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Dairy Science Department, South Dakota State University, Brookings 57007-0647
Corresponding author: D. J. Schingoethe; e-mail: david_schingoethe{at}sdstate.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: conjugated linoleic acid • vaccenic acid • rumen digesta • plasma triglycerides
Abbreviation key: CLA = conjugated linoleic acid, DHA = docosahexaenoic acid, ECM = energy-corrected milk, FO = fish oil, EPA = eicosapentaenoic acid, HLO = high linoleic acid, HLN = high linolenic acid, HO = high oleic acid, HS = high stearic acid, TVA = vaccenic acid
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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In the rumen, cis-9, trans-11 CLA is formed primarily from isomerization of dietary linoleic acid (C18:2n6) during the first step of the biohydrogenation process (Harfoot and Hazlewood, 1988). Once the cis-9, trans-11 CLA is formed, biohydrogenation of the cis-9 bond occurs by microbial reductase (group A microorganisms) to form vaccenic acid (TVA; trans-11C18:1). The extent to which TVA is hydrogenated to stearic acid (C18:0; group B microorganisms) depends on conditions in the rumen (Jenkins, 1993). Dietary linolenic acid (C18:3n3) also undergoes biohydrogenation by being first isomerized to a conjugated triene (cis-9, trans-11, cis-15 C18:3), followed by reductions of double bonds at carbons 9, 15, and 11 to yield trans-11, cis-15 C18:2, TVA, and C18:0, respectively (Wilde and Dawson, 1966). The high correlation reported by Jiang et al. (1996) between cis-9, trans-11 CLA and TVA in milk fat led Griinari et al. (1997) to hypothesize that a portion of cis-9, trans-11 CLA appearing in milk fat was of endogenous origin. Subsequent work (Griinari et al., 2000; Corl et al., 2001) showed that approximately 64 to 78% of cis-9, trans-11 CLA appearing in milk fat is synthesized in the mammary gland from TVA via delta-9 desaturase.
Our previous research (Whitlock et al., 2002; AbuGhazaleh et al., 2002a; AbuGhazaleh et al., 2003) demonstrated that feeding fish oil (FO) along with mono- and polyunsaturated fatty acid oils, especially oils high in C18:2n6, increased the concentrations and yields of milk cis-9, trans-11 CLA and TVA. The purpose of the current study was to determine the effects of FO supplementation of diets differing in fatty acid profiles on rumen, plasma, and milk fatty acid profiles with emphasis on cis-9, trans-11 CLA and TVA.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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) were composed of 50% (dry basis) concentrate mix, 25% corn silage, 12.5% alfalfa silage, and 12.5% alfalfa hay. Menhaden FO (Omega Protein Inc., Hammond, LA) was used in this experiment. Rumo-fat (Robt Morgan Inc. Paris, IL) was used as a source of C18:0. Regular sunflower seeds and flax seeds were obtained from local dealers. A local farmer donated the high oleic sunflower seeds. Sunflower and flax seed shells were cracked by rollers; however, because flax seeds are quite small, most of the seed shells remained intact. Fatty acid profiles of diets and fat supplements are given in Table 2.
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Concentrate mixes, alfalfa hay, haylage, and corn silage were sampled weekly and stored frozen at -20°C until processed for further analysis. For analysis, samples were dried in an oven at 55°C for 48 h, ground through a model no. 3 Wiley mill (Arthur H. Thomas Co., Philadelphia, PA) with a 2-mm screen, and composited by period. Feed samples were dried for 24 h at 105°C for determination of DM content. Contents of CP, ether extract, ash, Ca, P, and Mg were determined by AOAC (1997) methods. For analysis of NDF, ADF, and acid detergent lignin, the sample was reground through an ultracentrifuge mill (Brinkman Instruments Co., Westbury, NY) with a 1-mm screen. NDF (procedure B, Van Soest et al., 1991), ADF (Robertson and Van Soest, 1981), and acid detergent lignin (Lowry et al., 1994) were determined by ANKOM fiber analyzer using Filter Bag Technique (ANKOM Technology Corp., Fairport, NY). The BCS (Wildman et al., 1982) and BW were recorded at the beginning of the experiment and the end of each period.
Samples of ruminal contents were collected at 2 and 6 h after the morning feeding on d 27 and at 4 h on d 28 of each period. Contents (approximately 450 g) were removed by hand from four different locations in the rumen and mixed. Additional ruminal contents were taken and squeezed through four layers of cheesecloth, and 100 ml of the fluid was added to each sample. Ruminal samples were then placed into resealable plastic bags and stored on ice until processing in the laboratory. Every sample was mixed one more time by hand, subsampled (approximately 200 g), and oven dried at 38°C for 48 h. Dried samples were then ground to pass a 0.5-mm screen and composited into one sample per cow per period. Methods used to extract and determine ruminal fatty acids composition were described previously (AbuGhazaleh et al., 2002b).
Blood samples (50 ml) were obtained from the jugular vein at 4 h after the morning feeding on d 28 of each period. Blood was collected into a 50-ml tube containing 0.5-ml heparin and placed on ice immediately until processing in the laboratory. Blood was centrifuged at 3000 x g for 15 min for harvesting plasma. Plasma was stored at -20°C until analysis. Lipids were extracted from plasma (15 ml) with chloroform/methanol (2:1, vol/vol). The plasma triglyceride fraction was separated on a 500-mg silicic acid column (309250, Alltech Assoc., Deerfield, IL) according to Christie (1982). The residues (phospholipids, cholesterol esters, and free fatty acids) were dissolved in hexane, dried under N2, and analyzed for fatty acid profiles at 65:1 split ratio as described for milk samples (AbuGhazaleh et al., 2002a). Analysis of total fatty acids of plasma triglyceride fraction required injection of 3 µl of butyl esters at a 15:1 split ratio. Fatty acids were then determined as described for milk samples (AbuGhazaleh et al., 2002a).
Samples of alfalfa hay, alfalfa haylage, corn silage, and concentrate mix were composited into TMR within each treatment period and fat was extracted in a mixture of ether and acetone (1:1, vol/vol). Approximately 15 mg of the extracted fat was transferred into 13- x 100-mm test tubes with Teflon-lined screw caps and then analyzed for fatty acids as described by AbuGhazaleh et al. (2002a). Nonadecanoic acid (C19:0), dissolved in butanol, was used as an internal standard for feed fatty acid analysis.
Data were analyzed as a Latin square using the mixed model procedures of SAS (1996) with fixed effects of periods and treatments; the random effect was cow. Least significant difference at P < 0.10 was used to determine significant differences among means.
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RESULTS AND DISCUSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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. Diets contained similar DM, CP, ADF, and NDF. Acid detergent fiber and NDF concentrations for the HS were balanced by adding soy hulls (Table 1). The CP content of all diets were lower than anticipated because of a lower CP for alfalfa hay than anticipated. The four fat supplements were chosen because of the differences in their fatty acids composition (Table 2) and the measured profiles were typical of the fat supplements. Rumo-fat showed high contents (64.2%) of C18:0. Oleic acid (cis-9 C18:1, 83.9%) was the major fatty acid in high oleic sunflower seeds, while C18:2n6 (60%) was the major fatty acid in regular sunflower seeds. The flax seeds and FO were characterized by their contents of omega-3 fatty acids. C18:3n3 (50.1%) is the major fatty acid in flax seeds, while C20:5n3 (eicosapentaenoic acid, EPA, 10.9%) and C22:6n3 (docosahexaenoic acid, DHA, 11.9%) were the main polyunsaturated fatty acids in FO.
Milk Yield, Milk Composition, and DMI
Table 3 gives mean values for concentrations and yields of major milk constituents. Treatment had no significant effect on milk production (P = 0.30), although there was a trend towards higher milk production for cows fed the HS and the HO diets (P < 0.15). The HO and the HLO diets depressed milk fat concentration compared with values of the other two diets. Cows fed the HS had similar milk fat percentages to cows fed the HLN. The HLO caused the greatest depression in milk fat percentages and accordingly had the lowest fat, 3.5% FCM, and energy-corrected milk (ECM) yields, while the HS had the highest fat, 3.5% FCM, and ECM yields. Milk true protein percentages and yields, total milk solids percentages and yields, SCC, BW, BCS, and DMI were not different among treatments (P > 0.10). Further discussions about the effect of these treatments on milk yield, milk composition, and DMI by cows in a companion study are reported elsewhere (AbuGhazaleh et al., 2003).
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The high proportion of cis-9 C18:1, C18:2n6, and C18:3n3 acids in ruminal content of cows fed the HLN diet indicates that flax seeds were partially protected from microbial biohydrogenation. Additionally, the high proportion of ruminal cis-9 C18:1 and C18:2n6 acids with the HO and the HLO diets, respectively, indicates that biohydrogenation of these fatty acids did not proceed to completion. Greater intake of dietary C16:0 (132, 91, 94, and 89 g/d for HS, HO, HLO, and HLN, respectively) and C18:0 (185, 33, 32, and 29 g/d for HS, HO, HLO, and HLN, respectively) explain the higher proportion of these fatty acids in ruminal digesta of cows fed the HS diet.
The degree of biohydrogenation of individual fatty acids could not be estimated in this study; however, others (Wu et al., 1991; Kalscheur et al., 1997; Wachira et al., 2000; Lock and Garnsworthy, 2002) have reported different rates of biohydrogenation of cis-9 C18:1, C18:2n6, and C18:3n3 fatty acids. Wachira et al. (2000) reported that biohydrogenation of C18:2n6 and C18:3n3 ranged between 80 and 93% when lambs were fed FO and/or whole linseed. When Kalscheur et al. (1997) fed high cis-9 C18:1 and C18:2n6 sunflower oil to dairy cows at 3.7% of dietary DM, biohydrogenation of cis-9 C18:1c9, C18:2n6, and C18:3n3 acids ranged from 72 to 85%. Wu et al. (1991), however, observed a lesser biohydrogenation of cis-9 C18:1 where the level of biohydrogenation varied from 71% when cows were offered a linseed diet to 60% when cows were offered a FO diet. Previous researchers (Kalscheur et al., 1997; Beam et al., 2000; Jenkins and Adams, 2002) reported that the factors with the greatest influence on rates of biohydrogenation of unsaturated fatty acids were rumen pH, amount of added fat, number of double bonds in fatty acid, and ruminal turnover. Variation in rates was relatively small according to diet, time of day that the inoculum was collected, or degree of esterification of the added fat (Beam et al., 2000).
The proportion of C18:1 trans isomers in ruminal digesta was increased (P < 0.10) when cows were fed the HO, HLO, and the HLN compared with the HS diet, and was greatest with the HLO diet (Table 4). As has been noted herein and by others (AbuGhazaleh et al., 2002b; Piperova et al., 2002), TVA is the major trans-C18:1 isomer in the rumen and duodenum fatty acids. The significant increase in trans-C18:1 fatty acids in general, and TVA in particular, with the HO compared with the HS diet support the finding of Mosley et al. (2002) that cis-9 C18:1 could serve as a precursor for several trans-fatty acid isomers including TVA. The cis-9 C18:1 might have also interfered with biohydrogenation of other polyunsaturated fatty acids in the diet, resulting in the accumulation of trans-C18:1 (Mosley et al., 2002). In addition, cows fed the HO diet had a slightly greater intake of C18:2n6 (177 vs. 156 g/d.) compared with cows fed the HS diet. This also could have contributed to greater ruminal content of TVA for cows fed the HO diet compared with cows fed the HS diet. The fact that the HLN diet had lesser ruminal TVA concentration compared with HLO diet further support our speculation that flax seeds were partially protected from ruminal biohydrogenation.
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The concentration of cis-9, trans-11 CLA in ruminal digesta was also increased (P < 0.04) with the HO, HLO, and the HLN compared with the HS diet (Table 4), and there were no significant differences between cows fed the HO, HLO, and the HLN diets. This lack of differences might indicate that hydrogenation of C18:2n6 into cis-9, trans-11 CLA in the HLO diet was not a rate-limiting step. It is not clear why cis-9, trans-11 CLA concentration was high with the HO and the HLN diets. The cis-9 C18:1 and C18:3n3 or their derivatives might have caused a shift in rumen microbial populations and/or interfered with the biohydrogenation of C18:2n6 in the diet, resulting in the formation of cis-9, trans-11 CLA. The effect of mono- and polyunsaturated fatty acids in rumen microbial populations and biohydrogenation is an area that needs further investigation. The greater TVA to cis-9, trans-11 CLA ratio in the rumen digesta for cows fed all diets compared with milk indicated that fat supplements increased milk cis-9, trans-11 CLA concentration mainly by increasing ruminal production of TVA, which also illustrates the significant role the mammary delta-9 desaturase plays in milk CLA production (Piperova et al., 2002).
Another CLA isomer of interest is trans-10, cis-12. Recent studies (Baumgard et al., 2001; Peterson et al., 2002) have established a relation between milk fat depression and the increase trans-10, cis-12 CLA content in milk fat. Milk fat concentration was reduced by 24, 37, and 46% when cows received 3.5, 7.0, and 14.0 g/d of trans-10, cis-12 CLA (Baumgard et al., 2001). Baumgard et al. (2002) reported that trans-10, cis-12 CLA inhibits milk fat synthesis by decreasing the mRNA expression of acetyl CoA carboxylase, fatty acid synthetase, lipoprotein lipase, and other enzymes involved in uptake and transport, de novo synthesis, and triglyceride formation of circulating fatty acids. Ruminal concentration of trans-10, cis-12 CLA tended to be greater (P < 0.11) with the HO and the HLO diets compared with the HS and HLN diets (Table 4) and corresponds with the decrease in milk fat with the HO and the HLO diets (Table 3). It is not clear why trans-10, cis-12 CLA is high in the HO diet, but as indicated before, cis-9 C18:1 or its derivatives might have interfered with the biohydrogenation of C18:2n6 in the diet, resulting in the formation of trans-10, cis-12 CLA. Evidence indicates that under some dietary conditions, such as a high grain diet, an increased activity of bacterial cis-9, trans-10 isomerase becomes the dominant first step in biohydrogenation, resulting in formation of trans-10, cis-12 CLA from C18:2n6 (Bauman et al., 2000).
There was a substantial decrease in the concentrations of EPA and DHA in the ruminal digesta fatty acids compared with dietary fatty acids (Tables 2 and 4). This was probably caused by biohydrogenation of EPA and DHA. Wachira et al. (2000) reported biohydrogenation values between 72 and 79% for EPA and DHA in diets that contained FO or linseed and FO. The lower proportion of DHA in rumen digesta across diets compared with EPA might indicate that DHA disappeared at a greater rate than EPA.
Fatty Acid Composition of Plasma Triglycerides and Nontriglyceride Fraction
Phospholipids and cholesteryl esters are the principal components of blood lipid and together account for about 95% of the total lipids in the plasma of ruminant animals. However, triglycerides and free fatty acids represent <5% and 1% of total plasma lipid, respectively (Christie, 1981). Polyunsaturated fatty acids that escape ruminal biohydrogenation are preferentially esterified to the plasma cholesteryl esters and phospholipid (Christie, 1981). Plasma cholesteryl esters and phospholipids have comparatively slow turnover, while triglyceride and free fatty acids fractions have a rapid turnover and supply fatty acids to other tissues such as the mammary gland and adipose tissue (Christie, 1981). Therefore, the profile of fatty acids of plasma triglycerides represents the profile of fatty acids available to the mammary gland.
The profile of fatty acids in plasma triglycerides and nontriglyceride fractions are shown in Tables 5 and 6. There is a clear difference in the distributions of fatty acids in the plasma triglycerides and nontriglyceride fractions. The proportion of polyunsaturated fatty acids, C18:2n6, C18:3n3, and EPA, were higher in the nontriglyceride fraction. Another important difference between the fatty acid profiles of plasma triglycerides and nontriglyceride fractions is the distribution of trans C18:1 and CLA isomers (Tables 5 and 6). Both trans C18:1 and CLA isomers were preferentially incorporated into plasma triglycerides, except for trans-10, cis-12 CLA, which showed greater incorporation into plasma nontriglyceride fractions. This greater incorporation of trans-10, cis-12 CLA into plasma nontriglyceride fractions may explain the low transfer efficiency (20.9 4.1%) of this isomer into milk fat when Baumgard et al. (2001) infused trans-10, cis-12 CLA into the abomasum. Loor et al. (2002) studied the effect of feeding extruded soybeans to lactating cows on plasma fatty acid profiles. They observed that TVA was exclusively found in plasma triglycerides. In our study, the free fatty acids were part of the nontriglyceride fraction, which might explain the presence of small amounts of TVA in this fraction. Kitessa et al. (2001); however, fed tuna oil to sheep and observed that trans-C18:1 were increased in plasma triglyceride, free fatty acid, and phospholipid fractions.
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). However, there were no differences among treatments in the concentration of cis-9, trans-11 CLA in plasma triglycerides. This lack of increase in plasma cis-9, trans-11 CLA was unexpected but might be related to changes in the delta-9 desaturase enzyme activity in the intestinal mucosa. Bickerstaffe and Annison (1969) demonstrated the presence of delta-9 desaturase in the intestinal tissues of ruminants, but enzyme activity was low. Baumgard et al. (2002) reported that the activity of delta-9 desaturase was reduced when trans-10, cis-12 CLA was infused into the abomasum at a higher level (7 and 14 g/d) but not at a low level (3.5 g/d). Cows fed the HS diet had the least proportion of trans-10, cis-12 CLA in their ruminal digesta (Table 4).
The addition of high cis-9 C18:1 sunflower, C18:2n6 sunflower, and flax seed increased (P < 0.10) the proportion of cis-9 C18:1, C18:2n6, and C18:3n3 FA in plasma triglycerides, respectively (Table 5). The high proportion of cis-9 C18:1, C18:2n6, and C18:3n3 acids in plasma triglycerides indicates that biohydrogenation of these fatty acids did not proceed to completion in the rumen. The proportion of DHA in plasma triglycerides was greater than that of EPA, which explains why DHA concentration is greater than EPA in milk fat (Table 7). When Kitessa et al. (2001) fed tuna oil to sheep, they observed a greater concentration of DHA in plasma triglycerides compared with EPA; however, EPA was incorporated to a greater degree into plasma cholesteryl esters compared with DHA.
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, 5, and 6) were seen in this study. The temp and run program used for fatty acid analysis on our gas chromatograph lead to an extensive amount of fatty acid isomers separation (100 to 130 fatty acid isomers), where most of them were unknown to us since we did not have standards for them.
Fatty Acid Composition of Milk
Another objective of this study was to determine the effects of cis-9 C18:1, C18:2n6, and C18:3n3 acids on cis-9, trans-11 CLA and TVA concentration in milk fat. We are not aware of previous investigations of milk fat CLA with diets containing FO and high cis-9 C18:1 or C18:3n3 sources. However, others (Dhiman et al., 2000; Chouinard et al., 2001; Lock and Garnsworthy, 2002) have added plant oil alone or Ca salts of plant oil high in cis-9 C18:1 and C18:3n3 and observed an increase in milk cis-9, trans-11 CLA concentrations. In this study, the concentrations of cis-9, trans-11 CLA were increased (P < 0.10) when cows were fed the HO, HLO, and the HLN compared with the HS, and were greatest with the HLO (Table 7). Because of the drop in milk fat content, cis-9, trans-11 CLA yields were increased (P < 0.10) only with the HLO diet. Milk fat concentrations of cis-9, trans-11 CLA did not differ (P > 0.10) between cows fed the HO and the HLN. The fact that our HLN did not increase cis-9, trans-11 CLA concentrations over the HO might have been due to the low availability of flax seed oil for ruminal biohydrogenation (Table 4). High milk trans-10, cis-12 CLA concentrations for the HO and HLO compared with the HLN and HS explain the lower milk fat content with these diets. Recent studies (Baumgard et al., 2001; Peterson et al., 2002) have established a relation between milk fat depression and the increase trans-10, cis-12 CLA content in milk fat.
Unfortunately, the presence of trans-9, trans-11 CLA at this level in milk fat indicates that some isomerization of cis-9, trans-11 CLA occurred during butylation. Consequently, the reported isomer distributions should be interpreted with caution. Acid catalyzed methylation has been shown to cause isomerization of cis-, trans-CLA to their corresponding trans-, trans-CLA isomers and/or convert them to allylmethoxy derivatives (Kramer et al., 1997).
As with cis-9, trans-11 CLA, the concentration of TVA in milk fat increased (P < 0.10) when cows were fed the HO, HLO, and the HLN compared with the HS and were greatest with the HLO (Table 7). However, TVA yields were similar for the HS and the HO diets (Table 8). Additionally, milk fat concentrations and yields of TVA did not differ (P > 0.10) between cows fed the HO and the HLN diets. Feeding FO (Whitlock et al., 2002) or FO as fish meal with extruded soybeans (AbuGhazaleh et al., 2002a) increased milk TVA concentrations by three- to five-fold. When Chouinard et al. (2001) fed dietary supplements of Ca salts of fatty acids from canola oil, soybean oil, and linseed oil, milk TVA concentrations increased and were greatest for cows fed Ca salts of soybean oil, intermediate for cows fed Ca salts of linseed oil, and least for cows fed Ca salts of canola oil. The lower availability of flax seed oil for ruminal biohydrogenation may have been the reason for lack of differences in TVA concentration in milk from cows fed the HO and the HLN. Further discussion about the effect of these treatments on milk fatty acid profiles by cows in a companion study are reported elsewhere (AbuGhazaleh et al., 2003).
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). Previously, this isomer was misidentified as cis-6 C18:1 by our laboratory (AbuGhazaleh et al. 2002a, AbuGhazaleh et al., 2002b; Whitlock et al., 2002). A few milk samples from this experiment were sent to Bauman’s laboratory, where it was confirmed that the peak previously identified by our laboratory as cis-6 C18:1 was trans-10 C18:1. As a result, values previously reported as cis-6 C18:1 by our group should be amended and considered values for trans-10 C18:1. |
CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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FOOTNOTES |
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2 Present address: Department of Animal and Veterinary Science, Clemson University, Clemson, SC 29634.
Received for publication November 8, 2002. Accepted for publication April 19, 2003.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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-9-desaturase in the production of cis-9, trans-11 CLA. J. Nutr. Biochem. 12:622–630.[Medline]
-9 desaturase. J. Nutr. 130:2285–2291.This article has been cited by other articles:
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  M. Bharathan, D. J. Schingoethe, A. R. Hippen, K. F. Kalscheur, M. L. Gibson, and K. Karges Conjugated Linoleic Acid Increases in Milk from Cows Fed Condensed Corn Distillers Solubles and Fish Oil J Dairy Sci, July 1, 2008; 91(7): 2796 - 2807. [Abstract] [Full Text] [PDF]
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P. J. Moate, W. Chalupa, R. C. Boston, and I. J. Lean Milk Fatty Acids. I. Variation in the Concentration of Individual Fatty Acids in Bovine Milk J Dairy Sci, October 1, 2007; 90(10): 4730 - 4739. [Abstract] [Full Text] [PDF]
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A. A. AbuGhazaleh and L. D. Holmes Diet Supplementation with Fish Oil and Sunflower Oil to Increase Conjugated Linoleic Acid Levels in Milk Fat of Partially Grazing Dairy Cows J Dairy Sci, June 1, 2007; 90(6): 2897 - 2904. [Abstract] [Full Text] [PDF]
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A. A. AbuGhazaleh and W. R. Buckles The Effect of Solids Dilution Rate and Oil Source on Trans C18:1 and Conjugated Linoleic Acid Production by Ruminal Microbes in Continuous Culture J Dairy Sci, February 1, 2007; 90(2): 963 - 969. [Abstract] [Full Text] [PDF]
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J. J. Loor, A. Ferlay, A. Ollier, M. Doreau, and Y. Chilliard Relationship Among Trans and Conjugated Fatty Acids and Bovine Milk Fat Yield Due to Dietary Concentrate and Linseed Oil J Dairy Sci, February 1, 2005; 88(2): 726 - 740. [Abstract] [Full Text] [PDF]
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A. A. AbuGhazaleh, D. J. Schingoethe, A. R. Hippen, and K. F. Kalscheur Conjugated Linoleic Acid Increases in Milk When Cows Fed Fish Meal and Extruded Soybeans for an Extended Period of Time J Dairy Sci, June 1, 2004; 87(6): 1758 - 1766. [Abstract] [Full Text] [PDF]
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