sci. 45(2): 224– 25.
Moran ET Jr (1982). Comparative nutrition of fowl and swine. The gastrointestinal systems. University of Guelph.
Ocak N, Erener G, Burak F, Sungu M, Altop A and Ozmen A (2008). Performance of broilers fed diets supplemented with dry peppermint (Mentha piperita L.) or thyme (Thymus vulgaris L.) leaves as growth promoter source. Czech J. Anim. Sci. 53(4): 169–75.
Oyen LPA and Dung NX (1999). Plant Resources of South–East Asia No 19. Essential–oil plants, Backhuys Publishers, Leiden.
Papadopoulos G and Boskou D (1991). Antioxidant effect of natural phenols on olive oil. J. Am. Oil Chemi. Soci., 68: 669–71.
http://dx.doi.org/10.1007/BF02662292
Platel K and Srinivasan K (2000). Influence of dietary spices and their active principles on pancreatic digestive enzymes in albino rats. Nahrung, 44: 42–46.
http://dx.doi.org/10.1002/(SICI)1521-3803(20000101)44:1<42::AID-FOOD42>3.0.CO;2-D
Pradeep, KU and Geervani P (1994). Influence of spices on protein utilization of winged bean (Psophocarpus tetragonolobus) and horsegram (Dolichos biflorus). Plant foods for human nutri. 46: 187–93.
http://dx.doi.org/10.1007/BF01088989
PMid:7855088
Qureshi AA, Mangels WR, Din ZZ and Elson CE (1988). Inhibition of hepaticmevalonate biosynthesis by the monoterpene, d–limonene. J. Agri. Food Chem. 36: 1220–24.
http://dx.doi.org/10.1021/jf00084a023
Raza SA, Rehman AU, Ahmad A and Qureshi F (2009). Comparison of antioxidant activity of essential oil of Centella asiatica and Butylated hydroxyanisole in sunflower oil at ambient conditions. Biharean Biologist, 1: 71–75.
Rezaei–Moghadam A, Mohajeri D, Rafiei B, Dizaji R, Azhdari A, Yeganehzad M, Shahidi M and Mazani M (2012). Effect of turmeric and carrot seed extracts on serum liver biomarkers and hepatic lipid peroxidation, antioxidant enzymes and total antioxidant status in rats. BioImpacts, 2: 151–57.
PMid:23678453 PMCid:PMC3648928
Ross ZM, Ogara EA, Hill DJ, Sleightholme HV and Maslin DJ (2001). Antimicrobial properties of garlic oil against human enteric bacteria: evaluation of methodologies and comparisons with garlic oil sulfides and garlic powder. Appli. Environ. Micro. 67: 475–80.
http://dx.doi.org/10.1128/AEM.67.1.475-480.2001
PMid:11133485 PMCid:PMC92605
Roura E, Homedes J and Klasing KC (1992). Prevention of immunologic stress contributes to the growth–permitting ability of dietary antibiotics in chicks. J. Nutri. 122: 2383–90.
PMid:1453223
Royo M, Fernandez–Pan I, Mate JI (2010). Antimicrobial effectiveness of oregano and sage essential oils incorporated into whey protein films or cellulose–based filter paper. J. Sci. Food and Agri. 90 (9): 1513–19.
http://dx.doi.org/10.1002/jsfa.3977
PMid:20549805
Saija A, Rombetta T, Tomaino D, Lo Cascio A, Princi R, Uccella P, Bonina N and Castelli F (1998). In vitro evaluation of the antioxidant activity and biomembrane interaction of the plant phenols oleuropein and hydroxytyrosol. Int. J. Pharmac. 166: 123–33.
http://dx.doi.org/10.1016/S0378-5173(98)00018-0
Sambaiah K and Srinivasan K (1991). Secretion and composition of bile in rats fed diets containing spices. J. Food Sci. Tech. 28: 35–38.
Schwarz K, Ernst H and Ternes W (1996). Evaluation of antioxidative constituents from thyme. J. Sci. Food and Agri. 70: 217–23.
http://dx.doi.org/10.1002/(SICI)1097-0010(199602)70:2<217::AID-JSFA488>3.0.CO;2-Y
http://dx.doi.org/10.1002/(SICI)1097-0010(199602)70:2<217::AID-JSFA488>3.3.CO;2-P
Seigler DS (1998). Phenylpropanoids: Plant secondary metabolism D. S. Seigler ed. Kluwer Academic Publishers, Boston.106–129.
Thomke S and Elwinger K (1998). Growth promotants in feeding pigs and poultry. III. Alternatives to antibiotic growth promotants. Ann. Zootech. 47: 245–71.
http://dx.doi.org/10.1051/animres:19980201
http://dx.doi.org/10.1051/animres:19980402
http://dx.doi.org/10.1051/animres:19980301
Vasanthakumar P, Chandrasekaran D, Shivi M, Malmarugan S, Kathirvelan C, Purushothaman MR and Senthilkumar S (2012a). Efficacy of poly herbal product Salcochek on gut health and reducing the impact of Clostridium species induced enterities in broilers. Int. J. Agric. Environ. Biotech. 5(4): 361–66.
Vasanthakumar P, Pangayarselvi B, Sasikumar P, Chandrasekaran D and Kathirvelan C (2012b). Performance of broilers fed various herbal powders and extracts to alleviate heat stress during summer season (ANFT In press).
Visioli, PB, Grande S and Galli C (2004). Olive oil and oxidative stress. Grasas Aceites. 55: 66–75.
http://dx.doi.org/10.3989/gya.2004.v55.i1.148
Viuda–Martos M, Ruiz–Navajas Y, Fernandez–Lopez, J and Perez–Alvarez J A (2009). Effect of adding citrus waste water, thyme and oregano essential oil on the chemical, physical and sensory characteristics of a bologna sausage. Innovative Food Sci. and Emerging Technologies.10: 655–60.
http://dx.doi.org/10.1016/j.ifset.2009.06.001
Viuda–Martos M, Ruiz–Navajas Y, Fernandez–Lopez J and Perez–Alvarez J A (2011). Spices as functional foods. Critical Rev. Food Science and Nutri. 51(1):13–28.
http://dx.doi.org/10.1080/10408390903044271
PMid:21229415
Waldroup PW, Oviedo–Rondo EO and Fritts CA (2003). Comparison of Bio–MOS and antibiotic feeding programme in broiler diets containing copper sulphate. J. Poult. Sci. 2: 28–31.
http://dx.doi.org/10.3923/ijps.2003.28.31
Wenk C (2000). Recent advances in animal feed additives such as metabolic modifiers, antimicrobial agents, probiotics, enzymes and highly available minerals. Review. Asian–Australian J. Ani. Sci. 13: 86–95.
Williams P and Losa R (2001). The use of essential oils and their compounds in poultry nutrition. Worlds Poult. 17: 14–15.
Windisch W, Schedle K, Plitzner C, Kroismayr A (2008). Use of phytogenic products as feed additives for swine and poultry. J. Anim. Sci. 86: 140–48.
http://dx.doi.org/10.2527/jas.2007-0459
PMid:18073277
Wiseman SA, Mathot JN, de Fouw NJ and Tijburg LB (1996). Dietary non–tocopherol antioxidants present in extra virgin olive oil increase the resistance of low density lipoproteins to oxidation in rabbits. Atherosclerosis, 120: 15–23.
http://dx.doi.org/10.1016/0021-9150(95)05656-4
Youdim KA and Deans SG (1999). Dietary supplementation od thyme (Thymus vulgaris L.) essential oil during the lifetime of the rat: its effects on the antioxidant status in liver, kidney and heart tissues. Mechanisms of ageing and development. 109(3): 163–75.
http://dx.doi.org/10.1016/S0047-6374(99)00033-0
Youdim KA and Deans SG (2000). Effect of thyme oil and thyme dietary supplementation on the antioxidant status and fatty acid composition of the ageing rat brain. Br. J. Nutri. 83(1): 87–93.
PMid:10703468
Yu SG, Abuirmeileh NM, Qureshi AA and Elson CE (1994). Dietary β–ionone suppresses hepatic 3–hydroxy–3–methylglutaryl coenzyme A reductase activity. J. Agri. and Food Chem. 42: 1493–96
http://dx.doi.org/10.1021/jf00043a019