J. Verbr. Lebensm. DOI 10.1007/s00003-011-0749-5
Journal fu¨r Verbraucherschutz und Lebensmittelsicherheit Journal of Consumer Protection and Food Safety
RESEARCH ARTICLE
Effects of dietary conjugated linoleic acid on the growth performance of chickens and ducks for fattening and fatty acid composition of breast meat Ingrid Halle • Gerhard Jahreis • Martina Henning ¨ nicke Peter Ko ¨ hler • Sven Da
•
Received: 14 July 2011 / Accepted: 31 October 2011 Ó Bundesamt fu ¨ r Verbraucherschutz und Lebensmittelsicherheit (BVL) 2011
Abstract The effects of dietary conjugated linoleic acid (CLA) supplementation on feed intake, growth performance, carcass composition and fatty acid composition of meat tissue were investigated in broiler chickens and Pekin ducks. A total of 108 male chickens for fattening and a total of 96 male and 96 female Pekin ducks were allocated to 3 dietary treatments (0.0, 0.1 and 0.2 % CLA) and fed for 35 or 49 days. The results showed that 0.2 % CLA supplementation in the first 3 weeks improved the daily feed intake of the broilers and the feed to gain ratio, but did not significantly influence body weight, weight and the percentage of abdominal and visceral fat as well as the intramuscular fat in breast muscles. In the duck trial, the daily feed intake was significantly higher through the first 3 weeks of male control group and male 2 g CLA group compared with the female control group. The daily weight gain of all male ducks was significantly higher compared Electronic supplementary material The online version of this article (doi:10.1007/s00003-011-0749-5) contains supplementary material, which is available to authorized users. ¨nicke I. Halle (&) S. Da Institute of Animal Nutrition, Friedrich-Loeffler-Institut (FLI), Federal Research Institute for Animal Health, Bundesallee 50, 38116 Brunswick, Germany e-mail:
[email protected] G. Jahreis Institute of Nutrition, Friedrich Schiller University Jena, Dornburger Str. 24, 07743 Jena, Germany M. Henning P. Ko ¨ hler Institute of Farm Animal Genetics, Friedrich-LoefflerInstitut (FLI), Federal Research Institute for Animal Health, Ho ¨ ltystr. 10, 31535 Neustadt, Germany
to female ducks of all groups and was not influenced by the CLA supplementation. The feed to gain ratio of the 1 g CLA-male ducks was lowest compared to male and female control ducks and 1 and 2 g CLA female ducks. Supplementing diets with CLA modified the fatty acid composition of breast muscle. The proportion of CLA was increased in broiler meat. In duck meat, the proportions of CLA, saturated fatty acids and polyunsaturated fatty acids were increased and monounsaturated fatty acids were decreased. Keywords Conjugated linoleic acid Growth performance Tissue fatty acid composition Broiler Pekin duck
1 Introduction Conjugated linoleic acid (CLA) is a collective term for a mixture of positional and geometric isomers of linoleic acid in which the double bonds are conjugated. The rumenic acid cis9,trans11 is the predominant CLA and represents 90 % of CLAs in milk and 75 % in beef fat. The CLA concentrations in the meat of monogastric animals, fish and vegetables are low (Chin et al. 1992). The interest in CLA can be explained by its potential beneficial health effects (Ha et al. 1987; Lee et al. 1994; Miller et al. 1994; Chew et al. 1997) and the aim to provide leaner and CLA-enriched meat (Tischendorf et al. 2002) and milk products (Pappritz et al. 2010) for human consumption. Studies with broiler chickens and laying hens showed that CLA is readily incorporated in tissue lipids in birds (Szymczyk et al. 2001) and in eggs
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I. Halle et al.
(Chamruspollert and Sell 1999; Raes et al. 2002) after supplementation of CLA to the diets. However incorporation of CLA in tissue lipids leads to changes of the fatty acid composition by reducing the levels of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) and increased percentage of saturated fatty acids (SFA) (Du et al. 2001; Szymczyk et al. 2001). The purpose of these studies was to determine the effect of dietary CLA supplementation on feed intake, growth performance, feed to gain ratio, carcass composition and fatty acid composition of meat tissue in broiler chickens and Pekin ducks.
2 Materials and methods In trial 1, a total of 216 one-day old male chickens for fattening (Ross) were randomly distributed to 3 treatments with 12 chickens per pen and 6 pens per group. The duration of the trial was 35 days. Body weight was recorded for each broiler individually at day 14, 21 and 35 of age. Feed was weighed back on a pen-basis weekly. One bird per pen representing the mean body weight of broilers of this pen was slaughtered at the end of the trial (6 males per group) to determine carcass composition. Weights of total breast meat (without skin), complete right leg, liver, heart, gizzard, spleen and sum of abdominal and visceral fat were individually recorded. All parts were expressed as percentage of body weight. Breast meat of slaughtered broiler was analysed with using near infrared transmission spectroscopy (NIT). This is a rapid method for the evaluation of intramuscular fat, protein and moisture content in meat of farm animals. Calibration of NIT measurements for chicken breast meat was done according to the procedure of breast meat of ducks. (Ko ¨hler et al. 1995). In trial 2, a total of 96 male and 96 female one-day old Pekin ducks were randomly distributed in treatments with 6 ducks per pen and 6 (control)/5 (CLAgroups) pens per group. The duration of the trial was 49 days. Body weight was recorded for each duck individually at days 21 and 49 of age. Feed was weighed back on a pen-basis weekly. One bird per pen representing the mean body weight of ducks of this pen was slaughtered at the end of the trial (6/5 male and 6/5 female per group) to determine carcass composition. Weights of total breast meat (without skin), complete right leg, liver, heart, gizzard, spleen and sum of abdominal and viscera fat were individually recorded. All parts were expressed as percentage of body weight.
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Pelleted feed (Supplementary table 1) was provided for ad libitum consumption as a one-phase feed for broilers and second-phase feed (starter feed: day 1–21, fattening feed: day 22–49) for Pekin ducks. In the basal diet soya oil (5/10 g/kg) was substituted with CLA preparation (5/10 g/kg diet; Lutrell pure, BASF SE, Ludwigshafen, Germany) (Supplementary table 2) and was formulated to supplement per kilograms with 1 or 2 g CLA. Breast meat of broilers and male Pekin ducks was homogenized and freeze dried and the fat was extracted. Analysis of fatty acid methyl esters (FAME) was conducted using gas chromatographs equipped with flame ionisation detectors (GC-17A Version 3, Shimadzu, Japan). For a detailed analysis of the fatty acid composition two different gas chromatographical separation methods have been used. The first method included the separation and identification of FAME ranging from 4 to 25 carbon atoms and was conducted using a medium polarity column (DB-225 mf, 60 m 9 0.25 mm, i.d.; 0.25 lm; J&W Scientific, Germany). The second method including the separation and identification of the cis and trans isomers of the C18:1 FAME was realized with a high polarity column (SelectTM FAME, 200 m 9 0.25 mm, i.d.; 0.25 lm; VARIAN Inc., Germany). Both methods used different mixed FAME reference standards [No. 463, 674 (Nu-Chek Prep, Inc., Elysian, USA), BR2, BR4, ME 93 (Larodan, Malmo ¨, Sweden), PUFA No. 3, CLA, linoleic, linolenic and octadecenoic acid methyl ester mix (Supelco, Bellefonte, USA)] to discriminate FAME according to their retention time. The results were expressed as percentage of total FAME. Data from the two trials was evaluated by one way ANOVA: YIJ = M ? AI ? EIJ, where yij represents performance and slaughter parameters, breast meat nutrient content, fatty acid composition of breast meat of an individual i fed diet j, l = overall mean, ai = diet (control, diets with increasing CLA additions), eij = error term. Mean value differences were evaluated by the Student–Newman–Keuls test (p B 0.05). All statistics were carried out using the SAS operating system (Version 9.1, 2002/2003).
3 Results 3.1 Trial 1: broiler chickens Up to two animals per group died during the fattening period of the broiler trial, apparently without relevance to the group. The daily feed intake was significantly higher through the first 3 weeks and in
Conjugated linoleic acid in feed of chickens and ducks for fattening
the mean of the total fattening period of the 2 g CLA group compared with the control and 1 g CLA group (Table 1). But the daily weight gain (65–66 g/broiler/ day). Thus final body weight was not influenced by the CLA supplementation. As a result, the feed to gain ratio of the 2 g CLA-broiler was significantly higher in comparison to the other groups. Slaughtering of six male broilers after the 35th day of life (Table 2) showed a statistically higher percentage part of breast meat of the 2 g CLA-broiler. The weight and the percentage of abdominal and visceral fat were not different between groups.
Table 1 Performance features of broilers (mean, SD) Treatments age (days)
Control
1 g CLA/kg diet
2 g CLA/kg diet
Feed intake (g/broiler/day) 1–14
37.7 b ± 0.8
38.2 b ± 1.1
39.6 a ± 1.3
15–21
97.5 b ± 2.7
98.3 b ± 3.3
102.6 a ± 2.0
22–35
150.0 ± 2.8
147.9 ± 4.7
152.0 ± 1.8
94.3 ± 1.4
94.1 ± 2.9
97.2 ± 1.4
31.0 ± 1.4 75.6 ± 3.2
32.1 ± 1.6 77.3 ± 1.8
1–35
Body weight gain (g/broiler/day) 1–14 15–21
31.0 ± 1.0 75.1 ± 2.4
22–35
95.8 ± 3.9
94.7 ± 3.3
94.5 ± 1.6
1–35
65.7 ± 1.4
65.4 ± 2.0
66.1 ± 0.8
Feed to gain ratio (kg/kg) 1–14
1.22 ± 0.02
1.24 ± 0.03
1.24 ± 0.03
15–21
1.30 ± 0.02
1.30 ± 0.04
1.33 ± 0.05
22–35
1.57 ± 0.06
1.56 ± 0.03
1.61 ± 0.02
1.44 b ± 0.03
1.44 b ± 0.01
1.47 a ± 0.02
1–35
Body weight (g) 14
475 ± 53
476 ± 45
492 ± 48
21
1,001 ± 106
1,005 ± 94
1,033 ± 90
35
2,340 ± 190
2,330 ± 184
2,347 ± 190
Means with different letters differ significantly within rows
Analysing the nutrients in the fresh breast matter (Supplementary table 3) did not result in any differences between the three groups. Fatty acid composition in breast meat of broilers showed an increased content of CLA with increased supplementation in the feed and a significantly higher content in meat of broilers of the 2 g CLA group (Table 3) compared to the control and 1 g CLA group. 3.2 Trial 2: Pekin ducks One duck died during the fattening period in the duck trial, apparently without relevance to the group. The daily feed intake was significantly higher through the first 3 weeks of the male control group and male 2 g CLA group compared with the female control group (Table 4). The daily weight gain (76 g/ day) and the body weight (3,773–3,803 g) of all male ducks was significantly higher compared to female ducks of all groups and was not influenced by the CLA supplementation. The feed to gain ratio of 2.44 kg/kg of the 1 g CLA-male ducks was lowest (p B 0.05) compared to male and female control ducks and 1 and 2 g CLA female ducks. The ducks after the 49th day of life (Table 5) showed a significantly higher percentage of liver of 1 and 2 g CLA male duck groups compared to male and female control ducks as well as a higher gizzard content of the male control ducks compared to female ducks of all groups. The weight and the percentage of abdominal and visceral fat were not different between groups. Fatty acid compositions in breast meat of male ducks are shown in Table 6. The proportions of CLA, SFA and PUFA in meat was increased in CLA-fed groups (p \ 0.05). The proportion of MUFA was decreased.
Table 2 Slaughter performance of broilers (n = 6) (% of body weight) (mean, SD)
4 Discussion
Treatments
The effect of CLA on growth, body composition and fatty acid composition of breast meat was studied in broiler chickens and Pekin ducks. The results showed that 1 g CLA/kg diet did not influence feed intake in the broiler group, whereas the 2 g CLA/kg diet increased daily feed intake for the first 3 weeks of age. However, the daily weight gain and the final body weight during the experimental period (35 days) did not differ between the broiler groups. CLA feeding did not depress feed intake of Pekin ducks. Daily weight gain and final body weight after
Carcass Breast meat
Control
1 g CLA/kg diet
2 g CLA/kg diet
71.1 ± 1.4
70.2 ± 1.2
72.1 ± 0.9
15.2 b ± 0.8
14.8 b ± 1.0
16.5 a ± 0.7 20.9 ± 1.3
Legs
20.0 ± 0.8
20.3 ± 1.2
Liver
2.2 ± 0.3
2.2 ± 0.2
2.3 ± 0.4
Heart
0.4 ± 0.0
0.4 ± 0.0
0.5 ± 0.07
Gizzard
1.1 ± 0.2
1.4 ± 0.2
1.4 ± 0.2
Spleen
0.1 ± 0.0
0.1 ± 0.1
0.2 ± 0.1
Fat
1.3 ± 0.2
1.5 ± 0.3
1.6 ± 0.2
Means with different letters differ significantly within rows
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I. Halle et al. Table 3 Fatty acid composition in breast meat of broilers (n = 6) (% of total FAME) (mean, SD)
Treatments
Control
C 16:0
2 g CLA/kg diet
18.4 ± 2.4
17.8 ± 0.6
18.8 ± 0.6
C 16:1t9
0.24 a ± 0.01
0.21 b ± 0.02
0.24 a ± 0.02
C 16:1c9
1.31 ± 0.18
0.99 ± 0.34
1.26 ± 0.03
C 18:0
7.5 ± 0.6
8.2 ± 0.7
8.2 ± 0.8
C 18:1t9
0.09 ± 0.04
0.06 ± 0.01
0.08 ± 0.02 25.4 ± 2.8
C 18:1c9
25.4 ± 4.9
22.3 ± 1.9
C 18:1c11
1.54 ± 0.21
1.59 ± 0.11
1.46 ± 0.08
C 18:2c9,c12 (n-6)
33.2 ± 5.4
35.2 ± 1.1
32.9 ± 1.4
C 18:3c6,c9,c12 (n-6)
0.12 ± 0.04
0.15 ± 0.03
0.14 ± 0.01
C 18:3c9,c12,c15 (n-6)
2.72 ± 0.54
2.84 ± 0.26
2.62 ± 0.22
C 20:1c11 (n-9)
0.22 ± 0.05
0.20 ± 0.02
0.22 ± 0.01
C 20:2c11,c14 (n-6)
0.62 ± 0.20
0.71 ± 0.15
0.64 ± 0.16
C 20:3c8,c11,c14 (n-6)
0.37 ± 0.12
0.41 ± 0.08
0.37 ± 0.11
C 20:4c5,c8,c11,c14 (n-6)
2.62 ± 0.97
2.98 ± 0.98
2.29 ± 0.67
0.097 ± 0.044 0.12 ± 0.04
0.123 ± 0.028 0.137 ± 0.08
0.107 ± 0.05 0.103 ± 0.04 0.66 ± 0.14
C 20:3c11,c14,c17 (n-3) C 22:5 (n-6) C 22:4 (n-6)
0.74 ± 0.27
0.76 ± 0.27
C 22:5 (n-3)
0.68 ± 0.26
0.77 ± 0.26
0.62 ± 0.19
C 22:6 (n-3)
0.37 ± 0.15
0.38 ± 0.16
0.30 ± 0.10
SFA, sum
27.0 ± 2.9
27.1 ± 0.7
28.0 ± 0.6
MUFA, sum
28.9 ± 4.9
25.4 ± 2.2
28.7 ± 2.9
45.0 ± 1.5
41.6 ± 2.1
PUFA, sum
42.1 ± 7.6
n-3, sum
4.0 ± 1.1
n-6, sum CLA, sum CLA 9c, 11t Means with different letters differ significantly within rows
1 g CLA/kg diet
4.3 ± 0.2
3.8 ± 0.4
37.8 ± 6.9
40.3 ± 1.3
37.1 ± 1.6
0.24 b ± 0.30
0.38 b ± 0.03
0.68 a ± 0.12
0.11 b ± 0.17
0.22 b ± 0.02
0.39 a ± 0.07
n-6/n-3 ratio
9.6 ± 1.2
9.3 ± 0.3
9.8 ± 0.8
Table 4 Performance features of male and female ducks (mean, SD) Treatments age (days)
Control Male
1 g CLA/kg diet
2 g CLA/kg diet
Female
Male
Female
Male
Female
Feed intake (g/duck/day) 1–21
110.9 a ± 3.0
22–49 1–49
102.5 b ± 1.8
109.4 ab ± 5.8
107.8 ab ± 6.4
111.4 a ± 3.4
262.0 ± 10.4
243.9 ± 11.1
244.0 ± 11.4
244.9 ± 15.7
253.2 ± 11.2
106.6 ab ± 4.8 251.9 ± 6.8
197.2 ± 6.8
183.3 ± 6.4
186.3 ± 8.9
186.1 ± 11.0
191.6 ± 7.6
189.6 ± 5.4
Body weight gain (g/duck/day) 1–21
68.8 a ± 1.8
63.3 b ± 1.5
69.3 a ± 2.9
64.6 b ± 2.5
68.9 a ± 1.9
65.2 b ± 1.7
22–49 1–49
81.3 a ± 2.7 75.9 a ± 1.4
73.7 b ± 3.9 69.3 b ± 1.9
81.8 a ± 2.6 76.4 a ± 0.8
72.6 b ± 4.9 69.2 b ± 3.4
80.0 a ± 6.3 76.4 a ± 1.5
73.3 b ± 3.2 69.9 b ± 2.0
1.62 ab ± 0.01
1.63 ab ± 0.04
3.18 b ± 0.29
3.44 a ± 0.14
Feed to gain ratio (kg/kg) 1.61 ab ± 0.04
1.62 ab ± 0.04
1.58 b ± 0.03
1.67 a ± 0.04
22–49
1–21
3.23 ab ± 0.20
3.33 ab ± 0.18
2.99 b ± 0.22
3.38 a ± 0.12
1–49
2.60 ab ± 0.11
2.65 ab ± 0.08
2.44 c ± 0.12
2.69 a ± 0.07
2.51 bc ± 0.11
2.72 a ± 0.07
Body weight (g) 1
54 ± 2
56 ± 2
54 ± 2
54 ± 1
55 ± 1
55 ± 1
21
1,498 a ± 131
1,386 b ± 111
1,508 a ± 104
1,412 b ± 120
1,502 a ± 108
1,425 b ± 121
49
3,773 a ± 228
3,449 b ± 297
3,797 a ± 239
3,445 b ± 250
3,803 a ± 262
3,478 b ± 248
Means with different letters differ significantly within rows
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Conjugated linoleic acid in feed of chickens and ducks for fattening Table 5 Slaughter performance of male and female ducks (n = 6/5) (% of body weight) (mean, SD) Group
Control Male
Carcass Breast skin Breast meat
1 g CLA/kg diet Female
Male
2 g CLA/kg diet Female
Male
Female
67.6 ± 0.9
69.1 ± 1.6
67.9 ± 0.8
69.3 ± 0.1
67.4 ± 0.9
3.7 ± 0.6
4.4 ± 1.2
3.6 ± 0.9
4.1 ± 0.9
3.8 ± 0.8
3.6 ± 0.6
14.9 ± 2.5
14.4 ± 2.6
14.0 ± 0.6
13.0 ± 1.0
14.2 ± 1.1
14.5 ± 1.3
68.1 ± 1.1
Leg
12.8 ± 1.0
13.6 ± 0.5
13.3 ± 1.5
13.2 ± 0.5
12.9 ± 1.0
14.2 ± 1.2
Liver
1.8 b ± 0.1
1.9 b ± 0.1
2.2 a ± 0.1
2.0 ab ± 0.3
2.3 a ± 0.2
2.0 ab ± 0.2
Heart Gizzard Spleen Fat
0.6 ± 0.0
0.6 ± 0.0
0.6 ± 0.1
0.6 ± 0.0
3.4 a ± 0.2 0.07 ± 0.03
2.7 b ± 0.4 0.07 ± 0.02
3.0 ab ± 0.0 0.07 ± 0.02
2.7 b ± 0.2 0.06 ± 0.01
1.1 ± 0.3
1.3 ± 0.4
1.0 ± 0.4
1.5 ± 0.3
0.5 ± 0.0 3.2 ab ± 0.3 0.07 ± 0.00 1.2 ± 0.2
0.6 ± 0.1 2.8 b ± 0.3 0.06 ± 0.02 1.4 ± 0.1
Means with different letters differ significantly within rows
Table 6 Fatty acid composition in breast meat of male ducks (n = 6/5) (% of total FAME) (mean, SD)
Means with different letters differ significantly within rows
Group
Control
1 g CLA/kg diet
2 g CLA/kg diet
C 16:0
24.6 ± 2.2
24.6 ± 1.5
25.0 ± 0.3
C 16:1t9
0.30 a ± 0.04
0.24 b ± 0.03
0.19 c ± 0.02 0.97 b ± 0.15
C 16:1c9
2.06 a ± 0.38
1.15 b ± 0.18
C 18:0
8.5 c ± 1.3
12.1 b ± 1.6
13.9 a ± 0.9
C 18:1t9
0.22 a ± 0.05
0.19 ab ± 0.03
0.15 b ± 0.01
C 18:1c9
37.4 a ± 5.0
C 18:1c11
1.55 ± 0.08
28.8 b ± 3.0 1.43 ± 0.24
23.4 c ± 1.8 1.49 ± 0.18
C 18:2c9,c12 (n-6)
17.5 ± 3.3
19.3 ± 2.9
18.8 ± 0.5
C 18:3c6,c9,c12 (n-6)
0.04 ± 0.01
0.05 ± 0.01
C 18:3c9,c12,c15 (n-6)
0.97 ± 0.28
1.08 ± 0.36
0.85 ± 0.09
C 20:1c11 (n-9)
0.28 a ± 0.02
0.25 b ± 0.02
0.21 c ± 0.02
C 20:2c11,c14 (n-6)
0.30 ± 0.14
C 20:3c8,c11,c14 (n-6)
0.25 b ± 0.09
C 20:4c5,c8,c11,c14 (n-6)
2.49 c ± 1.53
C 20:3c11,c14,c17 (n-3) C 20:5 (n-3)
0.007 b ± 0.016 0.045 b ± 0.041
C 22:5 (n-6)
0.23 c ± 0.14
C 22:4 (n-6)
0.46 b ± 0.29
0.04 ± 0.005
0.40 ± 0.11
0.48 ± 0.05
0.38 b ± 0.11
0.59 a ± 0.09
4.20 b ± 1.32
6.20 a ± 0.50
0.022 ab ± 0.020 0.102 a ± 0.050
0.042 a ± 0.032 0.150 a ± 0.03
0.51 b ± 0.19
0.74 a ± 0.06
0.74 ab ± 0.19
0.95 a ± 0.10
C 22:5 (n-3)
0.19 b ± 0.14
0.37 a ± 0.10
0.51 a ± 0.05
C 22:6 (n-3)
0.12 c ± 0.08
0.24 b ± 0.07
0.40 a ± 0.09 40.6 a ± 1.1
SFA, sum
34.1 b ± 3.0
38.2 a ± 3.4
MUFA, sum
42.0 a ± 5.4
32.2 b ± 3.0
26.6 c ± 1.8
PUFA, sum
22.7 b ± 5.6
27.8 a ± 1.4
30.4 a ± 0.6
n-3, sum
1.32 b ± 0.49
1.82 a ± 0.16
1.95 a ± 0.14
n-6, sum
21.3 b ± 5.2
CLA, sum
0c
0.41 b ± 0.13
0.68 a ± 0.10
CLA 9c, 11t
0c
0.23 b ± 0.08
0.40 a ± 0.05
n-6/n-3 ratio
17.0 ± 3.0
49 days did not differ between male duck groups and female duck groups. Javadi et al. (2007) observed depressed feed intake by broilers after feeding of 1 g CLA/100 g diet but no change in body weight gain in
25.6 ab ± 1.1
14.1 ± 0.9
27.8 a ± 0.7
14.3 ± 1.3
a 3-week study. Zhang et al. (2007) investigated as well that CLA supplementation (0.25, 0.5, 1.0 and 2.0 %) did not significantly influence body weight of chickens fed for 126 days. However, Suksombat et al.
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I. Halle et al.
(2007) noted no effect of CLA (0.5, 1.0 and 1.5 %) on daily feed intake (42 days) but the daily weight gain was significantly and linearly decreased. Depressed growth performance as result of decreased feeding of CLA (0.5, 1.0 and 1.5 %) diets was also shown (Szymczyk et al. 2001). Tanai et al. (2011) measured significantly increased body weight after feeding 0.5 and 1.0 % CLA diets but significantly decreased body weight after feeding 2 % CLA diet of broilers at the age of 42 days. No comparable results exist for CLA feeding to Pekin ducks. In the present studies, feed to gain ratio was significantly higher in the 2 g CLA-group of broilers; significantly decreased by 1 g CLA/kg diet of male Pekin ducks and unchanged in female duck groups. Suksombat et al. (2007) and Zhang et al. (2007) observed an increased feed to gain ratio with increasing CLA, whereas Javadi et al. (2007) did not observe significant differences. In the broiler and duck trials, the supplementation of 1 and 2 g CLA/kg diet did not lead to changes in the abdominal and visceral fat percentage compared to the control animals. Also the fat and protein content of broiler breast meat were not affected. Du and Ahn (2002) measured no differences in abdominal fat weight, the total body fat and protein content in broilers fed diets with 0.25, 0.5 or 1 % CLA. However the whole body fat content decreased from 14.2 % in the control to 11.9 and 12.2 % in the 2 and 3 % CLAgroups, respectively. Also Zhang et al. (2007) found that feeding 1 and 2 % CLA as well as Szymczyk et al. (2000) for feeding of 1 % CLA decreased abdominal fat percentages. A higher fat proportion in the body of three-week old broilers fed 1 g CLA/100 g diet when compared to controls was noticed by Javadi et al. (2007). Suksombat et al. (2007) observed significantly reduced fat content of broiler drumstick meat with increasing CLA supplementation, whereas those of thigh and pectoralis major muscle were similar. The supplementation of 1 and 2 g CLA/kg diet of male Pekin ducks significantly increased the liver percentages. Also Du and Ahn (2003) established significantly increased liver weights of broilers after CLA feeding but there was no difference in liver fat content among the different CLA treatments. Longterm feeding of CLA in laying birds leads to an increase in liver triacylglyceride and may predispose birds to fatty liver hemorrhagic syndrome (Cherian and Goeger 2004). As expected, feeding incremental levels of dietary CLA (0.0, 0.1 and 0.2 %) resulted in linear increases in the concentration of CLA isomers in breast meat of broilers and ducks. Szymczyk et al. (2001) and
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Suksombat et al. (2007) found that incorporation of individual CLA isomers into body lipids differed as indicated by preferential incorporation of cis9,trans11 CLA at the expense of trans10,cis12 CLA. In the present study the cis9,trans11 CLA isomer accounted for 56–59 % of the total CLA in breast muscle lipids by broilers and ducks. Also Sirri et al. (2003), Aletor et al. (2003), Du and Ahn (2002) and Tanai et al. (2011) investigated the effects of increasing CLA concentration in feed and found a linear increase of CLA in tissue samples. Supplementing diets with 1 or 2 g CLA kg diet increased the proportions of SFA and PUFA, whereas the proportion of MUFA was decreased in breast muscle of ducks but supplementation was without significant effect on the breast muscle of broilers. Several reports indicated that CLA supplementation increased the amount of SFA and decreased the MUFA fraction in tissues of broilers (Szymczyk et al. 2001; Du and Ahn 2002; Sirri et al. 2003; Zhang et al. 2007). The decrease of proportion of MUFA results from a reduced delta-9 desaturase activity in consequence of feeding CLA (Lee et al. 1998; Park et al. 2000). Studies showed that the cis9,trans11 CLA isomer does not reduce the activity of the delta-9 desaturase whereas the trans10,cis12 CLA isomer is biologically highly active (Park et al. 2000; Eder et al. 2002). Zhang et al. (2007) measured increased PUFA proportion of breast muscle compared to the present study. Javadi et al. (2007) and Szymczyk et al. (2001) found a decreased PUFA proportion in the abdominal fat and muscles. Supplementation of CLA to broiler diets with corresponding increase of proportions of SFA and decrease of MUFA reduced thiobarbituric acid reactive substances values in raw meat and improved oxidative stability (Kawahara et al. 2009) but the meat was harder and drier after cooking the broiler breast meat from 2 or 3 % CLA treatments (Du and Ahn 2002).
5 Conclusion The present studies showed that feeding CLA in low diet concentrations (0.1 or 0.2 % of diet) to broiler chickens does not negatively affect the feed intake, body weight gain and carcass composition of the birds. These CLA concentrations were high enough to produce CLA-enriched meat and thus the potential health-related benefits of CLA consumption in humans. Supplementation of CLA in higher concentrations ([2 % of diet) could depress feed intake and growth performance of broilers and increase the
Conjugated linoleic acid in feed of chickens and ducks for fattening
amount of SFA in adipose and muscle tissue as well as decrease MUFA and PUFA. A higher saturation ratio of fat in broiler meat is less desirable from a human health perspective. In addition, the results of the Pekin duck study showed that supplementation of 0.1–0.2 % CLA per kg feed did not change the performance of the birds and increased the proportions of the CLA isomers and of PUFA in breast meat. The proportion of SFA was also increased and of MUFA decreased.
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