Cardiovascular diseases are one of the major sources of morbidity and mortality across the globe(Reference Mitka1, Reference Yach, Hawkes, Gould and Hofman2). It is now widely accepted that dietary long-chain ( ≥ C20) n-3 PUFA (n-3 LC-PUFA) play a significant role in minimising the risk of CVD(Reference Kris-Etherton, Harris and Appel3, Reference Ruxton, Reed, Simpson and Millington4). The American Heart Association recommends an average intake of about 500 mg EPA and DHA/d for CVD risk reduction(Reference Gebauer, Psota, Harris and Kris-Etherton5). The estimated population average daily n-3 LC-PUFA intake in 1995 in Australia, at 246 mg/d, was less than half of this target, especially considering 71 mg of that estimated intake was from docosapentaenoic acid (DPA)(Reference Howe, Meyer, Record and Baghurst6), which is not included in the American Heart Association figure. Fish and seafood are the richest sources of EPA and DHA(Reference Nichols, Mooney, Virtue and Elliott7), but there are significant amounts of n-3 PUFA in pasture-fed livestock products(Reference Howe, Meyer, Record and Baghurst6). From Australia's 1995 National Nutrition Survey, Howe et al. (Reference Howe, Meyer, Record and Baghurst6) estimated that 43 % of the n-3 LC-PUFA consumed by adults originated from meat, poultry and game while 48 % originated from fish and seafood.
Meat is a major component of the Western-style diet. For instance, York & Gossard(Reference York and Gossard8) estimated the annual per capita meat and fish consumptions for Australia at 110 and 18 kg, respectively. A survey of European diets indicated meat and meat products provide 21 % of the total fat intake(Reference Hulshof, van Erp-Baart and Anttolainen9). The trend in developing nations is also for increased meat consumption with increasing affluence(Reference Myers and Kent10). Myers & Kent(Reference Myers and Kent10) estimated that between 1997 and 2020 developing countries as a whole would increase their demand for meat by 92 % and that the great bulk of this increase would be to serve new consumers. The estimates for poultry meat consumption growth rate in Organisation for Economic Co-operation and Development (OECD) and non-OECD countries between 2003 and 2013 is 1·7 and 2·5 % per annum, respectively(11). In the UK, poultry meat accounts for 41 % of the consumption of meat and meat products(Reference Rymer and Givens12).
It can be reasonably argued therefore that increasing the n-3 LC-PUFA content of meat needs to be part of the global strategy to minimise the impact of chronic diseases. In previous studies, we have shown that the concentration of EPA and DHA in lamb can be tripled by supplementing lambs with protected tuna oil(Reference Kitessa, Gulati, Ashes, Scott and Fleck13). Similarly, various authors have shown that poultry meat can also be enriched with EPA and DHA by supplementing their diets with marine-based n-3 LC-PUFA sources(Reference Rymer and Givens12). However, the use of seafood products and by-products in livestock feed will not be a sustainable strategy if the current rates of harvest remain. Worm et al. (Reference Worm, Barbier and Beaumont14) predicted that seafood resources would face total collapse mid this century. Although their drastic predictions have been challenged(Reference Worm, Barbier and Beaumont15), it is generally accepted that increasing demand for aquatic feed and human consumption has brought into question the sustainability of capture fisheries(16). In recognition of this future imbalance in supply and demand for n-3 LC-PUFA, some authors advocate the production of n-3 LC-PUFA in land plants through plant biotechnology(Reference Ursin17, Reference Damude and Kinney18). Some early results in enriching plants with n-3 PUFA through transgenesis have been reported in Arabidopsis (Reference Robert, Singh, Zhou, Petrie, Blackburn, Mansour, Nichols, Liu and Green19), soyabean(Reference Sato, Xing, Ye, Schweiger, Kinney, Graef and Clemente20) and rapeseed(Reference Ursin17). In the short term though, existing vegetable oils offer some scope for enriching meat with n-3 PUFA as most of them contain α-linolenic acid (ALA; 18 : 3n-3). Many studies have considered the quantitative conversion of dietary ALA to n-3 LC-PUFA but the most reliable estimates of these conversions in man come from stable-isotope tracer studies(Reference Brenna21–Reference Goyens, Spilker, Zock, Katan and Mensink24). These tracer studies have considered overall(Reference Brenna21–Reference Goyens, Spilker, Zock, Katan and Mensink24) conversion as well as compartmental analysis(Reference Pawlosky, Hibbeln, Novotny and Salem23) and modelling(Reference Goyens, Spilker, Zock, Katan and Mensink24) to quantify conversion into n-3 LC-PUFA. It was estimated that up to 60 % of dietary ALA in man is oxidised to carbon dioxide(Reference Brenna21), with the majority of the remainder serving as acetate precursor for synthesis of saturates and monounsaturates(Reference Brenna21), which left very little to be stored as ALA or conversion to EPA and DHA. The estimates for the percentage of dietary ALA that is converted to EPA and DHA is 7 and < 1 %, respectively(Reference Goyens, Spilker, Zock, Katan and Mensink24). Plourde & Cunnane(Reference Plourde and Cunnane25) put the estimated ALA conversion to DHA in man at less than 0·5 %. This low-level conversion is also supported by the in-depth compartmental analysis reported by Pawlosky et al. (Reference Pawlosky, Hibbeln, Novotny and Salem23), which showed that only about 0·2 % of the plasma ALA in healthy individuals was destined for synthesis of EPA. Hence, there seems to be very limited opportunity for using ALA-containing oils to influence EPA and DHA levels in tissues. For health outcomes from dietary ALA itself, there is a comprehensive recent review by Burdge & Calder(Reference Burdge and Calder26), which concluded that from the perspectives of both conversions to n-3 LC-PUFA and amelioration of cardiovascular risk factors, there was very little evidence for arguing for increased consumption of ALA.
Stearidonic acid (SDA) or octadecatetraenoic acid (18 : 4n-3) is in the same family of n-3 PUFA as ALA, EPA, DPA and DHA. For more background on the metabolism and nutritional importance of SDA, the reader is referred to a very recent review by Guil-Guerrero(Reference Guil-Guerrero27). In the present study our focus was on the relative efficiency of ALA- and SDA-containing oils in enriching poultry meat with n-3 LC-PUFA. Since SDA lies in a more advanced position than ALA in the n-3 biosynthetic pathway, there is a justifiable ground for hypothesising that oils containing this fatty acid would be better precursors for EPA and DHA than ALA-containing oils. Recently, Miller et al. (Reference Miller, Nichols and Carter28) reported results of a study where salmon were supplemented with oil extracted from Echium plantagineum, which has common names in Australian including Patterson's Curse, Salvation Jane, Riverina Bluebell, Blue Weed and Purple Bugloss. It is a broadleaf temperate pasture weed introduced into Australia from Europe during the mid-19th century. Miller et al. (Reference Miller, Nichols and Carter28) showed that salmon parr fed on Echium oil-supplemented diets had more EPA and DHA than those fed on rapeseed oil-supplemented feeds. Furthermore, the authors noted that the amounts (mg/g) of EPA and DHA in the Echium-supplemented groups were comparable with those supplemented with fish oil. We investigated if these findings would hold true in domestic livestock, and help us develop animal products as the vehicle for supply of n-3 LC-PUFA. Therefore, the aim of the present study was to compare the level of enrichment of broiler meat with n-3 PUFA, including the health-benefiting n-3 LC-PUFA, when broilers were supplemented with rapeseed or Echium oil.
Materials and methods
All the animal housing, feeding and sampling procedures undertaken in the present experiment were approved by the Commonwealth Scientific and Industrial Research Organisation's (CSIRO's) Animal Ethics Committee according to the guidelines set out by the National Health and Medical Research Council for the ethical care and handling of animals under experimental conditions(29).
Animals, diet and design of experiment
We obtained twenty-four broilers (age 21 d) of mixed sex from a commercial poultry farm in Western Australia (Ingham Enterprises Pty Ltd, Perth, Australia). The broilers were randomly allocated into two groups of twelve chicks, balanced for sex and live weight. We had two blocks of twelve pens in our facility and we randomly assigned six chicks from each treatment group to individual pens in each block. Our experimental design was a randomised complete block design with two treatments, two blocks and six chicks per block (n 24). The pen dimensions for each animal were 40 cm high by 45 cm wide and 50 cm deep, which was equivalent to 0·09 m3 per bird (three times that provided in commercial farms). Each pen had two separate bowls for food and water secured to the gate from the inside. The pens were designed to allow air flow on all sides except at the base, which was solid and covered with sawdust. Fresh sawdust was provided on Mondays and Thursdays when the chicks were removed for weighing. Each broiler received a weighed amount of feed at 08.00 hours after the residue from the previous day was removed and weighed. The feeding plan used was adopted from Ingham Enterprises Pty Ltd, Perth, Australia. The recommended feed offer/bird per d is shown in Fig. 1. Ingredient and lipid compositions of the diets are shown in Table 1. The treatment diets only differed in the type of vegetable oil added (Table 1). The Echium oil used in the present study was supplied by Croda Australia (product name Crossential SA14; product code SR03959/SAMP; batch 0000154257; Croda Australia, Villawood, NSW, Australia). Rapeseed oil was obtained from the local supermarket in Perth (WA, Australia). All animals were weighed twice per week on Mondays and Thursdays.
Fig. 1 Daily DM intake (DMI) and live weight (LW) of broilers offered finisher rations supplemented with rapeseed or Echium oil. (
), DMI of rapeseed oil-supplemented birds; (
), DMI of Echium oil-supplemented birds; (–⋄–), LW of rapeseed oil-supplemented birds; (- -■- -), LW of Echium oil-supplemented birds; (- - -●- - -), recommended feed offer used by Ingham Enterprises Pty Ltd, Perth, Australia. Values are means, with standard deviations represented by vertical bars.
Table 1 Ingredients, total fat content and fatty acid composition of treatment diets
SDA, stearidonic acid; LA, linoleic acid; GLA, γ-linolenic acid; ALA, α-linolenic acid.
Slaughter and carcass sampling
All broilers were slaughtered when they reached the age of 56 d, as per commercial farm practices in the region. Each bird was de-feathered in an automated plucking device, the internal organs removed, and total carcass yield weighed. The thigh and breast muscles were weighed separately after de-boning, and samples were taken from each muscle for total intramuscular fat and fatty acid analysis. The heart, liver and gizzard of each animal were also weighed separately.
Lipid analysis
The total intramuscular fat in each muscle sample was determined using a SoxTec™ 2050 auto-extraction unit following hydrolysis with a SoxCap™ 2047 according to Foss application note AN 3904 (Foss Pacific Pty Ltd, Sydney, Australia). Briefly, each sample was hydrolysed for 1 h in 4 m-HCl then rinsed with water until the pH was 6·5–7·0. It was then dried in a microwave oven for 15 min or until a constant weight was achieved. The fat was then extracted with petroleum ether on a SoxTec™ 2050 using a boiling time of 30 min, rinsing time of 45 min, evaporation time of 10 min and pre-drying time of 1 min. The extraction cups containing the fat were then dried in an oven at 103°C for 30 min or until constant weight was reached.
Fatty acid methyl esters were prepared by published methods(Reference Worm, Barbier and Beaumont14). Briefly, lipid was extracted using chloroform–methanol (2 : 1, v/v). The lipid-containing fraction was recovered and evaporated to dryness under N2. Fatty acid methyl esters were prepared using 1 % H2SO4 in methanol on a dry block at 50–60°C for 1·5 h, and were extracted into petroleum ether and transferred to a GC vial for analysis. The gas chromatograph was a Perkin-Elmer Autosystem GC (PerkinElmer Life and Analytical Sciences Pty Ltd, Melbourne, Vic, Australia) fitted with a flame ionization detector and a split injector, and BPX70 column (SGE Analytical Science Pty Ltd, Melbourne, Vic, Australia). We created a 110 m capillary column by connecting 60 m and 50 m BPX70 columns both with internal diameters of 0·32 mm and film thicknesses of 0·25 μm. The carrier gas was He. The injector and detector temperatures were 210 and 250°C, respectively. The initial oven temperature was 150°C and it was ramped up at 1°C/min up to 223°C, when the rate was changed to 45°C/min to 250°C which was held for 13·96 min. The internal standard used during extraction and the standard fatty acid methyl esters mixture used for peak identifications were sourced from Sigma-Aldrich Pty Ltd. (Sydney, NSW, Australia). Fatty acid methyl ester standards were a C4–C24 mix (Supelco product no. 18 919; Sigma-Aldrich Pty Ltd), methyl all-cis-7,10,13,16,19-docosapentanoate (Sigma product no. D5679; Sigma-Aldrich Pty Ltd) and methyl stearidonate (Fluka product no. 43 959; Sigma-Aldrich Pty Ltd). The internal standard used with each extraction was tridecanoic acid (Sigma product no. T0502; Sigma-Aldrich Pty Ltd).
Statistical analysis
All data analyses were performed by using ANOVA for a randomised complete block design(Reference Snedcor and Cochran30) with two treatments, two blocks and six observations per block. The statistical software used was GenStat® version 4.2 (Lawes Agricultural Trust, Rothamsted, Herts, UK)(31).
Results
Intake, live-weight gain, carcass yield and organ weights
Daily DM intake and live-weight gain of the two groups of broilers were nearly identical throughout the 5-week feeding period (Fig. 1). Under both treatments the broilers adapted to their feed within week 1 and were consuming more than 80 % of the recommended feed offer after week 1 (Fig. 1). The similarity in daily DM intake was also reflected in the similarity in the rate of live-weight change and final live weight achieved under both treatments (data not shown). This was also true of the comparative magnitudes of boned muscle yield and organ weights (Table 2).
Table 2 Boned muscle yield and organ weights of broilers supplemented with rapeseed or Echium oil*
(Means values and standard errors of difference)
* None of the differences were significant at P < 0·05.
Fatty acid composition of muscles
In thigh muscle, Echium oil supplementation resulted in a significantly greater increase in concentration of all n-3 fatty acids, except DHA (0·32 v. 0·37 %; P>0·05; Table 3). The contrast between the two diets was similar for breast muscle except that the difference between the treatments in DHA concentration was statistically significant (P < 0·01). In both thigh and breast muscles we found traces of SDA (0·21 and 0·10 %, respectively) in birds that were in the rapeseed oil treatment groups. Among all n-3 PUFA, the biggest difference between the rapeseed- and Echium oil-supplemented birds was in SDA concentration (0·21 v. 1·69 % for thigh and 0·10 v. 1·45 % for breast muscle, respectively). The total n-3 concentration of both muscles more than doubled when the birds were supplemented with Echium oil compared with rapeseed oil. The content of EPA plus DHA in the thigh muscle from Echium oil-fed birds was 53 % higher than those fed rapeseed oil (49 v. 32 mg/100 g). The n-6 : n-3 ratio in muscle from Echium oil-supplemented groups was less than half that from birds supplemented with rapeseed oil. Echium oil supplementation did not alter the total SFA from that observed with rapeseed oil supplementation. The same was true of the concentration of total n-6 PUFA despite the nearly 10-fold increase in γ-linolenic acid (18 : 3n-6) in both muscles (Table 3).
Table 3 Fatty acid composition (g/100 g total fatty acids) of muscle tissues of broilers supplemented with rapeseed or Echium oil
(Means values and standard errors of difference)
IMF, intramuscular fat; nd, not detected; LA, linoleic acid; GLA, γ-linolenic acid; ALA, α-linolenic acid; SDA, stearidonic acid; AA, arachidonic acid; DPA, docosapentaenoic acid.
Mean value was significantly different (within a muscle tissue) from that of the rapeseed oil-supplemented birds: *P < 0·05, **P < 0·01, ***P < 0·001.
Intramuscular fat and yield of selected fatty acids in thigh and breast muscle
Table 4 shows the fatty acid yield based on the total intramuscular fat extracted (TAG and phospholipids) from a sample from each animal against the percentage of each fatty acid in that animal. There was more than twice as much intramuscular fat in thigh muscle than in breast muscle (Table 4). In terms of individual fatty acid yields (100 g × intramuscular fat % × fatty acid %), the use of Echium oil was more effective in enriching both muscles with n-3 PUFA. The magnitude of difference between the two treatments for thigh muscle ranged from almost two-fold with DPA (47 v. 85 mg/100 g) to almost 40-fold for SDA (4·1 v. 141 mg/100 g) (Table 4). Consequently, the total n-3 PUFA yield/100 g muscle in Echium-supplemented birds was more than twice than in those supplemented with rapeseed oil. There was no treatment difference in the DHA yield/100 g muscle in either muscle tissue. This was also true of the total SFA yield and total n-6 PUFA yield (Table 4).
Table 4 Total intramuscular fat (IMF) and fatty acid yield of thigh and breast muscle from broilers fed rations with rapeseed or Echium oil as a lipid supplement
(Means values and standard errors of difference)
LA, linoleic acid; GLA, γ-linolenic acid; ALA, α-linolenic acid; SDA, stearidonic acid; AA, arachidonic acid; DPA, docosapentaenoic acid.
Mean value was significantly different (within a muscle tissue) from that of the rapeseed oil-supplemented birds: *P < 0·05, **P < 0·01, ***P < 0·001.
Discussion
For both the rapeseed and Echium oil-fed groups, the mean final live weight was close to the 3·0 kg industry target in the region, where tallow is the most common lipid supplement. Hence both supplements showed no adverse growth performance or carcass yield outcome. The present results clearly demonstrated that Echium oil was more effective than rapeseed oil in increasing EPA. The results also showed that although the improvements in n-3 LC-PUFA in breast muscle were statistically significant, the absolute changes (mg/100 g) were of little, if any, nutritional significance. Therefore, we will focus our discussion to the contrasts in enrichment of thigh muscles between the treatment groups. The total n-3 PUFA in the Echium group was more than double that in the rapeseed group (265 v. 676 mg/100 g), but the change in EPA plus DHA was less pronounced (32 v. 49 mg/100 g), because of lack of change in DHA. In relation to the recommended daily intake, 100 g of thigh muscle from the rapeseed and Echium groups provided approximately 6 and 10 %, respectively, of the recommended 500 mg EPA plus DHA(Reference Gebauer, Psota, Harris and Kris-Etherton5). It is worthwhile noting that the thigh muscle EPA and DHA content from the Echium group (49 mg/100 g serve) will meet the ‘source’ category of claims for n-3 LC-PUFA content of foods under standards set by Food Standards Australia and New Zealand(32). The label claim categories for ‘source’ and ‘good source’ reflect the degree to which a meal contributes to the consumer achieving daily values for a nutrient(32). Food Standards Australia and New Zealand's cut off points for ‘source’ and ‘good source’ claims for n-3 LC-PUFA are 30 and 60 mg/serve, respectively. Under the US Food and Drug Administration guidelines meals which provide 10–19 % of the recommended daily intake (for example, 500 mg for n-3 LC-PUFA) can be called a ‘good source’, while those which provide 20 % or more can be called ‘high’, ‘rich in’ or ‘excellent source’(33). In addition to enabling product differentiation, the 17 % increase in EPA plus DHA achieved by using Echium oil instead of rapeseed oil would be a nutritionally significant improvement as part of a normal diet, and we contend that both supplements would produce chicken meat with a better n-3 PUFA profile than that produced locally where tallow is the most prevalent lipid supplement in large commercial operations. The enrichment with ALA achieved using Echium oil, at 540 mg/100 g muscle, takes the thigh muscle tissues within 30 % of the 1·5 to 3 g/d recommended ALA intake(Reference Gebauer, Psota, Harris and Kris-Etherton5).
The lack of substantiation of epidemiological claims for the health benefits of ALA(Reference Brouwer, Katan and Zock34) with direct cause–effect relationship between ALA intake and cardiovascular risk(Reference Burdge and Calder26), and the emerging nature of evidence for the benefits of SDA(Reference Guil-Guerrero27, Reference James, Ursin and Cleland35), forces us to look at the value of vegetable oils in terms of their contribution to n-3 LC-PUFA synthesis. Furthermore, current dietary strategies aimed at increasing the n-3 PUFA content of human diets are targeted at the marine-based LC-PUFA – EPA and DHA(Reference Gebauer, Psota, Harris and Kris-Etherton5). Echium oil supplementation to chickens did not significantly improve the content of DHA (mg/100 g muscle) in either muscle any more than rapeseed oil did. Since Echium oil contained about 14 % SDA, which is one step closer to DHA than ALA, we anticipated that SDA-supplemented birds would contain more DHA in their muscle than ALA-supplemented birds. The present results do not concur with the observations of Miller et al. (Reference Miller, Nichols and Carter28) on salmon, where SDA supplementation was just as effective as fish oil supplementation in increasing DHA in muscle. Harris et al. (Reference Harris, DiRienzo, Sands, George, Jones and Eapen36) supplemented adult male Beagle dogs with a range of doses of SDA (21, 64 and 193 mg/kg body weight) and observed significant changes in erythrocyte and heart tissue DHA at the highest dose. However, when averaged across all time points (across 12 weeks) and treatment groups the authors noted that DHA levels were unaffected in their study. In all cases (including the present study) there was conclusive evidence that SDA supplementation is consistent in its effectiveness in improving tissue EPA concentrations. Hence, our findings on SDA supplementation agree with previous ALA supplementation studies in chickens where it was also noted that there was a weak relationship between dietary ALA and the edible tissue content of EPA, and no relationship between dietary ALA and edible tissue DHA (for a review, see Rymer & Givens(Reference Rymer and Givens12)).
Our diets did not include any fishmeal or other seafood by-products. Therefore, we propose that the content of EPA, DPA and DHA in all the tissues resulted from biosynthetic conversion of dietary ALA and SDA. In the past, the conversion of ALA to EPA and DHA in man was suggested to be relatively more efficient when the background diet is low in n-6 fatty acids(Reference Chan, McDonald, Gerrard, Bruce, Weaver and Holub37). Recent evidence has shown that conversion of ALA is related to the absolute amount of ALA rather than its ratio to linoleic acid(Reference Goyens, Spilker, Zock, Katan and Mensink38). Furthermore, a recent UK workshop which analysed the usefulness of the n-6 : n-3 ratio in understanding n-3 metabolism or addressing cardiovascular risk concluded that the focus should be on the absolute amounts rather than the ratio(Reference Stanley, Elsom, Calder, Griffin, Harris, Jebb, Lovegrove, Moore, Riemersma and Sanders39). Therefore, we exclude the background n-6 : n-3 ratio as the cause of lack of treatment difference in DHA response to ALA or SDA supplementation.
Although SDA supplementation did not enrich broiler muscles with DHA, the enrichment achieved in terms of the SDA content itself may be of some health benefit to consumers. For instance, studies on human and rat microsomal tissues showed that SDA plays an inhibitory role in 5α-reductase activity(Reference Liang and Liao40), which is a prostate cancer risk biomarker. Other health claims for SDA include an anti-inflammatory role through inhibition of the 5-lipoxygenase pathway which was comparable with EPA when tested in vitro (Reference Guichardant, Traitler, Spielmann, Sprecher and Finot41). There are also claims for anti-thrombotic activity for SDA through competition with arachidonic acid metabolism(Reference Kockmann, Spielmann, Traitler and Lagarde42). Perhaps a stronger evidence for SDA health benefit that was based on human studies is that reported by Surette et al. (Reference Surette, Edens, Chilton and Tramposch43). The authors showed that Echium oil supplementation to hypertriacylglycerolaemic human subjects significantly increased plasma and neutrophil long-chain n-3 PUFA and decreased serum TAG by about 30 % from baseline. The caveat regarding that study is that it was a single-centre, open-label design with no placebo groups. Nonetheless, we calculated the doses used in that study to be in the order of 1875 mg SDA/d offered in fifteen capsules/d (five capsules at each meal time). Our enriched thigh muscle yielded 141 mg SDA/100 g, which is about 8 % of that dose. Hence, it remains to be determined what the magnitude of benefit in reduced cardiovascular risk factors would be from eating our enriched poultry meat. Without discounting the above caveats and considering the health benefits of SDA reported from short-term studies(Reference Guil-Guerrero27, Reference James, Ursin and Cleland35), we propose that Echium oil supplementation creates a poultry meat with an improved n-3 fatty acid profile and, importantly, n-3 LC-PUFA that will benefit the consumer. We also suggest that SDA-containing oils are more effective supplements for enriching poultry meat with SDA and EPA than vegetable oils that only contain ALA.
In terms of recommendation for using Echium oil in animal feed for improving the health benefits of animal-derived foods, the current price per tonne is prohibitive unless cheaper sources are made available in land crops through plant biotechnology. The Echium plant naturally found in Australia is toxic (pyrrolizidine alkaloids) to grazing livestock(Reference Seaman, Turvey, Ottaway, Dixon and Gilmour44) and the Croda product is a purified ‘food-grade’ product intended for human consumption. In the past, plant breeders have been able to create safer varieties of crops from wild types containing toxic alkaloids (for example, lupins), but the feasibility of use of plant biotechnology from a technical standpoint has already been demonstrated in rapeseed and soyabean, and involves the insertion of Δ-6 desaturase in ALA-producing plants(Reference Ursin17, Reference Damude and Kinney18, Reference Sato, Xing, Ye, Schweiger, Kinney, Graef and Clemente20). In contrast, producing DHA in land plants requires an assembly of a number of desaturase and elongase genes(Reference Robert, Singh, Zhou, Petrie, Blackburn, Mansour, Nichols, Liu and Green19). Even under the ideal situation where we have ample and cheap SDA-containing oils, there needs to be further large-scale and rigorous studies to confirm the health benefits for human consumers from SDA itself, as the conversion to DHA seems very little at best.
Conclusions
Birds fed Echium oil-supplemented rations had more tissue ALA, SDA, EPA and DPA than those fed similar rations supplemented with rapeseed oil. The total n-3 PUFA content of edible meat from birds supplemented with Echium oil was more than double that of those supplemented with rapeseed oil. Echium oil was more effective than rapeseed oil in changing the EPA levels in chicken meat, but the two vegetable oil sources were similar in that they both had no impact on the amount of DHA in edible tissues.
Acknowledgements
We are grateful to Mr Michael Carthew for his assistance during the feeding experiment and the slaughter of the chickens. Ingham Enterprises Pty Ltd, Perth, Australia, kindly supplied the 21-d-old chicks for this experiment. Croda Australia supplied the Echium oil used in the study. This project was wholly funded by the CSIRO Food Futures Flagship. The animal and laboratory facilities were provided by CSIRO Livestock Industries. S. M. K. developed the proposal, designed the experiment, analysed the data and drafted the manuscript. P. Y. managed the feeding experiment, conducted all the laboratory analyses and helped with the design and analysis of the data. Both authors have no conflict of interest to disclose.
