Effect of dietary conjugated linoleic acid on body composition and energy
balance in broiler chickens
Marjan Javadi1, Math J.H. Geelen1*, Henk Everts1, Robert Hovenier1, Shahram Javadi2, Henk Kappert1
and Anton C. Beynen1
1Department of Nutrition, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 104 P.O. Box 80.152, 3508 TD Utrecht,
2Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Yalelaan 108, P.O. Box 80.154, 3508 TD
Utrecht, The Netherlands
(Received 12 January 2007 – Revised 27 April 2007 – Accepted 30 April 2007)
The effect of dietary conjugated linoleic acid (CLA) on body composition and energy metabolism was investigated in broiler chickens. Male
broiler chicks were assigned to receive either a control diet (1% sunflower oil) or a diet containing CLA (1% of a 1:1 mixture of trans-10,
cis-12 and cis-9, trans-11 isomers of octadecadienoic acid). The diets were fed ad libitum for 3 weeks and there were eight replicates per diet,
each replicate including four chickens so that each treatment had thirty-two animals. The proportion of body fat was lower in the control
group than in the CLA group. No significant differences as to the proportions of body water, ash and protein were observed. Feed and energy
intake were significantly lower in CLA-fed birds. The percentage of ingested energy lost in excreta was higher after CLA feeding and heat expen-
diture as a percentage of ingested energy was lower in the CLA-fed group. The CLA-fed group showed a higher percentage of SFA and lower
percentages of MUFA and PUFA in carcass fat. It is concluded that CLA stimulated de novo fatty acid synthesis and lowered desaturase activity.
Conjugated linoleic acid: Body composition: Energy metabolism: Broilers
The term conjugated linoleic acid (CLA) is used to designate a
mixture of positional and geometric isomers of linoleic acid in
which the double bonds are conjugated. Considerable attention
CLA. CLA was found to act as a growth factor1, as a fat-to-lean
usually not affected by incorporation of CLA in the diets and,
therefore, the body fat-lowering effect of CLA is most likely
mediated by enhanced energy expenditure. Measuring the
energy expenditure of mice in metabolic chambers fed CLA
indeed demonstrated an increase of energy expenditure12.
Szymczyk et al.13showed that feeding CLA to broiler
chickens resulted in subtantial incorporaton of CLA isomers
into their tissue lipids, thus providing a potential CLA-rich
source for human consumption. In their study, feeding CLA
(8–21d) period, but no effect was noted during the grower–
finisher (22–42d) period. Abdominal fat deposition was sig-
nificantly reduced whereas the relative proportion of breast
muscles was unaffected and that of leg muscles significantly
increased13. It could be suggested that CLA feeding influences
body composition and energy metabolism of broiler chickens.
The objective of the present study was to test whether the
earlier observed CLA-induced reduction of abdominal fat in
chickens13is associated with enhanced energy expenditure
by investigating the influence of dietary CLA on growth,
body composition and energy balance in broilers. In addition,
the fatty acid composition of total carcass lipid was evaluated.
The experimental protocol was approved by the animal exper-
iments committee of the Faculty of Veterinary Medicine,
Utrecht University, The Netherlands.
Animals and diets
One-day-old male broiler chickens (Ross 308) were purchased
from a local hatchery. On arrival, they were wing-banded,
weighed and housed in wire-floored, suspended cages. The
temperature of the animal house was controlled and continu-
ous lighting used throughout the entire experimental period.
There were two dietary treatments, each consisting of eight
replicates. A replicate was identical to a cage with four
birds so that each treatment had thirty-two animals. Ten
birds were killed at the beginning of the study to determine
pre-experimental body composition. Sixty-four broilers were
used for the feeding trial. The base diet was in pelleted
form (Table 1) and fed for 7d. To produce the experimental
*Corresponding author: Dr M. J. H. Geelen, fax þ31 (0)302534125, email firstname.lastname@example.org
Abbreviation: CLA, conjugated linoleic acid.
diet, sunflower oil was replaced by 1g CLA per 100g diet.
The fatty acid composition of the diets is given in Table 2.
CLA was purchased from Lipid Nutrition B.V. (Wormerveer,
The Netherlands). It came in the form of a Clarinol G-80e
preparation that contained 79·5% of CLA as TAG. The
CLA preparation consisted of cis-9, trans-11 and trans-10,
cis-12 CLA in equal amounts. The birds were fed the exper-
imental diet for a period of 21d. Feed and water were pro-
vided ad libitum. Individual body weight and feed intake per
replicate were monitored weekly. From day 7 on, excreta
were collected quantitatively.
At the end of the experiment, the birds were weighed and
killed by cervical dislocation. Carcasses were cut in pieces
and ground (Retsch, SM 2000, Haan, Germany) and the car-
casses for each replicate were mixed, sampled, weighed and
then dried in a forced-hot air oven at 608C for a period of
3d. The dried carcasses were weighed again and the percen-
tage of water was calculated. Subsequently, the dried car-
casses were ground in a coffee grinder and the homogenised
samples were stored in plastic containers until analysed. The
excreta were collected during the experimental period of 3
weeks and were also dried for a period of 3d and homogen-
ised in a coffee grinder.
Total lipids in the dried, homogenised carcasses and excreta
GLCfor determinationofthefatty acid compositionoffeed and
carcasses. The protein content of the dried carcasses was deter-
minedwith themacroKjeldahlmethod16.For thedetermination
of the ash content, about 0·5g dried, homogenised carcass was
added to a small porcelain crucible and put in an oven that was
programmed as follows: 1h at 2008C, 2h at 3008C, 3h at
4008C and 10h at 5008C17.
The gross energy content in dried, homogenised carcasses,
faeces, diets and oils was determined with a bomb calori-
meter (IKA Calorimeter C4000 Adiabatic, IKA Analystech-
nik, Heitersheim, Germany). As a thermochemical standard
benzoic acid (BDH Ltd, Poole, UK) was used18. The total
amount of energy that was lost as heat (heat production or
energy expenditure) was calculated
energy lost as heat ¼ energy in food 2 energy in excreta
2 energy stored in body. Energy stored in the body was
determined as total energy at the end of the 21d feeding
period minus energy in the body at the beginning ( ¼
mean body weight £ energy content) of the 21d feeding
period. The same procedure was used to calculate the reten-
tion of water, protein, fat and ash.
with the formula:
Four birds in a cage were considered as one experimental unit.
This resulted in eight experimental units per dietary treatment.
Mean data per cage were used in a one-way ANOVA with diet
(sunflower oil v. CLA) as an independent variable. The level
of statistical significance was preset at P,0·05.
Body weight and body composition
Food intake was lower in CLA-fed birds than in controls, the
lowering almost reaching statistical significance (Table 3).
There was no difference in body weight gain and feed
conversion rate between CLA-fed birds and controls. The pro-
portion of body fat was higher in the CLA-fed group than in
the control group (P¼0·044). There were no differences in
the proportions of body water, protein and ash between the
Table 1. Composition of the diets (g/kg)†
IngredientsControl dietCLA-containing diet
Wheat (þ xylanase)
Soyabean meal (47·6% cp)
Sunflower meal (32·0% cp)
Fish meal (72·0% cp)
Natuphos 5000G (phytase)
cp, crude protein.
†The diets were prepared by Research Diets Services (Wijk bij Duurstede, The
‡The 5g Premix consisted of 12000IU vitamin A (4·1 mg retinol acetate); 2400IU
vitamin D3(0·06 mg cholecalciferol); 30mg vitamin E; 1·5mg vitamin K3; 2·0mg
vitamin B1; 7·5mg vitamin B2; 3·5mg vitamin B6; 20mg vitamin B12; 35mg nia-
cin; 10mg D-pantothenate; 460mg choline chloride; 1·0mg folic acid; 0·2mg bio-
tin; 80mg Fe; 12mg Cu; 85mg Mn; 60mg Zn; 0·4mg Co; 0·8mg I; 0·1mg Se;
200mg Ca; 125mg anti-oxidant (Oxytrap PXN).
Table 2. Selected fatty acids (% of FAME) in the diets†
†Total fat content of the diets: 7·53 and 7·32% for the control
and the CLA-containing diet, respectively.
CLA, conjugated linoleic acid.
Energy intake was lower in CLA-fed birds, lowering almost
reaching statistical significance (Table 3). Apparent fat digest-
ibility and energy metabolisability were higher in the control
group (P¼0·026 and 0·003, respectively). Energy expenditure
was calculated as the difference between the energy intake and
the energy stored and excreted in the excreta. The higher heat
production calculated for the control group differed from that
for the CLA group (P¼0·002). Energy storage was not
affected by CLA feeding. The proportion of energy intake
that was stored in the body was lower in controls than in
the CLA-fed group (0·34 (SEM 0·02) and 0·37 (SEM 0·02),
Feed and carcass fatty acid composition and feed efficiency
As CLA was added to the experimental diet at the expense of
sunflower oil, the ingested amounts of SFA, MUFA, PUFA-n-
6 and PUFA-n-3 dropped (Table 4). The amounts of fatty acid
Table 3. Body composition and energy balance in broiler chickens fed the control diet or a conjugated linoleic acid (CLA)-containing
diet for 21d
(Mean values with their standard errors for eight units with each unit including four birds)
SE SEM (pooled)P value
Feed intake (g/21d)
Feed conversion (g feed/g weight gain)
Initial body weight (g)
Final body weight (g)
Weight gain in 21d (g)
Apparent fat digestibility (%)
Energy metabolisability (%)
Body composition after 21d
Deposition in body
Retained in body (MJ/21d)
Heat production (MJ/21d)
Table 4. Selected fatty acids as ingested in broiler chickens fed a control or a conjugated linoleic acid
(CLA)-containing diet for a period of 21d (g/21d)
(Mean values with their standard errors for eight units with each unit including four birds)
6·083 1·67 0·001
†Total fatty acid contents were calculated as follows: total fat measured £ 0·95 £ percentage of selected fatty acid.
stored in the carcasses are shown in Table 5. The amount of
SFA in carcasses was increased in the CLA-fed group
(P,0·001) and the amount of MUFA and PUFA were
decreased (P¼0·003 and P,0·001, respectively).
CLA consumption markedly increased the efficiency of
incorporation (fatty acid deposited/fatty acid ingested) of
SFA and decreased the incorporation of PUFA-n-3 (Table 6).
Taking into account the amounts of fatty acids in the body at
the start of the experiment, the ingested amounts of fatty acids
and the amounts of fatty acids at the end of the experiment,
one can estimate the minimal rate of de novo fatty acid syn-
thesis during 21 d or the maximal rate of fatty acid degra-
dation/disappearance in that period. The data indicated that
CLA feeding preferentially induced SFA synthesis and that
degradation/disappearance of PUFA is unaffected (Table 6).
The effect of CLA on body composition and energy expendi-
ture was studied in broiler chickens fed 1g CLA/100g diet.
CLA feeding depressed feed intake, fat digestibility and
energy metabolisability. This must result in a lower amount
of metabolisable energy in the CLA treated group. However,
weight gain during the experimental period did not differ
between the dietary treatments. Moreover, deposition of fat,
water, protein, ash and energy was not different (Table 3).
CLA feeding had no negative effect on body fat deposition.
Feed conversion was non-significantly lower in the CLA-fed
birds, which is consistent with the finding by Szymczyk
et al.13. The fat proportion, however, was higher in the
body of birds fed CLA when compared to controls. This
result is consistent with the finding by Du & Ahn19who
found that feeding a diet containing 0·5% CLA to broilers
at 3 weeks of age, for a period of 3 weeks, resulted in an
increase in abdominal fat content. Several studies have
shown that incorporation of 1% or less CLA in the diet
can substantially reduce the proportion of body fat in
mice7,12,20, rats21,22, chickens13and man23,24. The effects in
mice appear more striking than in other species25. Badinga
et al.26found that feeding CLA at the level of 5% to 1-d-
old broiler chickens for a period of 21d significantly lowered
the proportion of body fat and increased the proportion of
body water. Szymczyk et al.13found lower abdominal fat
in the body when they fed birds a diet with 1% CLA. As
mentioned earlier, Du & Ahn19observed an increase in
abdominal fat in broilers fed CLA. Thus, experimental con-
ditions such as age, genotype and metabolic status of the
animal, as well as the level, the type of isomer and duration
of CLA treatment may play an integral role in how CLA
affects body composition. The lack of agreement between
previous works suggests mechanisms involved are compli-
cated and multiple.
Table 5. Selected fatty acids stored in the body of broiler chickens fed
a control or a conjugated linoleic acid (CLA)-containing diet for a period
of 21d (g/21d)
(Mean values with their standard errors for eight units with each unit
including four birds)
†Total fatty acid contents were calculated as follows: total fat measured £ 0·95
£ percentage of selected fatty acid.
Table 6. Minimum rate of de novo fatty acid synthesis, maximum rate of fatty acid disappearance and efficiency of incorporation of selected fatty acids
in the body of broiler chickens fed a control diet or a conjugated linoleic acid (CLA)-containing diet for a period of 21d
(Mean values for eight determinations per treatment group)
Fatty acidDiet Intake (g/21d)Retained (g/21d) Efficiency† Minimum synthesis‡ (g/21d)Maximum disappearance§ (g/21d)
C16: 0 CLA
Mean values were significantly different from those of the control diet: *P,0·05, **P,0·01, ***P,0·001.
†Efficiency is expressed as the ratio of fatty acid deposited in the body and dietary fatty acid.
‡The values for the minimum amount of fatty acid synthesised are obtained by subtracting the amount of intake from the amount of retained.
§The values for the maximum amount of fatty acid disappearing are obtained by subtracting the amount of retained from the amount of intake.
Much to our surprise, the energy balance indicated that the
calculated heat production was about 20% lower in CLA-fed
birds compared to the controls. This is opposite to what hap-
pens in mice after CLA consumption7. The present study does
not give any information on the mechanism responsible for the
decrease in energy expenditure in broilers fed CLA. However,
it is tempting to speculate that the decrease in energy expen-
diture is related to the increase in the proportion of body
fat. Another possibility is an effect of CLA on non-shivering
thermogenesis, which is quite different in birds as compared
to mammals where brown adipose tissue is the site for non-
shivering thermogenesis. Birds lack brown adipose tissue27.
Lee et al.28observed that CLA has the ability to alter the
fatty acid composition of tissues by reducing the levels of
MUFA which is consistent with the present findings. Choi
et al.29observed that the ratio of SFA to MUFA in mice fed
CLA was increased and indicated that this was related to a
lipid-lowering effect of CLA. Studies in rats30,31and chick-
ens13,32have shown that the percentage of SFA in the body
increases whereas those of MUFA and PUFA decrease. The
same was true for egg yolks of eggs produced by hens fed
CLA33,34. In the present study, we also found a marked
increase in SFA, but no lipid-lowering effect of CLA was
observed. Carcasses of rats fed CLA also contained a higher
proportion of SFA and less PUFA35. The reduction in
MUFA (oleic acid) may be the result of a reduced D-9 desa-
turase activity due to feeding CLA36–38. The arachidonic
acid concentration decreased in the carcasses. The present
results are consistent with those of Belury & Kempa-Steczko39
who proposed that CLA, acting as a substrate for D-6 desatur-
ase, inhibited the conversion of linoleic acid into arachidonic
acid. Consistent with the present observations is the finding
that CLA dramatically reduced the percentages of MUFA in
all tissues investigated through inhibition of D-9 desatur-
ase29,36,40,41. The trans-10, cis-12 CLA isomer has been
shown to have the highest biological activity in this respect,
whereas cis-9, trans-11 CLA does not reduce the activity of
The changes in fatty acid composition greatly increase the
melting point for fat retained in the CLA-fed group (from
21 to around 358C). What kind of effects this will trigger in
the broilers is unknown yet. A similar change in fatty acid
composition results in complete loss of hatchability of eggs
from CLA-fed chickens33,34. In the broilers such a change in
fatty acid composition makes chicken meat harder and drier19.
When we calculate the amounts of fatty acids stored in the
body during the experimental period and also the amounts of
fatty acids ingested, we can determine the efficiency of fatty
acid incorporation into the body. Calculation revealed a dra-
matically higher efficiency for SFA and a lower efficiency
for PUFA-n-3 (Table 6). The CLA-induced differences in effi-
ciency of incorporation might be related to preferential effects
on synthesis or degradation of certain fatty acids. If the incor-
poration ratio was higher than 1·0, then the minimum amount
of de novo synthesis of a specific fatty acid was calculated as
deposited amount (g/21d) minus the ingested amount (g/21d).
If the incorporation ratio was lower than 1·0, then the maxi-
mum amount of oxidation (or degradation) of a specific
fatty acid was calculated as the ingested amount (g/21d)
minus the deposited amount (g/21d). Both calculations can
only indicate the lower and upper limit, respectively, because
actual information about digestibility of individual fatty acids
and the efficiency of incorporation of dietary fatty acids in
deposited fatty acids is not available in the present experiment.
The calculations show that CLA feeding preferentially
induced SFA synthesis. This may explain the CLA-induced
increase in body fat, which was statistically significant when
expressed as percentage of the body. Much to our surprise
the oxidation of PUFA was unaffected. This is contrary to
PUFA39,43,44. In contrast, some studies have shown that
CLA may have a modest enhancing effect on the level of
PUFA45,46. Yet other studies, like the present one, show no
effect of CLA on PUFA levels31,47–49. It appears that the abil-
ity of CLA to alter PUFA levels is tissue and species depen-
dent. Consistent with the present results on fatty acid
synthesis and degradation are our earlier observations showing
CLA-induced activity of the lipogenic pathway in mice as evi-
denced by enhanced activities of acetyl-CoA carboxylase and
fatty acid synthase50. In that same study it was shown that
CLA did not alter the activities of 3-hydroxy-acyl-CoA dehy-
drogenase and citrate synthase, suggesting that fatty acid oxi-
dation was not affected by CLA feeding50.
It might be argued that differences in fatty acid composition
between the control and CLA-containing diet may have
caused differences in fatty acid deposition. There are indeed
differences in fatty acid intake between the two experimental
diets, as can be seen from Table 2 with the analysed fatty acid
composition of the experimental diets. These differences are
due to the fact that CLA was added at the expense of sun-
flower oil. The differences are minor except for linoleic
acid. However, earlier work14indicates that the difference in
linoleic acid intake cannot have caused the diet effects
observed in the present study. The difference in ingested
fatty acids as calculated in Table 4 is mainly caused by the
difference in feed intake between the treatments.
Several studies have shown that the specific mechanisms by
which dietary CLA reduces the body fat content are likely to
vary from one animal species to another. Whether reduced
accumulation of liver lipid in broilers fed CLA as observed
by Badinga et al.26reflected enhanced b-oxidation or reduced
de novo lipid synthesis warrants further investigation, but the
present observation indicates higher de novo synthesis and
lower desaturase activity. Measurement of enzyme expression
and/or activity would complement the present data.
This study was supported in part by the Stichting Toxicolo-
gisch Onderzoek Utrecht. The CLA used in this research
was supplied by Loders Croklaan b.v, Wormerveer, The Neth-
erlands. The technical assistance of Jan van der Kuilen is
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