Effect of genotype, feeding system and slaughter weight on the quality of light lambs

Livestock Production Science 77 (2002) 187–194 www.elsevier.com / locate / livprodsci

Research paper

Effect of genotype, feeding system and slaughter weight on the quality of light lambs II. Fatty acid composition of meat J. Santos-Silva*, R.J.B. Bessa, F. Santos-Silva ˜ Zootecnica ˜ Agraria ´ ´ , Fonte Boa, 2000 -763 Vale de Santarem ´ , Portugal Estac¸ao Nacional, Instituto Nacional de Investigac¸ao Received 27 September 2001; accepted 6 March 2002

Abstract One hundred and eight Merino Branco and crossbred Ile de France 3 Merino Branco ram lambs were used to evaluate the effects of genotype, feeding system and slaughter weight on fatty acid composition of meat (longissimus thoracis muscle). At 60 days of age, lambs were assigned to the experimental feeding systems: P—pasture with dams; SP—pasture with dams, plus concentrate ad libitum; C—weaning and concentrate ad libitum. Lambs were slaughtered at 24 and 30 kg live weight. The meat had a low fatty acid content. Intramuscular fatty acid (FA) composition was not affected by genotype. Pasture raised lambs (P and SP) showed higher proportion of n-3 FA, conjugated linoleic acid (CLA) and trans-octadecenoic FA, and lower n-6:n-3 ratio, than C lambs. When slaughter weight increased, total FA content increased. Palmitic acid and monoenoic FA increased and polyunsaturated FA decreased with slaughter weight. The CLA proportion increased with slaughter weight, but only for lambs raised on pasture (P and SP). Fatty acid profile was effective in the identification of lamb feeding systems.  2002 Elsevier Science B.V. All rights reserved. Keywords: Sheep; Merino; Carcass quality; Meat quality; Fatty acid composition

1. Introduction Fatty acid (FA) composition plays an important role in the definition of meat quality, as it is related to differences in organoleptic attributes, especially flavour (Melton, 1990; Wood and Enser, 1997, Wood et al., 1997) and in nutritional value of fat for human consumption. The amount of fat in the human diet *Corresponding author. Tel.: 135-124-376-7300; fax: 135124-376-7307. E-mail address: [email protected] (J. Santos-Silva).

and especially the proportion of saturated FA have been considered as major risk factors of coronary heart diseases (CHD) (Kritchevsky, 1998). The ratio between polyunsaturated and saturated FA (P/ S) and the ratio between n-6 and n-3 FA are considered two important indexes for nutritional evaluation of fat (Department of Health, 1994). Over the last decades, research has focused on the effects of individual FA upon lipid metabolism and prevention of CHD. More recently, research was focused on a minor group of FA characteristic of fat from ruminants, the conjugated linoleic acid (CLA), due to its potent anticar-

0301-6226 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 02 )00059-3

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cinogenic and antilipogenic activity in several animal models (Ip et al., 1994; Pariza et al., 2001). The characteristics of lamb carcasses produced in European countries of the Mediterranean region are very specific and different from most other regions. Lambs are slaughtered very young, just after weaning (between 30 and 60 days) or after a small period of fattening, that may be conducted in pasture but also very frequently in intensive feeding systems. Although the effect of feeding management on fatty acid composition of lamb tissues has been studied ¨ (Nurnberg et al., 1998), there is limited information about quantitatively minor FA that have nutritional relevance (CLA, n-3 and n-6 FA and trans-octadecenoates), as it is evident in the database recently compiled (Bas and Morand-Fehr, 2000). Moreover, there is little information about the effect of feeding management on meat quality of light lambs produced in Mediterranean areas. Merino Branco (MB) is the most widespread sheep breed in Portugal. It is the base of lamb meat production in this country, and there are three lamb carcass types produced from MB ewes, which are protected as Geographic Indication by the European Union. Changes in traditional extensive production systems occurred over the last few years, involving an increase in the proportion of concentrate in the diet. Merino Branco lambs, which are normally slaughtered at live weights up to 25 kg, could produce slightly heavier carcasses if such an increase in slaughter weight does not compromise the quality ˜ of the products (Sanudo et al., 1996; Santos-Silva and Portugal, 2000, 2001). This would give more flexibility in production systems and would allow a higher productivity. The aim of this trial was to evaluate the effects of genotype, feeding system and slaughter weight on lambs performance and product characteristics. The results for growth, carcass composition and some meat quality traits are discussed in a companion paper (Santos-Silva et al., 2002). In this one, results on FA composition of intramuscular fat of longissimus thoracis muscle are presented.

2. Materials and methods Animal handling followed the recommendations of European Union directive 86 / 609 / EEC concerning animal care.

2.1. Experimental design and animal management One hundred and eight lambs of two genotypes (54 Merino Branco and 54 crossbred Ile de France 3 Merino Branco) were used in a trial carried out in ˜ do Centro Alentejo’ ‘Centro de Experimentac¸ao (Reguengos de Monsaraz, Portugal). Lambs were reared with their dams and, at an age ranging from 42 to 60 days, were randomly assigned to the experimental groups, corresponding to 3 different feeding systems: P—reared with their dams on pasture (Lollium multiflorum var. lemnos); SP— reared with their dams on pasture, and supplemented with a commercial concentrate based on maize and soybean meal (11.5 MJ ME / kg dry matter (DM); 18% crude protein (CP) DM) ad libitum; C—weaning, and fed in confinement with the same concentrate referred for group SP plus wheat straw ad libitum. For every genotype 3 feeding system combination, nine lambs where slaughtered at 24 or 30 kg live weight. Lambs where weighed weekly, until they reached the planned slaughter weight.

2.2. Slaughter and sampling Lambs were weighed in the farm, before trans˜ portation (150 km) to the abattoir of ‘Estac¸ao ´ Zootecnica Nacional’, where they were slaughtered on the same day. Carcasses were kept at room temperature for 6 h after slaughter, and then were chilled at 0 8C. Forty-eight hours after slaughter, the joint containing the muscle longissimus thoracis (LT), between the 6th and 13th thoracic vertebrae, was vacuum packed and chilled for 5 days. At the 7th day after slaughter, the LT muscle was isolated and, after removal the epimysium, minced and frozen at 2 20 8C, freeze-dried and stored at 4 8C, until the analytical procedure, that occurred in 30 days.

2.3. Analytical procedures Lyophilised muscle samples were weighed into a culture tube, and FA were extracted and methylated by the method of Rule (1997). Quantification of fatty acid methyl esters (FAME) was done using 2 mg of hexeicosanoic acid (C21:0) as internal standard, with analysis conducted by GLC, using a 60-m fusedsilica capillary column SP-2380 (Supelco, Bellefonte, PA, USA) with a 0.25-mm internal diameter

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and a 0.20-mm film thickness. A HP5890A series II chromatograph (Hewlett-Packard, Avondale, PA, USA), working with nitrogen as gas carrier and a flame ionisation detector, was used. The initial column temperature of 130 8C was held for 10 min, increased to 165 8C at 5 8C / min and held for 5 min. Then, the temperature was increased to 180 8C at 3 8C / min and held 6 min. The last ramp was increased with a rate of 1.5 8C / min to 230 8C, at which point it was maintained for 25 min. The injector and detector temperature were 230 and 280 8C, respectively. Peak identification was based on co-chromatography with known standards of FAME (Sigma, St. Louis, MO, USA). The C18:1 trans-isomers are reported as one value, as this column incompletely resolves them, and we cannot exclude some minor contamination with other C18:1 isomers. The CLA was computed as the major peak in conjugated octadecadienoic region of the chromatogram that had elution time consistent with cis-9, trans-11 octadecadienoic FAME (Sigma, St. Louis, USA). All FA results are presented in weight percentages (weight%) of total FA assuming direct proportionality between peak area and fatty acid methyl ester weight.

2.4. Statistical analysis Total FA and the proportion of each FA were studied by analysis of variance, using the GLM procedure of SAS (1989). The models included the effects of genotype, feeding system, slaughter weight and their interactions, which were only maintained in the model when significant. When the F-test was significant, the least-squares means were compared. The possibility of discriminating feeding systems from FA composition of meat was tested using a canonical discriminant analysis. The analysis was carried out by a forward stepwise method of Statistica software (Statsoft, 1995). The objective of this analysis was to evaluate the reliability of using an animal’s FA profile to allocate it to a given production system.

3. Results The results for total FA and FA composition of LT muscle are presented in Table 1. Genotype and

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feeding system did not affect total FA, which increased 23.5% (P , 0.001) with slaughter weight. Fatty acid composition was independent of genotype, contrarily to what was observed for feeding system and slaughter weight. Stearic (C18:0) and arachidonic (C20:4 n-6) were the only FA not affected by feeding system. Pasture lambs (P and SP) showed higher proportions of myristic (C14:0) and pentadecanoic (C15:0) acids, and a lower proportions of palmitic (C16:0), palmitoleic (C16:1 cis9) and oleic (C18:1 cis-9) acids than C lambs. For polyenoic FA, P lambs showed higher proportions of FA of the n-3 series. The proportion of linoleic acid (C18:2 n-6) was higher for C and SP lambs, but the difference was only significant for 30 kg slaughter weight. The proportion of CLA was higher for P and SP lambs, and the difference increased with slaughter weight. For most of the FA, the results for SP lambs were similar (P . 0.05) to P lambs. However, for C15:0, C18:1 trans, CLA, C20:5 n-3 and C22:5 n-3 SP lambs showed intermediate values. When slaughter weight increased, C16:0 and monoenoic FA increased, while n-6 and n-3 polyunsaturated FA (PUFA) decreased, except for C18:2 n-6, which remained unchanged. The effect of slaughter weight increase on C18:2 n-6 and CLA was dependent on feeding system, such that C18:2 n-6 decreased for P lambs remaining unchanged for the other two groups, and CLA increased in lambs raised on pasture (P and SP) remaining constant for C lambs. To assess nutritional value of fat, the ratios n-6:n3 PUFA and hypocholesterolaemic:hypercholesterolaemic FA (as defined in Table 1) were considered. The n-6:n-3 ratio was affected by feeding system, with a higher value obtained for C, intermediate for SP and lower for P lambs. The ratio between hypocholesterolaemic:hypercholesterolaemic FA decreased (P , 0.05) when slaughter weight increased. The discriminant analysis reduced the number of variables from 14 to seven FA. It generated two significant uncorrelated linear combinations of seven FA, which efficiently discriminate the three feeding systems (Table 2 and Fig. 1). However, the eigenvalues show that root 1 had a much higher discriminant power than root 2, accounting for 90.9% of the total variation between feeding systems.

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Table 1 Analysis of variance and least-squares means of total fatty acids (mg / 100 g muscle) and fatty acid composition (weight%) of intramuscular fat of muscle longissimus thoracis of lamb carcasses of Merino Branco (MB) and Ile de France3Merino Branco (IF3MB), subjected to three feeding systems and slaughtered at 24 and 30 kg Genotype (G)

Total fatty acids C14:0 C15:0 C16:0 C16:1 cis-9 C17:0 C18:0 C18:1 trans C18:1 cis-9 C18:2 n-6 CLA

24 kg 30 kg 24 kg 30 kg

C18:3 n-3 C20:4 n-6 C20:5 n-3 C22:5 n-3 C22:6 n-3 n-6/n-3 HH

Feeding system (FS)

Slaughter weight (SW, kg)

Effects

MB

IF3MB

S.E.

P

SP

C

S.E.

24

30

S.E.

G

FS

SW

FS3SW

1917 3.1 0.43 19.0 1.31 0.96 14.2 3.13 31.2 5.70

1949 3.1 0.42 19.1 1.33 0.93 14.6 3.12 30.3 5.75

69.1 0.10 0.016 0.29 0.028 0.022 0.24 0.115 0.50 0.177

ns ns ns ns ns ns ns ns ns ns

ns *** *** *** *** * ns ** ***

*** ns ns ** ** ns ns ** ** ***

*

ns

***

*

**

1.15 2.58 0.70 0.92 0.39 3.20 1.92

1.19 2.71 0.71 0.90 0.40 3.41 2.01

0.052 0.101 0.035 0.037 0.018 0.162 0.077

85.0 0.127 0.019 0.36 0.033 0.027 0.30 0.142 0.61 0.31 0.31 0.038 0.038 0.064 0.123 0.043 0.044 0.022 0.200 0.094

69.1 0.10 0.016 0.29 0.027 0.022 0.24 0.114 0.50

0.021

1843 2.5 a 0.33 a 20.2 b 1.48 b 1.00 b 14.4 2.87 a 32.4 b 6.41 b 6.14 b 0.32 a 0.24 a 0.51 a 2.67 0.40 a 0.66 a 0.29 a 5.47 c 1.84

2137 3.1 0.44 19.7 1.38 0.95 14.2 3.36 31.8

0.55

2087 3.3 b 0.42 b 18.7 a 1.23 a 0.89 a 14.2 3.16 ab 30.4 a 6.19 b 5.69 b 0.58 b 0.72 c 1.30 b 2.62 0.74 b 0.97 b 0.42 b 2.59 b 2.04

1730 3.0 0.42 18.4 1.26 0.94 14.5 2.89 29.7

0.59

1871 3.5 b 0.54 c 18.2 a 1.24 a 0.95 ab 14.5 3.34 b 29.4 a 5.86 b 4.09 a 0.71 c 0.87 d 1.69 c 2.63 0.97 c 1.11 c 0.48 b 1.85 a 2.02

ns ns ns ns ns ns ns

*** ns *** *** *** *** ns

ns *** ** *** *** ns *

1.21 3.01 0.77 1.01 0.46 3.31 2.07

1.13 2.28 0.63 0.82 0.34 3.30 1.85

0.052 0.101 0.035 0.037 0.018 0.162 0.077

†

Number of animals per treatment: G and SW554, FS536, FS3SW518; P5pasture, SP5supplemented pasture, C5concentrate, S.E.5standard error, ns5not significant. † P,0.10; * P,0.05; ** P,0.01; *** P,0.001; means in the same row with different superscripts are different (P,0.05). n-6 / n-35(C18:2 n-6, C20:4 n-6) /(C18:3 n-3, C20:5 n-3, C22:5 n-3 and C22:6 n-3). HH5hypocholesterolaemic / hypercholesterolaemic ratio5[(sum of C18:1 cis-9, C18:2 n-6, C20:4 n-6, C18:3 n-3, C20:5 n-3, C22:5 n-3 and C22:6 n-3) /(sum of C14:0 and C16:0)].

Table 2 Results of canonical discriminant analysis: loadings of correlation matrix between predictor variables and discriminant functions (root 1 and root 2) and some statistics for each function Root 1 C18:3 CLA C18:2 C20:4 C15:0 C14:0 C16:1

n-3 n-6 n-6

cis-9

Canonical R Eigenvalue Cumulative proportion Wilk’s lambda Probability.F

Root 2

20.748 20.739 0.168 20.007 20.423 20.332 0.200

20.161 20.297 20.306 0.006 0.239 20.231 0.301

0.867 3.029 0.909 0.191 P,0.001

0.481 0.301 1.000 0.768 P,0.001

Fig. 1. Spatial distribution of fatty profile from three feeding systems in the plane defined by the two discriminant functions.

J. Santos-Silva et al. / Livestock Production Science 77 (2002) 187–194 Table 3 Classification functions for allocation to the three feeding systems

Constant C18:3 CLA C18:2 C20:4 C15:0 C14:0 C16:1

P

SP

C

246.0 7.86 24.7 1.69 3.27 15.50 1.17 22.2

240.8 5.49 23.1 3.53 0.55 4.15 2.19 21.0

234.2 2.28 14.0 3.75 20.097 5.22 0.92 24.1

P5pasture, SP5supplemented pasture, C5concentrate. Table 4 Frequencies of discriminant analysis [allocation to the feeding systems: assigned (columns) against real data (rows)]

P SP C Total

P

SP

C

Total

34 3 1 38

1 31 2 34

1 2 33 36

36 36 36 108

P5pasture, SP5supplemented pasture, C5concentrate.

Besides the discriminant power of FA for feeding systems, the statistical program computes the classification functions, which can be used to determine to which group each individual most likely belongs to (Table 3). As presented in Table 4, the animals correctly allocated to feeding systems P, SP and C were 94, 86 and 92%, respectively.

4. Discussion The values obtained for concentration of total FA in LT muscle were low and similar to those reported ˜ by Sanudo et al. (2000) for the m. longissimus lumborum of light lambs (10.0–11.5 kg carcass weight) of two Spanish breeds. Although total fat content was not determined, the values obtained for total FA indicate that it may be classified as lean meat according to Food Advisory Committee (1990) criteria (i.e. less than 5% of fat). FA composition was not significantly affected by genotype, with similar values for both genotypes in every parameter analysed. Other authors found dif˜ ferences in FA composition between sheep (Sanudo et al., 2000) and beef breeds (Choi et al., 2000; Laborde et al., 2001). However, in those trials, the

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breeds compared were very different in origin and / or aptitude, contrarily to the present study, where the two genotypes evaluated were less different. Contrarily to genotype, feeding system had a clear influence on lipid composition of intramuscular fat. Myristic acid (C14:0) was higher in lambs raised on pasture (P and SP) than in C lambs, which may be related to the fact that those lambs were raised with their dams, and ewe’s milk is normally richer in C14:0 than lambs post-weaning diets (Bas and Morand-Fehr, 2000). Some authors have argued that fat from grass-fed ruminants is more saturated, mainly due to higher proportions of C18:0 (Rowe et al., 1999; Bas and Morand-Fehr, 2000; Rhee et al., 2000), and this may be related to the inhibition of rumen biohydrogenation, common in concentrate-fed animals (Doreau and Ferlay, 1994). Our results are not in accordance with this general trend, as C18:0 and total saturated FA (results not shown) were not affected by feeding system. However, differences in animal fatness may affect the proportion of individual FA and could lead to misinterpretations when the results of different trials are compared. In our trial fat content of muscle was low, and not affected by treatment, therefore results are not directly comparable with others where fat content is not similar. Lambs raised on pasture showed a three-fold higher proportion of linolenic acid (C18:3 n-3) and more than twice the n-3 PUFA than lambs raised with concentrate. These results are in accordance with other reports, which compared FA composition of grass-fed vs. concentrate-fed lambs (Rowe et al., 1999; Fisher et al., 2000), steers (Marmer et al., 1984) or goats (Rhee et al., 2000) and reflect the effect of diet, as grass lipids are particularly rich in C18:3 n-3 (Palmquist, 1988). The C18:2 n-6 was lower for P lambs slaughtered at 30 kg. The differences between feeding systems were less expressive for C18:2 n-6 than for n-3 FA, which is in accordance to the results of Wiklund et al. (2001) in deer, Marmer et al. (1984) in steers, and Rowe et al. (1999) in lambs. The method of transesterification used for the preparation of FA methyl esters, causes the isomerization of CLA (Kramer et al., 1997), decreasing the proportion of cis-9, trans-11 octadecadienoic acid. So, the real values of CLA in intramuscular fat are certainly higher than those of chemical analysis

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which are presented in Table 1. The proportion of CLA present in intramuscular fat was dependent on feeding system. CLA was higher for lambs raised on pasture, particularly when they were not supplemented. To our knowledge, there are no reports about the effect of feeding system on CLA concentration in lamb tissues. However, it is well established for dairy cows that milk from grazing animals has a higher CLA concentration than milk from confined animals (Jahreis et al., 1997; Precht and Molkentin, 1995, 1999). Our results showed that meat from grass-fed lambs has higher proportions of CLA and also of C18:1 trans FA than meat from concentrate-fed lambs. The effect of feeding system on C18:1 trans FA was not observed by Marmer et al. (1984) or Enser et al. (1998), who compared the fatty acid profile muscle lipids of beef cattle raised on grass vs. concentrate.The effect of feeding system on C18:1 trans followed the same pattern referred for CLA. A close relationship between CLA and C18:1 trans has also been observed in other studies conducted to evaluate the effect of lipid supplementation on milk from dairy cows (Sauer et al., 1998) and meat from lambs (Bessa et al., 2000) or beef cattle (Enser et al., 1999). This direct relationship between CLA and C18:1 trans FA could compromise the interest of producing ruminants on pasture. However, the C18:1 trans isomers present in fat from ruminants, and particularly trans vaccenic (C18:1 trans-11), do not seem to be related to the risk of occurrence of CHD in humans (Willett et al., 1993). The ratio between PUFA of the n-6 and n-3 series is an index commonly used to assess the nutritional value of fats. Linolenic acid (C18:3 n-3) is the precursor of n-3 PUFA, such as eicosapentaenoic acid (C20:5 n-3) and docosahexaenoic (C22:6 n-3), which are effective in preventing CHD (Williams, 2000). The typical Western diet is characterised by a high intake of n-6 PUFA and low intake of n-3 PUFA. Nowadays, according to the recommendations of nutritional advisers, the attempt is to increase the levels of n-3 PUFA in the diet, such that n-6:n-3 ratio does not exceed 4.0 (Department of Health, 1994). For C lambs, the value obtained for n-6:n-3 FA is above this recommendation (5.47). On the other hand, for lambs raised on pasture, and especially for P lambs, this ratio was clearly below

(1.85 for P lambs and 2.59 for SP lambs). These results are in agreement with those of Enser et al. (1998) and Wiklund et al. (2001) obtained in beef and deer, respectively. Also, Bas and Morand-Fehr (2000) refer the same pattern for the effect of diet on lamb FA, although they have only considered C18:2 n-6 and C18:3 n-3. Polyunsaturated FA / saturated FA (P/ S) is another index normally used to assess the nutritional value of fat and the recommended value for the diet is 0.45 (Department of Health, 1994). Fats presenting low P/ S are considered unfavourable, because they may induce an increase in cholesterolaemia. Fat from ruminants, especially when raised on pasture, normally presents P/ S values below the recommenda˜ tion (Enser et al., 1996, 1998; Sanudo et al., 2000). However, an index such as P/ S, based only on the chemical structure of FA, may not be an adequate way to evaluate the nutritional value of fat because it considers that all saturated FA induce an increase in cholesterol and ignore the effects of monounsaturated FA. A better approach to the nutritional evaluation of fat should be the utilization of indexes based on functional effects of FA, e.g. the ratio hypocholesterolaemic:hypercholesterolaemic FA (H / H), computed according to present knowledge of the effects of individual FA on cholesterol metabolism (Dietschy, 1998; Williams, 2000). The values obtained for this ratio ranged between 1.8 and 2.1, and were not affected by feeding system (Table 1). A similar value (2.08) was obtained for pork chops, when H / H was calculated from data presented by Wood and Enser (1997). However, if P/ S ratio was considered, the value of 0.58 obtained for pork chops is much higher, and so more favourable, than the ratios obtained in our study (0.29 and 0.34). When slaughter weight increased, FA composition changed, increasing the proportions of C16:0 and monoenoic FA and decreasing the proportions n-6 and n-3 PUFA. This effect could be explained by the ¨ increase of intramuscular fat deposition (Nurnberg et al., 1998). Stearic acid (C18:0) was not affected by slaughter weight. Bas and Morand-Fehr (2000), refer that in the 20 weeks after weaning, there is a decrease in the proportion of C14:0 and an increase in C18:0 in lamb fatty tissues, probably as a result of the changes in lipid composition of the diet. However, they also showed that C18:0 remained un-

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changed in intramuscular fat, while in subcutaneous and kidney fat it increased. The overall changes in FA composition with slaughter weight increase determined a decline (P , 0.05) in HH, affecting negatively the nutritional value of meat. The effect of slaughter weight on CLA was dependent on feeding system. The CLA increased with slaughter weight when lambs were fed on pasture (P and SP), but decreased, although not significantly, when lambs were fed with concentrate (C). These results suggest that the effect of grass intake on CLA deposition is cumulative, as the difference between feeding systems is larger for lambs slaughtered at 30 kg (Table 1). Discriminant analysis, based on FA profiles as indicators of lambs feeding system, resulted in a combination in two axes of seven FA, of which C18:3 n-3 and CLA showed the highest discriminant power (Table 2). The difference between groups in FA composition can be evaluated by the values of squared Mahalanobis distance (D 2 ). The high values of D 2 obtained correspond to large differences between groups, but these were smaller between P and SP (4.2) than between SP and C (7.9) or P and C lambs (17.9), as illustrated in Fig. 1. Concentrate fed lambs were the only ones that were weaned, so the greater proximity of the results for P and SP lambs may be related to the intake of grass, milk or both. However, the distribution of feeding systems along the first axis was according to the proportion of concentrate, indicating that FA profile was efficient to allocate lambs to one of the three feeding systems with good accuracy.

5. Conclusions Fatty acid composition of meat was similar for MB and crossbred IF3MB lambs. From the nutritional stand point, fat from lambs raised on pasture seems to be more adequate, than lambs raised in confinement with concentrate because of their higher proportion of n-3 PUFA and CLA and lower n-6:n-3 ratio. This can be used to promote light lambs raised in natural environments, in spite of the increased performance and better carcass quality obtained when lambs are raised in intensive production systems.

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Discriminant analysis was important in identifying the FA, which allow the distinction between feeding systems. The high percentage of lambs correctly allocated by this method suggests that the study of FA profile of lamb tissues could be efficiently used as a marker of the feeding systems in which lambs are produced. These potential applications of FA profiles can be of great interest, considering the increase in consumer concerns about food origin and safety.

Acknowledgements This research was supported by ‘Programa de ˜ Agrıcola ´ Apoio a` Modernizac¸ao e Florestal’ (project PAMAF number 3037). People at the Centro de ˜ do Centro Alentejo (DRAAl) are Experimentac¸ao greatly acknowledged for their assistance in animal management. The authors would also like to thank Luis Gama for revising the manuscript.

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