Effect of dietary conjugated linoleic acid and monounsaturated fatty acids on productive, carcass and meat quality traits of pigs

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(2008) 155–164www.elsevier.com/locate/livsci

Livestock Science 117

Effect of dietary conjugated linoleic acid and monounsaturated fattyacids on productive, carcass and meat quality traits of pigs

Diana Martin a, Elena Muriel a, Elena Gonzalez b, Javier Viguera c, Jorge Ruiz a,⁎

a Tecnologia de Alimentos, Facultad de Veterinaria, Universidad de Extremadura, Avda. Universidad s/n, 10071 Caceres, Spainb Producción Animal, Escuela de Ingenierias Agrarias, Universidad de Extremadura, Ctra. Caceres s/n, 06071 Badajoz, Spain

c Imasde Agropecuaria, S.L. C/ Nápoles 3, 28224 Pozuelo de Alarcón, Spain

Received 12 June 2007; received in revised form 13 November 2007; accepted 5 December 2007

Abstract

Three levels (0, 1 and 2%) of conjugated linoleic acid (CLA) were combined with two levels (low and high) of mono-unsaturated fatty acids (MUFA) for pig feeding. Productive, carcass and meat quality traits were studied. Large White♂×Landrace×Large White ♀ gilts (n=288) weighting 70 kg were randomly allotted to 6 different feeding treatments and fed to afinal average weight of 107 kg. Loins were taken from 48 animals (8 animals randomly selected from each treatment). Nodifferences due to dietary CLA, MUFA or CLA×MUFA interaction were found on average daily gain, average daily consumption,feed conversion ratio, carcass yield, backfat thickness, loin weight, loin pH and loin colour. A significant increase in intramuscularfat content ( p=0.010) and in saturated fatty acids (SFA) ( pb0.001), and a decrease in MUFA ( p=0.001) and desaturase indiceswere found as consequence of dietary CLA, regardless the MUFA level. Therefore, dietary CLA, MUFA and their interaction didnot influence productive and carcass traits of pigs. However, the use of CLA for swine feeding increased the intramuscular fatcontent and modified the fatty acid profile, regardless the MUFA level of the diets.© 2007 Elsevier B.V. All rights reserved.

Keywords: Conjugated linoleic acid; MUFA; Pig; Fatty acid profile; Meat quality

1. Introduction

Dietary supplementation with conjugated linoleicacid (CLA) has gained an increasing attention in the fieldof swine production last decades. CLA has been pointedout as an effective tool for improving productive andmeat quality traits such as growth rate, feed conversionratio (FCR), average daily gain (ADG) or intramuscularfat content in swine. Nevertheless, contradictory effects

⁎ Corresponding author. Tel.: +34 927 257123; fax: +34 927 257110.E-mail address: [email protected] (J. Ruiz).

1871-1413/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.livsci.2007.12.005

have been found in different studies concerning CLA-fedpigs (reviewed by Dugan et al., 2004).

CLA supplementation has been also suggested as apotential strategy for obtaining meat and meat productsenriched in CLA, since accumulation of CLA isomers intissues from CLA-supplemented pigs has been reportedin several studies (reviewed by Schmid et al., 2006).

On the other hand, it is well known that CLA feedingleads to modifications in the fatty acid profile of differenttissue lipids, increasing the proportion of saturated fattyacids (SFA), while decreasing that of monounsaturatedfatty acids (MUFA) (reviewed by Dugan et al., 2004).This is a positive effect from a technological point of

156 D. Martin et al. / Livestock Science 117 (2008) 155–164

view, due to the less fluid and more consistent lardsobtained (Ruiz and López-Bote, 2002). However, theincrease in the ratio saturated to unsaturated fatty acidscould have negative health implications from the con-sumer standpoint (Ulbricht and Southgate, 1991). Theinclusion of high MUFA levels in pig diets when usingdietary CLA supplementation could be a potential strat-egy for counteracting the decrease in MUFA caused byCLA. However, the likely interactive effect betweendietary CLA and MUFA should be studied. As far as weknow, only one work (Gatlin et al., 2002) has dealt withthe effect of diet supplementation with CLA togetherwith other fat sources.

Therefore, the aim of this work was to study theeffect of the combination of different levels of CLA andMUFA in pig diets on several productive, carcass andmeat quality traits.

2. Materials and methods

2.1. Experimental diets

Three levels (0, 1 and 2%) of commercial enriched CLA oilsupplementation (CLA-60, BASF, Dortmund), containing ap-proximately 56% of CLA isomers (28% cis-9, trans-11 and28% trans-10, cis-12) and two levels of MUFA (high andlow) were combined for pig feedings (Table 1). CLA wassupplied in the form of free fatty acid. The different levels ofMUFA in the experimental diets were obtained by supple-mentation with olive olein at different proportions dependingon the feed. Palm oil, soy olein and hydrogenated palm stearinwere used for balancing both the level of supplemented fat andthe proportion of the rest of fatty acids. All diets were for-mulated to provide similar protein and energy levels, fulfillingthe advised nutritional needs for female pigs at consideredages by the National Research Council (NRC, 1998). Repre-sentative samples of mixed diets were taken before thebeginning of the trial to determine the chemical and fatty acidcomposition.

2.2. Animal feeding

The experiment was conducted using 288 finishing gilts(Large white ♂×Landrace×Large white ♀). Pigs weighting70 kg and at about 140 days of age were randomly allotted tothe 6 different feeding treatments in 4 replicates of each treat-ment (12 pigs per replicate). Pigs were housed in an envi-ronmentally controlled experimental grower/finisher shed.Temperature was automatically controlled in accordancewith the age of the animals. Combination of natural and ar-tificial (no programmable) light was used. Boxes had partialslat with heating on the centre by radiant floor. There was anonly fan controlled by temperature sensor. Pigs were group-housed in 12 m2 boxes and had ad libitum access to feed(single space dry feeders) and water (nipple drinkers). The

animals were weighted at 0, 14, 28 and 53 days from the be-ginning of the trial to a final average weight of 107 kg. ADG,average daily consumption (ADC) and FCR values werecalculated.

Feed was withheld from animals 24 h before slaughtering.Animals were electrically stunned and exsanguinated. Internalorgans were removed and warm carcass weight was obtained.Carcass yield was calculated (carcass weight as a percentage oflive weight before slaughtering). Backfat thickness wasmeasured between the 3th and the 4th last ribs on the midlineof the carcass. The whole loin (mainly containing the musclesLongissimus dorsi, Spinalis and Semispinalis) was obtainedand weighted from 48 animals (8 animals randomly selectedfrom each treatment).

2.3. Meat quality

pH of the excised loins was measured at 45 min and 24 hpost-mortem (Mod. 52–32, Crison Instruments, S.A., Barce-lona, Spain) at half the length of each loin. Instrumental colourof the loins (CIE L⁎ a⁎ b⁎) was measured approximately inthe same place, once the loin was cut across the surface of themuscle, after 30 min of blooming, at 24 h post-mortem and atroom temperature in triplicate using a Minolta ChromameterCR-300 (Minolta Camera Corp., Meter Division, Ramsey, NJ).

2.4. Chemical composition of diets and samples

Analysis of the feeds was performed according to theAssociation of Official Analytical Chemist (AOAC, 2000): drymatter (reference 935.29), crude protein (reference 954.01),crude fat (reference 920.39), crude fiber (reference 962.09)and ash (reference 942.05). The obtained composition of thediets is shown in Table 1.

Loins were analyzed for chemical composition. Moisturewas determined using the official method (AOAC, 2000).Total lipids were extracted with chloroform/methanol (2:1 v/v)according to the method of Folch et al. (1957). Total proteincontent was analyzed following the procedure described byLowry et al. (1951).

2.5. Fatty acid analysis

After solvent evaporation under nitrogen, fatty acid methylesters (FAMEs) from total extracted lipids were obtained byacidic transesterification following the method described bySandler and Karo (1992). Briefly, 5 mg of extracted lipidsplaced in a glass vial was thoroughly mixed with 1 mL of 5%sulfuric acid in methanol and kept for 30 min at 80 °C in anoven. Afterward, FAMEs were extracted with 1 mL of hexane.Hexane was evaporated to dryness under a nitrogen stream,and FAMEs were dissolved in 1 mL of hexane. FAMEs wereanalyzed by gas chromatography using a Hewlett-Packard HP-6890N gas chromatograph, equipped with an on-column in-jector and a flame ionization detector (FID). Separation wascarried out on a polyethyleneglycol capillary column (60 m×

Table 1Ingredients, chemical and fatty acid composition of the experimental treatments for pig feeding

Ingredient (%) Low MUFA feed High MUFA feed

0%CLA 1%CLA 2%CLA 0%CLA 1%CLA 2%CLA

Barley 53.3 53.3 53.3 53.3 53.3 53.3Wheat 15.0 15.0 15.0 15.0 15.0 15.0Bran 8.0 8.0 8.0 8.0 8.0 8.0Soybean meal 44% 16.0 16.0 16.0 16.0 16.0 16.0Palm oil 1.6 1.1 0.6 1.0 0.5 0.0Soy olein 0.4 0.4 0.4 0.0 0.0 0.0Olive olein 0.0 0.0 0.0 3.0 3.0 3.0Hydrogenated stearin palm 3.0 2.5 2.0 1.0 0.5 0.0CLA 0.0 1.0 2.0 0.0 1.0 2.0Carbonate 1.2 1.2 1.2 1.2 1.2 1.2Phosphate 0.4 0.4 0.4 0.4 0.4 0.4Salt 0.4 0.4 0.4 0.4 0.4 0.4L-lysine 50 0.17 0.17 0.17 0.17 0.17 0.17L-threonine 0.03 0.03 0.03 0.03 0.03 0.03Coline 75 0.04 0.04 0.04 0.04 0.04 0.04Vitamin and mineral premix 0.5 0.5 0.5 0.5 0.5 0.5

Chemical composition (%)Dry matter 89.2 89.6 89.4 89.3 89.5 89.6Ash 4.9 5.1 5.0 5.1 5.6 5.3Crude fiber 4.2 4.3 4.1 4.7 4.3 4.6Crude fat 7.7 6.9 7.3 7.2 7.1 6.8Crude protein 16.4 16.0 15.8 16.7 16.5 15.8Nitrogen free extractives 62.8 64.1 64.0 62.4 62.7 63.8Calculated ME (kcal/kg) 3238.8 3240.8 3242.8 3257.8 3259.8 3261.8

Fatty acid composition (%)C14:0 0.8 0.6 0.5 0.5 0.3 0.3C16:0 35.3 30.4 25.6 25.4 19.7 15.0C16:1 0.1 0.1 0.1 0.5 0.4 0.4C18:0 22.8 20.1 16.6 11.4 7.6 4.6C18:1 n−9 18.1 18.0 18.7 37.8 37.9 37.8C18:2 n−6 19.9 20.2 19.8 20.6 22.2 22.5C18:3 n−3 1.8 1.7 1.6 1.8 2.1 2.1cis-9, trans-11 CLA 0.0 3.9 8.0 0.0 4.3 7.9trans-10, cis-12 CLA 0.0 3.7 7.9 0.0 4.2 8.1SFA 59.7 52.0 43.5 38.8 28.4 20.6MUFA 18.8 18.6 19.2 38.9 38.8 38.7PUFAa 21.5 21.9 21.5 22.4 24.4 24.7

CLA (conjugated linoleic acid), SFA (saturated fatty acids), MUFA (monounsaturated fatty acids), PUFA (polyunsaturated fatty acids), ME(metabolizable energy).a Excluding CLA isomers.

157D. Martin et al. / Livestock Science 117 (2008) 155–164

0.32 mm i.d.×0.25 μm film thickness) (Supelcowax-10,Supelco, Bellafonte, PA). Oven temperature started at180 °C. Immediately, it was raised 5 °C min−1 to 200 °C;held for 40 min at 200 °C and, increased again at 5 °C min−1 to250 °C and held for 21 min at 250 °C. Injector and detectortemperatures were 250 °C. Carrier gas was helium at a flowrate of 0.9 mL min−1. Individual compounds were identifiedby comparison of their retention times with those of standards(Sigma, St Louis, MO). Results were expressed as proportionof each fatty acid methyl ester in relation to total FAMEdetected.

2.6. Statistical analysis

The boxwas the experimental unit for productive traits whilethe pig was the unit for carcass quality and meat quality traits.The effect of considered factors (CLA and MUFA content ofdiets) and their respective interaction (CLA×MUFA) on theproductive, carcass and meat quality traits was evaluated by atwo-way analysis of variance using the general linear modelsprocedure of SPSS (V.15.0).When the effect of any of the factorswas significant (p≤0.05), differences between groups wereanalyzed by using Tukey's posthoc test.

158 D. Martin et al. / Livestock Science 117 (2008) 155–164

3. Results and discussion

3.1. Experimental diets

Ingredients, chemical composition, and fatty acidprofile of experimental diets are shown in Table 1. Dietsshowed levels of crude fat between 6.8 and 7.7%, ofcrude protein between 15.8 and 16.7% and of calculatedME between 3238.7 and 3261.7 kcal/kg. Fat contentwas considerably high due to the inclusion of 5% ofdifferent fat sources in each experimental diet.

As a consequence of including different levels of thecommercial CLA oil, increased proportions of cis-9,trans-11 and trans-10, cis-12 CLA were achieved inconcentrates, each isomer reaching 8% of total fattyacids in diets with a 2% of commercial CLA oil, andaround 4% in 1% CLA-enriched diets. Such levels arewithin commercial recommendations for CLA supple-mentation of swine diets and are similar to the levelsconsidered by other authors who have previously stud-ied the effect of CLA supplementation on swine pro-ductive parameters (reviewed by Dugan et al., 2004).

Apart from CLA isomers, major fatty acids in exper-imental diets were palmitic, stearic, oleic and linoleicacid. The proportion of MUFA in diets enriched witholive oleins (high MUFA diets) reached almost 39% oftotal fatty acids, whereas in lowMUFAmixed diets suchlevels were around 19%. The proportions of PUFA(excluding CLA isomers) ranged from 21.5% to 24.7%,whereas SFA content was lower in high MUFA thanin low MUFA experimental diets. To keep constant thefat content of the diets, and the MUFA and PUFA

Table 2Productive traits of pigs from 70 kg (0 days) to 107 kg (53 days) of live we

CLA level M

0% 1% 2% L

0–14 daysAverage daily consumption (kg/day) 2.3 2.2 2.2Average daily gain (g/day) 794.6 717.3 757.8 7Feed conversion ratio (kg/kg) 2.8 3.1 3.0

14–28 daysAverage daily consumption (kg/day) 2.4 2.4 2.3Average daily gain (g/day) 667.2 702.4 708.6 6Feed conversion ratio (kg/kg) 3.6 3.5 3.4

28–53 daysAverage daily consumption (kg/day) 2.4 2.3 2.4Average daily gain (g/day) 657.6 691.3 695.4 6Feed conversion ratio (kg/kg) 3.6 3.4 3.4

CLA (conjugated linoleic acid), MUFA (monounsaturated fatty acid), SEM

proportions when increasing the content of CLA, theformulation of the feeds necessarily implied the de-crease in the content of the saturated fat sources (palmoil and hydrogenated palm stearin). Thus, the proportionof total SFA in experimental diets decreased with in-creasing proportions of CLA in the diet.

3.2. Productive traits

Results of productive traits are shown in Table 2. Nosignificant differences due to CLA, MUFA or the inter-action CLA×MUFAwere found in any of the evaluatedproductive traits during the trial. Data concerning theweight of the animals throughout the feeding are notshown because all the groups showed approximately thesame weight in all the controls (average weight of 70 kgat day 0 and 107 kg at slaughter). These results sug-gest that neither dietary CLA, nor its combination withdietary MUFA, seem to have any effect on pig pro-ductive traits at the studied experimental conditions.

These findings are in agreement with other studiesin which CLA had no effect on ADG, ADC or FCR(Ramsay et al., 2001; Gatlin et al., 2002). However, insimilar experiments, CLA inclusion significantly im-proved FCR and/or ADG (Thiel-Cooper et al., 2001;Wiegand et al., 2001). This shows that informationconcerning the main productive traits in pigs as affectedby CLA is widely heterogeneous and further investiga-tions are necessary to state clear conclusions (Duganet al., 2004). Aspects such as the assayed dietary levelsof CLA, the proportion of the different CLA isomers,the weight of the animals at the beginning of the trials,

ight as affected by different levels of CLA and MUFA

UFA level SEM p

ow High CLA MUFA CLA×MUFA

2.2 2.2 0.0 0.653 0.847 0.28960.9 752.1 17.0 0.186 0.792 0.2512.9 3.0 0.1 0.265 0.649 0.150

2.4 2.4 0.0 0.625 0.523 0.77481.8 703.7 22.8 0.763 0.662 0.6203.6 3.4 0.1 0.458 0.232 0.435

2.3 2.4 0.0 0.820 0.720 0.24988.4 674.5 12.8 0.389 0.567 0.0813.4 3.5 0.1 0.342 0.401 0.231

(standard error of the mean).

159D. Martin et al. / Livestock Science 117 (2008) 155–164

the length of the CLA treatment or the slaughter agehave been pointed out as some of the parameters thatmight explain the different results found in the scientificliterature (Bee, 2001; Dugan et al., 2004).

3.3. Carcass quality

Results for carcass quality traits are shown in Table 3.Carcass yield, backfat thickness and loin weight wereunaffected by CLA, MUFA or CLA×MUFA interaction( pN0.05). These findings suggest that the use of CLAin pig feeding does not seem to affect the subsequentcarcass quality traits. Furthermore, the combination ofCLA with either low or high MUFA levels in pig dietsdid not affect such traits. These results agree with mostof the studies found in the scientific literature (Corinoet al., 2003; Lauridsen et al., 2005), which have notshown a significant effect of CLA on carcass yield and/or backfat thickness. Similarly to the present work,Corino et al. (2003) did not find either a significant ef-fect of dietary CLA on loin weight from CLA-fed pigs.Gatlin et al. (2002) also reported backfat thicknessvalues unaffected by CLA supplementation combinedwith two different fat sources (yellow grease and tal-low). Nevertheless, other studies have shown lowerbackfat thickness in CLA-fed pigs (Eggert et al., 2001;Thiel-Cooper et al., 2001).

Table 3Carcass and meat quality and meat composition of pigs as affected by dietar

CLA level A MUFA

0% 1% 2% Low

Carcass qualityCarcass yield (%) 80.6 80.2 80.4 80.6Backfat thickness (mm) 22.9 22.9 24.1 23.6Loin weight (kg) 3.9 3.8 3.9 3.9

Meat qualitypH

45 min 6.0 6.0 5.9 6.024 h 5.4 5.5 5.5 5.5

Colour B

L⁎ 57.4 55.9 59.1 56.8a⁎ 8.2 8.1 8.5 8.3b⁎ 2.8 2.5 3.1 2.6

Meat compositionMoisture (%) 72.0 72.2 72.3 72.1Protein (%) 18.3 18.7 17.9 17.6Fat (%) 2.6 b 3.4 a 2.6 b 2.9

CLA (conjugated linoleic acid), MUFA (monounsaturated fatty acid), SEMA Different letters within the same row differed significantly ( p≤0.05).B Instrumental colour was measured 24 h after slaughtering.

Besides other factors, lipolytic and lipogenic enzymesplay an important role in the deposition of lipids in thesubcutaneous adipose tissue and, in turn, in the backfatthickness value. In a previous work (Martin et al., 2006),the lipolytic activity of subcutaneous adipose tissue fromthe same animals studied in the present work wasassayed. In such study, it was concluded that dietaryCLA did not seem to be involved on lipolytic enzymemodifications in subcutaneous adipose tissue. That resultmight be in agreement with the lack of effect of CLA onbackfat thickness values detected in the present work.

3.4. Meat quality and composition

Results for meat quality traits are shown in Table 3.No effect of CLA, MUFA or CLA×MUFA was foundon pH values (45 min post-mortem and 24 h post-mortem) and loin lightness (L⁎ parameter). A significanteffect of the interaction CLA×MUFA on redness (a⁎,p=0.013) and yellowness (b⁎, p=0.011) of meat sam-ples was detected (although experimental groups werenot significantly different by using the posthoc Tukey'sTest). These a⁎ and b⁎ values were, respectively: 7.8and 2.1 at 0% CLA-low MUFA diets, 7.7 and 2.1 at 1%CLA-low MUFA diets, 9.4 and 3.5 at 2% CLA-lowMUFA diets, 8.6 and 3.4 at 0% CLA-high MUFA diets,8.5 and 2.8 at 1% CLA-high MUFA diets and 7.7

y CLA and MUFA

level SEM p

High CLA MUFA CLA×MUFA

80.2 0.3 0.783 0.356 0.25323.0 0.6 0.639 0.614 0.6393.8 0.1 0.852 0.464 0.610

6.0 0.1 0.599 0.715 0.9965.5 0.0 0.588 0.352 0.240

58.1 0.6 0.084 0.261 0.4338.3 0.2 0.603 0.993 0.0133.0 0.2 0.203 0.168 0.011

72.2 0.3 0.905 0.803 0.13919.1 0.4 0.701 0.062 0.4292.8 0.1 0.010 0.827 0.415

(standard error of the mean).

160 D. Martin et al. / Livestock Science 117 (2008) 155–164

and 2.7 at 2% CLA-high MUFA diets. Therefore, theobtained results suggest that meat quality traits arenot affected by CLA supplementation. Moreover, thecombination of dietary CLA with different levels ofMUFA in pig diets would not either imply a relevanteffect on those traits. These results agree with most ofthose previously reported both for pH and colour valuesfrom CLA-fed pigs (Joo et al., 2002; Corino et al., 2003;Dugan et al., 2003). However, other works have pointedout significant effects of CLA on increasing values forcolour parameters (Migdal et al., 2004), and increasingor decreasing pH values of the meat (Thiel-Cooper et al.,2001; Dunshea et al., 2002; Migdal et al., 2004).

No effect of CLA, MUFA and CLA×MUFA wasfound on moisture and protein content of loins. This lackof effect of CLA agrees with the studies of Pastorelliet al. (2005) in loins and Corino et al. (2003) in dry-curedhams from CLA-fed pigs.

A significant effect of CLA on intramuscular fat con-tent was obtained ( p=0.010). The intramuscular fat con-tent from pigs fed 1% CLA diets (3.4%) was higher( pb0.05) than that from pigs fed 0% CLA (2.6%) orthose fed 2% CLA (2.6%). This finding suggests that theeffect of dietary CLA on increasing intramuscular fatcontent in pigs might depend on the level of CLA sup-plementation, but not following a linear behaviour, be-cause CLA doses higher than 1% did not imply a higherintramuscular fat content in our study. Moreover, theeffect of CLA on intramuscular fat was independent onthe MUFA level ( p CLA×MUFA=0.415).

The effect of CLA on increasing intramuscular fatcontent has not been clearly elucidated. Dugan et al.(1999) also reported higher intramuscular fat contenton L. dorsi from pigs supplemented 2% CLA comparedto animals receiving 2% of sunflower oil. Likewise,Wiegand et al. (2002) and Joo et al. (2002) found a sig-nificant increase in intramuscular fat in loins from pigsfed 0.75% CLA and 5%, respectively. However, otherauthors (Tischendorf et al., 2002; Pastorelli et al., 2005)have not found a significant effect of dietary CLA onintramuscular fat content in pigs.

In a previous work (Martin et al., 2006), dietary CLAat 1% led to a higher activity of some lipolytic enzymesof the same loins considered in the present work. How-ever, those findings are not in agreement with the sub-sequent higher fat content obtained in the present workat 1% CLA in the diets. This might suggest that otherproposed mechanisms attributed to CLA, such as en-hancing lipogenesis or preadipocites differentiation(Corino et al., 2003), might play a more important roleon the accumulation of fat in muscle tissues, but not aneffect of CLA on decreasing lipolysis.

3.5. Fatty acid profile of meat

The fatty acid profile of meat samples from CLA-supplemented pigs combined with both low and highlevels of MUFA is shown in Table 4. The use of cis-9,trans-11 CLA and trans-10, cis-12 CLA in pig feedingcaused an increase in the content of both CLA isomers inintramuscular fat ( pb0.001). Thus, at 0%, 1% and 2% ofCLA in the swine diets, the total content of CLA on themeat samples was 0.22%, 0.94% and 1.40%, respectively.Neither MUFA level nor the interaction CLA×MUFAwas involved on the accumulation of CLA isomers in theintramuscular fat. This result shows that the incorporationof CLA in pork followed a dose-dependent behaviour andit was independent of the MUFA level of the diets. Thiseffect was observed for both CLA isomers. Nevertheless,the accumulation of the cis-9, trans-11 CLA isomer wasapproximately twice higher than that of the trans-10, cis-12 CLA isomer. This result suggests that the trans-10,cis-12 CLA isomer was incorporated less efficiently ormetabolized more intensively than the cis-9, trans-11CLA. A different ratio of accumulation of CLA isomershas been also reported in other studies in pigs (Tischen-dorf et al., 1999), broilers (Simon et al., 2002) and mice(Park et al., 1999).

The use of CLA in pig feeding had a significant effecton the total SFA, MUFA and PUFA contents ( pb0.001,p=0.001 and p=0.013, respectively). A significantincrease in total SFA content ( pb0.05) was detected asa consequence of using CLA-enriched diets (36.03% at0% CLA, 40.61% at 1% CLA and 39.94% at 2% CLA).Such an effect was mainly due to the significant increasein palmitic acid (C16:0) and stearic acid (C18:0) pro-portions. Nevertheless, the content of minor SFA, suchas lauric acid (C12:0) or myristic acid (C14:0) also in-creased with CLA supplementation. It must be pointedout that such an increase in the SFA content of intra-muscular fat was obtained despite the lower SFA contentof pig diets with increasing doses of CLA (Table 1).

A parallel decrease in the MUFA content of intra-muscular fat ( pb0.05) was caused by dietary CLA(43.96% at 0% CLA, 41.34% at 1% CLA and 40.06%at 2% CLA). This result was mainly due to the signifi-cant decrease in the proportion of oleic acid (C18:1 n−9) by CLA. Moreover, CLA also caused a significantlydecrease in the content of several minor MUFA, such asheptadecenoic acid (C17:1), eicosenoic acid (C20:1 n−12) and nervonic acid (C24:1 n−9).

It should be pointed out that the increase in SFAcontent and the decrease in that of MUFA of intramus-cular fat with dietary CLA seems to reach a plateau atCLA levels higher than 1% in the diets, since there was

Table 4Fatty acid profile of intramuscular fat of loin (%) from pigs as affected by dietary CLA and MUFA

CLA level A MUFA level SEM p

0% 1% 2% Low High CLA MUFA CLA×MUFA

C12:0 0.03 b 0.04 a 0.04 a 0.03 0.03 0.00 0.000 0.133 0.204C14:0 0.72 b 0.97 a 0.96 a 0.89 0.87 0.02 0.000 0.363 0.493C14:1 n−5 0.10 0.09 0.11 0.10 0.10 0.01 0.295 0.834 0.499C15:0 0.04 0.04 0.04 0.04 0.04 0.00 0.906 0.472 0.384C16:0 20.56 b 22.77 a 22.65 a 22.21 21.77 0.23 0.000 0.217 0.429C16:1 n−7 2.36 2.25 2.50 2.40 2.34 0.05 0.446 0.520 0.636C17:0 0.23 0.23 0.23 0.23 0.23 0.01 0.964 0.732 0.223C17:1 0.20 a 0.17 b 0.17 b 0.18 0.18 0.01 0.001 0.986 0.568C18:0 13.70 b 15.96 a 15.38 a 15.27 14.76 0.21 0.000 0.246 0.684C18:1 n−9 36.74 a 34.92 a b 33.33 b 34.49 35.50 0.38 0.001 0.248 0.462C18:1 n−7 3.66 a 3.11 b 3.18 b 3.34 3.29 0.05 0.000 0.519 0.726C18:2 n−6 13.75 12.52 13.17 13.18 13.11 0.27 0.186 0.908 0.836C18:3 n−6 0.12 a 0.09 b 0.09 b 0.09 0.10 0.00 0.000 0.123 0.796C18:3 n−3 0.58 0.57 0.58 0.55 0.60 0.01 0.917 0.048 0.428C20:0 0.16 0.17 0.16 0.18 0.16 0.00 0.344 0.059 0.932C20:1 n−9 0.79 a 0.74 a b 0.68 b 0.72 0.75 0.01 0.008 0.266 0.301C20:2 n−6 0.38 0.38 0.35 0.35 0.39 0.01 0.167 0.009 0.958C20:3 n−6 0.46 a 0.28 b 0.31 b 0.35 0.35 0.02 0.000 0.790 0.964C20:4 n−6 3.21 a 1.86 b 2.25 b 2.48 2.39 0.15 0.000 0.758 0.714C21:0 0.08 0.09 0.08 0.08 0.09 0.00 0.316 0.004 0.882C20:5 n−3 0.21 a 0.13 b 0.23 a 0.20 0.19 0.01 0.000 0.598 0.341C22:0 0.05 0.06 0.06 0.06 0.05 0.00 0.274 0.159 0.084C22:1 n−9 0.04 a b 0.03 b 0.05 a 0.05 0.03 0.00 0.021 0.123 0.020C22:2 n−6 0.06 0.06 0.05 0.06 0.06 0.00 0.091 0.509 0.918C22:5 n−3 0.42 a b 0.31 b 0.58 a 0.48 0.39 0.01 0.020 0.277 0.102C24:0 0.45 a 0.29 b 0.34 b 0.36 0.36 0.02 0.001 0.800 0.888C24:1 n−9 0.06 a 0.04 b 0.05 a b 0.05 0.05 0.00 0.001 0.774 0.576C22:6 n−3 0.20 a 0.14 b 0.19 a b 0.17 0.18 0.01 0.009 0.611 0.972cis-9, trans-11 CLA 0.15c 0.62 b 0.93 a 0.56 0.57 0.05 0.000 0.772 0.659trans-10, cis-12 CLA 0.07c 0.32 b 0.47 a 0.29 0.28 0.03 0.000 0.850 0.492Total SFA 36.03 b 40.61 a 39.94 a 39.35 38.37 0.41 0.000 0.155 0.387Total MUFA 43.96 a 41.34 b 40.06 b 41.32 42.25 0.43 0.001 0.367 0.656Total PUFAB 19.40 a 16.33 b 17.79 a b 17.92 17.76 0.43 0.013 1.000 0.946

CLA (conjugated linoleic acid), MUFA (monounsaturated fatty acids), SFA (saturated fatty acids), PUFA (polyunsatured fatty acids), SEM (standarderror of the mean).A Different letters within the same row differed significantly ( p≤0.05).B Excluding CLA isomers.

161D. Martin et al. / Livestock Science 117 (2008) 155–164

not a significant increase/decrease in the content of thesefatty acids at 2% CLA dietary level.

Dietary CLA also affected the total PUFA content(excluding CLA isomers) of intramuscular fat ( p=0.013). Linolenic acid (C18:3 n−6), eicosatrienoic acid(C20:3 n−6), and arachidonic acid (C20:4 n−6) pro-portions decreased with increasing levels of dietaryCLA. Moreover, eicosapentaenoic acid (C20:5 n−3)and docosahexaenoic acid (C22:6 n−3) decreased at 1%dietary CLA. Dietary CLA had no effect on the value ofcis-9, cis-12 linoleic acid (C18:2 n−6).

Concerning to the effect of dietary MUFA, neitherMUFA level nor the combination CLA×MUFA causedsignificant modifications of the total SFA, MUFA andPUFA contents. However, a higher proportion of total

MUFA and a lower of SFA might be expected in intra-muscular fat from pigs fed a high MUFA diet, regardlessthe CLA level. The level of MUFA supplementation inthe high MUFA treatments was not probably enough forobtaining a marked enrichment in MUFA of the intra-muscular fat. In fact, other authors have reported sig-nificant increases in the MUFA content of intramuscularfat when feeding diets showing much higher levels ofMUFA than that used in the present work (Miller et al.,1990, Myer et al., 1992; Rey et al., 2004). Nevertheless,MUFA content of intramuscular fat tended to be higherat higher dietary MUFA levels (41.3% in low MUFAand 42.3% in high MUFA treatments).

The obtained results show that dietary CLA modifiedthe fatty acid profile of pig muscle tissue towards an

162 D. Martin et al. / Livestock Science 117 (2008) 155–164

increase in the ratio SFA to unsaturated fatty acids. Thiscould be desirable from the technological point of view,since less fluid and more consistent lards would beachieved (Ruiz and López-Bote, 2002). On the contrary,it would be less suitable from the human nutritionalstandpoint, due to the likely implication of dietary sat-urated fats in cardiovascular diseases (Ulbricht andSouthgate, 1991). Nevertheless, the decrease in MUFAcontent of intramuscular fat caused by dietary CLAcould be likely counteracted by the increase in theMUFA levels of pig feeding, although higher levels ofdietaryMUFA than those used in the present work wouldbe necessary.

Our findings agree with most studies found in thescientific literature concerning CLA enrichment of in-tramuscular fat of pork through feeding diets supple-mented in CLA, as well as the modification of the SFA,MUFA and PUFA contents due to CLA supplementa-tion (Ramsay et al., 2001; Thiel-Cooper et al., 2001;Ostrowska et al., 2003; Lo Fiego et al., 2005). Theinhibition of the Δ9 desaturase by CLA (Smith et al.,2002) has been suggested as the main reason explainingthe modifications in the total SFA and MUFA contentsas a consequence of CLA supplementation. Thus, theratios C18:1/C18:0 or C16:1/C16:0 have been used byseveral authors as a tool for estimating the desaturaseenzyme activity in response to dietary CLA (Lee et al.,1998; Corl et al., 2001; Smith et al., 2002). On the otherhand, the inhibitory effect of dietary CLA on otherdesaturase activities could be also the reason explainingthe observed decrease in the content of some individualPUFA (Simon et al., 2002). Therefore, Δ5, Δ6 and Δ9desaturase indices were estimated according to theirproduct-precursor ratios (Table 5). Dietary CLA signif-icantly depressed Δ6 and both Δ9 (C16:1 n−7/C16:0)and Δ9 (C18:1 n−9/C18:0) indices. Tukey's test alsodetected lower values of Δ9 (C14:1 n−5/C14:0) at in-creasing contents of dietary CLA. Thus, at 2% CLA,such decreases were 22% for Δ6, 27% for Δ9 index ofC14:1 n−5/C14:0, 8% for Δ9 index of C16:1 n−7/

Table 5Estimated desaturase indexes of loin from pigs as affected by dietary CLA a

CLA level A MU

0% 1% 2% Low

Δ5 (C20:4n−6/C20:3n−6) 6.93 6.48 7.24 6.74Δ6 (C18:3n−6/C18:2n−6) 0.009 a 0.007b 0.007b 0.00Δ9 (C14:1n−5/C14:0) 0.15 a 0.10b 0.11ab 0.12Δ9 (C16:1n−7/C16:0) 0.12 a 0.10b 0.11ab 0.11Δ9 (C18:1n−9/C18:0) 2.97 a 2.40b 2.38b 2.49

CLA (conjugated linoleic acid), MUFA (monounsaturated fatty acids), SEMA Different letters within the same row differed significantly ( p≤0.05).

C16:0 and 20% for Δ9 index of C18:1 n−9/C18:0respect to the values at 0% dietary CLA. Moreover, di-etary MUFA level significantly decreased the Δ6 indexand increased that of theΔ9 (C18:1 n−9/C18:0), but didnot affect theΔ9 (C14:1 n−5/C14:0) and theΔ9 (C16:1n−7/C16:0) indices. The Δ5 index was conditioned bythe interaction CLA×MUFA, the combination of diet-ary CLAwith low MUFA diets increasing this ratio (7.0for 0% CLA and 7.9 for 2% CLA), whereas the mixtureCLAwith high MUFA diets did not affect the Δ5 index(6.9 for 0% CLA and 6.6 for 2% CLA). On the otherhand, the plateau reached for the increase in SFA and thedecrease in MUFA of intramuscular fat at dietary CLAlevels higher than 1% in pig diets pointed out previ-ously, was also revealed in the values of Δ6 and thethree Δ9 desaturase indices.

Therefore, CLA seems to have an effect on modi-fying the fatty acid profile of muscle tissues by a likelyinhibition of the desaturation of major fatty acids such asC18:2 n−6, C16:0 or C18:0. But, curiously, the higherdepression for desaturase indices was found for a minorfatty acid (C14:0). Furthermore, our findings reveal thatthese effects seem to be independent on the MUFAlevel of the diet, as the lack of interaction CLA×MUFAshowed. Moreover, it seems that the effect of CLA ondecreasing the desaturase activities might reach a pla-teau at high dietary CLA levels.

Lee et al. (1998) calculated a decrease in approxi-mately 50% of Δ9 desaturase index in livers of micefed CLA-enriched diets. Simon et al. (2002) reported adepressing of C18:0 and C16:0 desaturation of approxi-mately 50% and 25%, respectively, in CLA-fed broilers.Corino et al. (2003) also found a lower value for the Δ9desaturase index in ham adipose tissue from CLA-supplemented pigs.

4. Conclusions

The use of dietary CLA did not cause any effect onproductive and carcass quality traits when combined

nd MUFA

FA level SEM p

High CLA MUFA CLA×MUFA

6.78 0.15 0.086 0.289 0.0298 0.007 0.00 0.000 0.020 0.742

0.12 0.01 0.056 0.710 0.5280.11 0.00 0.012 0.856 0.7802.65 0.06 0.000 0.032 0.431

(standard error of the mean).

163D. Martin et al. / Livestock Science 117 (2008) 155–164

with either low or high MUFA levels in pig diets.Dietary CLA levels up to 1% increased the intramus-cular fat content, whereas a linear CLA enrichment ofpork was achieved with increasing dietary CLA levels.Moreover, dietary CLAmodified the fatty acid profile ofintramuscular fat by increasing the ratio of SFA tounsaturated fatty acids following a CLA dose-dependentbehaviour. All these effects were independent on theMUFA level of the diets. In order to counteract thedecrease in the MUFA content of pork fat, MUFA en-richment of pig diets when supplementing CLA wouldbe an attractive strategy, although higher levels of di-etary MUFA than those used in the present work wouldbe necessary.

Acknowledgments

This research was supported by the Ministerio deEducación y Ciencia, Spain (AGL 2003-03538). CLAwas generously provided by BASF. The valuablecooperation of Dr. Clemente López-Bote, the valuablesuggestions of Dra. Teresa Antequera and the colabora-tion of I+D Agropecuaria in designing the experimentaldiets, sampling and pig management are also acknowl-edged. Diana Martín thanks the Ministerio de Educacióny Ciencia for funding her research.

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