Essential oils and aromatic plants in animal feeding—A European perspective. A review

Abstract

The last two decades have seen a substantial increase in the use of aromatic herbs and essential oils as feed additives in animal nutrition. One of the main reasons for this trend is to substitute antibiotic growth promoters, which have been completely banned as feed additives in the European Union since 2006 because they are suspected of contributing substantially to increasing resistance among human pathogens. Recent investigations have shown significant antimicrobial effects of several essential oils and essential oil compounds against enteropathogenic organisms in farm animals. Porcine proliferative enteropathy caused by specific Escherichia coli strains could be controlled by in-feed application of carvacrol-rich essential oils, and the effect of some essential oil components against Clostridium perfringens and necrotic enteritis was confirmed in poultry. In ruminants, an improvement of the digestion was observed, resulting in reduced methanogenesis and nitrogen excretion. In addition, the antioxidative activity of aromatic plants and essential oil compounds contributes to the stability and palatability of animal feed and has, moreover, resulted in an improved shelf-life and quality of animal products, due to reduced oxidation. The ‘growth-promoting effect’ of essential oils (feed conversion rate, daily weight gain, etc.) is not as evident, since a large number of publications are (commercial) product-driven, lacking data on the starting material. Nonetheless, the overall efficacy of essential oils and aromatic herbs, especially their non-nutritive value with impact on the health status and benefit of animals and humans (via the food chain), is encouraging further research and development in this field. Copyright © 2009 John Wiley & Sons, Ltd.

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Flavour Fragr. J. 2010, 25, 327–340 Copyright © 2009 John Wiley & Sons, Ltd.
Review
Received: 2 November 2009; Accepted: 23 November 2009; Published online in Wiley Online Library: 22 December 2009
(wileyonlinelibrary.com) DOI 10.1002/ .1967
Essential oils and aromatic plants in animal
feeding – a European perspective. A review.†,#
C. Franz,a* K. H. C. Baserb and W. Windischc
ABSTRACT: The last two decades have seen a substantial increase in the use of aromatic herbs and essential oils as feed addi-
tives in animal nutrition. One of the main reasons for this trend is to substitute antibiotic growth promoters, which have been
completely banned as feed additives in the European Union since 2006 because they are suspected of contributing substan-
tially to increasing resistance among human pathogens. Recent investigations have shown signi cant antimicrobial e ects of
several essential oils and essential oil compounds against enteropathogenic organisms in farm animals. Porcine proliferative
enteropathy caused by speci c Escherichia coli strains could be controlled by in-feed application of carvacrol-rich essential
oils, and the e ect of some essential oil components against Clostridium perfringens and necrotic enteritis was con rmed in
poultry. In ruminants, an improvement of the digestion was observed, resulting in reduced methanogenesis and nitrogen
excretion. In addition, the antioxidative activity of aromatic plants and essential oil compounds contributes to the stability
and palatability of animal feed and has, moreover, resulted in an improved shelf-life and quality of animal products, due to
reduced oxidation. The ‘growth-promoting e ect’ of essential oils (feed conversion rate, daily weight gain, etc.) is not as
evident, since a large number of publications are (commercial) product-driven, lacking data on the starting material.
Nonetheless, the overall e cacy of essential oils and aromatic herbs, especially their non-nutritive value with impact on the
health status and bene t of animals and humans (via the food chain), is encouraging further research and development in
this  eld. Copyright © 2009 John Wiley & Sons, Ltd.
Keywords: essential oils; animal feeding; growth-promoting e ects; antimicrobial activity; antioxidative activity
* Correspondence to: C. Franz, University of Veterinary Medicine Vienna,
Department of Farm Animals and Veterinary Public Health, Institute for
Applied Botany and Pharmacognosy, Veterinaerplatz 1, A-1210 Vienna,
Austria. E-mail: Chlodwig.Franz@vetmeduni.ac.at
† This article is part of the Special Issue of Flavour and Fragrance Journal enti-
tled ‘Aromatic Plants, Spices and Volatiles in Food and Beverages’, edited by
Ana Cristina Figueiredo and M. Graça Miguel
# Authors would like to dedicate this paper to their colleague and friend, Prof.
Dr. Heinz Schilcher, who is celebrating his 80th birthday (Zaumberg, Germany)
a University of Veterinary Medicine Vienna, Department of Farm Animals and
Veterinary Public Health, Institute for Applied Botany and Pharmacognosy,
Vienna, Austria
b Anadolu University, Faculty of Pharmacy, Department of Pharmacognosy,
26470 Eskisehir, Turkey
c BOKU Vienna, Institute of Animal Nutrition, Products & Nutrition Physiology,
A-1190 Vienna, Austria
Introduction
Many essential oil plants have been used throughout history in
ethnoveterinary practice and animal health management. This is
still valid for the majority of developing countries, but also for
East and South East Asia.[1] The most common uses were in
Europe, e.g. the use of pine oils against ectoparasites and for
wound disinfection, camomile and yarrow to treat in ammations
or anise, fennel and caraway fruits to prevent gastrointestinal
problems, especially colic and  atulence. Tropical and subtropi-
cal spices, oleoresins and essential oils have also been mentioned
in the historical European veterinary literature since the eight-
eenth century.[2] Some of the most commonly used species in
traditional European animal healthcare are listed in Table 1.
Following the development in Western medicine in the course
of the last century, the use of plants, extracts and essential oils
has been replaced by synthetic chemicals in mainstream animal
healthcare. Public awareness of the potential health risks and
environmental problems caused by the excessive use of in-feed
antibiotics, growth hormones and some synthetic pharmaceuti-
cals, combined with trends towards more natural approaches to
food production, has, however, changed attitudes.[3–5] In-feed
antibiotics have been used in subtherapeutic dosages for growth
promotion and prophylaxis against enteric pathogens in large-
scale livestock production for the last almost 50 years. Since the
1990s it has become obvious that their continuing use as
performance enhancers in animals contributed to a growing
resistance among human pathogens and commensal micro-
organisms.[6] Due to human health and safety concerns, the
European Union (EU) reacted strongly with regulations a ecting
the feed additives market: by the end of 1998 all but four antibi-
otic growth promoters had been banned, and Regulation (EC)
1831/2003[7] completed the phasing-out of antibiotics used for
growth promotion, which have now been prohibited to be used
in EU member states since the beginning of 2006. In the USA
there is until now less legislative regulation but a reduction of
antibiotic use has been achieved by other mechanisms, and
lobbies led by the American Medical Association exerted pres-
sure to eliminate the inappropriate use of antibiotics in agricul-
ture and especially in food-producing animals.[3,5] Based on the
strong European regulations and the increasing movements in
the USA, a worldwide ban of antibiotic growth promoters seems
likely on the horizon,[8] although this is probably not the World
Health Organization (WHO) position.
327

C. Franz et al.
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The second reason behind the regulations concerning feed
additives, especially the ban of antibiotics and hormones, is a
response to consumer pressures to eliminate all xenobiotic
agents from food-producing animals and their respective food
chains. Proposed alternatives to in-feed antibiotics are extremely
diverse and include organic acids, pre- and probiotics and espe-
cially herbs and herbal products, e.g. as essential oils.
With regard to horses and pet animals, essential oils are fre-
quently applied not only in the  eld of feed additives but also in
hygiene and medical treatments. For this reason one has legally
to distinguish between drugs (pharmaceuticals), healthcare and
hygiene products and feed additives with regard to the enhanced
performance of animals (Figure 1). Problems of species-speci c
di erences, (in)compatibilities, doping and medical applications
are, however, not the topic of this review. On the other hand,
products to be applied to food-producing animals are, at least in
Europe, much more strongly regulated than feed additives and
drugs for pet animals, since the latter are not part of the human
food chain and have no environmental impact on arable land.
In an ambiguous position in this respect are horses, as they can
be sports animals and/or slaughter equines.
General Aspects
Herbal products are currently used by the feed industry largely
as sensory additives,  avouring and appetizing substances.
Although the understanding of their mode of action is a prere-
quisite for their optimal application in terms of e cacy, a full
understanding of these aspects in animals has not yet been
achieved. For example, aromatic compounds and essential oils
act along the animal digestive tract to improve appetite and
modulate the bacterial  ora, and are able to induce a number of
other bene ts.[9] The antimicrobial properties of essential oils and
extracts can be dose-dependently bacteriostatic and/or bacteri-
cidal. In addition, several investigations have shown their antioxi-
dative e ect, their e ects on digestive physiology and digestion
at weaning[10] and on the microbiology of the gut,[11] or have been
performed in order to implement test models in poultry.[12] One
advantage of essential oils is that they occur in nature as complex
mixtures rather than as single compounds, hence resistance is
less likely to become a problem than with single synthetic
compounds. The number of papers published on the use of
essential oils, and especially those containing the phenolic
compounds carvacrol and thymol, has increased dramatically
over recent years, the majority reporting, however, on produc-
tion parameters (feed uptake, feed conversion, weight gain)
only. Comparatively little information is given about their mode
of action, metabolism or generally on their science-based func-
tionality, because many reports deal with the results of commer-
cial products, avoiding statements on pharmacological e ects or
health claims.
Generally speaking, feed additives are used with healthy
animals not only for nutritional purposes but also for additional
functionality on a permanent basis (possibly throughout the
entire production period of the respective species), in contrast to
veterinary drugs, used just to treat health problems under the
control of a veterinarian and applied for a limited period only
(Table 2).
Feed additives are de ned by Regulation EC 1831/2003[7] as
substances or preparations, other than feed material or premix-
tures, which are intentionally added to feed or water in order to:
• Favourably a ect the characteristics of the feed, e.g. as  avour-
ings or antioxidants.
• A ect the characteristics of animal products regarding micro-
bial load, shelf-life or taste.
• A ect the environmental consequences of especially large-
scale livestock production, e.g. by reduction of ammonia
excretion or methane production.
• Favourably in uence animal production, performance or
welfare by a ecting the gastrointestinal  ora and the digesti-
bility of feeding stu s.
• Have a coccidiostatic or histomonostatic e ect.
Growth-Promoting E ects and Palatability
Many aromatic herbs and essential oils are used for improving
the  avour and palatability of feed or to a ect other parameters
Table 1. Most commonly used herbs and essential oils in traditional animal health
care and livestock production in Austria and neighbouring countries
Latin name Common name Parts/products used
Achillea millefolium s.l. Yarrow Infusion
Arnica montana Arnica Extract
Boswellia sacra Frankincense Resin
Carum carvi Caraway Seed, essential oil
Citrus sp. Citrus oil Essential oil
Curcuma longa Curcuma Rhizome
Foeniculum vulgare Fennel Seed
Matricaria recutita Camomile Infusion, essential oil
Mentha sp. Mint Infusion, essential oil
Pimpinella anisum Aniseed Seed, essential oil
Pinus sp. Turpentine Essential oil, (oleo)resin
Salvia o cinalis Sage Infusion, essential oil
Syzygium aromaticum Cloves Buds, essential oil
Zingiber o cinale Ginger Rhizome
Modi ed after Zitterl-Eglseer et al.[2]
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Essential oils and aromatic plants in animal feeding – a European perspective
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in livestock production (see the Community Register of Feed
Additives for a full list of authorized additives). Numerous feeding
trials have been performed with such additives, but most of the
results are reduced to the growth-promoting parameters: feed
intake, weight gain and feed conversion rate (Tables 3, 6).
In pigs, the improvement of performance was on average 2%
increase in weight gain and 3% in feed conversion e cacy,
ranging from −5% to +9% for weight gain (with one extraordi-
nary exception: Kyriakis et al.[13] reported 23% improvement) and
from +4 to −10% in feed conversion rate. These  gures are com-
parable to the potential of ‘conventional’ growth promoters (anti-
biotics, organic acids, probiotics), where advantages of roughly
4% are to be found in the respective literature.[14–16] The di erent
results are due to the type and origin of the essential oil or herb
species, the quantity added to the feed and the environmental
conditions of the trial. Investigations under practical conditions
of large-scale animal production have shown better responses to
the treatment[13,17] than more recent studies under controlled
experimental conditions with a higher level of hygiene[18] (Tables
4, 5). Whilst in large-scale piggeries with 250–500 mg oregano
oil/kg feed improvements on zootechnical parameters of up to
20% and a heavy decrease in mortality of weaners[13] and piglets[17]
could be obtained, no signi cant di erences were observed in
an experimental station between control and the addition
of either antibiotics or several essential oils.[18] Richter and
Löscher[19] stated in 2002 that antibiotic growth promoters also
Table 2. Principles of use of feed additives vs. veterinary drugs
Feed additives Veterinary drugs
User/applicant Farmer, feed producer Veterinarian only
Animals Healthy animals Sick animals
Aim of use Improve productivity Restore health
Duration of use Permanently Temporarily
Safety No safety risk accepted,
severe safety check
before authorization
Risk–bene t analysis,
waiting periods before
consumption of products
Figure 1. EC regulations[7] concerning feed, feed additives and veterinary drugs and their signi cance for farm and pet animals
Feed Additives / Supplements
Regulation (EC) 1831/2003
Regulation (EC) 429/2008
Directives (EC) 2491/2001,
834/2007 and 889/2008
Medicinal Products
Horses and Companion Animals
Food-producing Animals
Dir. (EC) 2377/90 (MRL- Values)
Dir. (EC) 2491/2001, 834/2007
and 889/2008
(
Or
g
anic Production
)
Guideline 2004/28/EU (Community Codex
Veterinary Drugs)
Directive (EC) 726/2004 (Human- & Veterinary
Medicinal Products)
Directives (EC) 2491/2001, 1834/2007
and 889/2008 (Organic Production)
Farmer: Veterinarian:
329

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Table 3. E ect of aromatic herbs and essential oils as feed additives on the performance in piglets
Feed additive Dietary
dose
(g/kg)
Treatment e ects (% di erence to untreated control) References
Feed
intake
Body
weight
Daily
weight gain
Feed
conversion rate*
Essential oils
Caraway 0.1 −9/−2−/0 −7/−−3/−2Schöne et al.[20.21]
Cinnamon 0.1 +5+2+3Gollnisch et al.[18]
Cinnamon 0.1 −50−5Wald et al.[22]
Clove (5 ml) −50−5Tartrakoon et al.[23]
Clove 0.1 +10+3Gollnisch et al.[18]
Clove 0.1 +3+7−4Wald et al.[22]
Essential oil blend 0.04 +4+6−2Kroismayr et al.[24]
Essential oil blend 0.1 +30+3Gollnisch et al.[18]
Fennel 0.1 +3/+3−/+6+4/−−2/−3Schöne et al.[20,21]
Lemongrass (5 ml) −3+2−5Tartrakoon et al.[23]
Lemongrass 0.1 −2+2−4Wald et al.[22]
Oregano 0.1 +3+20 Gollnisch et al.[18]
Oregano 0.1 0 +5−5Wald et al.[22]
Oregano 0.5 −3+7−9Günther and Bossow[25]
Oregano 0.5 +12 +23 −9Kyriakis et al.[13]
Peppermint (5 ml) −4−3−2Tartrakoon et al.[23]
Peppermint 0.1 −9−3−7Wald et al.[22]
Pimento 0.1 −8−4−5Wald et al.[22]
Herbs and spices
Coriander 2.0 +4+7−3Schuhmacher et al.[26]
Garlic 1.0 −7/+5+2/+1−8/+4Schuhmacher et al.[26]
Oregano 2.0 −1/+4+9/+5−10/0 Schuhmacher et al.[26]
Sage 2.0 +3+7−4Schuhmacher et al.[26]
Thyme 2.0 +4+6−3Schuhmacher et al.[26]
Thyme 1.0 −1+1−1−4Hagmüller et al.[27]
Thyme 5.0 −1−2−1+4Hagmüller et al.[27]
Yarrow 2.0 +1+4−4Schuhmacher et al.[26]
* Feed conversion rate: kg feed/kg body weight gain.
Table 4. Control of porcine proliferative enteropathy (PE) by in-feed application of
Origanum essential oils[17]
Parameter Control Oregano oil
250 g/t 500 g/t
Average daily gain (g) 573 653 687
Feed conversion rate 3.04 2.74 2.66
Diarrhoea score 2.88 2.16 1.81
Mortality (%) 25.0 13.0 10.0
Observation period, days 25–161.
Table 5. E ect of some essential oils on the performance of rearing piglets in comparison to a standard antibiotic[18]
Additive Group 1 Group 2 Group 3 Group 4 Group 5
None Avilamycin Oregano oil Clove oil Cinnamon oil
Average daily gain (g/day) 398 437 407 392 407
Feed intake (g/day) 596 636 614 602 625
Feed conversion rate (kg/kg) 1.50 1.46 1.51 1.54 1.54
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Essential oils and aromatic plants in animal feeding – a European perspective
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compensated for lack of hygiene only when the weight gain was
improved by 10% and the feed conversion rate by 6% in com-
parison to control.
Aromatic herbs and essential oils are often claimed to improve
the  avour and palatability of feed, thus enhancing zootechnical
performance. Indeed, there are some reports of higher feed
intake of piglets through  avouring additives. However, a rise in
feed intake is commonly observed with growth-promoting feed
additives and primarily re ects the higher consumption capacity
of larger grown animals compared to untreated controls, but not
necessarily a speci c enhancement of voluntary feed consump-
tion due to improved palatability. Very few experimental assess-
ments of feed acceptance, preference and palatability a ected
by  avouring additives have been reported so far, indicating
reduction of voluntary feed intake in piglets through increasing
amounts of fennel and caraway oils[21] and thyme and oregano
herbs,[28] respectively.
In a randomized block design, Ungerhofer[44] investigated
the acceptance of thyme and oregano herbs as feed additives
in pigs. The animals could freely choose between standard feed
without herbs, two concentrations of the single herbs (approxi-
mately 0.12% and 1.2%, respectively) or mixtures of both herbs
(0.06% and 0.6% of each herb, respectively), corresponding to
20 and 200 mg essential oil/kg feed, respectively. There was a
signi cant preference for standard feed without herbs, and
within the treated feeds there was a clear tendency to preference
for thyme compared with oregano. This might be due to the
fact that oregano in general has a ‘stronger’  avour and taste.
A statement on performance was, however, not possible,
since the animals were not forced to ingest a speci c additive.
Overall, no better palatability was achieved by adding these
herbs.
In poultry, most studies have shown no signi cant change in
feed intake caused by herbal or essential oil additives, although
growth was often enhanced and the feed conversion rate
improved (Table 6). Since poultry are known to adjust feed intake
according to energy demand, the feed conversion rate is there-
fore a better parameter of the e ects of growth promoters.
Published results are, however, contradictory. In one experiment,
where broilers were fed with 200 mg/kg feed-stu carvacrol or
thymol, carvacrol lowered the feed intake, weight gain and feed
conversion rate, whereas thymol showed no e ect.[30] Addition of
oregano herb in quantities of 2–20 g/kg feed or of oregano oil
(100–1000 mg/kg feed) resulted, in contrast, in all cases in better
Table 6. E ect of aromatic herbs and essential oils as feed additives on the performance in poultry
Animals/feed
additives
Dietary
dose
(g/kg)
Treatment e ects (% di erence to untreated control) References
Feed
intake
Body
weight
Daily
weight gain
Feed
conversion rate
BROILERS
Essential oils
Anis 0.15 −1+1−1Mayland-Quellhorst[29]
Carvacrol 0.2 +2+2−1Lee et al.[30]
Cinnamaldehyde 0.1 −2−30 Lee et al.[30]
Cinnamon 0.1 −4−3−1Wald[31]
Clove leaf 0.1 −3−4+1Wald[31]
Lemongrass 0.1 +1−1+2Wald31]
Oregano 0.15/0.3 −6/−3−2/+1−4/−2Basmacioglu et al.[32]
Oregano 0.1/1.0 −1/+3+8/+6−9/−3Halle et al.[33]
Oregano 0.1 −2−1−1Wald[31]
Peppermint 0.1 −3−2−1Wald[31]
Rosemary 0.15/0.3 0/−2−1/+1−1/−4Basmacioglu et al.[32]
Thymol 0.1/0.2 +1/−5+1/−3−1/−3Lee et al.[30]
Essential oil blend 0.024/0.048 −4/−50/0 −4/−6Cabuk et al.[34]
Essential oil blend 0.075/0.15 −7/−7−3/−1−4/−1Basmacioglu et al.[32]
Essential oil blend 0.036/0.048 +3/+2−8/−8−5/−4Alcicek et al.[36]
Essential oil blend 0.024/0.048 −2/0 0/+14 −2/−12 Alcicek et al.[35]
Essential oil blend 1.0 −7−3−4Halle et al.[37]
Essential oil blend +20+2Westendarp et al.[38]
Aromatic herbs
Garlic 1.0 −5−50 Sarica et al.[39]
Oregano 5.0 +5+7−2Florou-Paneri et al.[40]
Thyme 1.0 +1+2−1Sarica et al.[39]
Thyme 1.0/10 0/−1−3/−5−2/−4+3/+6Haselmeyer[41]
Hops 0.25 +2+5+4−3Cornelison et al.[42]
TURKEYS
Aromatic herbs
Oregano 1.25 −5+2Bampidis et al.[43]
Oregano 2.5 −6+1Bampidis et al.[43]
331

C. Franz et al.
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performance of broiler chicks.[45] Another trial made by this
research group[38] using carvacrol, p-cymene and γ-terpinene as
pure substances in approximately 50 (carvacrol) or 25 (terpinene,
p-cymene) mg/kg showed no signi cant e ects. Haselmeyer[41]
studied the e ect of thymol in four concentrations from 0.1% to
1.0% as feed additive in broilers. No signi cant di erence in per-
formance was observed over the whole growing period (35 days).
Turkeys fed with 1.25–3.75 g/kg dried oregano leaves showed, in
contrast, a clearly improved feed conversion rate.[43] Adding
60 ppm carvacrol-rich thyme oil to the diet of quails resulted in
signi cantly higher body weight gain and better feed e ciency
as well as decreased abdominal fat weight.[46] Finally, the addition
of 250 mg/kg hops to the diet of broilers resulted in signi cant
improvements in feed conversion and feed e ciency at all ages,
and also improved the body weight when compared to the nega-
tive control[42].
Many more positive results on animal performance are
reported with herbal or essential oil mixtures and especially com-
mercial products. From a scienti c point of view many of these
reports are di cult to assess, since detailed information on the
formulation used and on the phytochemical and sensorial quality
is missing. This is also often true for published reports on feeding
trials. However, even if there are some uncertainties associated
with the reporting of studies, there is su cient evidence that
herbs and essential oils are able to improve zootechnical per-
formance in piglets and poultry.
As regards ruminants, very little is known about the e ect
on feed intake and palatability of aromatic plants or volatile
compounds.[3,5] Estell et al.[47] reported that terpene volatiles
could a ect feed intake in sheep, which is quite important
when grazing in Mediterranean pastures. Better knowledge of
speci c chemical interactions with feed intake would be useful
for altering feeding management. In addition, the potential of
essential oils as manipulators of rumen metabolism is of high
signi cance.
Impact on Gut and Intestine Functions
The primary mode of action of growth promoting feed additives
appears to arise from stabilizing feed hygiene and from bene -
cially a ecting the ecosystem of gastrointestinal micro ora by
controlling potential pathogens. This applies especially to those
critical phases of the animals’ development where a higher sus-
ceptibility to digestive disorders may be present, e.g. the weaning
phase of piglets, the early life span of poultry or restocking at
young bull fattening.
Improved intestinal health favoured by feed additives may
mean that animals are less exposed to microbial toxins or other
undesired metabolites, e.g. ammonia and biogenic amines.
Consequently, additives such as aromatic herbs or volatile oils
may relieve the animals from having to mount an enhanced
immune defence during critical situations, increasing the intesti-
nal availability of essential nutrients for absorption and, thus,
assisting the animal to grow better within its genetic potential.
A large number of aromatic plants, spices and essential oils are
known for digestive or carminative activity. This is due to the
stimulation of digestive secretions, e.g. saliva, bile, mucus, as
well as enhanced enzyme activity being a core mode of bene -
cial nutritional action.[48] Rats additionally fed anise oil reacted
with a pronounced nutrient absorption, especially that of glucose
in the small intestine.[49] Manzanilla et al.[50] fed a combination of
essential oils with carvacrol and cinnamaldehyde as the main
compounds together with capsaicin to piglets and reported an
increased gastric retention time of ingested feed (Figure 2),
resulting in better nutrient absorption and favouring intestinal
stability against digestive disorders. Thus, there is evidence that
essential oils and aromatic compounds may favourably a ect
gut functions.
Essential oils used as feed additives for broilers were shown to
enhance the activities of trypsin, of amylase in tissue homoge-
nates of the pancreas, as well as the jejunal chyme content.[30,51]
A mixture of carvacrol, cinnamaldehyde and capsaicin also stimu-
lated the intestinal secretion of mucus: Jamroz et al.[52] stated that
the increased release of large amounts of mucus and the creation
of a thick layer of mucus on the glandular stomach and jejunum
wall in chicks fed with the above mixture could be responsible
for the reduced adherence of pathogens (E. coli, Clostridium
perfringens and others) to the gut epithelium.
This con rms – as already known from human nutritional
physiology[53] and phytopharmacology[54] – that the mode of
action of spices and essential oils on gut function arises at least
partly from an irritation of the epithelial tissues, leading to higher
secretions of mucus and enzymes.
Remarkably little has been published on the e ects of essen-
tial oils and aromatic plants on rumen metabolism. Broudiscou
et al.[55] observed in vitro that Lavandula o cinalis promoted the
extent of rumen fermentation and that Salvia o cinalis had a
possible inhibitory e ect on methane production. Some essen-
tial oils have been reported to inhibit enzyme activity,[56] e.g.
thymol is a strong deaminase inhibitor.[57] Cardozo et al.[58] found,
furthermore, that higher doses of cinnamaldehyde decreased
ruminal L-lactate concentration.
An interesting in vitro investigation was performed by Busquet
et al.,[59] who incubated selected essential oils (e.g. oregano, cin-
namon and clove bud oil) and isolated compounds (carvacrol,
carvone, cinnamaldehyde and eugenol) for 24 h in diluted ruminal
 uid with a 50:50 forage:concentrate diet. At 3.0 g/l the oils and
compounds resulted in an up to 50% reduction in ammonia con-
centration. Since the rumen is a complex bioreactor, it is of note
that some essential oil compounds can withstand 24 h exposure
to rumen  uid in a rumen simulation technique apparatus
(RUSITEC) but others, such as neral, geranial, linalool or thujone,
were metabolized (Figure 3).[60] This might be due to the interac-
tion with the rumen  ora as well as acidity and could have an
impact on the ammonia and methane production of ruminants.
More knowledge about the e ects of essential oils on rumen
function would be useful, particularly on enzymes associated
with proteolysis and deamination. Such activities of essential
Figure 2. Gastric emptying of piglets retarded by essential oils[50]
332

Essential oils and aromatic plants in animal feeding – a European perspective
Flavour Fragr. J. 2010, 25, 327–340 Copyright © 2010 John Wiley & Sons, Ltd. View this article online at wileyonlinelibrary.com
oils/compounds could limit rumen ammonia concentrations and
consequently lead to more e cient utilization of dietary nitro-
gen.[3] The use of essential oils to manipulate ruminant digestion
is, however, to date under-exploited.[5]
Antimicrobial Activity
The antimicrobial activity of essential oils and essential oil com-
pounds, whether bacteriostatic or bactericidal, or against other
food-borne pathogens such as fungi and protozoa, is well docu-
mented.[61–64] Most active in this respect are the phenolic com-
pounds carvacrol, thymol and eugenol, but also other substances,
such as phenylpropane, limonene, geraniol or citronellal.[65,66]
One mode of action of essential oil compounds as antimicrobi-
als is the rapid depletion of the intracellular ATP pool through the
reduction of ATP synthesis and simultaneously increased hydro-
lysis. The reduction of the transmembrane electric potential
being the driving force of ATP synthesis enhances the proton
permeability of the membrane. The leakage of ions, e.g. potas-
sium and phosphate, out of the cell indicates membrane damage,
resulting in disturbances of the osmotic pressure of the cells.[67–69]
Furthermore, changes in the fatty acid compositions of bacterial
cell membranes have been observed at sublethal doses of several
essential oil compounds.[70]
Other e ects are shown by substances such as carvacrol,
which prevents the synthesis of  agellin, causing bacterial/cells
to be a agellate and therefore non-motile. Such cells are signi -
cantly less able to adhere to epithelial cells, which renders poten-
tially pathogenic strains of bacteria non-infective,[71] a mechanism
similar to that known from galacturonic acids in the diet.[72]
In vitro antimicrobial activities have been measured with a
number of essential oils and single compounds, mainly against
the enteropathogenic strains Escherichia coli, Salmonella spp. or
Clostridium perfringens. Using either the broth microdilution
method or the agar di usion test, essential oils with a higher
percentage of phenolic compounds showed the strongest inhibi-
tory capacity in terms of minimum inhibitory concentration
(MIC).[73–75] Di erences in activity have been observed, however,
between plant species and plant parts on the one hand and the
sensitivity of species and strains of the microorganisms on
the other (Figures 4, 5).[66] This is due to the varying chemical
composition of the plant materials (chemotype, morpho- and
0
20
40
60
80
100
a-Pinene
b-Pinene
Myrcene
Limonene
Cineol
Fenchone
Linalool
Thujone
Fenchyl alcohol
Camphor
Menthone
Menthofurane
Menthol
Citronellol
Nerol
Geraniol
Piperitone
Thymol
Carvacrol
Recovery %
Figure 3. Recovery rate of essential oil compounds after 24 h
incubation with ruminal  uid[60]
0
10
20
30
40
50
60
Zone Diameter of Inhibition [mm]
FL 1 LV 1 FL 2 LV 2 FL 3 LV 3
O. x intercedens O.onites O.vulgare
B.cereus*
E. coli
S. typhimurium
S. aureus*
Y. enterolitica
Figure 4. Antibacterial activity of Origanum spp. FL,  ower oil; LV, essential oil from leaves[66]
333

C. Franz et al.
View this article online at wileyonlinelibrary.com Copyright © 2010 John Wiley & Sons, Ltd. Flavour Fragr. J. 2010, 25, 327–340
ontogenetic variation), which is often neglected in microbiologi-
cal or animal studies. From Figure 4 it is evident that several
pathogens respond di erently to various Origanum spp. and oils
from di erent plant parts. Figure 5 shows the plant-to-plant vari-
ation in activity against E. coli of sage (Salvia o cinalis) essential
oils, both caused by phytochemical polymorphism. The in vitro
active levels exceeded in general the dietary doses accepted by
animals (Table 7), which results in few studies available so far
demonstrating the e cacy of essential oil(s) (compounds)
against speci c pathogens in vivo. Killing the intestinal  ora, on
the other hand, as happens with broad-spectrum antibiotics, is
undesirable, but a stabilization of the microecology in the gut
and equilibrium of the intestinal  ora could be achieved by such
treatments. Kroismayr et al.[24] found, in a piglet study, that adding
40 mg/kg of a mixture of carvacrol, thymol, anethol and limonene
to the diet reduced E. coli colony counts at the end of the ileum,
and as a consequence smaller amounts of toxic biogenic amines,
e.g. cadaverine and scatol, were found in the gut lumen resulting
from microbial degradation (Figures 6, 7). The fact that Hagmüller
et al.[27] failed to measure di erences in the number of E. coli in
fecal samples from pigs treated with thyme might be due to a
sublethal dose leaving the bacteria alive but with reduced viabil-
ity. On the other hand, some studies with poultry showed a clear
reduction of Clostridium perfringens in the jejunum and caecum
Figure 5. Antibacterial activity of sage (Salvia o cinalis) essential oils on Escherichia coli (each column represents one individual plant/clone)[66]
1
2
3
4
5
6
7
8
9
10
11
12
13
15
16
17
18
19
20
21
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Zone Diameter of Inhibition [mm]
1
2
3
4
5
6
7
8
9
10
11
12
13
15
16
17
18
19
20
21
Sage Oil Samples
Table 7. Minimum inhibitory concentration (MIC) of several essential oils and some compounds on selected microorganisms
(in μl/ml)[65,66,76]
Escherichia
coli
Salmonella
typhimurium
Staphylococcus
aureus
Listeria
monocytogenes
Bacillus
cereus
Rosemary 4.5–10.0 >20.0 0.4–10.0 0.2 0.2
Sage 3.5–5 10–20 0.75–10 0.2
Oregano 0.5–1.2 1.2 0.5–1.2
Thyme 0.4–1.2 0.45–20 0.2–2.5 0.2–0.5
Clove 0.4–2.5 >20.0 0.4–2.5 0.3
Lemongrass 0.6 2.5 0.6
Limonene 0.70
Carvacrol 0.1–5.0 0.2–0.25 0.2–0.45 0.4–0.5 0.25
Thymol 0.10–0.45 0.06 0.17–0.25 0.20–0.45 0.35–0.45
Geraniol 0.15 0.35 1.25 0.35
Eugenol 0.55 0.75 0.55 0.30
334

Essential oils and aromatic plants in animal feeding – a European perspective
Flavour Fragr. J. 2010, 25, 327–340 Copyright © 2010 John Wiley & Sons, Ltd. View this article online at wileyonlinelibrary.com
of broilers fed with a mixture of essential oil components (Figure
8).[77,78] The same blend of components as well as oregano oil or
crude drug was e ective against Eimeria spp. infections in broil-
ers, thus reducing the need for conventional coccidiostats.[79–81]
Some authors argue that essential oils increase the mucus secre-
tion in the intestine, which protects the surface of villi.[52] Two
further bene ts may follow from the addition of essential oils to
animal feed: the reduction of feed microbial load and improve-
ment of the microbial hygiene of the carcass.[82,83] The number of
reports in this area is, however, too limited to draw conclusions.
Antioxidative E ect
Many essential oil plants and essential oils are known for their
antioxidative properties, based mainly on phenolic compounds in
the oil (Figure 9) or in other phytochemical fractions. Some non-
phenolic substances may also show a considerable antioxidative
potential (Figure 10). Such substances contribute to the protec-
tion of feed lipids from oxidative damage, partly substituting the
use of α-tocopheryl acetate and related compounds as feed addi-
tives or preservatives. Essential oils may also a ect lipid metabo-
lism in the animal: a dietary supply of thyme oil or thymol to
ageing rats showed a bene cial e ect on the antioxidative
enzymes superoxide dismutase and glutathione peroxidase, as
Figure 7. Reduction of biogenic amines by compounds from essential
oils (carvacrol, thymol, anethol and limonene) or an antibiotic
(avilamycin) as feed additives (40 mg/kg) in rearing piglets[24]
Figure 6. In uence of a mixture of essential oil compounds (carvacrol,
thymol, anethol and limonene) as feed additive (40 mg/kg) on bacterial
counts at the end of the ileum of rearing piglets[24]
Jejunum
0%
20%
40%
60%
80%
100%
Caecum
0%
20%
40%
60%
80%
100%
CA B CA B C AB
CA B C A B C A B
< log 2 log 2 - log 6 >log 6
14 21 30 days
14 21 30 days
Figure 8. Relative frequency of Clostridium perfringens concentrations
in the jejunum and caecum of broilers in the presence of essential oil
compounds used as feed additives.[77] A, Thymol, eugenol, curcumin,
piperin; B, thymol, carvacrol, eugenol, curcumin, piperin; C, control
0
10
20
30
40
50
60
70
80
90
100
AI%
25000 3125 390.6 48.83 6.1 0.76 0.09
Concentration
(
ppm
)
Essential Oil Components
Borneol(Sage/Oregano)
Thymol(Sage/Oregano)
Carvacrol(Sage)
Figure 9. Thiobarbituric acid reactive substances (TBARS) assay for
borneol, thymol and carvacrol. AI (%), antioxidative index[66]
0
10
20
30
40
50
60
70
80
90
100
AI%
25000 3125 390.6 48.83 6.1 0.76 0.09
Concentration(ppm)
Essential Oil Component
b
-Caryophyllene(Oregano/Sage)
Terpinen-4-ol(Oregano/Sage)
d-3-Carene(Oregano)
a
-Terpinene(Oregano/Sage)
Figure 10. Thiobarbituric acid reactive substances (TBARS) assay for
β-caryophyllene, terpinen-4-ol, δ-3-carene and α-terpinene.
AI (%), antioxidative index[66]
335

C. Franz et al.
View this article online at wileyonlinelibrary.com Copyright © 2010 John Wiley & Sons, Ltd. Flavour Fragr. J. 2010, 25, 327–340
well as on polyunsaturated fatty acid composition in various
tissues. Animals receiving these supplements had higher enzyme
levels and higher concentrations of polyunsaturated fatty acids in
phospholipids of the brain than the untreated controls.[84] Oregano
added in doses of 50–100 mg/kg to the diet of chickens exerted an
antioxidant e ect in the animal tissues;[85] the pattern of fatty acids
of the abdominal fat of chicken was also altered by oregano oil[31]
and dietary carvacrol lowered plasma triglycerides.[30] In food-
producing animals such e ects are of importance for product
quality: they may improve the dietary value and lead to a better
oxidative stability and longer shelf-life of fat, meat and eggs.[86,87]
Oxidation of meat and membrane phospholipids from broilers fed
with 500 mg/kg diet rosemary and sage extracts was signi cantly
lower after 9 days refrigerated storage compared to 200 mg/kg
α-tocopherol and the control, respectively.[88] The concentration
of total cholesterol oxidation products was also reduced, and a
similar trend was observed in microsomal fraction isolates, in
which the rate of metmyoglobin/hydrogen peroxide-catalysed
lipid peroxidation was lower in birds receiving essential oil plants
than in controls fed on basal diet only. A diet containing 1% Salvia
o cinalis or Origanum vulgare crude herbal drug, either alone or
in a 1:1 mixture, was tested with pigs. Raw belly bacon produced
from animals fed with only oregano as the additive showed a sig-
ni cantly improved stability and lower cholesterol oxide content
compared to controls after 34 weeks storage (Figure 11).[89] Sage as
the additive, in contrast, had a much lower impact.
The e ect of dietary thyme (3% ground herb of Thymus vul-
garis as feed additive for laying hens) on the oxidative stability of
eggs over 60 days storage in the refrigerator was evaluated by
Botsoglou et al.[86] Thyme feeding reduced the oxidation of liquid
yolk, but a comparative examination of the activity of various
antioxidants added to yolk suggested that thymol alone could
not be responsible for the oxidative resistance of eggs from
thyme-fed animals.
The fact that substances other than the essential oil compo-
nents, e.g. rosmarinic acid, carnosol and carnosic acid, are at least
as important as antioxidants was clearly demonstrated by feeding
experiments with distillation residues on small ruminants. Sheep
and goats fed with 10–20% distilled rosemary or thyme in the
diet for several months showed a higher antioxidant stability of
the meat, a higher concentration of polyphenolic antioxidants
in the meat, a higher concentration of polyphenolic antioxidants
in the milk, lower susceptibility of oxidative stress in suckling
goat kids and,  nally, an increased content of polyphenols with
antioxidant capacity in the cheese.[90–92]
Results obtained by the EU-funded research and development
project SAFEWASTES[93] (2005–2008) demonstrated that residues
of several essential oil plants after distillation could  nd a proper
use in animal feeding as zootechnical additives. Traditionally
known in this respect is the use of parsley stalks (a co-product
of the production of dried parsley leaves) in dairy cows to
enhance milk production. However, care is necessary, since
essential oils and other compounds, e.g. phenolic substances,
could in uence the  avour and taste of the products or even
cause an ‘o - avour’. But the taste and  avour of the animal
product can also be positively a ected by herbs and essential
oils. Greber[94] fed fattening pigs a diet containing 0.3–1.2% sage
(Salvia o cinalis) leaves and found, with increasing addition of
sage, not only some of the monoterpenes (camphene, 1,8-
cineole and others) in the animal tissue but also an aromatic-
spicy note in the cooking and frying test. Anyone who has ever
tasted products of the black Corsican ‘Nustrale’ pig knows that
feed intake in the Mediterranean macchia with many essential oil
plants results in a naturally  avoured tasty meat, ham and bacon
(Keyserlingk, pers. commun.). Comparable results are known
from sheep grazing in Mediterranean pastures.[47]
Conclusion
The trend over recent decades towards the use of herbal prod-
ucts in human medicine and as dietary supplements in human
nutrition has also resurrected interest in their use in animal hus-
bandry. Until the 1990s, optimizing the nutritive value of the
animal diet has been the main objective of large-scale livestock
production, driven by quantitative economic reasons only. In the
meantime, quality aspects and con dence in safe and healthy
foodstu s of animal origin are of the utmost signi cance, as seen
by the establishment of the European Food Safety Authority
(EFSA) in 2002 and a number of recently issued EU regulations.[7]
In this context, the ‘non-nutritive value’ of food and feed compo-
nents, especially secondary plant products with impact on the
health status of animals and humans (via the food chain). has
attracted science, since the functionality of these substances was
poorly understood. As this has changed, interest in the applica-
tion of herbs as feed ingredients and extracts and especially
essential oils as feed additives has increased tremendously, and
not only in organic livestock farming. Due to many well-known
characteristics, the functions and e ects of essential oils and
essential oil plants and their value when used in animal hus-
bandry can be summarized under three headings, as follows:
1. Improvement of feed characteristics. Depending on the chemi-
cal composition, there is an antimicrobial and proven antioxi-
dative e ect on feed, especially of essential oils containing
phenolic compounds, improving the shelf-life. To avoid losses
and reactions with air, and with regard to further activities in
the animal body, essential oils and aroma compounds should
be microencapsulated.[95] This also o ers the advantage of a
sustained e ect. Results on palatability and the stimulation of
feed intake are contradictory. In general, the ‘sweeter’ essen-
tial oils taste (to humans), the better is the acceptance and the
more pungent, the more adverse e ects have been noticed.
In any case, a period of adaptation would be helpful, espe-
cially in pigs.
2. Improvement of digestion and performance. Well proven is an
overall stimulation of the zootechnical performance, espe-
cially as regards the feed conversion rate. This might be due
Figure 11. In uence of herbs as feed additive in fattening of pigs
(1% herbs, 6 months storage) on the shelf-life of bacon. CO, cholesterol
oxide content[89]
0
1
2
3
4
5
6
7
8
9
Control Sa
g
e Mixture Ore
g
ano
CO in fat (ppm)
336

Essential oils and aromatic plants in animal feeding – a European perspective
Flavour Fragr. J. 2010, 25, 327–340 Copyright © 2010 John Wiley & Sons, Ltd. View this article online at wileyonlinelibrary.com
Table 8. Di erent species called ‘oregano’ worldwide[96]
Family Species Commercial name(s) found in literature
Labiatae Calamintha potosina Schaf. oregano de la sierra, oregano, origanum
Coleus amboinicus Lour. (syn. C. aromaticus Benth) oregano, oregano brujo, oregano de Cartagena,
oregano de Espana, oregano Frances
Coleus aromaticus Benth. oregano de Espana, oregano, origanum
Hedeoma  oribunda Standl. oregano, origanum
Hedeoma incana Torr. oregano
Hedeoma patens Jones oregano, origanum
Hyptis albida H.B.K. oregano, origanum
Hyptis americana (Aubl.) Urb. (H. gonocephala Gris.) oregano
Hyptis capitata Jacq. oregano, origanum
Hyptis pectinata Poit. oregano, origanum
Hyptis suaveolens (L.) Poit. oregano, oregano cimarron, origanum
Monarda austromontana Epling oregano, origanum
Ocimum basilicum L. oregano, origanum
Origanum compactum Benth. (syn. O. glandulosum Salzm,
ex Benth.)
oregano, origanum
Origanum dictamnus L. (Majorana dictamnus L.) oregano, origanum
Origanum elongatum (Bonent) Emberger et Maire oregano, origanum
Origanum  oribundum Munby (O. cinereum Noe) oregano, origanum
Origanum grosii Pau et Font Quer ex Letswaart oregano, origanum
Origanum majorana L. oregano
Origanum microphyllum (Benth) Vogel oregano, origanum
Origanum onites L. (syn. O. smyrneum L.) *Turkish oregano, oregano, origanum
Origanum scabrum Boiss et Heldr. (syn. O. pulchrum Boiss
et Heldr.)
oregano, origanum
Origanum syriacum L. var. syriacum (syn. O. maru L.) oregano, origanum
Origanum vulgare L. subsp. gracile (Koch) Letswaart (syn.
O. gracile Koch, O. tyttanthum Gontscharov)
oregano, origanum
Origanum vulgare subsp. hirtum (Link) Ietswaart (syn. O.
hirtum Link)
*oregano, origanum
to retarded gastric emptying and stabilization of the intestinal
microbiota and/or higher enzymatic activity, and therefore
better absorption of the digestible nutrients. The antimicro-
bial activity of essential oils is well demonstrated in vitro but
in only a few cases con rmed in vivo. A bene cial modi cation
of the ruminal  ora has been veri ed, as has an e ect as coc-
cidiostat and against clostridia in poultry. Another mode of
action is described as a slight irritation of the intestine tissues
followed by pronounced mucus production, preventing the
adhesion of enteropathogenic organisms. The overall bene t
of this might be summarized as a favourable e ect on the gut
microbiota with less microbial activity in the small intestine
and consequently less exposure to microbial toxins, reduced
innate immune defence and therefore better digestion.
3. Improved characteristics of animal products. Of particular
importance is the improved oxidative stability of the carcass,
the meat and fat and the egg yolk, caused by several antioxi-
dative compounds in essential oils or the respective plants.
Flavour might be bene cially or detrimentally in uenced.
Particular caution is required for some species, e.g. parsley and
caraway causing ‘o  avour’ of milk due to a carry-over of
some essential oil compounds.
Less is known about the possible interactions of essential
oils and aroma compounds with other substances, especially
other feed additives. All feed additives, including aromatic herbs
and essential oils, have to follow the safety regulations, i.e. the
product has to be safe to the animal, to the user (farmer, worker),
to the consumer and to the environment.[7]
In general, there is su cient evidence that essential oils and
aromatic plants can be used as feed materials and additives for
the bene t of animals, the bene t of the farmer and last, but not
least, the quality of the products. However, there are several
obstacles when evaluating the published results.
Quite often one can  nd confusion in the de nitions of the
material used, and many authors are unable to di erentiate
between herbs, extracts, (distilled) essential oils, isolated essen-
tial oil compounds, synthetic compounds and other aromatic
(plant) products. Within a single paper the terms may change,
especially between extracts and essential oils, but also in using
the botanical and/or common plant name in the title and feeding
isolated (or synthetic) compounds according to material and
methods. Especially when commercial products are used in a
feeding experiment, caution is required, since other synthetic
substances may be added, adulterating the results.
In a case where a herb is used as a feed additive, the botanical
species might be unclear or unde ned, especially if only the
common name is used. For instance, there are dozens of species
in the world called ‘oregano’, belonging not only to the 39 species
of the genus Origanum, but also to other genera and plant
families (Table 8), all having more or less the sensorial properties
of oregano. In addition, the chemotype and especially the
337

C. Franz et al.
View this article online at wileyonlinelibrary.com Copyright © 2010 John Wiley & Sons, Ltd. Flavour Fragr. J. 2010, 25, 327–340
Origanum vulgare subsp. virens (Ho manns et Link)
letswaart (syn. O. virens Ho manns et Link)
oregano, origanum, oregano verde
Origanum vulgare subsp. viride (Boiss.) Hayek (syn. O.
viride) Halacsy (syn. O. heracleoticum L.)
*Greek oregano, oregano, origanum
Origanum vulgare L. subsp. vulgare (syn. Thymus
origanum (L.) Kuntze)
oregano, origanum
Origanum vulgare L. oregano, orenga, Oregano de Espana
Poliomintha longi ora Gray oregano
Salvia sp. oregano
Satureja thymbra L. oregano cabruno, oregano, origanum
Thymus capitatus (L.) Ho manns et Link (syn.
Coridothymus capitatus (L.) Rchb.f.)
*Spanish oregano, oregano, origanum
Verbenaceae Lantana citrosa (Small) Modenke oregano xiu, oregano, origanum
Lantana glandulosissima Hayek oregano xiu, oregano silvestre, oregano,
origanum
Lantana hirsuta Mart. et Gall. oreganillo del monte, oregano, origanum
Lantana involucrata L. oregano, origanum
Lantana purpurea (Jacq.) Benth.& oregano, origanum
Hook. (syn. Lippia purpurea Jacq.) Lantana trifolia L. oregano, origanum
Lantana velutina Mart.&Gal. oregano xiu, oregano, origanum
Lippia myriocephala Schlecht.&Cham. oreganillo
Lippia a nis Schau. oregano
Lippia alba (Mill) N.E. Br. (syn. L. involucrata L.) oregano, origanum
Lippia Berlandieri Schau. oregano
Lippia cordiostegia Benth. oreganillo, oregano montes, oregano, origanum
Lippia formosa T.S.Brandeg. oregano, origanum
Lippia geisseana (R.A.Phil.) Soler. oregano, origanum
Lippia graveolens H.B.K. *Mexican oregano, oregano cimarron, oregano,
origanum
Lippia helleri Britton oregano del pais, oregano, origanum
Lippia micromera Schau. oregano del pais, oregano, origanum
Lippia micromera var. helleri (Britton) Moldenke oregano
Lippia origanoides H.B.K. oregano, origano del pais
Lippia palmeri var. spicata Rose oregano
Lippia palmeri Wats. oregano, origanum
Lippia umbellata Cav. oreganillo, oregano montes, oregano, origanum
Lippia velutina Mart. et Galeotti oregano, origanum
Rubiaceae Borreria sp. oreganos, oregano, origanum
Scrophulariaceae Limnophila stolonifera (Blanco) Merr. oregano, origanum
Apiaceae Eryngium foetidum L. oregano de Cartagena, oregano, origanum
Asteraceae Coleosanthus veronicaefolius H.B.K. oregano del cerro, oregano del monte, oregano
del campo
Eupatorium macrophyllum L. (syn. Hebeclinium
macrophyllum DC.)
oregano, origanum
* Species of main economic importance, according to Lawrence and Reynolds.[97]
Table 8. Continued
Family Species Commercial name(s) found in literature
detailed chemical composition are frequently missing, since this
is only voluntary information in reports on feed additives. A
similar situation is found with (commercial) essential oils – source
unknown or at least undeclared, chemotype and/or composition
not mentioned in the paper. Finally, very often commercial prod-
ucts are tested in ‘scienti c papers’ where at best the (main) ingre-
dients are mentioned only but the exact composition remains
undisclosed.
A concise relationship between active principles (substances)
and observed e ects can only rarely be established; more
often only general conclusions can be drawn concerning growth
parameters and productivity, i.e. feed intake, weight gain and
feed conversion rate. This shows clearly that information on
essential oils and aromatic herbs as feed additives is still mainly
‘product-driven’ instead of following a scienti cally ‘function-
driven’ approach. Apart from the examples presented and
discussed here, there is still need for information regarding
absorption, distribution, metabolism and excretion (ADME)
and, in general, the mode of action of essential oils and their
components in animal nutrition, especially with respect to
338

Essential oils and aromatic plants in animal feeding – a European perspective
Flavour Fragr. J. 2010, 25, 327–340 Copyright © 2010 John Wiley & Sons, Ltd. View this article online at wileyonlinelibrary.com
animal health and welfare and the sensory and hygienic charac-
teristics of animal products. Nonetheless, the overall e cacy of
essential oils and aromatic herbs for the bene t of animals and
the quality of animal-derived food seems to be promising.
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