Fatty Acid Composition and Productive Traits of Broiler Fed Diets Containing Conjugated Linoleic Acid F. Sirri,1 N. Tallarico, A. Meluzzi, and A. Franchini Department of Food Science, Alma Mater Studiorum-University of Bologna, 40126 Bologna, Italy ABSTRACT An experiment was carried out to evaluate the transfer of dietary CLA to broiler chicken tissues (breast, drumstick meat, skin, and abdominal fat) and its effect on productive traits and on carcass yields of birds. Cobb 500 females (n = 360), divided into three groups, received from 22 d to slaughtering age (47 d) a grower diet supplemented with 2% conjugated linoleic acid (CLA) source containing 60% CLA methyl esters (CLA2) or 4% CLA source (CLA4). The control group had no supplementation. The addition of CLA source to chicken diet decreased the content of monounsaturated fatty acid (MUFA) (oleic and palmitoleic acids) in breast and drum-
stick meat. The deposition of CLA in muscles significantly increased as the dietary CLA increased, whereas only little amounts of CLA were detected in the control group. Arachidonic acid (ARA) content was significantly depressed and linearly related to the addition of CLA to the chicken diet. Other non-CLA polyunsaturated fatty acids (PUFA) were little affected by the dietary CLA supplementation. Saturated fatty acids (myristic and stearic acids) significantly increased about 30% in abdominal fat pad of both treated groups enhancing the firmness of abdominal fat. Productive performances—as well as carcass yields—were similar across dietary treatment of birds.
(Key words: conjugated linoleic acid, fatty acid composition, productive traits; slaughtering yields, broiler chicken) 2003 Poultry Science 82:1356–1361
INTRODUCTION Conjugated linoleic acid (CLA) is a mixture of several geometrical and positional conjugated isomers of the linoleic acid (C 18:2 cis-9, cis-12), an essential fatty acid of poultry diets. The CLA has double bonds in position 9 and 11 or 10 and 12 along the carbon chain, and the double bounds can be in the cis or trans configuration, but the most representative isomers and the most active biological forms are cis-9, trans-11 and trans-10 cis-12 isomers. They are synthesized by ruminal bacteria of herbivorous animals and were detected in dairy products whose content ranges from 2 to 30 mg/g of fat (Shantha et al., 1992). Even if CLA was first described seven decades ago (Booth et al., 1935), it has risen to the attention of researchers only recently. This group of lipids is currently recognized as having a beneficial effect on human health, exerting action against cancer growth, atherosclerosis, and ipercholesterolemia (Pariza and Hargraves, 1985; Chin et al., 1992; Ip et al., 1994; Lee et al., 1994). Conjugated linoleic acid can be also obtained by alkali isomerization (Ackman, 1998), and it can be used as a supplement of animal diets, thus, providing an interest-
ing opportunity to improve CLA concentration in products from monogastric animals. The CLA is incorporated into all the lipid classes of egg yolk in amounts proportional to the dietary levels of CLA (Chamruspollert and Sell, 1999; Du et al., 1999). Dietary CLA increased the proportion of saturated fatty acid and decreased monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) of yolk (Ahn et al., 1999). Du et al. (2000), feeding laying hens diets containing increasing amounts of CLA, reported a reduction of the content of MUFA fatty acid and non-CLA PUFA in meat patties. Furthermore, dietary CLA reduces the degree of lipid oxidation in raw chicken meat during storage, acting as an antioxidant, more potent than α-tocopherol (Ha et al., 1990). Some researchers claim that CLA reduces the fat content of the carcass, either in young or old animals, by enhancing the lean tissue deposition (Dugan et al., 1997; Banni and Martin, 1998). The objective of this study was to evaluate the transfer of dietary CLA to broiler chicken tissues (breast, drumstick meat, skin, and abdominal fat) and the effects on productive traits and carcass yields of birds.
MATERIALS AND METHODS Animal Care and Dietary Treatments Three hundred sixty day-old Cobb 500 females, divided into three groups of six replicates each, were reared on
2003 Poultry Science Association, Inc. Received for pubblication June 17, 2002. Accepted for publication April 30, 2003. 1 To whom correspondence should be addressed:
[email protected].
Abbreviation Key: ARA = arachidonic acid; CLA = conjugated linoleic acid; DHA = docosahesanoic acid; MUFA = monounsaturated fatty acid; PUFA = polyunsaturated fatty acid.
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CLA AND FATTY ACID COMPOSITION OF BROILER MEAT TABLE 1. Percentage composition of starter and grower diets Ingredient Corn Soybean meal (48% CP) Wheat shorts Sunflower seeds Soybean oil Corn gluten meal Soybean lecithin Salt Calcium carbonate Sodium bicarbonate Dicalcium phosphate Choline chloride Lysine DL-Methionine Vitamin mineral premix1 Phytase
Starter
Grower
62.97 27.00 0.00 2.00 0.80 1.70 1.00 0.23 1.60 0.21 1.20 0.08 0.34 0.26 0.50 0.10
54.00 21.00 12.00 3.00 3.00 1.60 1.20 0.22 1.60 0.16 1.00 0.05 0.33 0.25 0.48 0.10
1
Vitamin and mineral premix provided the following per kilogram of feed: vitamin A, 10,000 UI; cholecalcipherol, 3,000 UI; vitamin E, 70 mg (DL-alpha-tocopheryl acetate); vitamin K (menadione sodiumbisulfate), 4.2 mg; vitamin C, 150 mg; vitamin B1, 3 mg; vitamin B2, 9 mg; vitamin B6, 6 mg; vitamin B12, 0.03 mg; biotin 0.08 mg; Ca-pantothenate, 36 mg; nicotinic acid, 78 mg; folic acid, 1.5 mg; choline, 450 mg; Zn, 50 mg; Fe, 70 mg; Cu, 11 mg; Mn, 72 mg; Co, 0.08 mg; I, 0.9 mg; Se, 0.1 mg.
18 litter pens of 4 m2 each. The pens were allocated in a controlled environment poultry house with a light regimen of 1630 h light and 0730 h dark. Up to 21 d, birds received the same starter diet, and from 22 d to slaughtering age (47 d), birds received a grower basal diet (Table 1) either supplemented with 2% CLA source containing 60% CLA methyl esters (CLA2) or with 4% CLA source (CLA4). The diet fed to the control group had no supplementation (control). To avoid thermal damaging of diet components, the diet was administered as mash. At 21 and 47 d feed intake, BW gain were measured and feed efficiency was calculated as well as mortality. The birds were slaughtered in an industrial slaughterhouse, and carcass yield was calculated after 2 h of air cooling. Thirty carcasses per group were randomly selected and dissected into commercial cuts, two thighs plus drumsticks, deboned breast, and two wings, according to Romboli et al. (1996). The abdominal fat, including the adipose tissues lining proventriculus and gizzard, was evaluated as a percent of carcass weight. In order to avoid variation in cutting procedures, the same operator was employed. From six birds per group, whole breast, drumstick meat, abdominal fat, and skin were collected to evaluate the fatty acid composition and the total lipids. As for skin, two sections of back skin with adhering fat were cut at the neck base and in the rump area by using a suitable tool (10 cm2). All the samples were stored at −40°C until the lipid analysis.
2
Shimadzu Corporation, Tokyo, Japan. Varian Inc., Walnut Creek, CA. 4 Matreya Inc., Pleasant Gap, PA. 5 NU Check Prep Elysian, MN. 3
TABLE 2. Broiler chicken performance (47 d) Group1
Body weight, g Weight gain, g/bird/d Feed intake, g/bird/d Feed efficiency, kg/kg Mortality, %
Control
CLA2
CLA4
SEM
2,475 51.7 99.6 1.9 0.0
2,448 50.9 98.4 1.9 1.7
2,474 51.3 99.1 1.9 1.7
17.97 0.39 0.70 0.02 0.86
1 CLA2 = basal diet plus 2% conjugated linoleic acid source containing 60% CLA methyl esters, CLA4 = basal diet plus 4% conjugated linoleic acid source containing 60% CLA methyl esters.
Total Lipids and Fatty Acid Composition of Tissues and Diets Breast and drumstick meat were minced twice to obtain homogeneous samples. A representative sample of 8 g of breast or 5 g of drumstick were taken and lipids were extracted by the method of Folch et al. (1957), and the ether extract was divided into two aliquots and used for the total lipids determination and for the fatty acid analysis. Fatty acids were converted to methyl esters following the method described by Christopherson and Glass (1969). The separation of fatty acids was carried out by using a Shimadzu2 GC17A gascromatograph with a WP-4 Shimadzu integration system, equipped with a Varian CP-SIL883 capillary column (length: 100 m, i.d: 0.25 mm, film thickness: 0.20 µm, stationary phase: fused silica) and a flame ionization detector. The operating conditions of the gas chromatograph were as follows: oven temperature was held at 170°C for 15 min, increased to 190°C at a rate of 1°C/min, then increased to 220°C at a rate of 5°C/min and held at this temperature for 17 min. The temperature of the injector was 270°C and of the detector was 300°C. The carrier gas (helium) was maintained at the constant flow of 1.7 mL/min. The identification of individual fatty acids was carried out by using PUFA-24 fatty acid methyl ester standards and a mixture of methyl coniugated linoleate5 standard by comparing the relative retention times. The concentration of each fatty acid was calculated by using erucic acid (C 22:1) as internal standard and comparing the areas of the peaks. The fatty acid analyses were also done on skin, abdominal fat, and on grower diet by using 0.5 g, 0.3 g, and 5 g of sample, respectively.
Statistical Analysis All data were analyzed by ANOVA using the general linear model (GLM) procedures of the SAS Institute (SAS Institute, 1985), considering CLA dietary levels as fixed effects. As for carcass yields and mortality, percentage values were transformed into arc-sine of their square root prior to the statistical analysis. When significant effects were found, mean values were separated by using the Student Newman-Keuls test.
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SIRRI ET AL. TABLE 3. Carcass yield of broiler chicken
Eviscerated carcass3 (%) Breast4 (%) Leg4 (%) Wing4 (%)
TABLE 4. Lipid content and fatty acid composition of the experimental diets1,2 (expressed as a percentage)
Control
CLA21
CLA42
SEM
69.5 25.9 45.4 22.9
69.0 25.7 45.4 23.2
69.7 25.5 46.3 22.8
0.003 0.003 0.003 0.004
CLA2 = basal diet plus 2% conjugated linoleic acid source containing 60% CLA methyl esters. 2 CLA4 = basal diet plus 4% conjugated linoleic acid source containing 60% CLA methyl esters. 3 Eviscerated carcass = carcass without head, neck, and feet. 4 Percentage of eviscerated carcass. 1
RESULTS Productive Performance After 47 d of rearing, birds reached live BW ranging from 2,447 to 2,474 g without significant differences among groups. Daily weight gain and feed intake were also insensitive to the dietary treatment of birds. Mortality was very low as only two birds in CLA2 and CLA4 died (Table 2). The eviscerated carcass yield, calculated after removing head, neck, and feet, was about 70% in all groups. Also breast, thigh plus drumstick, and wing yields were similar for all groups (Table 3).
Total Lipid and Fatty Acid Composition of Diets and Tissues The proportion of CLA isomers of the CLA2 diet was 11.5%, equally distributed in cis-9, trans-11 and trans-10, cis-12. In CLA4, the proportion of CLA isomers was about twice as much than CLA2, whereas in the control diet no CLA isomers were detected (Table 4). The lipid content of grower diet increased with the addition of increasing doses of CLA sources from 5.73 (control) to 7.68 (CLA2) and 10.03 g/100 g (CLA4). The addition of CLA source to the chicken diet decreased the breast content of MUFA, particularly oleic acid (C 18:1) and palmitoleic acid (C 16:1). The last one decreased from 21 mg/100 g (control) to 7 and 8 mg/100 g (CLA2 and CLA4, respectively). Even if the content of stearic acid was higher in the breast of CLA4 group and in the drumstick of both treated groups, no statistically significant difference emerged for total saturated fatty acid (Tables 5 and 6). The deposition of CLA in breast increased (P < 0.01) as the dietary CLA increased (32.13 and 69.49 mg/100 g), whereas in the control breast only a small amount of CLA was detected (1.45 mg/100 g). Even if the ratio of CLA isomers cis-9, trans-11 and trans-10, cis-12 was 1:1 in the diet, the proportion of trans-10, cis-12 isomers was 37% in breast of both treated groups (Table 5). Arachidonic acid (ARA) content was reduced (P < 0.01) and linearly related to the addition of CLA to chicken diet, while the linoleic acid (cis-9, cis-12) was unaffected by the dietary treatment. Other PUFA were similar for
Total lipid Saturated 14:0 16:0 17:0 18:0 20:0 24:0 Total Monounsaturated 14:1 16:1 17:1 18:1 20:1 n-9 Total Polyunsaturated 18:2 n-6 CLA cis9,trans11 CLA trans10,cis12 18:3 n-6 18:3 n-3 20:4 n-6 (ARA) 20:5 n-3 22:5 n-6 22:5 n-3 22:6 n-3 (DHA) Total Total CLA Total n-3 Total n-6 n-6/n-3
Control
CLA2
CLA4
5.7
7.7
10.0
0.1 13.3 0.1 2.8 0.3 0.1 16.7
0.1 13.1 0.1 3.0 0.0 0.0 16.2
0.1 11.0 0.1 3.3 0.0 0.1 14.6
0.0 0.1 0.1 22.0 0.2 22.4
0.0 0.2 0.0 22.7 0.0 22.9
0.0 0.2 0.0 23.1 0.0 23.3
55.8 0.0 0.0 0.0 4.9 0.2 0.0 0.0 0.0 0.0 60.9 0.0 4.9 56.0 11.5
45.4 6.0 5.6 0.0 3.9 0.2 0.0 0.0 0.0 0.0 62.9 11.6 3.9 45.5 11.8
37.5 10.7 10.3 0.0 3.1 0.4 0.0 0.0 0.0 0.0 61.8 20.9 3.3 37.9 11.4
1
The values are means of duplicate determinations. CLA2 = basal diet plus 2% conjugated linoleic acid source containing 60% CLA methyl esters, CLA4 = basal diet plus 4% conjugated linoleic acid source containing 60% CLA methyl esters. 2
the dietary CLA (Table 5). The lipid concentration of breast was low and similar in the three groups, ranging from 1.16 to 1.30 g/100 g (Table 5). The fatty acid composition of drumstick meat (Table 6) was similar to that observed in breast with higher concentration of CLA in both treated groups with the exception of docosanoic acid (C 22:0), which significantly increased in CLA2 and CLA4 vs. control. The lipid content of drumstick ranged from 2.52 to 2.75 g/100 g without any difference among groups (Table 6). An increase (P < 0.01) of myristic and stearic acids was observed in the abdominal fat pad of the treated groups, irrespective of CLA level, so that the saturated fatty acids were approximately 30% higher than in control group (Table 7), confirming the observations made for breast and drumstick. Also, irrespective of CLA, the dietary level of MUFA and non-CLA-PUFA significantly decreased in both treated groups, whereas CLA isomers linearly increased with the dietary level of CLA. The fatty acid composition of the skin showed a similar behavior of abdominal fat (data not shown).
DISCUSSION The lipid content of breast and drumstick meat was stable in the three groups, even when the lipid content
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CLA AND FATTY ACID COMPOSITION OF BROILER MEAT TABLE 5. Lipid content (g/100 g of meat) and fatty acid composition of breast fillet (mg/100 g of meat) Total lipid Saturated 14:0 16:0 17:0 18:0 20:0 22:0 Total Monounsaturated 16:1 18:1 20:1 n-9 Total Polyunsaturated 18:2 n-6 CLA cis9,trans11 CLA trans10,cis12 Others CLA 18:3 n-6 18:3 n-3 20:2 20:3 n-6 20:4 n-6 (ARA) 20:5 n-3 22:5 n-3 22:6 n-3 (DHA) Total Total CLA Total n-3 Total n-6 n-6/n-3
TABLE 6. Lipid content (g/100 g of meat) and fatty acid composition of drumstick meat (mg/100 g of meat)
Control
CLA21
CLA42
SEM
1.3
1.2
1.3
0.003
3.8 194.7 1.2 77.5 0.1 0.0b 276.7
3.4 154.2 1.4 77.8 0.3 7.1a 244.3
4.2 177.8 1.6 95.2 0.5 4.3ab 283.6
0.61 19.50 0.14 6.91 0.14 1.48 26.07
21.2A 218.1a 2.2 241.4a
7.1B 134.9b 1.6 143.5b
8.4B 166.9b 1.5 176.7b
1.95 15.68 0.21 17.26
239.7 0.0C 0.0C 1.5 1.2 14.0 7.7 6.2 49.8A 1.7 6.6 5.3 333.6 1.5C 27.6 296.9 10.8
197.1 19.0B 11.6B 1.5 0.9 10.6 8.1 7.6 32.6B 5.4 7.3 5.3 310.5 32.1B 28.5 238.2 8.4
226.2 41.5A 26.7A 1.3 0.8 12.9 11.7 3.9 27.4B 3.1 5.2 3.3 360.0 69.5A 24.2 258.2 10.7
20.11 2.31 1.73 0.50 0.21 1.44 1.20 1.91 2.58 0.82 1.87 1.07 26.49 3.97 3.66 21.77 0.90
Total lipid Saturated 14:0 16:0 17:0 18:0 20:0 22:0 Total Monounsaturated 16:1 18:1 20:1 n-9 Total Polyunsaturated 18:2 n-6 CLA cis9,trans11 CLA trans10,cis12 Others CLA 18:3 n-6 18:3 n-3 20:2 20:3 n-6 20:4 n-6 (ARA) 20:5 n-3 22:5 n-3 22:6 n-3 (DHA) Total Total CLA Total n-3 Total n-6 n-6/n-3
Control
CLA21
CLA42
SEM
2.5
2.6
2.8
0.008
9.2 417.9 3.7 151.0 0.2b 1.1B 582.7
9.8 382.5 3.5 193.4 1.1ab 6.1A 596.4
10.3 395.9 3.7 206.8 1.6a 6.9A 625.2
1.23 40.48 0.40 17.02 0.36 0.62 58.94
79.7A 584.0a 6.3A 670.1A
26.7B 395.7b 3.0B 425.4B
28.1B 432.9b 2.00B 462.9B
4.40 43.88 0.81 48.34
677.0 0.4C 0.0C 0.0c 4.0 47.0 4.3B 10.8A 73.8A 2.4 9.3 6.1a 835.1 4.7C 64.7 691.9 10.8
571.2 51.7B 31.8B 2.2b 3.0 38.2 11.9A 5.3B 46.9B 2.1 7.4 4.0b 774.8 95.5B 50.8 581.1 11.4
573.8 100.5A 64.7A 3.5a 3.0 37.2 12.2A 4.3B 39.6B 2.3 6.7 3.6b 852.5 177.4A 51.0 579.5 11.4
65.31 4.96 4.19 0.37 0.38 5.51 1.00 0.72 4.40 0.38 0.79 0.65 80.69 9.68 6.50 66.18 0.19
a,b Values in the same row with no common superscript differ significantly (P < 0.05). A–C Values in the same row with no common superscript differ significantly (P < 0.01). 1 CLA2 = basal diet with 2% conjugated linoleic acid source containing 60% CLA methyl esters. 2 CLA4 = basal diet with 4% conjugated linoleic acid source containing 60% CLA methyl esters.
a,b Values in the same row with no common superscript differ significantly (P < 0.05); A–C Values in the same row with no common superscript differ significantly (P < 0.01). 1 CLA2 = basal diet plus 2% conjugated linoleic acid source containing 60% CLA methyl esters. 2 CLA4 = basal diet plus 4% conjugated linoleic acid source containing 60% CLA methyl esters.
of the diets increased from 5.73 to 7.68 and to 10.03 g/ 100 g in control, CLA2, and CLA4, respectively, showing that the lipid amount in meat is little affected by the lipid content of feed. Also, the percentage of abdominal fat of carcass was almost stable and ranged from 1.2 to 1.6 without statistical differences among groups. In high lipid diets, CLA promotes lean tissue deposition, thus, reducing the fat content of the carcass (Dugan et al., 1997; Park et al., 1997). Furthermore, from a visual evaluation, the firmness of abdominal fat was dramatically enhanced in the group receiving dietary CLA. Thiel et al. (1998) observed an increase in the hardness of pork fat due to a lower proportion of PUFA and a higher proportion of saturated fatty acid, which could increase the melting point of fat. In this study, there was an increase (P < 0.01) of saturated fatty acid, particularly myristic and stearic, and a corresponding decrease of MUFA and non-CLAPUFA. These modifications could be responsible for the higher firmness of abdominal fat. Du et al. (2000), feeding laying hen diets with increasing doses of CLA (0, 1.25, 2.5, or 5%) and broiler chickens (Du et al., 2002) with diets containing 0.25, 0.5, or 1.0 % CLA, observed a reduction of
the content of MUFA in patties made from fillet plus leg meat and in breast fillet. Chamruspollert and Sell (1999) also reported a decrease of MUFA in egg yolk when the hen diet contained 5% CLA. Our results in breast and drumstick meat agree with the findings of the above authors. Chamruspollert and Sell (1999) claimed that changes in MUFA could be ascribed to CLA, which inhibits the delta-9 desaturase enzyme system that is responsible for saturated fatty acid desaturation, converting them into MUFA. In this way, saturated fatty acid accumulation was increased, and MUFA formation was reduced. The fatty acid distribution and the CLA content have similar trends in both breast or drumstick meat: CLA increased as dietary concentration of CLA increased. Our data confirm previous findings in which a linear relationship between dietary CLA and yolk (Chamruspollert and Sell, 1999; Du et al., 1999) or meat patties’ CLA contents (Du et al., 2000) was showed. The ARA concentration decreased in all tissues of treated groups, particularly in the breast and drumstick. Our results are consistent with those of Belury and Kempa-Steczko, (1997) who proposed that CLA, acting
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SIRRI ET AL. TABLE 7. Fatty acid composition of abdominal fat samples (mg/g of fat)
Total lipid Saturated 14:0 15:0 16:0 17:0 18:0 20:0 22:0 Total Monounsaturated 16:1 18:1 20:1 n-9 Total Polyunsaturated 18:2 n-6 CLA cis9,trans11 CLA trans10,cis12 Others CLA 18:3 n-6 18:3 n-3 20:2 20:3 n-6 20:4 n-6 (ARA) 20:5 n-3 22:5 n-3 22:6 n-3 (DHA) Total Total CLA Total n-3 Total n-6 n-6/n-3
Control
CLA21
CLA42
SEM
3.8B 5.8 170.8 1.3 42.6B 0.4b 0.4 220.0B
5.7A 1.4 197.9 1.7 85.6A 1.0a 0.6 293.9A
5.8A 1.1 190.4 1.4 87.5A 0.7ab 0.3 287.1A
0.34 0.21 8.47 0.17 4.29 0.15 0.14 12.60
32.2A 277.7A 2.0 311.9A
13.8B 219.4B 1.9 234.8B
13.0B 216.8B 1.4 231.1B
1.13 8.59 0.33 9.51
282.5a 0.2C 0.0C 0.0B 1.7 22.5a 2.1B 1.0a 3.2a 0.6A 0.3 0.2 314.3B 0.3C 23.5a 288.4a 12.3
289.5a 28.9B 20.9B 1.7A 1.8 23.1a 2.8A 0.6b 1.4b 0.1B 0.0 0.0 370.7A 51.5B 23.3a 293.2a 12.6
253.5b 51.0A 38.6A 1.8A 1.2 19.6b 3.0A 0.1c 1.1b 0.1B 0.0 0.0 369.9A 91.4A 19.7b 255.9b 13.0
9.27 1.21 1.09 0.22 0.17 0.75 0.14 0.11 0.47 0.09 0.07 0.06 11.25 2.20 0.80 9.40 0.22
a,b Values in the same row with no common superscript differ significantly (P < 0.05). A–C Values in the same row with no common superscript differ significantly (P < 0.01). 1 CLA2 = basal diet plus 2% conjugated linoleic acid source containing 60% CLA methyl esters. 2 CLA4 = basal diet plus 4% conjugated linoleic acid source containing 60% CLA methyl esters.
as a substrate for delta-6-desaturase, inhibited the conversion of linoleic acid to ARA. On the contrary, Chamruspollert and Sell (1999) and Du et al. (1999) proposed that the reduced content of ARA in yolk was related to a lower amount of linoleic and linolenic acid (precursors of ARA and docosahexanoic acid, respectively) of diets added with CLA. This supposition was not confirmed in our trial. Upon calculating the total amount of linoleic acid, by considering its percentage and total lipid content in the diet, our results indicate that linoleic acid was higher in CLA-supplemented diets (34.8 and 37.5 g/kg in CLA2 and CLA4, respectively) than in an unsupplemented one (31.2 g/kg feed). The inhibition of delta-6 desaturase from CLA was confirmed by our data concerning n-3 PUFA contents: their concentration in muscles was not modified by the CLA supplementation, and furthermore, in some samples (skin and abdominal fat), their content slightly decreased in group receiving the highest dose of CLA, in accordance with Chamruspollert and Sell (1999) and Du et al. (1999). Conversely, Du et al. (2000), feeding laying hens diets added with a 4.1% flaxseed oil and 4.1% CLA source,
detected an increase of long-chain n-3 PUFA in tissues and yolk. Therefore, it appears that CLA inhibits the activity of ∆-6 desaturase in normal conditions, but with n-3 PUFA enriched diets, n-3 PUFA induce the enzyme to promote the synthesis of long-chain n-3 PUFA. Our experiment demonstrated that a CLA addition to the broiler diet did not affect broiler performances and carcass yields, although it could enrich tissues by enhancing their nutritional value and improving the human diet with a fatty acid (Ip et al., 1994). Furthermore, the reduction of ARA in meat could have a positive implication in consumer health because it is a precursor to some proinflammatory eicosanoids and it is involved in the modulation of immune response (British Nutrition Foundation, 1992).
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