Dietary CLA Affects Lipid Metabolism in Broiler Chicks
M. Du and D.U. Ahn*
Department of Animal Science, Iowa State University, Ames, Iowa 50011-3150
ABSTRACT: A total of 120 three-wk-old broiler chicks were
randomly assigned to three diets containing 0, 2, or 3% CLA and
fed for 5 wk. Fat content and FA composition of liver, plasma,
and feces were analyzed. Key enzymes involved in FA synthesis
and catabolism in liver, TG, cholesterol, and FFA content of
plasma were also determined. Dietary CLA increased TG, total
cholesterol, and HDL cholesterol levels in plasma. The increased
plasma TG level could be caused by increased FA synthesis in
the liver after CLA feeding, because the activity of FA synthase in
the liver increased after dietary CLA treatment. Dietary CLA
changed the FA composition of feces but had no effect on fat content. Compared to the amounts of linoleic and linolenic acids present in the control diet, the amounts excreted into the feces of
CLA-treated birds were significantly higher. Liver weights of broilers significantly increased after CLA feeding, but there was no difference in liver fat content among the different CLA treatments.
CLA treatment did not influence total FFA content in plasma;
however, there was a significant difference in the composition of
FFA. Dietary CLA reduced the content of linoleic and arachidonic
acids in both plasma and liver.
Paper no. L9126 in Lipids 38, 505–511 (May 2003).
Dietary CLA is reported to reduce fat accumulation in certain
animal models (1–3). Dietary CLA reduced retroperitoneal fat
pad weight by 13, 25, and 32% in rats fed 0.25, 0.5, and 1.0%
pure CLA, respectively (P < 0.05) (1). Similar effects were observed in parametrial fat pad (1). Feeding CLA at a low level
produced a rapid, marked decrease in fat accumulation but increased protein content without any major effects on food intake (2). Rats fed 0.5% CLA in a diet had significantly reduced
body fat but increased whole-body protein, water, and ash (3).
Dietary CLA is also reported to improve feed efficiency in rats
(4,5). The exact mechanism for the reduced fat accumulation
by dietary CLA is not yet clear, but it can be related to the inhibition of lipid absorption and lipogenesis and the promotion of
lipid oxidation.
In birds, the liver is the principal site of lipid synthesis. Unlike mammals, FA, rather than glucose, are the main energy
source for birds, and the liver of birds has a very high capacity
for lipogenesis. Numerous reports on the effect of dietary CLA
on FA metabolism in mammals have been published, but few
are available on birds (6,7). Further, most of the published
reports have concentrated on milk synthesis and adipose tissue,
and liver, an important organ in lipid metabolism, seems to
*To whom correspondence should be addressed at 2276 Kildee Hall, Department of Animal Science, Iowa State University, Ames, IA 50011.
E-mail: duahn@iastate.edu
Copyright © 2003 by AOCS Press
have been ignored. Therefore, the objective of this study was
to determine the effect of dietary CLA on FA status and key
enzyme activities in the liver of broiler chicks.
MATERIALS AND METHODS
Chicken feeding and sample preparation. A total of 120 threewk-old broiler chicks were kept in 12 pens. Four pens were randomly assigned to one of three dietary treatments containing 0,
2, or 3% CLA (Tables 1 and 2). The CLA source, which contained 62% CLA, was obtained from a commercial company
(Conlinco, Inc., Detroit Lakes, MN). Soybean oil and the CLA
source were substituted on a weight/weight basis in different
diets. After 5 wk dietary treatment, birds were slaughtered according to USDA guidelines, and feces were collected the night
before slaughter. For feces collection, birds from each treatment group were placed into four containers, with five birds in
each container. Birds were kept in containers for 2 h and all
feces were collected and pooled. Fecal samples were then dried
in a fume hood at 22°C for 48 h. Blood and whole liver were
collected during slaughter. Whole liver was weighed, and then
TABLE 1
Percentage Composition of Diets Fed to Broiler Chicks
Ingredients
Corn
Soy meal
Wheat middlings
Meat and bone meal
Limestone
Dicalcium phosphate
Mineral premixa
Vitamin premixb
DL-Methionine
Sodium chloride (iodized)
BMD (bacitracin methylene
disalicylate)
Soybean oil
CLA source
Calculated metabolizable
energy (kcal/kg)
Diet (1 to 3 wk)
51.15
38.38
22.85
3.00
1.05
0.85
0.30
0.30
0.25
0.09
0.025
4.61
0
3,100
Diet (4 to 5 wk)
50.34
28.57
10.26
3.00
0.96
0.85
0.30
0.30
0.15
0.25
0.025
5.0 to 0c
0 to 5.0c
3,100
a
Mineral premix provides (per kg of diet): Mn, 80 mg; Zn, 90 mg; Fe, 60 mg;
Cu, 12 mg; Se, 0.147 mg; sodium chloride, 2.247 g.
b
Vitamin premix supplies (per kg of diet): retinyl acetate, 8,065 IU; cholecalciferol, 1,580 IU; 25-hydroxy-cholecalciferol, 31.5 µg, DL-α-tocopheryl acetate, 15 IU; vitamin B12, 16 µg; menadione, 4 mg; riboflavin, 7.8 mg; pantothenic acid, 12.8 mg; niacin, 75 mg; choline chloride, 509 mg; folic acid,
1.62 mg; biotin, 0.27 mg.
c
In the 0% CLA group, soybean oil, 5.00%; CLA source, 0%. In the 2.0%
CLA group, soybean oil, 2.67%; CLA source, 3.33%. In the 3.0% CLA group,
soybean oil, 0%; CLA source, 5%.
505
Lipids, Vol. 38, no. 5 (2003)
506
M. DU AND D.U. AHN
TABLE 2
Crude Fat Content and FA Composition of Diets (4 to 5 wk)a
Crude fat content
FA composition
Palmitoleic
Palmitic
Stearic
Linoleic
Oleic
Linolenic
CLA (cis-9,trans-11)
CLA (trans-10,cis-12)
CLA (trans-9, trans-11)
Other CLA isomers
0% CLA diet
2% CLA diet
3% CLA diet
8.72 ± 0.40
8.68 ± 0.47
8.45 ± 0.38
0.32 ± 0.03b
13.71 ± 0.25a
4.62 ± 0.05a
46.45 ± 0.25a
30.96 ± 0.23b
3.77 ± 0.17a
0 ± 0.00c
0 ± 0.00c
0 ± 0.00c
0 ± 0.00c
0.34 ± 0.02a
9.43 ± 0.12b
2.76 ± 0.03b
21.47 ± 0.07b
33.02 ± 0.27a
1.67 ± 0.08b
9.20 ± 0.32b
11.69 ± 0.43b
4.88 ± 0.28b
5.04 ± 0.20b
0.37 ± 0.03a
8.12 ± 0.11c
2.39 ± 0.07c
15.14 ± 0.07c
33.37 ± 0.21a
1.34 ± 0.09c
11.23 ± 0.39a
14.02 ± 0.40a
5.87 ± 0.34a
7.14 ± 0.38a
a
Means within a row with no common roman superscript (a–c) differ significantly (P < 0.05). Livers (1 g/bird) from five
birds from the same pen were randomly selected and pooled, and four mixtures were prepared for analysis (n = 4).
a part of the liver was quickly frozen in liquid nitrogen and
used for chemical analyses. Ten milliliters of blood was collected in test tubes containing 200 µL of 5 mM EDTA, and
plasma was separated by centrifuging at 1500 × g for 15 min.
Analysis of total cholesterol, HDL cholesterol, and TG in
plasma. Fifteen plasma samples for each treatment (three or four
samples per pen) were randomly selected for analysis. Sigma kit
methods (catalog nos. 352-20 and 336-20; Sigma-Aldrich, St.
Louis, MO) were used to analyze plasma cholesterol, HDL cholesterol, and TG levels. Reagent (1.0 mL) was pipetted into a
tube, and 10 µL of plasma sample was added. The tube was incubated for 10 min (for cholesterol) or 18 min (for TG) at 25°C.
HDL cholesterol was measured after serum LDL and VLDL
lipoproteins were selectively precipitated and removed by centrifugation (Sigma kit, catalog no. 352-7). Absorbance was read
and recorded using a spectrophotometer at 500-nm wavelength.
Lipid extraction. Livers (1 g/bird, cut into small cubes) and
plasma (0.5 mL/bird), respectively, from five birds from the
same pen were randomly selected and pooled; thus, four mixtures each of liver and plasma were prepared. Two grams of
liver from the pooled liver pieces (total, 5 g) or 2 mL of
plasma mixtures were weighed into test tubes. The same
method was also used for fecal samples. Ten volumes of chloroform/methanol solution (2:1, vol/vol) was prepared following the method of Folch et al. (8). This solution (Solution 1)
was added to the samples, which were then homogenized with
a Brinkman polytron (Type PT 10/35; Brinkman Instruments,
Inc., Westbury, NY) for 10 s at high speed. Twenty-five micrograms of 10% BHA dissolved in 98% ethanol was added
to each sample prior to homogenization. The homogenate was
filtered through Whatman #1 filter paper into a 100-mL graduated cylinder and 0.25 vol (on the basis of Solution 1) of
0.88% NaCl solution was added. After the cylinder was
capped with a glass stopper, the filtrate was mixed well. The
inside of the cylinder was washed twice with 2 mL of
CHCl3/CH3OH/H2O (3:47:48, by vol; Solution 2), and the
contents were stored until the aqueous and organic layers
were clearly separated. The upper layer was siphoned off, and
Lipids, Vol. 38, no. 5 (2003)
the lower layer was moved to glass scintillation vials and
dried at 50°C under nitrogen.
Separation of FFA from plasma. The dried plasma lipids were
redissolved with chloroform to make a final concentration of 0.2
g lipid mL chloroform, and 50 mg of behenic acid (SigmaAldrich) was added as internal standard. The lipid/chloroform
solution (150 µL) was loaded onto an activated (120°C for 2 h)
silica gel plate (20 × 20 cm; Sigma-Aldrich). The plate was developed first in Solvent 3, composed of chloroform/methanol/
water (65:25:4, by vol), until the solvent line reached the middle
of the plate. The plate was air-dried and then redeveloped in Solvent 4, composed of hexane/diethyl ether (4:1, vol/vol), until the
solvent reached 5 cm below the top of the plate. After air-drying
for 10 min at room temperature (22°C), the plates were sprayed
with 0.1% 2′,7′-dichlorofluororescein in ethanol. Lipid classes
were identified under UV light, and the lane corresponding to
FFA was scraped into a separate test tube. FFA were extracted
three times using 5 mL of 1:1 (vol/vol) cholesterol/methanol.
The solvent was dried under a nitrogen flow, and FFA were used
for FA composition analysis.
Analysis of FA composition. One milliliter of methylating
reagent (3 N anhydrous methanolic HCl; Sigma-Aldrich) was
added into the test tube containing total lipids or FFA, capped
tightly, and incubated in a water bath at 60°C for 40 min. After
cooling to room temperature, 2 mL of hexane and 5 mL of
water were added, mixed thoroughly, and left at room temperature overnight for phase separation. The top hexane layer containing methylated FA was used for GC analysis. Analysis of
FA composition was performed with a gas chromatograph (HP
6890; Hewlett-Packard Co., Wilmington, DE) equipped with
an autosample injector and an FID. A capillary column (HP-5,
0.25 mm i.d., 30 m, 0.25 µm film thickness; Hewlett-Packard
Co.) was used. A splitless inlet was used to inject samples (1
µL) into the capillary column. Ramped oven temperature conditions (180°C for 2.5 min, increased to 230°C at 2.5°C/min,
then held at 230°C for 7.5 min) were used for the analysis of FA
composition of lipids from liver and feces. For the composition
of FFA in plasma, the initial oven temperature was lowered to
DIETARY CLA AND LIPID METABOLISM
140°C, held for 2 min, increased to 230°C at 5°C/min, and then
held at 230°C for 10 min.
The temperatures of both inlet and detector were 280°C. Helium was used as a carrier gas, and a constant column flow of 1.1
mL/min was used. Detector (FID) air, H2, and makeup gas (He)
flows were 350, 35, and 43 mL/min, respectively. FA were identified using a mass selective detector (Model 5973; Agilent Technologies, Wilmington, DE). The ionization potential of the mass
selective detector was 70 eV, and the scan range was 45 to 450
m/z. Identification of FA was achieved by comparing mass spectral data with those of the Wiley library and confirmed by comparing retention times with standards purchased from Matreya
(Pleasant Gap, PA) and Nu-Chek-Prep (Elysian, MN). The FA
compositions of lipids in liver and feces were reported as percentages, and the FFA in plasma were reported as actual amounts
calculated by using behenic acid as an internal standard.
Enzyme activity analysis. Ten livers per treatment (two or
three livers from each of the four pens) were randomly selected
for enzyme activity analysis. All the chemicals used in the analyses of enzyme activities were purchased from Sigma-Aldrich.
(i) Preparation of mitochondria and cytosolic fractions. One
gram of liver was homogenized in 5 vol of Solution 5 [0.25 M
mannitol, 5 mM Hepes (pH 7.4), and 1 mM EGTA] using a
polytron. One milliliter of homogenate was then transferred to
Eppendorf vials and centrifuged at 2,000 × g for 10 min. The
supernatant was collected and centrifuged again at 10,000 × g
for 10 min to sediment the mitochondria. The resulting supernatant was used as a cytosolic solution for FA synthase and
acetyl-CoA carboxylase analyses. The sediment (200 µL,
mainly mitochondria) was added to 500 µL of Solution 5,
mixed, and used for the analysis of carnitine palmitoyltransferase activity. The protein contents of cytosolic and mitochondrial solutions were analyzed with a protein analysis kit
(Sigma-Aldrich).
(ii) Carnitine palmitoyltransferase I and II. Carnitine palmitoyltransferase I and II activities were analyzed by measuring
the release of CoA catalyzed by carnitine palmitoyltransferases
(9). Briefly, two sets of Eppendorf vials were prepared. Vial A
contained a reaction mixture (200 µL) composed of 100 mM
Hepes buffer (pH 7.8), 1.25 mM EGTA, 1 mM DTNB, 0.15
mM palmitoyl-CoA, 1.25 mM carnitine, and an aliquot of mitochondrial mixture (0.6 mg protein). Vial B contained substances identical to Vial A but without 1.25 mM carnitine. After
3 min of incubation at room temperature, the reaction was
stopped by placing the vials in a boiling water bath. Samples
were cooled to room temperature and centrifuged at 8,000 × g
for 3 min; absorbance of the supernatant was then measured at
507
412 nm. To calculate the standard curve between absorbance
and CoA formation, a known amount of CoA was added instead of the mitochondrial mixture and the same procedure was
followed as above. The enzyme activity was calculated by the
difference in absorbance between Vials A and B. Enzyme activity was expressed as CoA formation min−1 mg protein−1.
(iii) Acetyl-CoA carboxylase. A reaction mixture (200 µL)
composed of 20 mM sodium citrate, 20 mM magnesium chloride, 1.0 mM DTT, 0.5 mg/mL FA-free BSA, 50 mM Hepes
buffer (pH 7.4), 200 µM acetyl-CoA, 5 mM ATP, 30 mM
[14C]sodium bicarbonate, and an aliquot of cytosolic fraction
(0.6 mg protein) was incubated for 8 min at 37°C; the reaction
was then stopped by adding 40 µL of HCl (6 N). The samples
were evaporated to dryness at room temperature and transferred to scintillation vials for reading. Enzyme activity was
expressed as [1-14C]bicarbonate incorporation into FA min−1
mg protein−1 (10,11).
(iv) FA synthase. A reaction mixture (200 µL) composed of
100 mM Hepes (pH 7.4), 3.0 mM EGTA, 1.0 mM dithioerythritol, 0.062 mM (4 Ci/mol) [1-14C]acetyl-CoA, 1.25 mM
NADP, 12.5 mM glucose-6-phosphate, 0.7 U glucose-6-phosphate dehydrogenase, 0.30 mM malonyl-CoA, and an aliquot
of cytosolic fraction (0.6 mg protein) was incubated at 37°C
for 8 min. The reaction mixture was then extracted directly
with 1 mL of Solution 1 and mixed vigorously. After phase separation, the bottom (chloroform) layer was used for scintillation counts. Enzyme activity was expressed as [1-14C]acetylCoA incorporation into FA min−1 mg protein−1 (10,11).
Statistical methods. Effects of dietary CLA on FA composition, weight, plasma TG, plasma cholesterol, and enzyme
activities were analyzed using SAS software (12). The Student–Newman–Keuls multiple range test was used to compare
differences among mean values (P < 0.05). Mean values and
SEM were reported.
RESULTS AND DISCUSSION
The ingredients in the diets of the broiler chicks are shown in
Table 1, and the fat content and FA composition of the diets are
shown in Table 2. There was no difference in fat content among
the diets. The content of linoleic acid in diets decreased as the
amount of CLA increased. The level of linolenic acid in the
CLA diets was lower, but that of oleic acid was higher than in
the control. The major CLA isomers present in the diets were
cis-9,trans-11 and trans-10,cis-12.
The TG and cholesterol levels of plasma are shown in Table
3. TG levels in plasma increased significantly with CLA diets,
TABLE 3
Plasma TG, Total Cholesterol, and HDL Cholesterol Content of Broilersa
TG
Total cholesterol
HDL cholesterol
Calculated LDL + VLDL cholesterol
0% CLA diet
2% CLA diet
b
a
42.1 ± 6.82
126.3 ± 12.57c
38.2 ± 4.18b
88.2
49.8 ± 9.85
152.9 ± 16.02b
46.8 ± 5.30a
106.8
3% CLA diet
50.2 ± 11.44a
170.4 ± 23.70a
48.3 ± 2.99a
122.1
a
Means within a row with no common roman superscript (a–c) differ significantly (P < 0.05). Plasma
samples were randomly selected (n = 15) from 15 birds per treatment.
Lipids, Vol. 38, no. 5 (2003)
508
M. DU AND D.U. AHN
TABLE 4
Activities of Selected Enzymes Related to FA Metabolism in Liversa
FA synthase
Acetyl-CoA carboxylase
Carnitine palmitoyl-CoA transferase
0% CLA diet
2% CLA diet
3% CLA diet
0.38 ± 0.03b
2.97 ± 1.28
11.41 ± 0.81
0.46 ± 0.04a
3.46 ± 1.01
11.99 ± 1.12
0.46 ± 0.06a
3.84 ± 1.76
12.24 ± 0.96
a
Means within a row with no common roman superscript (a,b) differ significantly (P < 0.05). Livers
were randomly selected for analysis from 10 birds per treatment (n = 10).
in agreement with previous reports: In rats, plasma TG concentrations were elevated significantly (P ≤ 0.01) after CLA feeding
(13,14). Feeding diets containing up to 1% CLA increased
VLDL TG (80 and 61%) in hamsters (15). Dietary CLA also
increased plasma cholesterol levels in broilers, an unexpected
result (Table 3). The total cholesterol level in plasma increased
from 126.3 mg/dL in the control diet to 152.9 and 170.4 mg/dL,
respectively, in the 2 and 3% CLA diets, an increase mainly
due to the increase in VLDL and LDL cholesterol. This result
was different from previous reports: Nicolosi et al. (16) reported that hamsters fed up to 1.1% CLA-containing diets for
11 wk had significantly reduced levels of plasma total cholesterol, non-HDL cholesterol, and TG with no effect on HDL
cholesterol. Diets containing CLA mixtures of 3 and 5% exhibited marked reductions of LDL and HDL cholesterol compared with rats receiving no CLA (17). However, in pigs there
was an increase in total plasma cholesterol after CLA feeding,
and the ratio of LDL cholesterol to HDL cholesterol was significantly increased in CLA diets (18). Our study indicated that
up to 1% dietary CLA did not influence plasma TG and cholesterol levels in broiler chicks (data not shown). Animal
species, dose of CLA, and duration of treatment could be responsible for the different responses in plasma cholesterol levels after CLA feeding.
The reason for the increased plasma TG and cholesterol levels in CLA-treated birds was not clear, but it could be related
to the changes in enzyme activities associated with lipid metabolism in the liver. In birds, liver is the main site of lipid synthesis. Table 4 shows the activities of FA synthesis, acetyl-CoA
synthase, and carnitine palmitoyl-CoA transferase in the liver.
A significant increase in FA synthase activity and an increase
(although not significant) in acetyl-CoA carboxylase activity in
the liver were observed with CLA feeding. Acetyl-CoA carboxylase and FA synthase are the main enzymes controlling FA
synthesis. The increase in FA synthase activity could account
in part for the increased TG levels in plasma. The effect of dietary CLA on enzymes of adipose tissues and mammary glands
has been reported previously, but changes in FA synthase and
acetyl-CoA carboxylase activities in the liver after CLA feeding have not yet been reported. In the mammary glands of
sows, FA synthase and acetyl-CoA carboxylase activities decreased after feeding CLA diets (19). Dietary CLA was also
involved in reducing the de novo FA synthesis and desaturation process in adipose tissues and mammary glands in sows
(20). In the adipose tissue of AKR/J mice, however, dietary
CLA increased fat oxidation but had no effect on de novo fat
biosynthesis (21). In adipose cell culture, the mRNA expres-
Lipids, Vol. 38, no. 5 (2003)
sion of FA synthase was not reduced by dietary CLA (22).
These results indicate that dietary CLA reduces lipogenesis in
adipose tissues and mammary glands but not in liver. This
could be the reason CLA is ineffective in reducing fat accumulation in birds (13), in which lipogenesis is concentrated in the
liver. Adipose tissues are important for FA synthesis in mice,
rats, and pigs, and inhibiting lipogenesis in adipose tissue by
CLA could significantly reduce fat accumulation in these animal species. No change was shown in acetyl-CoA carboxylase
activity in the liver of rabbits fed 0.5% CLA, but its activities
in adipose tissue were inhibited (23). The authors suggested
that the activities of lipogenic enzymes in the adipose tissues
and liver of rabbits are regulated differently (23). The overall
FA synthase and acetyl-CoA carboxylase activities measured
in this study were quite low (Table 4), a result that could be associated with the high fat content of the diets due to 5% oil addition (Table 1).
There was no difference in the activity of carnitine palmitoyl-CoA transferase with CLA feeding (Table 4). Jones et al.
(24) fed male Wistar rats a semipurified diet containing 0, 1.5,
or 5.0 energy percentage CLA for 4 wk and found that dietary
CLA did not change the activities of hepatic palmitoyl-CoA
oxidase and carnitine acetyl transferase. In hamsters, palmitoyl-CoA oxidase and carnitine acetyl transferase activities
were not increased by CLA (15). In rats, the activity of carnitine palmitoyltransferase I was not changed by dietary CLA either in liver or muscle, but its activity did increase more than
30% compared to the control value in epidydimal adipose tissue, showing that dietary CLA might increase FA oxidation in
adipose tissues (25).
The lipid content and FA composition of liver are shown in
Table 5. Liver weight increased as the level of dietary CLA increased, in agreement with the result of DeLany and West (21)
in mice. No difference in liver fat content was observed (Table
5). However, a recent study showed that dietary CLA reduced
the fat content in chicken liver (7). The proportions of saturated
FA, palmitic acid, and stearic acid increased as dietary CLA
level increased, and the content of monounsaturated FA decreased. This was in agreement with our previous report (26).
The FFA content in plasma from birds fed CLA diets is
shown in Table 6. Dietary CLA had no effect on the content of
FFA in plasma, whereas the content of individual FA changed.
Dietary CLA decreased the levels of palmitoleic, linoleic, and
arachidonic acids, whereas CLA isomers increased. Other FFA,
including stearic, palmitic, myristic, lauric, and capric acids, did
not change (Table 6). In pigs, a 1% level of CLA for 6 wk reduced plasma concentrations of nonesterified FA by 38% but
DIETARY CLA AND LIPID METABOLISM
509
TABLE 5
Weight, Crude Fat Content, and FA Composition of Livera
0% CLA diet
Liver weight
Crude fat content
FA composition
Myristic
Palmitoleic
Palmitic
Margaric
Linoleic
Oleic
Stearic
Linolenic
CLA (cis-9,trans-11)
CLA (trans-10,cis-12)
CLA (trans-9,trans-11)
Other CLA isomers
Arachidonic
Eicosapentaenoic
Docosahexaenoic
Unconfirmed
2.0% CLA diet
3.0% CLA diet
62.1 ± 9.94b
3.8 ± 0.53
64.2 ± 9.55b
3.6 ± 0.98
70.9 ± 9.12a
4.2 ± 1.20
0.23 ± 0.06
0.65 ± 0.09a
18.02 ± 0.63c
0.23 ± 0.03a
25.47 ± 1.79a
21.29 ± 2.11a
12.56 ± 0.85c
1.40 ± 0.12a
0 ± 0.00c
0 ± 0.00c
0 ± 0.00b
0 ± 0.00c
11.07 ± 2.74a
0.52 ± 0.05a
2.80 ± 0.55a
4.21 ± 1.12
0.19 ± 0.01
0.32 ± 0.07b
21.46 ± 0.54b
0.20 ± 0.01b
18.97 ± 1.18b
18.57 ± 1.17b
19.39 ± 0.93b
1.22 ± 0.08b
1.28 ± 0.13b
1.86 ± 0.30b
0.59 ± 0.15a
0.81 ± 0.10b
8.78 ± 1.19b
0.45 ± 0.31a
2.01 ± 0.31b
4.59 ± 1.22
0.19 ± 0.04
0.55 ± 0.18a
24.34 ± 1.32a
0.18 ± 0.01b
15.02 ± 2.82c
15.84 ± 1.14c
25.05 ± 1.01a
0.81 ± 0.06c
2.01 ± 0.35a
2.58 ± 0.66a
0.71 ± 0.15a
1.12 ± 0.22a
6.01 ± 0.89c
0.25 ± 0.03b
0.95 ± 0.18c
3.55 ± 0.61
a
Means within a row with no common roman superscript (a–c) differ significantly (P < 0.05); n = 40
for liver weight, and n = 4 for the analysis of fat content and FA composition.
the change was not statistically significant (18). The FFA content in serum has been shown to be associated with human diseases (27).
As Table 7 shows, there is no difference in the extractable
lipid content in feces from birds fed different CLA diets, indicating that CLA had no influence on total lipid excretion. No
differences in energy digestibility and metabolizable energy
between the control and CLA diets were reported in pigs (28).
A significant difference in the FA composition of feces was
found (Table 7). The content of CLA isomers in feces was
much higher in CLA-treated birds. Although the content of
linoleic acids in all treatments was similar, the linolenic acid
level was significantly higher in CLA-treated groups. When
comparing the contents of linoleic and linolenic acids in the
diet, their levels were more than two times lower in CLA diets
than in the control diet (Table 2), but the contents in feces of
birds treated with CLA were similar for linoleic acid and even
higher for linolenic acid. This indicates that the excretion of
linoleic and linolenic acids in birds fed CLA diets could be
much higher than in the control diet. This might be related to
an increased saturated FA content in the plasma and liver
(Table 5).
This study showed that high-level dietary CLA increased
plasma TG and cholesterol levels. The increase in TG level could
be due in part to increased FA synthase activity in the liver. Dietary CLA decreased the contents of linoleic and arachidonic
TABLE 6
Composition of FFA in Plasma (µg/mL plasma)a
FFA content
Individual FA content (µg/mL)
Capric
Lauric
Myristic
Palmitic
Palmitoleic
Stearic
Oleic
Linoleic
CLA (cis-9,trans-11)
CLA (trans-10,cis-12)
CLA (trans-9,trans-11)
Other CLA isomers
Arachidonic
0% CLA diet
2% CLA diet
3% CLA diet
501.7 ± 68.3
592.1 ± 80.3
552.3 ± 67.2
3.1 ± 0.93
4.1 ± 1.88
2.7 ± 0.40
133.8 ± 22.1
10.8 ± 1.0a
78.3 ± 10.3
156.6 ± 18.3
91.3 ± 13.1a
0 ± 0.00c
0 ± 0.00c
0 ± 0.00c
0 ± 0.00c
20.4 ± 2.7a
2.9 ± 0.77
4.8 ± 1.25
3.6 ± 0.43
163.9 ± 19.9
6.6 ± 0.8b
105.4 ± 15.8
164.0 ± 22.8
90.1 ± 8.8a
13.2 ± 3.4b
13.8 ± 2.9b
4.7 ± 1.8b
5.8 ± 2.3b
13.3 ± 2.2b
3.0 ± 0.81
7.2 ± 2.44
3.8 ± 0.59
163.0 ± 24.4
6.0 ± 0.7b
99.6 ± 13.8
141.6 ± 19.6
64.3 ± 6.4b
18.6 ± 3.7a
19.0 ± 3.7a
9.6 ± 1.7a
10.0 ± 2.8a
6.7 ± 1.7c
a
Means within a row with no common roman superscript (a–c) differ significantly (P < 0.05). Plasma
(0.5 mL/bird) from five birds from the same pen were randomly selected and pooled, and four mixtures were prepared for analysis (n = 4). FFA in plasma were reported as actual amounts calculated
by using behenic acid as an internal standard.
Lipids, Vol. 38, no. 5 (2003)
510
M. DU AND D.U. AHN
TABLE 7
Crude Fat Content and FA Composition of Feces from Broilersa
0% CLA diet
Crude fat content
FA composition
Myristic
Palmitoleic
Palmitic
Margaric
Stearic
Oleic
Linoleic
Linolenic
CLA (cis-9,trans-11)
CLA (trans-10,cis-12)
CLA (trans-9,trans-11)
Other CLA isomers
2.0% CLA diet
3.0% CLA
5.34 ± 0.78
5.55 ± 0.73
5.28 ± 0.84
0.17 ± 0.07
0.21 ± 0.03
14.08 ± 0.45a
0.20 ± 0.08
4.21 ± 0.65a
21.37 ± 5.95
52.30 ± 5.33a
0.90 ± 0.03b
0 ± 0.00c
0 ± 0.00c
0 ± 0.00c
0 ± 0.00c
0.12 ± 0.05
0.27 ± 0.04
12.23 ± 0.15b
0.13 ± 0.06
3.06 ± 0.18b
22.86 ± 6.39
45.45 ± 4.97b
1.16 ± 0.17a
2.86 ± 0.48b
2.88 ± 0.52
1.48 ± 0.28b
1.23 ± 0.08b
0.16 ± 0.03
0.26 ± 0.02
11.44 ± 0.16c
0.10 ± 0.06
3.21 ± 0.20b
26.92 ± 0.31
41.13 ± 1.27b
1.33 ± 0.15a
4.85 ± 0.20a
5.00 ± 0.25a
2.77 ± 0.63a
2.89 ± 0.41a
a
Means within a row with no common roman superscript (a–c) differ significantly (P < 0.05). Feces
collected from five birds in the same container were pooled and dried; four containers were used
(n = 4).
acids in the liver and the level of FFA in plasma. There was no
difference in the crude lipid content of feces among chickens
treated with different levels of dietary CLA. Even though the
contents of linoleic and linolenic acids in the CLA diets were
much lower than in the control diet, their contents in feces were
very similar to or even higher than in the control.
ACKNOWLEDGMENTS
Journal paper number J-19603 of the Iowa Agriculture and Home
Economics Experiment Station, Ames, Iowa 50011-3150. Project
No. 3706.
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[Received July 30, 2002, and in revised form April 28, 2003; revision accepted April 30, 2003]
Lipids, Vol. 38, no. 5 (2003)