J. Anim Sci. 2008. 86:1145-1155. doi:10.2527/jas.2007-0358
© 2008 American Society of Animal Science
The influence of diets supplemented with conjugated linoleic acid, selenium, and vitamin E, with or without animal protein, on the composition of pork from female pigs1
P. C. H. Morel2,
J. A. M. Janz,
M. Zou,
R. W. Purchas,
W. H. Hendriks and
B. H. P. Wilkinson
Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
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Abstract
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The objective of this study was to evaluate the effect of dietary manipulations on the fatty acid composition, Se content, and vitamin E content of pork. Sixty Duroc-cross gilts were randomly allocated at weaning to 1 of 4 dietary treatment groups (n = 15 per group). The 4 experimental diets were based on animal plus plant components or plant components only, with or without the inclusion of a dietary supplement (0.614%) containing CLA, Se, and vitamin E. The growth performance to approximately 100 kg of BW was similar with diets containing animal plus plant components or only plant components. Growth was also similar when either of these diets included the supplement. Inclusion of the supplement led to expected increases in Se and vitamin E contents (P < 0.001) of the LM. The differences found in the fatty acid profile of the lipid in LM, loin subcutaneous fat, and the belly cut (pork belly) between the groups with and without animal components in their diets largely reflected differences in the diet composition. Inclusion of the supplement led to greater CLA contents in all 3 tissues (P < 0.001), and also to lower contents of oleic acid (P < 0.001) and greater contents of stearic acid (P < 0.05), possibly due to an inhibition of stearoyl-CoA desaturase enzyme. The supplement also led to an increase in LM intramuscular fat (P < 0.05), but did not affect P2 fat depths (65 mm lateral to the midline of the spine at the last rib; mean depth of 11.8 mm). It is concluded that changing from a part animal component diet to an all plant diet will not change the growth performance of pigs but changes in the fatty acid profile of pork are likely to occur. It is further concluded that the nutritional value of pork may be successfully enhanced by simultaneously supplementing the diet with CLA, selenium, and vitamin E.
Key Words: conjugated linoleic acid • fatty acid • growth rate • mineral • pig
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INTRODUCTION
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Consumers are becoming increasingly aware of, and concerned about, the composition of food items both in terms of the nutrients present (Verbeke et al., 1999
), and bioactive non-nutritive component that confer benefits for health and well-being (Pennington, 2002). For pork, many studies have shown that diet modifications can lead to changes in the composition of both the lean and fat portions in term of PUFA (Raes et al., 2004; Teye et al., 2006), CLA (Ostrowska et al., 2003), selenium (Mahan et al., 1999; Wolter et al., 1999), and vitamin E (Jensen et al., 1997). Generally, the degrees of such changes have been demonstrated in separate experiments, but the feasibility of achieving a range of desirable changes simultaneously in the same animal has seldom been evaluated. A recent trend in pig production in many countries, the aftermath of the bovine spongi-form encephalopathy (BSE) experience, has been to decrease the dietary content of animal-derived protein and increase protein from plant sources because of concerns about feeding animal proteins to animals (Taylor et al., 1995). However, few direct comparisons of the effects of plant versus animal protein in the diet on the performance of pigs or on the composition and quality of the pork produced (Shelton et al., 2001) have been conducted.
The objectives of the current study were to evaluate the composition of the lean and fat portions of pork from female pigs that had received diets with or without animal protein, and with or without a supplement containing CLA, Se, and vitamin E.
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MATERIALS AND METHODS
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Animal Management and Dietary Treatments
All animals were managed according to the Massey University Animal Ethics Committee and the New Zealand Code of Practice for the Care and Use of Animals for Scientific Purposes.
Sixty-four female, Duroc x (Large White x Landrace) pigs from 16 litters, with 4 litters per sire, were obtained from a single commercial operation in the North Island of New Zealand. At weaning (approximately 23 d; mean BW of 6.7 ± 1.5 kg) the piglets were transported to the Massey University Pig Biology Research Unit. For the first 2 wk postweaning, all piglets received a commercial weaner diet (Table 1) on an ad libitum basis, with fresh water available at all times. After this acclimation period, the experimental diets (Table 1) were fed, with 1 piglet per litter randomly allocated to each of the 4 treatments. Pigs were initially housed in groups of 4 from different litters, and the experimental weaner diets were fed ad libitum for 4 wk to an average BW of 29.5 ± 4.6 kg. The pigs were then moved to grower-finisher facilities, where they were penned in groups of 8 (2 per treatment) and fed individually 0.11 kg of feed per kg of BW0.75 daily. Grower diets were fed until the pigs reached an average BW of 68.1 ± 2.2 kg, and the finisher diet was fed until an average slaughter weight of 101.9 ± 3.8 kg was achieved.
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Table 1. Ingredient composition on an as-fed basis for a commercial weaner diet and for diets during the weaner, grower, and finisher periods that contained animal and plant products (Animal) or plant products only (Plant)1
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The 4 dietary treatments were defined by diet base, either a combination of animal and plant feedstuffs or plant feedstuffs only, and according to the presence or absence of the nutritional supplement (Sanovite, 0.614% of the diet), which contained CLA and vitamin E (BASF, Auckland, New Zealand) and organic Se (Alltech Inc., Nicholasville, KY). The supplement was formulated based on information published in the literature and the product label recommendations. The supplement was first combined with the vitamin-mineral premix before being mixed with the remaining ingredients. The protein deposition potential of pig genotypes in New Zealand has been determined in the past, and the diets were formulated accordingly (Morel et al., 1993; Moughan et al., 2006). Digestible energy and digestible lysine for all diets were appropriate for New Zealand pig genotypes (Moughan et al., 2006). All other amino acids were in excess of the ideal balance (Baker and Chung, 1991), and the vitamin-mineral premix exceeded NRC (1998) requirements. Feed refusals were measured daily throughout the experiment, and BW was measured weekly. During the weaner phase, feed intake and growth efficiency were determined on a pen basis (n = 4), but were measured individually during the grower and finisher phases.
Slaughter and Carcass Processing
On the morning of each of 6 slaughter days, groups of 6 to 12 pigs (total n = 60) were delivered to a commercial processing plant. After a minimum of 1 h of lairage, the pigs were processed according to commercial standards, with the exception that each carcass was split and the head was removed after HCW was recorded. Each side was moved to the cooler (approximately 2°C), and at 45 min postmortem, the pH (Orion glass pH electrode, Model 8163; Orion Research Inc., Beverly, MA) and temperature (digital temperature probe; DeltaTRAK, Pleasanton, CA) were measured at a depth of approximately 20 mm in the left-side LM by making a cut at the P2 site (65 mm lateral to the midline of the spine at the last rib).
After an overnight chilling period (approximately 18 h), a 300-mm length of the left side of each LM (including the associated bone, fat, and skin) was removed cranially from the last lumbar vertebra; in addition, all the left side semimembranosus muscle, and a sample of the belly cut (i.e., the pork belly) 150 mm in length and 100 mm in width from just below the lateral edge of the LM and caudal to the last rib were taken from each carcass. These 3 samples were vacuum-packed and transported under refrigeration to the Massey University meat laboratory, where they were processed at approximately 48 h postmortem.
Subcutaneous fat thickness, including the skin, was measured at the midpoint of the superficial surface at the cranial end of each LM section, which corresponded to the site over the last rib. The area of a tracing of the LM made at this site was measured with a digital planimeter (KP-90NK, Placom, Koizumi, Tokyo, Japan). All visible external fat and connective tissue was removed from each LM sample, and a 150-mm length from the cranial end was minced twice through a 4.5-mm plate (Kenwood, MG 450 Mincer, Havant, Hampshire, UK). Approximately 100 g of the subcutaneous fat from the loin section was trimmed of skin and sliced into 2-to 3-mm-thick pieces. The belly cut sample was skinned, diced, and minced once through the 4.5-mm plate. The minced belly cut and LM and the sliced fat were stored frozen (approximately –20°C) until analysis.
Laboratory Analyses
A sample of each diet was analyzed for DM, CP (N x 6.25), and fat content (925.10, 968.06, and 991.36, respectively; AOAC, 2000). Selenium content in each diet was analyzed by an external laboratory (SpectraChem Analytical Ltd., Wellington, New Zealand) using the powder briquette/x-ray spectrometry method of Hunt and Kennedy (1992), with a minimum detection limit of 0.5 mg·kg–1. Vitamin E content in the diet samples was determined after saponification with ethanolic potassium hydroxide and extraction into light petroleum. After evaporation to remove the petroleum, the residue was dissolved in methanol and the vitamin E content of the solution was determined by HPLC according to ISO method 6867 (ISO, 2000).
The fatty acid profile of each diet was determined after an initial fat extraction step with chloroform:methanol (2:1, vol/vol) according to the method of Folch et al. (1957). Approximately 20 mg of extracted fat was weighed into a screw-top tube with methyl pentadecanoate (Sigma, P6250, Sigma Chemical, St. Louis, MO) added as an internal standard. An alkaline transesterification was performed using 0.5 M sodium methoxide in anhydrous methanol at 50°C for 20 min (Shantha et al., 1993), and the methyl esters were extracted with hexane and dried over anhydrous sodium sulfate. The fatty acid composition was then determined by gas chromatography (Shimadzu GC-17A, capillary column Supelco SP-2560, 100-m x 0.25-mm i.d., and 0.2-µm film; Shimadzu Corporation, Kyoto, Japan) with a flame ionization detector, hydrogen as the carrier gas, and the following standards: Supelco 37 component fatty acid methyl esters mix, Supelco cis-11-vaccenic methyl ester, Supelco trans-11-vaccenic methyl ester (Sigma-Aldrich New Zealand, Auckland, New Zealand), methyl 9-cis, 11-trans-octadecadienoate, and methyl 10-trans, 12-cis-octadecadienoate (Matreya LLC, Pleasant Gap, PA). The analyzed diet composition is presented in Table 2.
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Table 2. Analyzed composition of the weaner, grower, and finisher diets that contained animal and plant products (Animal) or plant products only (Plant) with or without a dietary supplement (Suppl)1
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Each carcass tissue (LM, belly cut, and subcutaneous fat) was subjected to similar analyses, with the exceptions that analysis of the CP in the subcutaneous fat and vitamin E and Se in the belly cut and the subcutaneous fat were not conducted, and the saponification/extraction method of Bayfield and Romalis (1979) was used for analysis of vitamin E content in the LM.
Statistical Analysis
Two animals were removed from the experiment before dietary treatment allocation, 2 were removed during the weaner phase (n = 60 pigs for the growth performance evaluation), and one carcass was removed from the processing line (n = 59 pigs for the meat composition assessments). Statistical analyses were performed using the GLM procedure (SAS Inst. Inc., Cary, NC).
During the weaner phase, the piglets were kept and fed in pens of 4, and the experimental unit for feed intake and G:F was the pen. During the grower-finisher phase, the pigs were kept in pens of 8 but were fed individually so the experimental unit for all other data was the animal. The statistical model for all variables included a sire effect (n = 4), a treatment effect (n = 4), and a set of 3 orthogonal contrasts between treatments that included a comparison between the diet containing animal and plant components (the animal group) and that containing plant components only (the plant group), a comparison between the control and supplemented diets within the animal group, and a comparison between the control and supplemented diets within the plant group. For fatty acid concentrations, the model was the same except that the concentration of all fatty acids combined was fitted as a covariate before testing for sire and treatment effects.
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RESULTS AND DISCUSSION
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Growth Performance
Generally differences in performance between the treatment groups were not large (Table 3), but those on the animal diet grew faster (P = 0.026) during the weaner period and had greater (P = 0.015) G:F during the grower period. As a result they reached the slaughter weight 3 d earlier. The greater performance of the pigs fed the animal diet during the weaner phase was likely due to the presence of blood meal (2.5%), fish meal (5%), meat and bone meal (5%), and skim milk power (10%) rather than soy protein isolate (10%) and peas (15%). It has been shown that legume proteins fed soon after weaning have a negative effect on nutrient digestibility, intestinal morphology, intestinal enzyme activities, and feed intake (Makkink et al., 1994; Salgado et al., 2002), thus causing a postweaning growth check as was observed in this study.
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Table 3. Least squares means for BW, growth performance, and carcass characteristics of pigs fed diets containing animal and plant products with (Suppl) or without (Control) a dietary supplement1
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The supplement containing Se, vitamin E, and CLA had no effect on growth performance, except feed intake between 30 and 69 kg of BW (P = 0.045). This is in general agreement with earlier reports. Mahan et al. (1999) did not find any effect of organic Se (Sel-Plex; Alltech, Nicholasville, KY) on growth performance of pigs. Vitamin E supplementation did not affect pig growth performance (Cannon et al., 1996; Hoving-Bolink et al., 1998; Eichenberger et al., 2004). The effect of CLA on pig growth performance is less clear. Improvements in ADG and G:F were reported by Thiel-Cooper et al. (2001) and G:F by Dugan et al. (1997). However, the latter research group did not find any effect of CLA supplementation on a growth performance in a subsequent study (Dugan et al., 2001). In several studies, the inclusion of CLA in the diet of pigs decreased backfat depth, but in reviewing those results, Dunshea et al. (2005) noted that this effect became more apparent with increasing backfat depth, and based on the depths of backfat shown in Table 3
(11 to 12 mm), the CLA effect can be expected to be negligible.
There were no statistically significant sire effects or treatment effects on carcass weight, dressing percentage, fat depth, or LM area, and for the last 3 characteristics, the fitting of carcass weight as a covariate did not change these results.
Longissimus Muscle Composition
Intramuscular fat contents (Table 4) were greater in the animal group, and within both the animal and plant groups, the contents were greater in the groups receiving the supplement, although this difference was only a trend for the animal group (P = 0.10). Dunshea et al. (2005) reviewed results from several studies where the intramuscular fat content or marbling was greater in pork from pigs receiving CLA and commented that it was unusual for treatments to affect fat depth and intramuscular fat contents in the opposite directions. In absolute terms, the intramuscular fat contents in Table 4 are appreciably lower than the content of 2 to 3% reported to be optimal for pork eating quality (Verbeke et al., 1999). The treatment effects on water and CP content of LM (Table 4) appear to be largely a reflection of the expected reciprocal relationship between fat and other components of muscle.
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Table 4. Least squares means for composition characteristics of the LM on a fresh tissue basis and for total fatty acid concentration on a fresh weight basis for LM, subcutaneous fat, and a belly cut of pigs fed diets containing animal and plant products either with (Suppl) or without (Control) a dietary supplement1
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As expected, the groups receiving diets with supplement had greater concentrations of Se and vitamin E (P < 0.001) in LM than those did not receive the supplement (Table 4). Although dietary vitamin E concentrations and duration varied, similar results have been reported previously. Jensen et al. (1997) supplemented pig diets with vitamin E at 100, 200, or 700 mg·kg–1 and reported a positive relationship between supplementation and vitamin E deposition in both the LM and psoas major muscles. Although muscle concentration of vitamin E increased with an increased dietary concentration, the proportion of vitamin E retained by the LM ranged from 1.5 to 4.1% and seemed to decrease as the supplementation increased. Hoving-Bolink et al. (1998) supplemented pigs for 84 d at 200 mg of vitamin E·kg–1 (vs. basal diet with 8 mg·kg–1) and reported a 5-fold increase in vitamin E content of LM, whereas Eichenberger et al. (2004) reported a 3.5-fold increase after supplementation at the same concentration for 106 d.
In the present study, the basal dietary vitamin E concentration was relatively high due to the use of tallow from grass-fed ruminant sources [an excellent source of naturally occurring vitamin E (Yang et al., 2002)] in the animal group, the provision of 50 mg·kg–1 diet from the premix, and the inclusion of plant materials in the diets. As such, vitamin E concentration in LM tissue from unsupplemented pork was also relatively high at 2.03 to 2.45 µg·g of tissue–1. By comparison, Cannon et al. (1996) achieved a 10-fold increase in longissimus vitamin E content after dietary supplementation for 84 d at 100 mg·kg–1, but the actual tissue concentration in the supplemented pork was only increased to 1.86 µg·g–1, whereas the concentration in the control group was practically devoid of vitamin E at 0.19 µg·g–1. Wood et al. (2003) suggested that a muscle tissue content near 3.5 µg·g–1 could be considered as the content above which additional dietary supplementation would not be expected to yield further improvement in meat color stability. The greater vitamin E contents of LM in the animal group relative to the plant group did reflect different concentrations in the diets. Vitamin E supplementation was not expected to affect carcass or tissue fatness. Hoving-Bolink et al. (1998) showed no effect of vitamin E supplementation at 200 mg·kg–1 for 84 d on intramuscular fat content in LM of pigs.
Meat from unsupplemented pigs contained a non-detectable amount of Se, while the LM from supplemented pigs contained about 0.18 µg·g–1. Mahan and Magee (1991) incorporated inorganic Se into pig diets at the US FDA-approved concentration (0.3 µgg–1) and reported concentrations in LM of 0.29 and 0.24 µg·g–1 for sodium and calcium selenites, respectively, after 56 d of feeding. In a subsequent study (Mahan et al., 1999) demonstrated a positive dose-response relationship between dietary Se concentration and content of Se in LM. Again, Se content in LM closely matched, or exceeded, dietary provision, even though the basal diet resulted in as much as 0.08 µg·g–1.
Recommended daily Se intakes for humans vary widely and have been reported to range from 0.07 to 0.085 mg·d–1 for Australians to 0.04 mg·d–1 for Europe-ans, whereas the requirements for US men and women have been set at 0.070 and 0.055 mg·d–1, respectively (Duffield et al., 1999). The authors suggested that these dietary standards for Se were available from habitual diets in each region, with a decreased estimate of 0.039 mg·d–1 being a realistic intake for New Zealanders. To achieve greater Se intake in New Zealand, the use of Se-enriched food was recommended. More recently recommended daily intakes of Se for Australia and New Zealand have been set at 70 ug·d–1 for men and 60 ug·d–1 for women (NHMRC, 2006), so that 100 g of pork from the supplemented plant group, for example, at 0.20 ug·g–1 would provide about one-third of the recommended daily intake.
Fatty Acid Contents
The results of total fatty acid contents are presented in Table 4, and the contents of individual fatty acids as a percentage of the total for LM, loin subcutaneous fat, and the belly cut samples are shown in Tables 5, 6, and 7, respectively. All fatty acids measured were included in the total, but with few exceptions, only those present at > 0.15% of the total are shown in the tables. Treatment effects on fatty acid composition were assessed after adjusting for differences in total fatty acid percentage and for sire effects. Total fatty acid percentage was fitted as a covariate because it is known that the pattern of fatty acids changes with increasing fat contents mainly because of a decrease in the proportion of polar structural phospholipids relative to neutral lipids (Marmer et al., 1984; De Smet et al., 2004).
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Table 5. Least squares means for the fatty acid profile of lipid from the LM of pigs fed diets containing animal and plant products with (Suppl) or without (Control) a dietary supplement1
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Table 6. Least squares means for the fatty acid profile of lipid from the loin subcutaneous fat of pigs fed diets containing animal and plant products with (Suppl) or without (Control) a dietary supplement1
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Table 7. Least squares means for the fatty acid profile of lipid from the belly cut of pigs fed diets containing animal and plant products with (Suppl) or without (Control) a dietary supplement1
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Treatment differences in fatty acid concentrations were mainly for the animal versus plant comparisons for all 3 tissues, and these can in almost all cases be attributed to differences in the fatty acid concentrations in the diets, with the plant diet containing decreased concentrations of SFA and MUFA and greater concentrations of PUFA. Consequently, the PUFA:SFA ratio was greater for the plant diets. Two important exceptions to the above generalization were the greater concentrations of the polyunsaturated fatty acids CLA and docosahexaenoic acid (DHA) in both the animal diets as well as the tissues of pigs receiving those diets. Each of these acids has beneficial effects in the human diet, the former because of its anti-cancer properties (Pariza, 2004), and the latter because of its cardioprotective effects as a very-long-chain n-3 fatty acid (Ruxton et al., 2005).
Direct effects of the supplement were shown in all 3 tissues with greater contents of CLA, although the increase was evident for the plant diet group (Figure 1) for both the subcutaneous and intramuscular fat. The plant control group had very low CLA contents; however, the increase with the supplemented plant diet resulted in CLA concentrations that were still only about half those for the unsupplemented group on the animal diet. This was true for both the subcutaneous fat and intramuscular fat (Figure 1), and the pattern for the belly cut (Table 7) was similar to that of the subcutaneous fat. Dunshea et al. (2005) reviewed other studies in which dietary CLA led to elevated contents of these acids in pork and fat, and noted that the transfer of CLA from the diet to subcutaneous fat was more efficient than to intramuscular fat, and that the transfer of the cis-9, trans-11 isomer was more efficient than the trans-10, cis-12 isomer. Both of these effects were demonstrated in the current study (Tables 2, 5, 6, and 7, and Figure 1). Figure 2 presents results for linolenic acid (C18:3, n-3) as an example of a fatty acid where the plant versus animal diet effect was very large due to diet composition, but the supplement effect was relatively small. As with CLA, the diet effect was more marked for subcutaneous fat than intramuscular fat.
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Figure 1. Changes in the concentration of conjugated linoleic acid (C18:2-cis-9, trans-11) with increasing lipid content of the loin subcutaneous fat (A) and within the LM (B) for the 4 dietary treatment groups.
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Figure 2. Changes in the concentration of linolenic acid (C18:3n-3) with increasing lipid content of the loin subcutaneous fat (A) and within the LM (B) for the 4 dietary treatment groups.
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Indirect effects of the supplement on other fatty acids are also shown by results presented in Tables 5, 6, and 7, and it is assumed that these are the results of the effect of CLA in the supplement, although it is not possible to rule out effects of other constituents in the supplement. Support for the contribution of CLA is provided by the results of other studies reviewed by Dunshea et al. (2005) where CLA administration has been the only treatment. Thus, for all 3 tissues the supplement groups had decreased proportions of C18:1 and C20:1 (but not C16:1), and generally greater proportions of C14:0, C16:0, and C18:0. This increase in concentrations of saturated fatty acids at the expense of monounsaturated fatty acids has been attributed to an inhibitory effect of CLA on the enzyme stearoyl-CoA desaturase, an effect that has been shown in laboratory studies to be mainly due to the trans-10, cis-12 isomer (Lee et al., 1998).
The ratios of PUFA:SFA and of linoleic acid to linolenic acid (as an index of n-6 to n-3 fatty acids) were both markedly different for all 3 tissues (Tables 5, 6, and 7) with the former being greater in the plant groups and the latter greater in the animal groups. Wood et al. (2003) noted that the recommended PUFA:SFA ratio for the health of humans consuming pork was 0.4, which means that pork from pigs on the animal diet was too low for all 3 tissues, whereas that from the plant diets was slightly low for LM and well above 0.4 for the other 2 tissues. The effects of the supplement on the PUFA:SFA ratio were small compared with the main diet effects. Wood et al. (2003) also discussed the evidence that a reduction in the risk of certain cancers and coronary heart disease could be expected when the ratio of n-6 to n-3 acids was reduced to less than 4. The linoleic to linolenic acid ratio is usually greater than the n-6 to n-3 ratio (Wood et al., 2003), so the values shown in Tables 5, 6, and 7 can be considered satisfactory, especially for the plant group. Pork from the animal-diet group had greater values, but it should be noted that the linoleic to linolenic acid ratio is only indicative of the overall ratio of n-6 to n-3 fatty acids, and that the main long-chain n-3 fatty acid is DHA (Ruxton et al., 2005), which was at concentrations at least 3 times greater in the animal group than the plant group for all 3 tissues. In contrast, the concentration of eicosapentaenoic acid was greater in the plant group than the animal group possibly due to the greater concentrations of linolenic acid (Burdge and Wootton, 2002). With the DHA concentration in the LM of the animal group being 0.232% of total fatty acid (Table 5), the total content of this acid in 100 g of pork containing 1.5% fatty acid would be 3.48 mg. This is well below the adequate intake for long chain omega-3 fatty acids of 160 and 90 mg·d–1 specified for men and women, respectively (NHMRC, 2006), and even further below intakes of up to 650 mg·d–1 that have been recommended (Kris-Etherton et al., 2000). The 0.232% is also much less than concentrations of over 18% of total fatty acids that have been reported for DHA for Rainbow trout (Testi et al., 2006).
Female pigs fed diets with and without animal-derived components had similar growth rates and efficiency of growth, and produced carcasses with similar contents of fat, but the composition of muscle and fat differed in ways that largely reflected differences in diet composition. Adding a supplement containing CLA, Se, and vitamin E successfully produced greater contents of all of these desirable components in the resulting pork, which, therefore, had several nutritional benefits as a human food. Changes in some other mineral and fatty acid composition characteristics of the pork and fat as a result of the supplement are unlikely to affect its overall nutritional quality.
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Footnotes
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1 Funding for this work was provided by the Foundation for Research, Science and Technology and the New Zealand Pork Industry Board. The skilled assistance of the technical staff at the Massey University Institute of Food, Nutrition and Human Health Nutrition Lab is greatly appreciated. Thanks are extended to Land Meat, Wan-ganui, New Zealand for carcass processing, and to M. Dugan and D. Rolland at the Agriculture and Agri-Food Canada Lacombe Research Centre for advice on CLA analysis. 
2 Corresponding author: p.c.morel{at}massey.ac.nz
Received for publication June 15, 2007.
Accepted for publication February 4, 2008.
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Abstract
INTRODUCTION
