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ANIMAL PRODUCTION |
Division of Nutritional Sciences, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire, LE12 5RD, UK
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: carcass • conjugated linoleic acid • sheep
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Conjugated linoleic acid cis-9, trans-11 may also be made endogenously in tissues of sheep from vaccenic acid (C18:1 trans-11) by stearoyl-CoA desaturase (Griinari et al., 2000).
Studies in rodents and various other species have shown that CLA cis-9, trans-11 possess anticarcinogenic properties, even when consumed at low levels (reviewed by Belury, 2002 and Bauman et al., 2006). Reduced body fat after supplementation with a mixture of the cis-9, trans-11 and trans-10, cis-12 CLA isomers has been reported in pigs (Ostrowska et al., 1999). Effects on body composition have also been attributed to the trans-10, cis-12 isomer in mice (Park et al., 1999) and rats (Sisk et al., 2001). Conjugated linoleic acid trans-10, cis-12 has also been linked to a reduction in milk fat content in dairy cows (Baumgard et al., 2001). A further effect of CLA is to alter tissue fatty acid composition, such as a decrease in monounsaturated fat (Choi et al., 2000, 2001), and such an effect is consistent with an inhibition of stearoyl-CoA desaturase.
Unsaturated fatty acids are readily biohydrogenated in the rumen (Annison, 1993). Therefore, supplemental unsaturated fatty acids must be protected before feeding to ruminants. The objectives of this study were to determine effects of a rumen protection of a mixed-isomer supplement on CLA enrichment of lamb tissues and lamb carcass characteristics.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Experiment 1
Sheep and Diets.
Three Mule x Charolais castrate adult sheep (10 mo of age, BW 55.3 ± 1.8 kg) were individually housed in an environmentally controlled metabolism unit, with continuous access to water, and were fitted with permanent ruminal and duodenal cannulas. A CLA supplement, CLA-80 (80% pure CLA), was obtained from Natural ASA (Hovdebygda, Norway). This CLA supplement contained 99 g of lipid/100 g, of which 77% was the 2 main CLA isomers (ratio of cis-9, trans-11 to trans-10, cis-12 = 0.98), 12% was oleic acid (C18:1 cis-9), and the remainder was palmitic (C16:0) and stearic (C18:0) acid.
The CLA-80 was protected from rumen degradation (Trouw Nutrition UK, Wincham, Northwich, Cheshire, UK) using a matrix of saturated fat of vegetable origin, with the final product being produced by prilling, spray drying, and chilling. The resulting protected CLA (pCLA) contained 67.7% (wt/wt) lipid, 22.6% (wt/wt) ash, 9% (wt/wt) carbohydrate, and 0.5% (wt/wt) moisture. Of the lipid component (as free fatty acids equivalents), 12.5% was the cis-9, trans-11 isomer of CLA, 12.5% was the trans-10, cis-12 isomer of CLA, 58% was C18:0, and 10% was C16:0.
Experimental Design.
A 3 x 3 Latin square design with 3 diets, 3 sheep, and 3 feeding periods was used. The diets were randomly allocated to each sheep in the first period and were reallocated in each subsequent period. Every sheep received each diet once, and all sheep and diets were present in every period. Over a period of 8 wk, each of the 3 sheep were fed 3 diets, which were 1.4 kg/d of a concentrate-based control diet, 1.4 kg/d of the control diet plus 22 g of CLA-80 (18.0 g/kg of DM)/d, or 1.4 kg/d of the control diet plus 110 g of pCLA (89.9 g/kg of DM)/d. The 2 CLA diets were balanced to provide approximately 17 g of CLA/d.
The concentrate diet was ground and contained (as-fed) 455 g of barley/kg, 160 g of oats/kg, 200 g of dehydrated grass pellets/kg (formed from a mixture of Perennial and Italian ryegrass, pellet diameter 13 mm; Whatton Estates, Loughborough, Leicestershire, UK), 100 g of molassed feed meal/kg (sugar cane molasses absorbed onto dry-extracted palm kernel and straw meal; Rumenco, Burton-On-Trent, UK), 50 g of extracted soybean meal/kg, 25 g of sheep mineral and vitamin mix/kg (Frank Wright Limited, Ashbourne, Derbyshire, UK), and 10 g of vegetable oil/kg.
After 7 d of feeding, sheep were ruminally infused with chromium EDTA and Yb acetate (aqueous solutions prepared according to Binnerts et al., 1968, and Siddons et al., 1985, respectively) for 7 d. After the period of marker infusion, samples of duodenal digesta were collected every 6 h for 48 h. These samples were used to determine the quantity of CLA reaching the small intestine daily. Marker concentrations in the duodenal digesta and infusate were measured as described by Faichney (1975) using atomic absorption spectrophotometry (Analyst 100, Perkin Elmer, Boston, MA). Dry matter flow rates to the duodenum, fatty acid compositions of the digesta samples, and flow rate of fatty acids to the duodenum were all calculated using the equations of Faichney (1975).
Statistical Analysis.
Data were analyzed using Genstat for Windows, release 6.1 (Lawes Agricultural Trust, Hertfordshire, UK). The effects of sheep, period, and treatment were determined by ANOVA.
Experiment 2
Lambs.
Thirty-six female Mule x Charolais lambs (72 ± 3 d of age, BW 27.9 ± 1.4 kg), which had previously been maintained on pasture with their dams, were individually housed in an environmentally controlled metabolism unit with continuous access to water. During a 3-wk adaptation period, all lambs were fed a concentrate diet containing (as-fed) 550 g of barley/kg, 350 g of oats/kg, 50 g of molassed feed meal/kg (Rumenco), 25 g of extracted soybean meal/kg, and 25 g of sheep mineral and vitamin mix/kg (Frank Wright Limited), which was fed as a meal (DM, as determined, was approximately 874 g/kg, lipid content was 29 g/kg, and energy content was 18.42 MJ of GE/kg of DM). Lambs also had access to a mineral block throughout the experiment. Feed offered was calculated according to the Ministry of Agriculture, Fisheries, and Food (1975) to achieve a growth rate of 180 g/d.
After the adaptation period, lambs were randomly assigned to 1 of 7 treatment groups and fed the same concentrate diet to achieve a growth rate of 180 g/d. Treatments were (n = 5 lambs/treatment): 25 g of pCLA/kg of diet DM (low pCLA), 50 g of pCLA/kg of diet DM (med pCLA), 100 g of pCLA/kg of diet DM (high pCLA), 21.7 g of Megalac/kg of diet DM, 43.3 g of Megalac/kg of diet DM, 86.6 g of Megalac/kg of diet DM, or no added supplement (control, n = 6). Megalac (Volac Ltd, Royston, Herts, UK) was used to control for the total lipid content of the pCLA, and both supplements were balanced for energy content at each intake level and provided extra energy above that of the basal ration. The GE content of the pCLA was 28.73 MJ/kg of fresh weight, and that of the Megalac was 33.17 MJ/kg of fresh weight. The chemical composition of the pCLA was as described above. The Megalac, however, contained 812 mg of lipid/g, and the major fatty acids were palmitic (C16:0, 48.8%) and oleic acid (C18:1 cis, 34.4%). Inclusion rates of the supplements and chemical and fatty acid composition of the treatment diets are shown in Table 1.
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On the left side of the carcass, the curve of the ribs was followed to the vertebral column, where the latter was severed at the junction of the 12th and 13th thoracic vertebrae. The following measurements were recorded from the anterior surface of this cross-section: width of the LM (maximum distance across the cross-section of the muscle from the end adjacent to the spinal process, distal along the rib), depth of the LM (longest distance, perpendicular to width measurement, on the same surface), and thickness of the backfat over the widest part of the LM.
The intact right side of the carcass was placed in a bag and stored at –20°C until determination of fat and protein content. For this, the frozen carcass was allowed to partially defrost before being minced with a Wolfking mincer (Slagelse, Denmark) once through a 13-mm screen and then twice through a 4-mm screen. A sample of approximately 100 g was taken and frozen at –40°C before freeze-drying in preparation for fat and protein analysis.
Determination of Fatty Acid Composition.
For analysis of the Megalac-containing diets, total lipid was obtained by boiling the samples in 4 M HCl for 1 h before extracting the lipid with diethyl ether (adapted from AOAC, 1995). For all tissue samples and the CLA digesta and diets, lipid was extracted using a 2:1 chloroform:methanol solution, according to the method of Folch et al. (1957), and stored in chloroform at –20°C. To minimize isomerization of cis-trans bonds, and to ensure that all fatty acids were methylated, fatty acid methyl esters were prepared using a combined acid-base methylation, based on the methods of Christie et al. (1999) and Kramer et al. (1997). For adipose tissue, which contains essentially all esterified fatty acids, a base methylation only was used (Christie et al., 1999).
Separation of fatty acid methyl esters was accomplished using a Perkin Elmer Autosystem Gas Chromatograph (Perkin Elmer, Norwalk, CT) equipped with a flame ionization detector, and a 100 m x 0.25-mm i.d. capillary column with a 0.2-µm film thickness (CP-Sil 88; Varian Inc., Walnut Creek, CA) and helium as a carrier gas. The initial oven temperature was held at 170°C for 50 min and then increased at a rate of 25°C/min to 240°C and held for 10 min. The injector temperature and detector temperature were both 255°C, with a split ratio of 50:1. Peaks in the chromatograms were identified using pure methyl ester standards (Sigma, St. Louis, MO), and although this made it possible to resolve several individual C18:1 trans isomers, only the data for trans-10 and trans-11 are shown. The data are expressed as moles of each fatty acid methyl ester/100 mol of all fatty acids identified, and the molecular weight of methyl oleate was used for all unidentified fatty acids, as this was the region in which most were found.
Determination of mRNA Levels.
The acidified, phenol-chloroform-guanidine thiocyanate method of Chomczynski and Sacchi (1987) was used to extract total RNA from samples of adipose tissue and liver. To remove any genomic DNA, samples were treated with DNase (Promega, Madison, WI), and RNA purity and yield were determined by measurement of absorbance at 260 and 280 nm using the GeneQuant-RNA/DNA Calculator (Amersham Pharmacia Biotech, Piscataway, NJ). For each total RNA sample, 5 µL (0.1 µg/µL) was added to 1 µL of random hexamers (Promega) and 9 µL of water and incubated at 70°C for 5 min to denature its secondary structure. Samples were then reverse-transcribed by addition of 1 µL of MMLV reverse transcription (Promega) and 5 µL of its respective buffer, 1.25 µL of deoxynucleoside triphosphate mix (10 mM), 0.5 µL of RNase inhibitor (Promega), and 2.25 µL of water, and incubation at room temperature for 10 min followed by 42°C for 1 h. Each reaction was then made up to 100 µL with water and stored at –20°C.
For the relative quantification of stearoyl-CoA desaturase, acetyl-CoA carboxylase, and ß-actin (internal standard) cDNA, quantitative, real-time PCR was performed using a PRISM 7700 Sequence Detector (Applied Biosystems, Foster City, CA). All primers and probes (TaqMan, Applied Biosystems) were designed from ovine-specific sequence data (Ensembl, Sanger Institute, Cambridge, Cambs, UK) using Primer Express. For each target gene, sequence homology was obtained only to the gene of interest, and the primer and probe sequences are presented in Table 2. All TaqMan probes were 5'-6-carboxyfluorescein- and 3'-6-carboxy-N,N,N',N'-tetramethylrhodamine-labeled. Prior optimization was conducted for each primer and probe set to determine the optimal primer concentrations and probe concentration and to verify the efficiency of the amplification. The exact size of PCR products was confirmed by separating them by gel electrophoresis and visualizing them by exposure to ultraviolet light.
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Statistical Analysis.
Data were analyzed using Genstat for Windows, release 6.1 (Lawes Agricultural Trust). Differences in carcass composition and fatty acid content between the treatment groups were also determined by ANOVA. Overall treatment variation was partitioned into the control group vs. all other treatment groups (control vs. other), and the variation among these other treatment groups was further partitioned to determine main effects of, and interactions between, type and amount of fat in the dietary treatments. A lamb from the high Megalac diet group was euthanized after exhibiting chronic pneumonia, and missing value routines were therefore included in the analysis and the degrees of freedom were reduced to account for the missing data.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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), confirming the effectiveness of the protection technique. Compared with the CLA-80 diet, there was an 8-fold increase in the amount of CLA flowing through the duodenum when pCLA was included in the diet; the ratio of the 2 main isomers remained similar to that in the pCLA fed. Approximately 65% of the pCLA was calculated to avoid rumen biohydrogenation. A small amount (8.5% of that fed) of the unprotected CLA-80 appeared at the duodenum.
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). The energy content of the diet increased with increasing of pCLA inclusion, but there were no differences in growth rate or carcass weight between lambs fed different diets. No effect of amount or type of diet was observed on the weights of the liver, LM, or adipose tissue depots studied. Backfat thickness of pCLA-fed lambs was not different to that of control lambs. Addition of pCLA to the diet did not alter depth and width of the LM. There was a tendency (P = 0.051) for muscle width to increase with the amount of fat in the diet, irrespective of the type of fat; muscle depth did not differ. No differences in the proportions of fat and nitrogen in the carcasses were identified. Likewise, no differences were noted in the minced LM. An effect of type of fat (P = 0.02) was detected in the fat content of liver samples with levels being greater in pCLA-fed lambs, but no effects of amount of fat were observed.
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. In the subcutaneous depot, no effect of any dietary treatment was observed on palmitic (16:0) or stearic acid (C18:0) content; however, effects of type of fat (P < 0.001 for both pCLA and Megalac) on palmitoleic (C16:1) and oleic acid (C18:1 cis) levels were seen with tissue from lambs fed pCLA containing the least. Although no effect (P > 0.26) of dietary treatment was noted on the stearic acid content of the omental depot, an effect of type of fat was evident on the levels of palmitic (P = 0.01) and palmitoleic (P < 0.001) acid with samples from lambs fed Megalac having greatest levels of both. There was also an amount of fat x type of fat interaction (P = 0.02) for oleic acid content of the omental depot because levels increased with increasing of Megalac and decreased with increasing of pCLA supplementation. For the perirenal depot effects of type of fat on the levels of palmitic acid, palmitoleic, and stearic acid (P < 0.02) were observed; tissue from lambs fed pCLA had lower levels of palmitic and palmitoleic acid and higher levels of stearic acid than lambs fed control or Megalac diets. Oleic acid content of the perirenal depot increased (P = 0.002) with increasing of Megalac and decreased with increasing of pCLA supplementation.
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Both isomers of CLA were identified in the adipose tissue depots. In lambs fed pCLA and Megalac, the amount of cis-9, trans-11 CLA exceeded the amount of trans-10, cis-12 CLA. In all 3 adipose tissue depots studied, the proportions of cis-9, trans-11 CLA increased (subcutaneous P = 0.020, omental and perirenal P < 0.001) with amount of pCLA fed but were not altered with increasing of Megalac inclusion. An amount of fat x type of fat interaction (P < 0.001 for all 3 depots) was also seen with the trans-10, cis-12 isomer, although in perirenal adipose tissue samples, a slight increase with amount of Megalac was identified. In all 3 adipose tissue depots, lambs fed high pCLA had 2-fold greater cis-9, trans-11 CLA content, and trans-10, cis-12 CLA content was over 15-fold greater compared with control lambs.
Muscle Fatty Acid Composition.
Fatty acid composition of the LM is shown in Table 6. There was an effect (P < 0.001) of type of fat on the tissue palmitoleic acid content with lambs fed pCLA having the lowest amounts. There was also an effect (P = 0.02) of type and amount of fat on oleic acid content because oleate decreased with increasing fat and was lowest in lambs fed pCLA diets. There were, however, no differences in the palmitic or stearic acid content of the LM samples.
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Both CLA isomers were identified in samples from all 7 treatments, with the proportion of cis-9, trans-11 CLA remaining higher than that of trans-10, cis-12 CLA. Tissue from lambs fed pCLA had greater (P < 0.001) proportions of cis-9, trans-11 CLA than tissue from lambs fed the Megalac or control diets. Trans-10, cis-12 CLA concentrations increased with increasing amount of pCLA supplement but remained constant on all other dietary treatments (P < 0.001). Although the extent of increase in tissue cis-9, trans-11 CLA content was not as great as in adipose tissue, the trans-10, cis-12 CLA content in lambs fed high pCLA was up to 30-fold greater than observed in the control group.
Liver Fatty Acid Composition.
There was no effect of dietary treatment on the liver palmitic or stearic acid content of liver samples. Lambs fed pCLA had lower levels (P = 0.05) of liver palmitoleic acid than did controls. An amount of fat x type of fat interaction (P = 0.004) was observed for liver oleic acid content. Increasing dietary Megalac increased oleate, whereas increasing dietary pCLA supplementation reduced oleate (Table 6
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Both C18:1 trans-10 and trans-11 were detected in liver; C18:1 trans-10 in tissue from lambs fed all diets and trans-11 generally only in tissue from lambs fed a pCLA diet. Levels of C18:1 trans-10 increased (P = 0.05) with the amount of pCLA and Megalac fed. For liver C18:1 trans-11 concentration, however, an amount of fat x type of fat interaction (P < 0.001) was observed; the concentrations increased with amount of pCLA fed but decreased with amount of Megalac fed.
Both CLA isomers were identified in liver samples; although CLA cis-9, trans-11 was the most abundant in lambs fed the 3 pCLA diets, substantial amounts of CLA trans-10, cis-12 were also detected. The concentrations of cis-9, trans-11 and trans-10, cis-12 CLA increased (P < 0.001 for both) with increasing of pCLA supplementation. Proportions of cis-9, trans-11 CLA also increased with inclusion of Megalac but much less rapidly (levels of cis-9, trans-11 CLA detected in control and Megalac lambs were approximately half that detected in liver samples from lambs fed the low pCLA diet), whereas levels of CLA trans-10, cis-12 were not altered with Megalac supplementation. The extent of increase in tissue CLA content was similar to that in adipose tissue.
Stearoyl-CoA Desaturase and Acetyl-CoA Car-boxylase mRNA Levels.
There were no effects of dietary treatments on ß-actin mRNA levels (Table 7) and so stearoyl-CoA desaturase and acetyl-CoA carboxylase measurements were normalized for the beta-actin control. There were no effects of dietary supplementation on stearoyl-CoA desaturase or acetyl-CoA carboxylase mRNA levels or the ratio of the 2 (Table 7). We suggest that the ratio of stearoyl-CoA desaturase to acetyl-CoA carboxylase would be indicative of the relative rates of desaturation and lipogenesis; however, no treatment effects were observed.
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Park et al., 1997; Sisk et al., 2001) demonstrated that feeding monogastric animals CLA at similar levels promotes a decrease in fat content, often coupled with an increase in lean content. In this study, the CLA mixture fed contained similar levels of cis-9, trans-11 and trans-10, cis-12, and the amount predicted to reach the duodenum was greater than levels used by Ostrowska et al. (1999, 2003a) in pig studies. At their maximum feeding level up to 1.6 g of CLA reached the duodenum per kg of diet fed; whereas in our study, we estimate that in the high pCLA group approximately 5.6 g of CLA reached the duodenum per kg of diet fed; thus an effect of CLA was expected. Subcutaneous adipose tissue from these lambs actually had more trans-10, cis-12 CLA (0.78 g/100 g of fatty acid methyl ester) than Ostrowska et al. (2003a; 0.25 g/100 g of fatty acid methyl ester) reported in the subcutaneous adipose tissue from pigs in which a reduction in carcass fat content was observed.
Although most studies in mice have shown that dietary CLA lowers body fat content, effects of CLA in other species are more variable. Decreases in body fat were observed in rats, hamsters, and pigs in some (Ostrowska et al., 1999; Sisk et al., 2001; Bouthegourd et al., 2002; Ostrowska et al., 2003b) but not all (Eggert et al., 2001; Demaree et al., 2002) studies. The variability in response may relate to dose or composition of CLA supplement or age or strain of animal studied. Reductions in fat content of mice are generally greater than those found in other species (Azain et al., 2000). Limited information is available describing the effect of CLA on carcass composition in ruminants. Gillis et al. (2004a, b) fed rumen-protected CLA to beef cattle and reported no significant effects on carcass parameters, including fat content, although the CLA content of tissues had been moderately enhanced. By contrast CLA (specifically the trans-10, cis-12 isomer) induces milk fat depression in the dairy cow (Baumgard et al., 2001), and recent evidence (Lock et al., 2006) suggests a similar effect in lactating ewes. Thus, not only do there appear to be species differences in the effect of CLA on fat deposition but also differences in tissue responsiveness.
Analysis of the rumen-protected CLA supplement indicated that both isomers were protected equally. However, there was approximately 40% less trans-10, cis-12 CLA in the tissues than cis-9, trans-11 CLA. As the dietary inclusion of pCLA increased, so would levels of C18:1 trans-11, a result of partial hydrogenation of the supplement in the rumen and so increasing the substrate available for stearoyl-CoA desaturase. Thus, it is not possible to determine whether this difference reflects an increased metabolism of trans-10, cis-12 CLA or merely the extra contribution of stearoyl-CoA desaturase to the pool of cis-9, trans-11 CLA. Martin et al. (2000) and Ip et al. (2002) postulated that the rate of ß-oxidation for trans-10, cis-12 CLA might be different from that of cis-9, trans-11 CLA. However, Sergiel et al. (2001) reported that the ß-oxidation of both isomers was essentially the same. It was later suggested that these conflicting results were probably due to differences in the sex and strain of the rat used or the length of the feeding period (Ip et al., 2002). Park et al. (1999) showed that despite feeding mice equal amounts of cis-9, trans-11 and trans-10, cis-12 CLA, the latter was only present at about half the concentration of cis-9, trans-11 CLA in liver, fat pad, and muscle. Additionally, trans-10, cis-12 CLA was cleared faster from the skeletal muscle than cis-9, trans-11 CLA following withdrawal of CLA from the diet. In agreement with Ip et al. (2002) and Martin et al. (2000), Park et al. (1999) concluded that trans-10, cis-12 CLA was preferentially metabolized. Similar differences in the incorporation of CLA isomers have been reported in pigs (Tischendorf et al., 2002) and in rats (Alasnier et al., 2002).
Feeding rumen-protected CLA reduced the concentrations of monosaturated fat (palmitoleate and oleate) in adipose tissue and liver; however, there was no evidence of a change in stearoyl-CoA desaturase mRNA levels. Studies examining the effect of CLA appear to vary with species because some (Lee et al., 1998; Choi et al., 2000; Baumgard et al., 2002) have shown CLA reduces both stearoyl-CoA desaturase enzyme activity and mRNA levels whereas others (Park et al., 2000; Choi et al., 2001) report CLA decreases in stearoyl-CoA desaturase activity directly without changes in gene expression. In reports where CLA inhibited SCD activity (Park et al., 2000; Smith et al., 2002), tissue levels of palmitoleic and oleic acid were reduced, as identified in this study. However, no reduction in conversion of C18:1 trans-11 to cis-9, trans-11 CLA was evident; the provision of more trans-10, cis-12 CLA (inhibitor) is linked to the provision of more C18:1 trans-11 (substrate) and thus an inhibition effect may well have been masked. Contrary to other studies (Baumgard et al., 2001) in which the degree of inhibition of stearoyl-CoA desaturase increased with amount of trans-10, cis-12 CLA fed, here the extent of inhibition of monounsaturated fatty acid synthesis did not increase with additional CLA, suggesting the level of CLA in the lowest diet was potent enough to inhibit enzyme activity to the maximum. The apparent inhibition of stearoyl-CoA desaturase activity may be responsible for the reductions in total lipid content seen when feeding of CLA (Ntambi et al., 1999). Baumgard et al. (2001) also reported that although at their lowest dose SCD index did not differ from that of control, milk fat was still depressed by 25%. Smith et al. (2002) and Beaulieu et al. (2002) also found no effect of a reduction in stearoyl-CoA desaturase index on the adiposity of piglets and heifers, respectively. A trans-10, cis-12 CLA-supplemented diet significantly reduced body fat in wild type and stearoyl-CoA desaturase-1-null mice (Kang et al., 2004). Thus it appears that a decrease in stearoyl-CoA desaturase activity is not a prerequisite for a decrease in fat content.
In conclusion, dietary inclusion of rumen protected CLA will increase the proportions of both cis-9, trans-11 and trans-10, cis-12 CLA in lamb tissues. However, dietary CLA may not reduce the overall fat content of sheep meat.
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Footnotes |
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2 The authors wish to acknowledge C. Bruce (Pfizer) for assistance with this project.
3 Corresponding author: peter.buttery{at}nottingham.ac.uk
Received for publication March 20, 2006. Accepted for publication July 16, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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9 –desaturase. J. Nutr. 130:2285–2291.This article has been cited by other articles:
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