12

secondary Plant compounds are more than essential oils

AbstractThe use of antibiotics for growth promoting

purposes in livestock is now banned for al-

most one decade in the European Union.

This has forced the development of alternati-

ve products replacing their beneficial effects

on health and productivity. Secondary plant

compounds have found their way into ani-

mal feed, since they possess promising pro-

perties known for centuries from their safe

and effective use in humans and animals. In

this review, we give a definition and classi-

fication of secondary plant compounds, de-

scribe their major mode of action and their

synergistic combination and we give examp-

les of their successful use in poultry.

IntroductionUnlike most animals, plants do not have

the ability to escape potential predators by

running away. To secure the survival of their

species, plants have evolved multiple me-

chanisms to defend themselves against po-

tential threats.

Most of these mechanisms are based on the

synthesis of a combination of compounds

with specific biological activities, which

have been recognized and used for appe-

tizing, digestive or therapeutic purposes for

many centuries in humans and animals.

In contrast to so called primary plant com-

pounds that are of importance for growth

and reproduction of a plant like carbohy-

drates, proteins and vitamins (Ehrlinger,

2007), secondary plant compounds are not

directly involved in the general energy and

nutrient metabolism but offer a benefit for

the plants in the natural selection process.

Some compounds, for example emit odors

to attract pollinating insects or as defensive

mechanism to protect against pathogens

or predatory herbivores thus preserving

the individual plant and the species respec-

tively (Westendarp, 2007).

The amount and the composition of secon-

dary plant compounds is determined by

many different factors like genetic configu-

ration and growth stage of the plant as well

as external influences like climate, weather

and soil conditions (Westendarp, 2007).

Between the different active substances

mutual interactions can be observed. The

special combinations determine the inten-

sity of the total impact and it is assumed

that substances with even very low con-

centrations can be significantly involved

in the mode of action (Westendarp, 2007).

This leads to the conclusion that isolated

or chemically synthesized single com-

pounds cannot have the same activity as

a mix of plant components acting synergi-

stically (Heinzl, 2010). Safrol for example as

single substance is very toxic for liver and

kidney and furthermore is assumed to be

carcinogenic. Consumed as an ingredient

of black pepper or nutmeg however, such

toxic effects are not observed. Secondary

plant compounds are of wide structural

variety. Most of the approximately 100,000

Secondary Plant Compounds are more than Essential Oils

Dipl. oec. troph. Rainer Aschenbroichrainer Aschenbroich studied human nutrition, food Law and food technolo-gy at the niederrhein university of Applied sciences and worked in key posi-tions in product development, quality assurance and quality management in the food industry before joining eW nutrition. he developed high technology blends of secondary plant compounds (natural oils, extracts and oleoresins) from herbs and spices for feed.

to contact the author: rainer.aschenbroich@ew-nutrition.com

Vol. 49 (1), July 2015 | LOHMANN Information

13

known secondary plant compounds are

believed to be involved in the plant defen-

se and reproduction system. This diversity

of ingredients also offers a multimodal use

in animal nutrition.

It has to be considered that a specific

and effective application can only be im-

plemented if there is specific knowledge

about their composition and mode of ac-

tion (Westendarp, 2007).

Classification of secondary plant compounds:Secondary plant compounds can be ca-

tegorized in different ways. They are eit-

her distinguished based on their active

groups, chemical characteristics, commo-

nalities in biosynthesis or impact and pur-

pose of use (Westendarp, 2007).

Phenolic or polyphenolic substances

Phenolic or polyphenolic compounds

comprise a large family with over 4,000

diverse compounds widely distributed in

plants and their fruits.

They are produced by the plant for co-

loring, growth, reproduction and as de-

fense mechanisms. They are formed by

several hydroxyls connected to one or

more aromatic rings and possess a high

antioxidant capacity. They can be found

in fruits such as apples or cherries, in ve-

getables such as broccoli or onions, but

are also contained in red wine, chocolate

or green tea. Depending on their natural

function in the plant they can act in an

antimicrobial and antifungicidal or anti-

parasitic way in the gastrointestinal tract

of the animal (Giannenas, 2008).

Essential oils

The ISO standard 9235 (1997) defines

„essential oils“ as products, which are ex-

tracted from plant material (one single

species) by either distillation with steam

(in case of e.g. menthol), by mechanical

treatment at room temperature (e.g. cold

pressed as orange oil or lemon oil) or by

dry distillation.

They are mixtures of volatile, liquid, lipo-

philic compounds. They can be synthe-

sized in each part of the plant. Some plants

have the ability to build essential oils with

different compositions in different parts of

the plant and in practice most of them are

extracted by steam distillation.

Approximately 3,000 compounds have

been isolated and analysed from essential

oils. Whilst in some essential oil types only

a few components are present ore one

compound dominates, other essential oils

can be composed of up to 100 compo-

nents (Wald, 2003).

Due to that diversity it is difficult to deter-

mine the proportional efficacy of single

compounds in often complex mixtures

(Westendarp, 2007). But more and more

scientific studies demonstrate a wide an-

timicrobial activity of many essential oils.

Tanning agents

Tannins are special types of phenols. They

can be found in variable concentrations

in different parts of a plant. Since they in-

teract with proteins on mucous membra-

nes they are traditionally used in cases of

unspecific diarrheas, inflammation of the

oral cavity and the pharynx as well as to

cure slight skin lesions. Additionally tan-

ning agents are radical scavengers and act

as antioxidants. Furthermore they have

antimicrobial and antiparasitic effects.

Bitter substances cannot be allocated

to a chemically consistent group of ele-

ments. The commonalities in this group

are based on their bitter flavor. With oral

administration the production of saliva

and anapepsia is stimulated by the excita-

tion of the taste buds.

Pungent substances cannot be assigned

to chemical group either. Besides a stimu-

lation of saliva and anapepsia production

the oral administration causes an enhan-

cement of gut motility. Other effects are

enhancement of blood circulation, anti-

emetic, antimicrobial, germicidal and in-

secticidal (Westendarp, 2007).

Alkaloids can have a direct impact on the

nervous system, by agonistic or antagoni-

stic binding to neurotransmitter receptors.

Furthermore they can inhibit metabolic

enzymes or have interactions with intra-

cellular proteins. Alkaloids are mainly used

as analgesics, sedatives or against diarrhea.

Saponins can be found in about 75 % of

all plants and the individual forms vary

greatly. They can reduce cholesterol levels,

act fungicidally and some types show an

immune stimulating effect (Westendarp,

2007; Heinzl, 2010). Saponins are also used

for their reducing effects on ammonia

emissions in animal feeding, by inhibition

of urease activity (Veit et al., 2011).

Mode of actionSecondary plant compounds not only

exert one specific mode of action. For

most SPCs a broad range of efficacy has

been demonstrated. In poultry produc-

tion, some of the most important benefi-

cial attributes are mentioned below.

Stimulation of digestion

Stimulation of the sensor cells in the gas-

trointestinal tract. This results in higher

concentration of calcium ions followed

by an increased release of Serotonin. This

chemical messenger activates the muscles

14

of the digestive tract and the secretion of

digestive juices, which as a consequence

improves resorption of nutrients (Braun et

al., 2007).

Antimicrobial interaction on bacterial

cell integrity

a) Through interactions with transmemb-

rane proteins secondary plant compounds

can lead to changes in the transport capa-

city of sodium and potassium ions, which

diminishes the membrane potential ac-

ross the bacterial cell membrane.

b) Through lipophilic interactions, secon-

dary plant compounds can increase the

permeability of the cell membrane, dis-

turbing the balance of ion concentrations

and thus leading to an impairment of os-

motic pressure regulation.

c) Through uncoupling of the electron

transport chain, secondary plant com-

pounds can impair ATP generation and

thus energy production in the bacterial cell.

Increase of antioxidative activity

The antioxidant activity is related to the

capacity of polyphenols to act as metal-

chelators, scavengers for superoxide or

hydroxyl radicals, hydrogen donators and

inhibitors of the enzymatic systems res-

ponsible for initiating oxidation reactions

(Mielnik et al., 2008; Gobert et al., 2010;

Sayago-Ayerdi et al., 2009). Higher oxida-

tion is an index for lower meat quality. Nu-

merous studies have pointed out the posi-

tive effect of secondary plant compounds

on meat quality (Viuda-Martos et al., 2010;

Janz et al., 2007; Viuda-Martos et al., 2010;

Al-Mamary et al., 2002; Russo et al., 2000).

Secondary plant compounds especially

polyphenols and flavonoids generate a

positive effect on meat quality and thus

increase shelf-life by:

Reduction of lipid oxidation and micro-

bial growth in meat during storage

Delayed degradation of vitamin E in meat

Improved meat color conservation du-

ring storage

Moderation of aldehydes and alcohols

related to off-flavor in meat

Synergistic effectsBetween the different components syner-

gistic interactions, leading to an increase

in the efficacy of the single active com-

pounds have been observed in numerous

studies (Figure 1). Therefore the type of

combination determines the intensity

of the total effect. In such a composition

also substances present in very low con-

centrations can significantly contribute to

the overall mode of action (Heinzl, 2010).

Other important factors, influencing the

efficacy of single active compounds and

their combinations are determined by the

uptake rate, metabolisation and their avai-

lability at the preferred site of action in the

organism (Westendarp, 2007).

Trials, demonstrating the in vivo efficacy of special combinationsAnimal trials were conducted with ACTIVO,

a product line containing several seconda-

ry plant compounds acting in a synergistic

way. The trial parameters shown below are

representative for the three main modes

of action.

Figure 2: Feed conversion rate

Figure 1: Synergistic effects

secondary Plant compounds are more than essential oils

Vol. 49 (1), July 2015 | LOHMANN Information

15

1. Activation of digestion:

The trial was conducted on a farm in the

Czech Republic with 189,300 (Control

group) and 62,300 (Trial group) Ross 308

chickens of mixed sex. The control group

was fed with standard feed + 150 g / ton of

a competitive product, the trial group recei-

ved standard feed + 100 g of ACTIVO / ton

(Figure 2). Outcome: Feed conversion rate of

animals fed ACTIVO significantly improves

when compared to a competitor product

2. Antimicrobial efficacy compared to

antibiotic growth promoters

In this trial commonly used feeding pro-

grams in Brazil applying AGP’s were com-

pared to a diet containing Activo based

on secondary plant compounds. For this

trial 1,120 Cobb male chicks were divided

into 7 different groups, which were fed as

mentioned in table 1. Experimental diets

were formulated with requirement le-

vels 10% lower than recommended. The

parameters “Feed intake”, “Growth”, “FCR”,

“Average final weight”, “Mortality” and “FEF

Index” were evaluated during 45 days (Fi-

gure 3). The trial was conducted in order

to show the positive effects of secondary

plant compounds in comparison to anti-

biotic growth promoters especially under

bad hygienic conditions. At days 11, 14,

17, and 24 birds were challenged with a

solution containing strained dirty (conta-

minated) bed litter and water in a propor-

tion of 15 g/L. Birds were allotted to boxes

containing reused wood shavings and fa-

cilities were not cleaned at the beginning

or during the experimental period as well.

Outcome: Activo shows similar results as

antimicrobial growth promoters in terms

of animal performance, thus indicating

good animal health. (Trial conducted by

Federal University of Viçosa, Viçosa, Minas

Gerais, Brazil)

3. Increase of antioxidative activities to

extend shelf life of meat

640 male animals were divided into 4

groups, each group with 8 replicates (20

animals / pen). The animals were fed as

shown in the following table.

After slaughter, breast samples were fro-

zen at -20°C for 30 days. Samples were

then thawed to examine lipid oxidation

level, by measuring the Malonedialdehy-

de content (Figure 4). Malonedialdehyde

(* MDA) is generated from reactive oxy-

gen species (ROS), and as such is assayed

in vivo as a bio-marker of oxidative stress

(Stancliffe et al., 2011). Outcome: ACTIVO

significantly decreases the level of lipid

oxidation during meat storage. Trial con-

ducted by Federal University of Viçosa, Vi-

çosa, Minas Gerais, Brazil.

SummaryBased on the current scientific knowledge,

numerous feeding trials and the successful

use in the market there is clear evidence

that well-matched combinations of secon-

dary plant compounds are superior to sin-

gle active substances in order to achieve

significant improvements in animal per-

formance.Figure 3: Replacment of AGPs

Figure 4: lipid oxidation

Day 1 to 21 Day 22 to 35 Day 36 to 45

t1 no Additive no Additive no Additive

t2 Activo® 100 g/t Activo® 100 g/t Activo® 100 g/t

t3 Activo® 100 g/t + enramycin 8 ppm

Activo® 100 g/t + enramycin 8 ppm 

Activo® 100 g/t 

t4 enramycin 8 ppm Activo® 150 g/t Activo® 150 g/t

16

With increased knowledge about secon-

dary plant compounds and their modes

of action, we will be able to further create

well-suited combinations of selected sub-

stances. It will allow us, to fully exploit their

potential for individual species during dif-

ferent stages in their life cycle.

The fact that in more and more countries

the use of antibiotics in feed will be ban-

ned or phased out in the near future, will

further increase the demand for phytoge-

nic products as natural alternatives to anti-

biotic growth promotors.

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Co-authorLea Hesselmann

secondary Plant compounds are more than essential oils

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