Scholarly article on topic 'Essential oil and aromatic plants as feed additives in non-ruminant nutrition: a review'

Essential oil and aromatic plants as feed additives in non-ruminant nutrition: a review Academic research paper on "Veterinary science"

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Academic research paper on topic "Essential oil and aromatic plants as feed additives in non-ruminant nutrition: a review"

Zeng et al. Journal of Animal Science and Biotechnology (2015) 6:7 DOI 10.1186/s40104-015-0004-5


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Essential oil and aromatic plants as feed additives in non-ruminant nutrition: a review

Zhaikai Zeng, Sai Zhang, Hongliang Wang and Xiangshu Piao*


This paper summarizes the current knowledge regarding the possible modes of action and nutritional factors involved in the use of essential oils (EOs) for swine and poultry. EOs have recently attracted increased interest as feed additives to be fed to swine and poultry, possibly replacing the use of antibiotic growth promoters which have been prohibited in the European Union since 2006. In general, EOs enhance the production of digestive secretions and nutrient absorption, reduce pathogenic stress in the gut, exert antioxidant properties and reinforce the animal's immune status, which help to explain the enhanced performance observed in swine and poultry. However, the mechanisms involved in causing this growth promotion are far from being elucidated, since data on the complex gut ecosystem, gut function, in vivo oxidative status and immune system are still lacking. In addition, limited information is available regarding the interaction between EOs and feed ingredients or other feed additives (especially pro- or prebiotics and organic acids). This knowledge may help feed formulators to better utilize EOs when they formulate diets for poultry and swine.

Keywords: Antimicrobial, Antioxidant, Essential oils, Feed additives, Growth promoter, Gut function, Immunity


Antibiotics fed at sub-therapeutic levels have been widely utilized in the swine and poultry industries to improve growth rate and efficiency of feed utilization, as well as reduce morbidity and mortality [1]. However, many countries have restricted or even banned (i.e. the European Union) the use of antibiotics as feed additives due to increased concerns regarding the transmission and the proliferation of resistant bacteria via the food chain. The restriction on the use of antibiotics as feed additives has driven nutritionists and feed manufacturers to develop alternatives such as organic acids, feed enzymes, and pro- or pre-biotics. These substances are well established in animal nutrition. In contrast, plant extracts, especially EOs, are a new class of feed additives and knowledge regarding their modes of action and aspects of application are still rather rudimentary [2].

In recent years, EOs have attracted increased attention from the swine and poultry industries. However, they are not simple compounds, rather a mixture of various compounds (mainly terpenes and terpene derivatives) [3],

* Correspondence:

State Key Laboratory of AnimalNutrition, Ministry of Agriculture Feed Industry Centre, China AgriculturalUniversity, Beijing 100193, China

which are concentrated hydrophobic liquids containing volatile aromatic compounds obtained from plants [4]. In terms of biological activity and effects, each individual chemical constituent has its own characteristic properties. This means that EOs are of a complex character with rather diverse effects. Furthermore, factors such as species, ecological factors and climatic conditions, harvest time, part of plant used and method of isolation all affect the chemical composition of EOs [4]. This variability complicates the assessment and application of EOs. The purpose of this paper is to provide an overview of the published data on the general applications of EOs in swine and poultry and discuss possible modes of action based on an in vivo model.

Performance response generated by EOs

Numerous studies have documented the benefits of EOs on the performance of swine and poultry. Franz et al. [5] reviewed 8 reports with piglets and Windisch et al. [2] reviewed 11 reports with poultry. They reported that the average improvement in weight gain, feed intake and feed conversion induced by EOs were 2.0, 0.9 and 3.0% for piglets and 0.5, -1.6 and -2.6% for poultry, respectively. We collected data missed in the 2 reviews, as well

© 2015 Zeng et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative C£ntr3l Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

as recently published data. For piglets, the improvement in performance was on average 10 and 3% while in poultry the improvement in performance was 3 and 3% for weight gain and feed conversion, respectively (Table 1). The different results for the two species are possibly caused by the different digestive physiology, the origin of the EOs or herb species, the quantity added to the feed and the environmental conditions used in the trial.

Another important consideration is the stability of EOs during feed processing. Maenner et al. [15] reported a considerable loss of activity of EOs when a pelleting temperature of 58°C was applied. These figures are smaller compared with conventional in-feed antibiotics, where advantages of 16.9% in weight gain (piglets) are reported in the literature [1]. However, in a recent feeding trial, Li et al. [19] compared the performance of piglets fed an unsupplemented control diet with that of piglets fed a diet supplemented with antibiotics or a combination of thymol and cinnamaldehye (Table 2). Weight gain, feed conversion and fecal consistency of pigs fed EOs was essentially equal to that of pigs fed antibiotics.

Aromatic herbs and EOs are often claimed to improve the flavor and palatability of feed, thus increasing voluntary feed intake resulting in improved weight gain. However, in a choice feed experiment conducted in growing pigs by Schöne et al. [12], the classification of fennel and caraway oils as flavor additives or as 'appetite promoters' in diets for pigs was questioned. Unfortunately, only 12 castrated male pigs (28 ± 1 kg) were used with 3 treatments and only a 4 day trial duration, which is weak due to the low level of replication and short feeding period used. Pigs may need a few days to adapt to the special flavor of EOs. Further studies are expected in this field to justify the assumption that herbs, spices and their extracts improve feed intake in pigs.

The application of EOs and aromatic plants in grower-finisher pigs seems unsuccessful. Janz et al. [21] and Yan et al. [22] failed to observe any improvement in performance generated by EOs or aromatic plants in finisher pigs. However, supplementation of EOs in sow diets, especially in lactation sow diets, has been attracting increasing interest. Miller et al. [36] reported that supplementation with 2 g/kg of a blend of EOs (Biomin P. E. P.), from 10 days prior to the estimated farrowing date through to weaning, improved the early lactation feed intake of sows, decreased sow weight loss during the first week of lactation and enhanced piglet body weight at weaning. In a study involving 2100 sows, Allan and Bilkei [37] reported that sows fed diets containing 1 g/kg oregano had higher voluntary feed intake, lower annual mortality rate (4.0 vs. 6.9%), reduced sow culling rate during lactation (8 vs. 14%), increased farrowing rate (77.0 vs. 69.9%), increased number of live born piglets per litter (10.49 vs. 9.95) and decreased stillbirth rate (0.91 vs. 0.81). Similar benefits generated by the feeding of EOs to sows have been reported by other authors [38-40].

Regulation of gut microflora

EOs and aromatic plants are well known to exert antibacterial, antifungal and antiviral activity in in vitro experiments [2]. It is generally accepted that EOs are slightly more active against gram-positive than gramnegative bacteria [41,42]. The EO showed dose-dependent effects on cell integrity, as measured using propidium iodide, of Gram-positive bacteria. However, growth inhibition of Gram-negative bacteria, in contrast, occurred mostly without cell integrity loss [43]. Comparable in vivo studies also found inhibiting effects against pathogens such as C. perfringens, E. coli or Eimeria species (Table 3). The controlled pathogen load also contributed to healthy microbial metabolites, improved intestinal integrity and protection against enteric disease [44-47].

Attention should also be paid to the potential negative effects induced by EOs on healthy intestinal bacteria. Horosová et al. [53] reported that oregano EO exhibited a strong bactericidal effect against Lactobacilli isolated from fecal samples of chickens fed diets with oregano. In a vivo anti-bacteria study, Thapa et al. [43] found that the beneficial commensal Faecalibacterium prausnitzii was sensitive to EO at similar or even lower concentrations than the pathogens. In addition, Cross et al. [28] and Muhl and Liebert [48] reported that EOs had no effect on the microbial population and composition in the digestive tract or fecal excretions of broilers and pigs.

In a review, Brenes and Roura [41] contended that minor components are critical to the bacteriostatic activity of EOs and may have synergistic effects. For example, carvacrol and thymol, the two structurally similar major components of oregano essential oil, were found to give an additive effect when tested against S. aureus and P. aeruginosa [57]. Cymene, a biological precursor of carvacrol, was found to have a higher preference for liposomal membranes, thereby causing more expansion. By this mechanism cymene probably enables carvacrol to be more easily transported into the cell so that a synergistic effect is achieved when the two are used together [58]. However, the major components of EOs obtained from conifers were reported to be more bacteriostatic than the crude essential oil of fir and pine, but were less active or had similar activity as the EO of spruce for L. monocytogenes 4 b and xh c [40,59,60]. Therefore, it is likely that the other components, or combinations of the different major components, have double-edged effects (negative or positive) on the antimicrobial activity of the EOs from fir and pine. These studies indicate that there is still much work to do in order to develop a blend of EOs with better antimicrobial properties.

Impact on nutrient absorption and gut morphology

EOs have been documented to improve nutrient digestibility in swine [15,19,21,61] and poultry [25,62]. The improvement in nutrient absorption may be partly explained by

Table 1 Effects of essential oils and aromatic plants on the performance of swine and poultry

Feed additive Dose,mg/kg Major components Treatment effects (%, difference to control) References


Plant extract 150 300 5% Carvacrol (Origanum spp.), 3% cinnamaldehyde and 2% capsicum oleoresin Weaned pigs -5 -2 -6 1 -2 Manzanilla et al. [6]

Herbalextracts 7,500 Cinnamon, thyme, oregano and a carrier Weaned pigs -10 -17 8 Namkung et al. [7]

EO blend 300 Fenugreek (40%), clove (12.5%), cinnamon (7.5%) and carrier (40%) Weaned pigs 7 5 -2 Cho, et al. [8]

Phytobiotics 1,000 Anis oil, citrus oil, oregano oil, and naturalflavors Nursery pigs 4 1 -2 Kommera et al. [9]

Plant extract 300 5% (wt/wt) Carvacrol, 3% cinnamaldehyde, and 2% capsicum oleoresin Weaned pigs 33 26 -4 Manzanilla et al. [10]

Plant extract 300 5% (wt/wt) Carvacrol (Origanum spp.), 3% cinnamaldehyde (Cinnamonum spp.), and 2% capsicum oleoresin (Capsicum annum) Weaned pigs 33 26 -4 Nofrarías, et al. [11]

Fennel 100 Fenneland caraway oilwere obtained by steam distillation from fennelor caraway seeds Weaned pigs 6 3 -3 Schone et al. [12]

Caraway 100 0 -1 -2

EO blend 100 Buckwheat, thyme, curcuma, black pepper and ginger Weaned pigs 0 -3 -4 Yan et al. [13]

EO blend 1,000 Cinnamomum verum, Origanum vuigare spp., Syzygium aromaticum, Thymus vulgaris and Rosmarinus Weaned pigs 2 - -2 Huang et al. [14]

EO blend 300 4.44 g of anise oil, 1.30 g of clove oil, and 2.0 g of cinnamon oil/kg of additive Weaned pigs 10 5 -4 Maenner et al. [15]

EO blend 300 27.8 g of anise (Pimpineiia anisum) oil, 12.5 g of clove (Syzygium aromaticum) oil, and 46.0 g of peppermint (M. arvensis) oil/kg of additive 7 4 -3

EO blend 50 100 150 Thymol, cinnamaldehyde Weaned pigs 11 22 22 7 19 15 325 --- Li etal. [16]

EO blend 1,000 Oregano, which contained 60% active substance (Cymene, Terpinene, Carvacrol) and 40% carrier (dextrin) Weaned pigs 2 2 -1 Zhang et al. [17]

Chinese medicinal herbs 1,000 3,000 20% of each of Dioscoreaceae batatas, A. macrocephaia, G. uraiensis and Piatycodon grandifiorum Weaned pigs 16 13 - -14 -11 Huang et al. [18]

EO blend 100 18% thymoland cinnamaldehyde (EOD) Weaned pigs 12 1 -10 Li etal. [19]

EO blend 100 Weaned pigs 10 -1 -10 Zeng et al. [20]

Oregano 500 Finisher pigs -10 -8 3 Janz et al. [21]

EO blend 100 100 Thyme, rosemary, oreganum extracts and kaolin Finisher pig 4 4 -1 2 -5 -2 Yan et al. [22]

EO blend 25 50 100 Blend of EO containing 2.9% active ingredients including thymol Broiler 5 3 -1 4 r -1 1 Jang et al. [23]

EO blend Syzigium aromathicum (clove); Cinnamon ceyianensis; Cinnamon camphocamphora (cinnamon) Broiler 5 1 2 Isabeland Santos [24]

Oregano EO 250 500 Carvacrol 84.0%; thymol 1.8% Broiler 3 3 4 -3 0 -8 Basmacioglu et al. [25]

Table 1 Effects of essential oils and aromatic plants on the performance of swine and poultry (Continued)

Oregano EO 300 77.3% carvacrol, 9.6% thymol Broiler -7 -4 2 Kirkpinar et al. [26]

Garlic EO 300 2-propenylthioacetonitril43.2%, trisulfide methyl2-propenyl23.4%, disulfide di-2-propenyl20.9% -3 -4 0

Oregano EO + 150/150 Carvacrol38.7%, thymol4.8%, 2-propenyl thioacetonitril 21.6%, trisulfide methyl2-propenyl -4 -5 -2

garlic EO 11.7%, disulfide di-2-propenyl10.4%

EO blend 100 Cinnamaldehyde and thymol Broiler 5 1 -3 Amerah et al. [27]

100 2 2 0

Thyme EO 1,000 Thymol44.1%, p-cymene 32.0%, terpineol9.6%, linalol 4.6% Broiler -4 -3 0 Cross et al. [28]

Oregano EO 300 Carvacrol86.7%; thymol3.3%; p-cymene 1.3%; y-terpinene 1.3% Broiler 3 2 -1 Roofchaee et al. [29]

600 5 0 -5

1,200 3 -2 -4

EO blend 125 Oregano, anis and citrus peel-active component (carvacrol) Broiler 5 -2 -6 Hong et al. [30]

EO blend 150 Carvacrol, thymol, eucalyptol, lemon Broiler 7 - -3 Alali et al. [31]

250 8 - -5

500 15 - -7

EO blend 100 Basil, caraway, laurel, lemon, oregano, sage, tea, thyme Broiler 7 0 -6 Khattak et al. [32]

200 7 0 -7

300 6 -2 -6

400 6 0 -5

500 7 -2 -8

Ginger EO 75 Zingiberene 27.2%; P-Sesquiphellandrene 13.7; Sabinene 13.4%; Ar-curcumene 10.7%; Broiler 7 6 0 Habibi et al. [33]

150 P-Bisabolene 9.9%; 0

Rosewood EO 150 Linalool84.8%; Minor oxigenated sesquiterpenes 3.4%; a-terpineol2.9%; geraniol 1.0% Broiler 2 1 -1 Aguilar et al. [34]

300 2 2 0

450 1 -1 -2

600 1 2 0

Thymol 30 Thymol Turkey 0 - -1 Ginnenas et al. [35]

EO blend 30 10% thymol, 0.5% eugenol, 0.05% piperine 7 - -8

Table 2 Effect of dietary essential oil and antibiotics on the performance and fecal consistency of weanling pigs1

Item Control Antibiotic1 Essential oil SEM P

Phase 1 (d 0 to 7)

Weight gain, g/d 354 378 416 28 0.33

Feed intake, g/d 473 478 502 26 0.71

Feed conversion 1.36 1.3 1.24 0.08 0.59

Phase 2 (d 8 to 35)

Weight gain, g/d 465b 539a 513a 15 <0.01

Feed intake, g/d 860 937 861 26 0.07

Feed conversion 1.87 1.73 1.69 0.07 0.18

Overall (d 0 to 35)

Weight gain, g/d 442b 505a 493a 15 0.02

Feed intake, g/d 783 846 789 24 0.13

Feed conversion 1.79 1.67 1.62 0.06 0.20

Feed consistency 1.53b 1.22a 1.30a 0.06 0.02

Li et al. [19].

1Control = Basal diet; Antibiotic = Basal diet supplemented with 150 mg/kg chlortetracycline, 80 mg/kg colistin sulfate, and 50 mg/kg kitasamycin); EO = Basal diet supplemented with 18 mg/kg of thymol and cinnamaldehyde. a-bMeans in the same row with different superscripts are significantly different (P<0.05).

increased secretions of saliva, bile and enhanced enzyme activity [56,63-65]. However, Muhl and Liebert [66] did not observe improved nutrient digestibility and enhanced pancreatic and duodenal activity of trypsin and amylase in weaned piglets fed diets containing a phytogenic product having carvacrol, thymol and tannins as key constituents. The inconsistent results in apparent digestibility may be caused by endogenous loss resulting from a stimulated secretion of mucus induced by plant extracts [67].

The improved nutrient absorption may allow appropriate modifications to diet nutrient density. In a randomized complete block design, Zeng et al. [20] investigated the acceptance of commercial EOs in low energy density weaned pig diets with wheat and extruded full-fat soybean as the major ingredients. The piglets could freely choose between a standard energy density diet (DE = 3,400 kcal/kg) or a low energy density diet (DE = 3,250 kcal/kg) with 0 or 0.25 g/kg EOs (4.5% cinnamaldehyde and 13.5% thymol). EO supplementation significantly increased weight gain and improved the apparent digestibility of dry matter, crude protein and energy compared with pigs fed the low energy density control diet. Supplementation of EOs to a low-energy pig diet has beneficial effects and leads to similar performance compared with a standard energy density diet (Table 4).

Decreased numbers of pathogenic bacteria in the gut may improve the ability of epithelial cells to regenerated villus and thus enhance intestinal absorptive capacity [68]. It is reasonable to expect such an effect by EOs due to their well-documented inhibitory effects against pathogens. However, the literature is equivocal regarding the use of

EOs as feed additives in relation to gut morphology. There are reports that show increased, unchanged as well as reduced villus length and crypt depth in the jejunum and colon for broilers and piglets fed EOs [6,10,19,20,52,69]. Considering the different reactions in gut morphology, Windusch et al. [70] hypothesized that one aspect of the phytogenic action of EOs seems to be irritation of intestinal tissues leading to reduced intestinal surface. In contrast, beneficial effects on gut health (i.e. reduced pathogen pressure) could favor increased villus length and gut surface. Consequently, the overall impact of EOs on gut morphology seems to depend on the balance between tissue irritation and beneficial effects on intestinal hygiene.

Immune status

The gastrointestinal tract's immune system is often referred to as gut-associated lymphoid tissue (GALT), which possesses the largest mass of lymphoid tissue and plays an important role in antigen defense in the human body [71]. In the results presented by Kroismayr et al. [72], using the techniques of quantitative real time-PCR and gut tissue morphology, EO and avilamycin significantly decreased the expression of the transcriptional factor NFkB, the apoptotic marker TNFa and the size of Peyer's patches in the intestine of weaned piglets, as well as the proliferation marker cyclin D1 in the colon, mesenteric lymph nodes and spleen. Reduced numbers of intraepithelial lymphocytes in the jejunum and reduced B lymphocytes in mesenteric lymph nodes were also observed by Manzanilla et al. [10,69] and Nofrairas et al. [11]. This might serve as direct evidence for a lower need for immune defense activity in the gut due to the antimicrobial action of EOs. The relieved intestinal immune defense stress may partly contribute to nutrient allocation towards growth rather than immune defense.

Investigations conducted under practical conditions of large-scale animal production have shown better responses to EO treatment than more recent studies conducted under controlled experimental conditions with a higher level of hygiene [5]. This might be explained by a lower pathogen pressure in the intestine and an improved immune status. Supplementing EOs has been reported to improve the immune status of piglets after weaning, as indicated by an increase in lymphocyte proliferation rate, phagocytosis rate, as well as in IgG, IgA, IgM, C3 and C4 serum levels [16,19,20]. Walter et al. [73] reported that pigs fed a diet with 3 g/kg oregano (60 g carvacrol and 55 g thymol per kilogram) had higher proportions of CD4:CD8, MHC class II antigens, and non-T/non-B cells in peripheral blood lymphocytes compared with pigs fed a control diet.

The bioactive substances are quickly absorbed after oral, pulmonary, or dermal administration and most are metabolized and either eliminated by the kidneys in the form of glucuronide or exhaled as CO2 [74]. The absorbed component might initiate an immune response indicated by

Table 3 Effects of essential oils and aromatic plants on the microflora in swine and poultry

Feed additive Dose, g/kg Species Measured responses References

Herbalextracts 7,500 Weaned p gs Reduced coiiform bacteria counts in fecal; less d iverse of m icrobiota in ileald igesta base on PCR-DGGE Namkung et al. [7]

EO blend 50-150 Weaned p gs Increased Lactobaciiius and decreased E. coii counts in feces Li et al. [16]

EO blend 1,000 Weaned p gs Increased Lactobaciiius counts Zhang et al. [17]

Chinese medicinalherbs 1,000/3,000 Weaned p gs Increased Lactobaciiii counts in ileum and decreased Coiiform counts in colon Huang et al. [18]

EO blend 100 Weaned p gs Reduced E. coii and totalaerobic bacteria in the rectum; increased Lactobaciiii to E. coii ratio in colon Li et al. [19]

Phytogenic additive 50-150 Weaned p gs Microbialcounts in feces (aerobes, gram negatives, anaerobes and lactobacilli) didn't change Muhl and Liebert [48]

EO blend 300 Bro ler Decreased intestinal Ciostridium, but no effect on totalorganisms, Streptococcus, Lactobaciiius and Coiiforms Kirkpinar et al. [26]

EO 100 Bro ler Increase in the mean numbers of bacterialspecies in the ilealcontent Amerah et al. [27]

EO blend 1,000 Bro ler No change in cecaland fecal Coiiforms, Lactobaciiius, C. perfringens and totalanerobes Cross et al. [28]

Oregano EO 300-1,200 Bro ler Decreased cecal E.Coii but no effect for 1200 ppm; no effect on cecal Lactobaciiii Roofchaee et al. [29]

EO 125 Bro ler No change in cecaltotalbacteria, Lactobacciiii, Enterococci, Coiiforms or Saimoneiiae colonization. Hong et al. [30]

EO blend 150-500 Bro ler Decreased crop Saimoneiia but no effect for 150 ppm; no effect on cecai Saimoneiia Alali et al. [31]

Thymol/EO 30 Bro ler Increased cecal Lactobacciiii and decreased Coiiform but no effect on crop and ileum Ginnenas et al. [35]

Oregano EO 300 Bro ler Lower bloody diarrhea, lesion score and oocyst numbers compared to control(E. teneiia challenge) Ginnenas et al. [49]

Oregano 330 Bro ler Decreased C. perfringens counts in cecum Waldenstedt et al. [50]

EO blend 100 Bro ler Reduction of C. perfringens concentration in the jejunum and colon Mitsch et al. [51]

Plant extract 100 Bro ler Reduction of E. coii, C. perfringens and fungi and increase of Lactobaciiius Jamroz et al. [52]

Oregano EO 0.5-1.25 Bro ler Oregano EO exhibited a strong bactericidal effect against Lactobaciiii at both doses tested Horosova et al. [53]

EO blend 100 Bro ler Increased ileal Lactobaciiius counts coupled with decreased E.Coii counts Rahimi et al. [54]

EO 500 Bro ler Decreased cecal Staphyiococci, Lactobacciiii and Enterobacteriaceae Placha et al. [55]

EO blend 25/50 Bro ler Decreased ileo-cecal E.Coii, and no change in Lactobaciiii Jang et al. [56]

Table 4 Effects of dietary essential oil on the performance, fecal consistency and nutrient digestibility of weaned pigs1



Weight gain, g/d 382a 348b 383a 4.50

Feed intake, g/d 633 636 631 11.98

Feed conversion 1.65a 1.82b 1.64a 0.04

Feed consistency 1.42b 1.44b 1.29a 0.07

Nutrient digestibility, %

Dry matter 81.2a 79.2b 81.2a 0.48

Crude protein 79.3a 73.3b 79.2a 0.85

Energy 79.9a 76.3b 81.1a 0.57

Calcium 56.3 57.0 59.5 1.65

Phosphorus 56.3 56.0 60.0 1.61

Zeng et al. [20].

Values represent the mean of twelve pens with four pigs per pen. The dietary treatments were: PC (positive control); NC (negative control, 150 kJ/kg DE lower than the PC diet); EO (NC diet supplemented with 0.025% EO product which contained at least 4.5% cinnamaldehyde and 13.5% thymol). a,bMeans in the same row with different superscripts are significantly different (P < 0.05).

changes in blood immunological parameters while the unabsorbed component may contribute to relief from intestinal immune defense stress. However, the precise mechanisms through which EOs function are not clear and further investigations are necessary.

Anti-oxidative effects

Stability is very important to minced meat during further processing or after cooking, or as surface treatments for whole cuts prior to storage. In order to prolong the storage

stability of foods, synthetic antioxidants are used for industrial processing. Nevertheless, the use of some of the common synthetic antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) has come into question due to their suspected carcinogenic potential as evidenced by toxicologists [75]. In addition, a general consumer rejection of synthetic food additives has been observed in recent times. For these reasons, there is an increasing interest in studies involving natural additives for use as potential antioxidants.

Herbs of the Labiatae family, particularly rosemary, oregano and sage, have been extensively studied for their anti-oxidant activity [41]. The potential of dietary EOs and aromatic plants to improve the oxidative stability of meat obtained from broilers, hens or turkeys, has been demonstrated in a series of studies [76-83]. However, Simitzis et al. [84] and Janz et al. [21] reported that dietary oregano EO failed to improve the lipid oxidation status of pork. This may be explained by the different fatty acid composition in the meat of poultry and swine. Although poultry meat contains a low lipid content, its relative concentration of polyunsaturated fatty acids is higher (60 vs 17%, of total fat content) than pork [21,85]. Thus, poultry meat is particularly susceptible to oxidative deterioration, which might contribute to a robust response on the lipid oxidation status of poultry meat that was generated by dietary EOs supplementation.

Beside benefits on meat quality, EOs or plant extracts are also reported to improve redox balance in different organs [55,86], and attenuate oxidative injury induced by different physiological stressors [87-89]. Table 5 shows the results of an experiment where different concentrations of ginger root powder and its EOs were fed to broilers raised

Table 5 Effect of ginger herb and its essential oil on antioxidant parameters and malondialdehyde in the erythrocytes, serum and liver of broilers raised under heat stress1

Item Control VE 100 H 7.5 H 15 EO 75 EO150 SEM P


Glutathione Peroxidase, U/mg Hb 35 36.6 36.9 36 34.5 34.8 0.63 0.87

Superoxide dismutase, U/mg Hb 1,414 1,398 1,268 1,243 1,270 1,210 27.80 0.16

Catalase, K/mg Hb 0.7 0.4 0.9 0.6 0.7 0.7 0.08 0.63

Totalantioxidant capacity, mmol/L 0.8b 1.0a 1.0a 1.0a 0.9a 1.0a 0.02 0.01

Malondialdehyde, nmol/mL 3.2a 2.5bc 2.2cd 2.1d 2.7b 2.6bc 0.08 0.05

Glutathione Peroxidase, U/mg protein 0.5 0.5 0.5 0.5 0.5 0.5 - 0.76

Superoxide dismutase, U/mg protein 3.6b 4.0ab 3.7b 4.0ab 4.3ab 4.8a 0.12 0.05

Catalase, K/mg protein 0.3 0.3 0.3 0.2 0.4 0.3 0.03 0.71

Malondialdehyde, nmol/mL protein 5.3a 4.4ab 3.3bc 2.2c 2.3c 2.5c 0.30 0.01

Habibi et al. [33]. Values are the mean of 4 replicates. Control = Basal diet without supplementation; VE 100 = Basal diet plus 100 mg/kg vitamin 7.5 or 15 g/kg of ginger root powder; EO 75 or EO 150 = Basal diet plus 75 or 150 mg/kg of ginger essential oil. E; H 7.5 or H 15 = Basal diet plus

Means in the same row with different superscripts are significantly different (P <0.05).

under heat stress conditions [33]. Broilers which received 150 mg/kg ginger EO had increased total superoxide dismutase (TSOD) activity and decreased malondialdehyde (MDA) concentrations in the liver compared with a control group. Dietary supplementation of vitamin E, ginger root powder or its EO, increased total antioxidant capacity (TAC) and decreased MDA concentrations in serum compared with a control group.

The efficacy of EOs

There is limited information concerning the interaction between EOs and nutritional factors (such as nutrient level, type of basal diet, as well as synergistic or antagonistic effects with other feed additives). Jamroz et al. [67] investigated the influence of diet type (corn vs. wheat and barley) on the ability of plant extracts (100 mg/kg containing 5% carvacrol, 3% cinnamaldehyde and 2% of capsicum oleoresinon) to modify morphological and histochemical characteristics of the stomach and jenunal walls in chickens. Their results showed significantly more jenunal wall villi in chickens fed the maize diet supplemented with plant extracts.

The incorporation of carvacrol, cinnamaldehyde, and capsicum oleoresin promotes positive and negative changes in digestive function, intestinal epithelium, micro-bial ecology, and fermentation in weaned pigs depending on the amount of protein included in the diet [69]. In a study conducted to investigate the effects of three doses of individual and combined dietary supplements of specific blends of organic acids and EOs on broiler performance, Bozkurt et al. [90] concluded that a combination of acidi-fiers and EOs may allow a reduced dosage to be used due to their synergistic effects.


The search for alternatives to antibiotics has generated considerable interest in recent years. The new generation of feed additives includes herbs and essential oils, and their beneficial effects for animal production have been well documented [2].

Although most of the latest research has noted the major components and original sources of EOs in vivo trials, only a few papers have identified the quantity of the principle components present. In addition, Brenes and Roura [41] argued that minor components present are critical to the activity of EOs and may have a syner-gistic influence. Sometimes the minor components may counteract the exerted effects. Therefore, in the future, the detailed constituents of EOs are needed to be determined in order to assess their different biological effects. In this way, it may be possible to compare different EO products and formulate mixtures that optimize their efficacy.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

ZZ carried out the literature review and manuscript writing. SZ, HW and XP

participated in literature review. All authors read and approved the final


Received: 3 October 2014 Accepted: 4 February 2015 Published online: 24 February 2015


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