J. Dairy Sci. 88:1685-1693
© American Dairy Science Association, 2005.
Comparison of Calcium Salts and Formaldehyde-Protected Conjugated Linoleic Acid in Inducing Milk Fat Depression*
M. J. de Veth1,
S. K. Gulati2,
N. D. Luchini3 and
D. E. Bauman1
1 Department of Animal Science, Cornell University, Ithaca, NY 14853
2 Faculty of Veterinary Science, University of Sydney/Rumentek (Pty) Ltd., Parkside, SA, Australia
3 Bioproducts Inc., Fairlawn, OH 44333
Corresponding author: D. E. Bauman; E-mail: deb6{at}cornell.edu.
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ABSTRACT
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Abomasal infusion studies have shown that trans-10, cis-12 conjugated linoleic acid (CLA) decreases milk fat synthesis. However, supplements of CLA must avoid rumen biohydrogenation for this technology to be applied to ruminants. Rumen protection methods would reduce CLA metabolism in the rumen and increase its supply to the small intestine. Our objective was to compare the efficacy of 2 forms of rumen-protected CLA at inducing milk fat depression. Three mid to late lactation Holstein cows each fitted with a rumen fistula were used in a 3 x 3 Latin square design. Treatments were: 1) control, 2) calcium salts of CLA (Ca-CLA), and 3) formaldehyde-protected CLA (FP-CLA). Supplements were designed to provide 10 g/d of trans-10, cis-12 CLA and were administered intraruminally once per day to ensure exact delivery of amount. Both CLA treatments substantially reduced milk fat yield and content compared with control, with the reductions in milk fat yield averaging 34% for the Ca-CLA treatment and 44% for the FP-CLA treatment. In contrast, milk yield, milk protein yield, and dry matter intake were unaltered by CLA treatment. Efficiency of transfer of trans-10, cis-12 CLA from the supplement into milk fat was 3.2 and 7.0% for Ca-CLA and FP-CLA, respectively. These values are much lower than transfer efficiencies reported for abomasally infused CLA, suggesting that much of the trans-10, cis-12 CLA present in the 2 formulations was biohydrogenated in the rumen. Overall, the extent of the reduction in milk fat yield indicates that both protection formulations are acceptable methods for the formulation of CLA supplements to induce milk fat depression in lactating dairy cows.
Key Words: conjugated linoleic acid • milk fat • milk fat depression • rumen protection
Abbreviation key: Ca-CLA = calcium salts of conjugated linoleic acid, CLA = conjugated linoleic acid(s), FP-CLA = formaldehyde-protected conjugated linoleic acid, MFD = milk fat depression
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INTRODUCTION
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Conjugated linoleic acids (CLA) represent octadecadienoic fatty acid isomers that comprise a number of different positional and geometric configurations. Under certain dietary conditions, the rumen environment is altered resulting in a shift in biohydrogenation and the production of trans-10, cis-12 CLA, a potent inhibitor of milk fat synthesis (Baumgard et al., 2000; Bauman and Griinari, 2003). The feeding of commercially synthesized lipid supplements high in trans-10, cis-12 CLA concentration presents a unique opportunity to manipulate milk fat synthesis in the dairy cow, but if added as a dietary supplement, rumen-protected formulations of CLA would be needed as a means to prevent biohydrogenation and increase the postruminal supply of CLA.
The 2 formulations of lipid supplements for ruminants most investigated and applied commercially are calcium salts of free fatty acids and formaldehyde-protected lipid. Calcium salts of FFA have typically been used to increase the energy density of the diet and are considered rumen inert as they do not adversely affect microbial degradation of feed (Jenkins and Palmquist, 1984). Formaldehyde protection involves encapsulation of lipid within a formaldehyde-treated protein matrix and enables the use of either FFA or esterified fatty acids (Ashes et al., 1979). The level of protection from rumen metabolism for calcium salts and formaldehyde protection have been extensively investigated for various fatty acids, with protection varying greatly in both in vitro and in vivo studies (Ashes et al., 1979; Doreau et al., 1997; Gulati et al., 1997a,b; Lundy et al., 2004). A number of recent studies have shown that calcium salts of CLA (Ca-CLA) fed to lactating dairy cows are effective at supplying trans-10, cis-12 CLA postruminally and inducing milk fat depression (MFD) (Giesy et al., 2002; Perfield et al., 2002; Bernal-Santos et al., 2003; Moore et al., 2004; Selberg et al., 2004). However, based on the levels of trans-10, cis-12 CLA in the supplement, all of these studies obtained an MFD response smaller than that predicted from a dose-response curve developed using results from abomasal infusion of trans-10, cis-12 CLA (de Veth et al., 2004); this indicates that Ca-CLA are not fully protected from rumen biohydrogenation. There have been no similar studies with formaldehyde-protected CLA (FP-CLA) in lactating cows, but Gulati et al. (2000) showed 30% biohydrogenation of FP-CLA after a 24-h in vitro incubation with rumen fluid.
The objective of the present study was to compare the efficacy of Ca-CLA and FP-CLA, at the same dose of trans-10, cis-12 CLA, at reducing milk fat synthesis in lactating dairy cows.
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MATERIALS AND METHODS
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Three lactating Holstein cows (202 ± 6 DIM; mean ± SE) fitted with rumen fistula were used in a 3 x 3 Latin square experiment. All procedures involving animals were approved by the Cornell University Institutional Animal Care and Use Committee. Cows were housed in metabolic tie stalls at the Large Animal Research and Teaching Unit at Cornell University. The diet was a TMR formulated to meet or exceed nutrient requirements using the Cornell Net Carbohydrate and Protein System (Fox et al., 2004). Cows were fed ad libitum with equal portions of fresh feed offered at 0600 and 1800 h daily (Table 1
). Orts were weighed and recorded on a daily basis. Water was available at all times. Feed samples were collected daily, composited by treatment period, and analyzed by wet chemistry (Dairy One Cooperative, Inc., Ithaca, NY).
Treatments were: 1) control, 2) Ca-CLA, and 3) FP-CLA. The Ca-CLA formulation was prepared by Bioproducts Inc. (Fairlawn, OH) from an FFA mixture of CLA. The FP-CLA formulation was prepared by Rumentek Ltd. (Parkside, SA, Australia) from a methyl ester mixture of CLA. Both the FFA and methyl esters of CLA mixtures were prepared by BASF-AG (Ludwigshafen, Germany), and came from the same production run. The FFA and the methyl ester form of trans-10, cis-12 CLA have been shown to have comparable postruminal digestion efficiency and potency at reducing milk fat synthesis (de Veth et al., 2004). Formulations of Ca-CLA and FP-CLA contained 72 and 42% fat, respectively. Treatments were designed to deliver 10 g/d of trans-10, cis-12 CLA, which corresponded to 51.4 and 85.9 g/d of Ca-CLA and FP-CLA supplements, respectively. The composition of the rumen-protected formulations of CLA and the amount of fatty acids provided each day are presented in Table 2. We chose not to use an unprotected fat source for the control treatment because the amount of fatty acids in the 2 rumen-protected supplements was minimal. The 2 supplements supplied only 16 g/d of fatty acids other than CLA isomers, with about 15 g/d of this being palmitic, stearic, and oleic acids (Table 2). Both rumen-protected formulations were administered intraruminally via the rumen fistula once per day immediately before the a.m. feeding; the control treatment received no supplement. Treatment periods were 7 d with an 8-d interval between periods.
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Table 2. Fatty acid profiles of the conjugated linoleic acid (CLA) supplements and amounts of fatty acids administered intraruminally.
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Cows were milked at 0600 and 1800 h daily. Milk was sampled and yield determined at each milking. One aliquot was stored at 4°C with a preservative (bronopol tablet; D&F Control System, San Ramon, CA) until analyzed for fat and true protein content (Dairy One Cooperative, Inc.) by methods previously described (Bernal-Santos et al., 2003). A second aliquot of milk was stored at –20°C. Fatty acids were extracted from FP-CLA as described by Ashes et al. (1979) and from Ca-CLA using a mixture of 2 N HCl and absolute ethanol (12.5 and 87.5%, respectively). Milk fatty acids were extracted using the method of Hara and Radin (1978). Methyl esters were prepared for the FFA from Ca-CLA using 1% sulfuric acid as described by Christie (1989). Fatty acid methyl esters from the milk fat extract and the FP-CLA supplement were prepared by base-catalyzed transmethylation according to Christie (1982) with modifications by Chouinard et al. (1999). Fatty acid methyl esters were analyzed by gas chromatograph (GCD system HP 6890+; Hewlett Packard, Agilent Technologies, Wilmington, DE) as detailed by Perfield et al. (2002), with the only modification being the use of a CP-SIL 88 fused silica capillary column (100 m x 0.25 mm (i.d.) with 0.2-µm film thickness; Varian, Inc., Walnut Creek, CA).
Data were analyzed using the PROC MIXED procedure of SAS (SAS Institute, 2001) with cow considered a random effect, and period and treatment fixed effects. All data are presented as least squares means. Orthogonal contrasts comparing 1) control vs. CLA treatments (combined Ca-CLA and FP-CLA) and 2) Ca-CLA formulation vs. FP-CLA formulation were conducted using the ESTIMATE statement of SAS.
Data from the present study were combined with results from 7 other investigations where lactating dairy cows were provided a calcium salt formulation of CLA (Giesy et al., 2002; Perfield et al., 2002; Bernal-Santos et al., 2003; Moore et al., 2004; Piperova et al., 2004; Selberg et al., 2004; Castañeda-Gutiérrez et al., 2005). One comparison was the transfer efficiency of the dose of trans-10, cis-12 CLA to milk fat. To calculate this, milk fat content of trans-10, cis-12 CLA in treated cows was first corrected for the content of this isomer in control milk fat and then transfer efficiency was calculated by comparing the amount secreted in milk fat with the dose of trans-10, cis-12 CLA presented as Ca-CLA. In 3 of the studies (Giesy et al., 2002; Piperova et al., 2004; present study), the amount of trans-10, cis-12 CLA secreted in milk fat was reported, whereas in the remaining studies, the amount of trans-10, cis-12 CLA was reported as a proportion of the total fatty acids in milk fat. Values expressed as a proportion of total milk fatty acids were converted to a milk fat basis by assuming milk fat was comprised of 88.2% fatty acids and 11.8% glycerol (de Veth et al., 2004).
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RESULTS AND DISCUSSION
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The intraruminal administration of the CLA formulations ensured an exact daily dose to allow direct comparisons of the efficacy of Ca-CLA and FP-CLA at inducing MFD. Although the CLA was in the form of FFA in the Ca-CLA treatment and as methyl esters in the FP-CLA treatment, they came from the same production run and were essentially a 2-CLA isomer mixture, cis-9, trans-11 CLA and trans-10, cis-12 CLA, in equal proportions (Table 2
). Other studies have shown that milk fat synthesis is reduced by trans-10, cis-12 CLA, but not cis-9, trans-11 CLA (Baumgard et al., 2000; 2002). We have previously shown that FFA and methyl ester forms of CLA are comparable in reducing milk fat synthesis when supplied by abomasal infusion (de Veth et al., 2004). In the present study, the CLA supplements resulted in a progressive reduction in milk fat content through the first few days of the treatment period. A decline was detectable after 2 d and approached a nadir by d 5 to 6 (Figure 1). Therefore, all subsequent performance and milk FA data are means reported from d 6 and 7 of each treatment period.
Overall, the rumen-protected CLA supplements substantially reduced milk fat yield and content compared with control, with the reductions in milk fat yield averaging 34% for the Ca-CLA treatment and 44% for the FP-CLA treatment (Table 3). Dry matter intake, milk yield, and milk protein yield and content were unaltered by CLA treatment or formulation of rumen-protected CLA, and SCC averaged <150,000 across treatments. The specificity of the effects of CLA supplements on milk fat synthesis is consistent with previous studies where rumen-protected formulations of CLA have been fed to lactating dairy cows (Perfield et al., 2002; Moore et al., 2004; Selberg et al., 2004; Castañeda-Gutiérrez et al., 2005).
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Table 3. Intake and milk production results during intraruminal administration of rumen-protected conjugated linoleic acid (CLA).
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When milk fatty acids were grouped based on their origin (Bauman and Griinari, 2003), decreases in response to CLA treatment were obtained for de novo synthesized fatty acids (<16 carbons), preformed fatty acids taken up from circulation (>16 carbons), and those fatty acids derived from both sources (16-carbon fatty acids; Figure 2). The reduction on a molar basis was less for the longer chain fatty acids; CLA treatments resulted in a 51, 49, and 31% decrease in milk fat secretion of fatty acid fractions <16 carbons, 16 carbons, and >16 carbons, respectively. Consequently, the proportion of preformed fatty acids in milk fat was increased with CLA treatment, whereas the short- and medium-chain fatty acids tended to decrease (Table 4). These same effects on milk fatty acid pattern have been reported in previous studies where cows have received Ca-CLA (Perfield et al., 2002; Moore et al., 2004; Castañeda-Gutiérrez et al., 2005), and studies involving abomasal infusion of trans-10, cis-12 CLA, where effects on de novo synthesized fatty acids become more pronounced as the dose of trans-10, cis-12 CLA increases (Baumgard et al., 2000, 2001; Peterson et al., 2002). As expected, the CLA treatments resulted in increased concentrations of trans-10, cis-12 CLA in milk fat, with the increase for the FP-CLA treatment being greater than the Ca-CLA treatment (Table 4). The 4 pairs of fatty acids that serve as a proxy for 
9-desaturase activity were unaltered by the CLA treatments, except for an increase in the desaturase index involving cis-9, trans-11 CLA to trans-11 18:1; this increase is consistent with the transfer of cis-9, trans-11 CLA from the supplement (Table 4). The absence of an effect of CLA treatment on desaturase index was also observed when trans-10, cis-12 CLA was abomasally infused, but only when low doses (<5 g/d) were infused; these results suggest that much of the 10 g/d of trans-10, cis-12 CLA provided in the CLA supplements may have been biohydrogenated in the rumen.
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Figure 2. Secretion of milk fatty acids classified by their origin. Treatments were control (no added lipid), calcium salts of CLA (Ca-CLA), and formaldehyde-protected CLA (FP-CLA). Different letters above bars represent treatment differences within each grouping of fatty acids. Fatty acids <16 carbons originate from de novo synthesis, >16 carbons are obtained from uptake of circulating fatty acids, and 16-carbon fatty acids are derived from both sources.
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When making comparisons of rumen-protected formulations of CLA across studies, it is useful to consider the transfer of trans-10, cis-12 CLA into milk fat as it accounts for alterations by rumen bacteria, bioavailability and absorption from the intestine, and mammary uptake and use for milk synthesis. In the present study, the transfer of trans-10, cis-12 CLA into milk fat for the Ca-CLA and FP-CLA formulations were significantly different (P < 0.005), averaging 3.2 and 7.0%, respectively (SEM = 0.18). This significant difference is consistent with the numerical difference in the reduction in milk fat yield for Ca-CLA and FP-CLA (34 vs. 44%). This difference in milk fat yield did not reach statistical significance, which may relate to the extent of MFD. The MFD for the FP-CLA treatment fell close to the nadir for the maximum reduction for CLA-induced MFD, where large differences in the dose of trans-10, cis-12 CLA have little additional effect on milk fat synthesis. de Veth et al. (2004) summarized studies (n = 7) involving abomasal infusion of trans-10, cis-12 CLA (dose range of 0 to 14 g/d) and demonstrated that the milk fat yield decayed exponentially as the dose of trans-10, cis-12 CLA increased (R2 = 0.86), with the nadir for the reduction being about 48%. For the FP-CLA treatment, this is the first study to examine the use of this protection method with CLA in dairy cows. However, a similar transfer of trans-10, cis-12 CLA into milk fat was observed when dairy cows were provided the same daily dose of trans-10, cis-12 CLA that was protected by forming an amide or lipid encapsulate. Perfield et al. (2004) obtained values of 7.1 and 7.9% transfer of trans-10, cis-12 CLA into milk fat with amide-protected and lipid-encapsulated formulations of CLA, respectively. Similarly, when lactating cows and goats were fed formaldehyde-protected fish oil, the transfer of eicosapentaenoic acid and docosahexaenoic acid into milk fat ranged from 5 to 8% (Kitessa et al., 2001; Gulati et al., 2003).
Relatively more studies have investigated feeding a Ca-CLA supplement to lactating dairy cows, and this allows examination of patterns across these studies. The 8 studies and the 14 levels of CLA supplementation are summarized in Table 5. Studies have involved cows at early, mid, or late lactation and different stages of the reproductive cycle. They have ranged in duration from a few days to 20 wk and all have observed MFD. In established lactation, the CLA-induced reduction in milk fat was immediate, whereas in early lactation there was minimal effect of CLA treatment during the first few weeks postpartum (Bernal-Santos et al., 2003; Selberg et al., 2004; Castañeda-Gutiérrez et al., 2005), unless a higher dose of CLA was used (Moore et al., 2004).
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Table 5. Summary of studies where calcium salts of conjugated linoleic acid (CLA) have been fed to lactating dairy cows.1
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Investigations of Ca-CLA supplements provided a dose range of 4 to 37 g/d of trans-10, cis-12 CLA (Table 5). Milk fat depression ranged from <10 to over 30% (Table 5), and within studies, reductions in milk fat yield occurred in a dose-dependent manner (Giesy et al., 2002; Moore et al., 2004; Castañeda-Gutiérrez et al., 2005). Abomasal infusion of trans-10, cis-12 CLA has been used as a convenient experimental means to bypass rumen metabolism, and de Veth et al. (2004) recently summarized these studies. Results indicated an exponential decay response in the degree of MFD as dose of trans-10, cis-12 CLA increased with a maximum reduction in milk fat yield occurring at about 10 g/d and the effective dose to achieve a milk fat reduction equal to 50% of maximum was 2.6 g/d of trans-10, cis-12 CLA. Clearly, the magnitude of the depression in milk fat at similar doses of abomasally infused trans-10, cis-12 CLA is substantially less in studies involving dietary supplements of Ca-CLA (Table 5).
Differences in response between dietary supplements of Ca-CLA and abomasal infusion of CLA presumably relate to ruminal biohydrogenation of the trans-10, cis-12 CLA in the Ca-CLA supplement given that rates of intestinal absorption of fatty acids derived from calcium salts are similar to that of FFA (Bauman et al., 2003). de Veth et al. (2004) also summarized data on the transfer of abomasally infused trans-10, cis-12 CLA into milk fat and showed that it linearly increased as dose increased (R2 = 0.94), with an average transfer efficiency of 21.8%. Comparison of transfer of trans-10, cis-12 CLA from Ca-CLA with that from abomasal infusion provides an estimate of the extent of rumen biohydrogenation of the CLA isomer. Across all 14 treatments, the Ca-CLA formulations averaged 3.9% for the transfer efficiency to milk fat with the median value being 3.3% (Table 5). By comparison with abomasal infusion equating to 100% protection, these transfer efficiencies for the Ca-CLA supplement equate to 83 to 85% of the CLA metabolized in the rumen and only 15 to 17% protected from rumen biohydrogenation. This level of protection of Ca-CLA is within the range of that previously reported when calcium salts of long-chain polyunsaturated fatty acids were fed to cattle (2 to 31% protection from biohydrogenation; Ferlay et al., 1993; Doreau et al., 1997; Scollan et al., 2001; Lundy et al., 2004). Thus, based on transfer efficiency comparisons, calcium salts afford only very limited protection from biohydrogenation for trans-10, cis-12 CLA.
Jenkins and Palmquist (1984) and Wu et al. (1991) emphasized that supplements involving calcium salts of fatty acids were designed to be ruminally inert with regard to effects on rumen digestion and microbial protein synthesis rather than be protected from rumen biohydrogenation. The range in transfer efficiency of trans-10, cis-12 CLA into milk fat across the studies using Ca-CLA supplements was 1.9 to 7.4% (Table 5), and this would represent 9 to 34% protection. The basis for this range in protection may reflect differences in the Ca-CLA formulations or in analytical differences in quantifying milk fat content of CLA isomers among laboratories. Additionally, differences in passage rate of digesta from the rumen may have contributed to some of the variation in estimated protection of Ca-CLA across studies as passage rate influences both rumen pH and the residence time of the material in the rumen (Fox et al., 2004). Although the transfer of trans-10, cis-12 CLA into milk fat appears low, when trans-10, cis-12 CLA was fed as an unprotected FFA to lactating dairy cows, its relative transfer into milk fat was less than half that of Ca-CLA in the only reported study comparing these 2 forms of CLA supplement (Hawley et al., 2001).
A similar calculation to estimate rumen protection can be made for FP-CLA (present study) and the formulations of amide-protected and lipid-encapsulated CLA reported by Perfield et al. (2004). These 3 methods of protection had similar transfer efficiencies of trans-10, cis-12 CLA into milk fat and comparison with transfer efficiencies observed with abomasal infusions suggests that they gave 32 to 36% protection for the trans-10, cis-12 CLA against rumen biohydrogenation. In contrast, Gulati et al. (2000) found the degree of protection of FP-CLA in vitro was approximately 70%, which is similar to that reported by Gulati et al. (1997a) for the metabolism of 18:1, 18:2, and 18:3 in canola/soybean supplements. However, using the same in vitro techniques (Gulati et al., 1997a, 2000), these investigators demonstrated that in vitro methods overestimate in vivo protection of formaldehyde-treated lipid, with 70% biohydrogenation protection predicted from in vitro studies equating to 29 to 52% protection from biohydrogenation as measured in vivo (Ashes et al., 1979).
To date, trans-10, cis-12 CLA is the only rumen biohydrogenation intermediate that has been shown to unequivocally inhibit milk fat synthesis, but Bauman and Griinari (2003) suggested that other unique rumen-derived fatty acids likely exist that can cause diet-induced MFD. By comparison with dose-response curves generated from abomasal infusion studies (de Veth et al., 2004), the reduction in milk fat yield observed with the supplements in the present study was greater than predicted from the milk fat content of trans-10, cis-12 CLA. This was also observed by Perfield et al. (2002) and Piperova et al. (2004) for Ca-CLA, and both groups suggested that some of the fatty acids in the CLA supplements might have been metabolized in the rumen to unique fatty acids that inhibited milk fat synthesis. Verifying this possibility and identifying additional biohydrogenation intermediates that inhibit milk fat synthesis during diet-induced MFD or when CLA-supplements are fed are important areas for future research.
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CONCLUSIONS
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Supplementing dairy cows with rumen-protected forms of CLA such as Ca-CLA or FP-CLA substantially reduced the yield and content of milk fat without altering other production responses. A summary of results from all studies with Ca-CLA indicates that the reduction in milk fat synthesis is consistent, occurs in a dose-dependent manner, and has no adverse effects on cow health or performance. The transfer of trans-10, cis-12 CLA into milk fat for both Ca-CLA and FP-CLA supplements was much lower thanb that previously reported when CLA was supplied postruminally, indicating that much of the trans-10, cis-12 CLA was biohydrogenated in the rumen. However, the extent of the reduction in milk fat yield indicates that both protection forms are effective methods for the formulation of CLA supplements to induce MFD in lactating dairy cows. Future research should be directed at improving existing protection methods or developing new methods of protection to reduce the extent of biohydrogenation of trans-10, cis-12 CLA in the rumen.
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ACKNOWLEDGEMENTS
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The authors greatly acknowledge the assistance of E. Castañeda-Gutiérrez, D. Dwyer, C. McConnell, J. McFadden, S. Beam, W. English, and G. Birdsall in implementing the study.
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FOOTNOTES
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* Supported in part by Bioproducts Inc. (Fairlawn, OH), BASF AG (Ludwigshafen, Germany), and Cornell Agricultural Experimental Station. 
Received for publication November 16, 2004.
Accepted for publication February 4, 2005.
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TOP
ABSTRACT
INTRODUCTION
), and formaldehyde-protected CLA (
). The CLA formulations provided 10 g/d of trans-10, cis-12 CLA, and the 7-d treatment period is indicated by broken lines. The milk fat content SEM averaged 0.3% during the infusion period.