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Changes in Milk Fat in Response to Dietary Supplementation with Calcium Salts of Trans-18:1 or Conjugated Linoleic Fatty Acids in Lactating Dairy Cows

¹ Animal and Avian Sciences Department, and
² Department of Chemistry and Biochemistry, University of Maryland, College Park 20742
³ US Food and Drug Administration, Center for Food Safety and Applied Nutrition, College Park, MD 20742
⁴ Bioproducts Inc., Fairlawn, OH 44333

Corresponding author: R. A. Erdman; e-mail: erdman{at}umd.edu.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Milk fat was investigated in lactating dairy cows fed diets supplemented with Ca salts of trans fatty acids (Ca-tFA) or Ca salts of conjugated linoleic acids (Ca-CLA). Forty-five Holstein cows (115 days in milk) were fed a control diet (51% forage; dry matter basis) supplemented with 400 g of EnerG II (Ca salts of palm oil fatty acids) for 2 wk; subsequently, 5 groups of 9 cows each were assigned for 4 wk to the control diet or diets containing 100 g of Ca-CLA or 100, 200, or 400 g of Ca-tFA in a randomized block design. Treatments had no effect on dry matter intake, milk production, protein, lactose, or somatic cell count. Milk fat percentage was reduced from 3.39% in controls to 3.30, 3.04, and 2.98%, respectively, by the Ca-tFA diets and to 2.54% by the Ca-CLA diet. Milk fat yield (1.24 kg/d in controls) was decreased by 60, 130, and 190 g/d with increasing dose of Ca-tFA and by 290 g/d with the Ca-CLA supplement. Consistent with increased endogenous synthesis of cis-9-containing CLA from precursors provided by the Ca-tFA diets, total CLA were similar in milk of cows fed Ca-CLA or Ca-tFA. Compared with controls, the Ca-CLA diet increased trans-10, cis-12-18:2 yield in milk, without altering levels of trans-18:1 isomers. In contrast, yields of most trans-18:1 isomers were elevated in milk of cows fed Ca-tFA diets, whereas yields of trans-10, cis-12-18:2 remained similar to control values. We conclude that milk fat depression can occur without an increase in trans-10, cis-12-18:2 in milk and that other components, perhaps the trans-10-18:1 isomer, may be involved.

Key Words: lactating cow • trans fatty acids • conjugated linoleic acids

Abbreviation key: Ca-CLA = Ca salt of conjugated linoleic acids, Ca-tFA = Ca salt of trans-18:1 fatty acids, CLA = conjugated linoleic acids, FAME = fatty acid methyl ester, MFD = milk fat depression, PUFA = polyunsaturated fatty acids, SFA = saturated fatty acids, tFA = trans-18:1 fatty acids

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Trans-18:1 fatty acids (tFA) and conjugated linoleic acids (CLA) produced during biohydrogenation of polyunsaturated fatty acids (PUFA) in the rumen are mixtures of positional isomers (Katz and Keeney, 1966; Griinari and Bauman, 1999), which subsequently are incorporated into milk fat of lactating cows (Parodi, 1977; Griinari and Bauman, 1999; Loor and Herbein, 2001; Piperova et al., 2002; Precht et al., 2002). Studies have demonstrated that levels of tFA (Kalscheur et al., 1997a; Griinari et al., 1998; Piperova et al., 2000) and CLA isomers (Piperova et al., 2000, 2002; Peterson et al., 2003) increase in milk fat of lactating cows fed a variety of diets associated with milk fat depression (MFD). Because of the active biohydrogenation process in the rumen, abomasal infusion has been the best approach to study effects of specific isomers on milk fat synthesis. Using abomasal infusion of trans-10, cis-12-18:2, Baumgard et al. (2000) provided evidence that this is one isomer involved in MFD. The role of tFA in MFD has been examined using partially hydrogenated vegetable oils, and we have previously shown (Gaynor et al., 1994; Romo et al., 1996) that abomasal infusion of partially hydrogenated vegetable oils in lactating cows results in elevated amounts of tFA in milk and a 14 to 25% reduction in milk fat percentage.

Griinari et al. (1998) and Griinari and Bauman (1999) reported a specific association between dietary-induced MFD and increased trans-10-18:1 in milk of lactating cows and found a linear relationship between trans-10-18:1 and trans-10, cis-12-18:2. Griinari and Bauman (1999) suggested that the trans-10-18:1 resulted from trans-10, cis-12-18:2 during rumen biohydrogenation, and recently Loor and Herbein (2001) provided direct evidence for this hypothesis. Subsequently, others have reported an increase in the concentrations of trans-10, cis-12-18:2 (Piperova et al., 2000; Peterson et al., 2003) and trans-10-18:1 (Newbold et al., 1998; Piperova et al., 2000; Piperova et al., 2002; Peterson et al., 2003) in milk of lactating cows fed MFD diets. Because of the concomitant increase in trans-10, cis-12-18:2 with trans-18:1 isomers, and especially trans-10-18:1, it has been difficult to demonstrate an independent effect of tFA during dietary-induced MFD.

Feeding diets supplemented with Ca salts of fatty acids is a practical way to bypass rumen biohydrogenation. Studies have already shown that diets supplemented with Ca salts of CLA (Ca-CLA) effectively reduce milk fat percentage and yield in lactating cows (Giesy et al., 2002; Perfield II et al., 2002; Bernal-Santos et al., 2003). Dietary Ca salts of tFA (Ca-tFA) supplementation could potentially increase the postruminal availability of trans-18:1 fatty acids and provide an alternative to abomasal infusion to test the potential effects of trans-18:1 fatty acids on milk fat synthesis. Hence, this study was undertaken to examine the effects of a dietary Ca-tFA or Ca-CLA supplementation on milk fat content and fatty acid isomer profile in lactating dairy cows.

	MATERIALS AND METHODS

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Animals, Treatments, and Sampling
The experiment was conducted according to a protocol approved by the University of Maryland Institutional Animal Care and Use Committee. The Ca-fatty acid supplements used in this study were provided by Bio-products Inc., (Fairlawn, OH). Forty-five lactating Holstein dairy cows (15 primiparous and 30 multiparous) at approximately 115 DIM were fed a control diet containing 51% forage and 49% concentrate (DM basis), supplemented with 400 g of EnerG II (Ca salts of palm oil fatty acids) during a 2-wk adjustment period. After the adjustment period, cows (n = 9 per group) were assigned to 1 of 5 treatments: control or 4 diets supplemented with either 100 g of Ca-CLA or with 100, 200, or 400 g of Ca-tFA in a randomized block design. In the treatment diets, the Ca-CLA and Ca-tFA supplements substituted for equal parts of EnerG II in the control diet. The amount of Ca-CLA fed in this study was based on results obtained by others using dietary Ca-CLA supplementation to reduce milk fat in lactating cows (Giesy et al., 2002; Perfield II et al., 2002). The 100 g of Ca-CLA supplement provided 13 g/d of total CLA, containing 4.65 g of trans-10, cis-12-18:2 isomer, which is within the range used by others to achieve MFD. The Ca-tFA supplement provided 32, 64, and 128 g/d of tFA with the 100, 200, and 400 g of Ca-tFA, respectively. We used data from previous experiments, especially Kalscheur et al. (1997a) and Piperova et al. (2002), to estimate the expected increase in the amounts of tFA (~30 g/d) and trans-10-18:1 (~10 g/d) in milk fat of lactating cows exhibiting MFD. Assuming ~50% biohydrogenation (Wu et al., 1991; Wu and Palmquist, 1991) of the Ca-tFA in the rumen, we calculated that the 200-g dose of Ca-tFA should provide the levels required. The fatty acid compositions of the supplements are shown in Table 1, and the distribution pattern of the tFA and CLA isomers in the Ca supplements is given in Table 2.

Milk FAME were analyzed for CLA content and isomer distribution using a combination of GLC and Ag⁺ HPLC as previously described (Piperova et al., 2000). Aliquots (60 µL) of each sample were diluted in 940 µL hexane and were used in HPLC analysis; a typical injection volume was 50 µL, containing 100 to 112 µg of FAME. Details on the identification and quantification of the CLA isomers by HPLC analysis have been reported elsewhere (Eulitz et al., 1999; Sehat et al., 1998).

Statistical Analysis
Data were analyzed using the Mixed Procedure of SAS (1998). The model included treatment as fixed effect and observations at the end of the adjustment period as covariate. The random portion of the model included the block effect. Tests of significance included linear and quadratic contrasts to test the effect of Ca-tFA dose (0, 100, 200, and 400 g), and contrasts for CLA vs. control and CLA vs. tFA treatments. Probability of P 0.05 was considered to be statistically significant.

	RESULTS

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Gas-liquid chromatography analysis of the Ca-tFA FAME revealed that trans-18:1 positional isomers with a double bond from delta-6 to delta-16 were present in the supplement, with trans-10 being the major isomer (Table 2). However, except for the trans-15 and trans-16-18:1, which were minor components, a considerable proportion of trans-11-18:1 was also present (20%), as well as from 10.2 to 11.5% of each of the remaining trans-18:1 components. In contrast, there was no evidence for trans-monoenes in the Ca-CLA supplement. The Ca-CLA contained nearly equal amounts of cis-9, trans-11-18:2 (4.56 g) and trans-10, cis-12-18:2 (4.65 g), as well as several other isomers. However, there was no evidence for trans-7, cis-9-18:2 (Table 2). The Ca-tFA supplement was also examined for CLA, but only trace amounts of uncharacterized trienes and trans, trans dienes were detected (data not shown).

Dietary DMI, milk production, and milk composition data are presented in Table 4. Feed intake and milk yield were unaffected by dietary treatments. Milk protein and lactose content and yield were similar among treatments. Compared with the control cows, milk fat percentage and yield were decreased 3, 10, and 12% (P < 0.03) and 5, 11, and 15% (P < 0.02), respectively, in cows fed the Ca-tFA diets. Milk fat depression was greatest in cows fed the Ca-CLA diet, as milk fat percentage and yield were reduced by 25% (P , 0.01) and by 23% (P < 0.01), respectively, compared with the control.

	DISCUSSION

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In addition to the trans-10, cis-12-18:2, dietary MFD has been associated with increased levels of tFA and, particularly, with an altered isomer pattern in which the trans-10-18:1 isomer was preferentially increased (Griinari et al., 1998; Newbold et al., 1998; Piperova, et al., 2000; Peterson et al., 2003). By design, the Ca-tFA supplement provided a high proportion of trans-10-18:1 and elevated amounts of this isomer were incorporated into the milk fat of cows fed this supplement. It is tempting to ascribe the MFD observed in cows fed the Ca-tFA diets to the trans-10-18:1 isomer. Nevertheless, the Ca-tFA supplement contained several tFA isomers in relatively high proportions, and, in addition to the trans-10-18:1, the yields of trans-9, trans-11, and trans-12-18:1 were consistently increased in milk of cows fed increasing doses of the Ca-tFA supplement. It is unlikely that these tFA isomers are independently involved in MFD, as others have shown that trans-9-18:1 (Rindsig and Schultz, 1974; Newbold et al., 1998), trans-11-18:1, and trans-12-18:1 (Newbold et al., 1998; Griinari et al., 2000) were ineffective in reducing milk fat in lactating cows.

Other tFA of interest were trans-6+7+8-18:1 and trans-13+14-18:1, which were also present in the Ca-tFA supplement and transferred in moderate amounts to the milk of cows fed this supplement. Increased concentrations of trans-6+7+8-18:1 and trans-13+14-18:1 have been reported previously in milk of cows fed MFD diets (Griinari et al., 1998; Piperova et al., 2000, 2002; Precht et al., 2002; Peterson et al., 2003). However, the increase in trans-6+7+8-18:1 and trans-13+14-18:1 reported by others (Griinari et al., 1998; Loor and Herbein, 2003) was not always consistent with reduction in milk fat. Moreover, comparisons among the Ca-tFA treatments herein make it unlikely that these 2 groups of tFA are involved in MFD. Although the increase in trans-6+7+8-18:1 (g/d) over the control value was greatest for the 200-g Ca-tFA diet, this treatment did not result in the greatest decrease in milk fat yield. Conversely, the yield of trans-13+14-18:1 was lowest in cows fed the 200 g of Ca-tFA despite the moderate MFD observed with this dose. In other previous work, reduction in milk fat was not achieved in cows fed diets supplemented with 3 different fats (Kalscheur et al., 1997b), even though subsequent analysis of the milk fat revealed elevated levels of trans-6+7+8-18:1 (0.53, 0.79, 0.82, and 0.77 g/d) and trans-13+14-18:1 (9.76, 13.45, 18.22, and 22.8 g/d) respectively, for cows fed the control and the fat-supplemented diets (L. S. Piperova, 2001, unpublished data). In view of the previous discussion, if a trans-18:1 isomer is involved in MFD, the trans-10-18:1 seems to be the most likely candidate.

In this study, sources of trans-10-18:1 in milk of cows fed the Ca-tFA diet included those arising from both rumen biohydrogenation of PUFA and Ca-tFA supplementation. Intake of trans-10-18:1 was 8.4, 16.8, and 33.4 g/d, respectively, with the 100-, 200-, and 400-g Ca-tFA diets. If rumen biohydrogenation was the only source contributing to trans-10-18:1 in milk of the control cows, then the amount derived from the Ca-tFA was calculated to be 1.8, 4.0, and 6.2 g/d, respectively, for the 100-, 200-, and 400-g Ca-tFA diets. These increases in trans-10-18:1 were not as large as those observed previously during dietary induced MFD (Griinari et al., 1998; Piperova et al., 2000; Peterson et al., 2003) and corresponded to 21, 23, and 19% apparent transfer efficiencies with increasing doses of Ca-tFA. Partial hydrogenation of the Ca-tFA supplement might account for at least some of the reduced tFA in milk. Wu et al. (1991) showed that protection of unsaturated fatty acids from rumen biohydrogenation is incomplete and that 57% of dietary unsaturated fatty acids, fed as Ca salts, were hydrogenated by rumen microorganisms. If we assume a biohydrogenation value of 57% for trans-10-18:1, as Ca salt, amounts of this isomer available for transfer to milk would have been 3.8, 7.7, and 15.4 g/d, respectively, for cows fed the 100-, 200-, and 400-g Ca-tFA diets. Thus, the increased yields of trans-10-18:1 in milk would reflect transfer efficiencies from 40 to 52%. These values are in general agreement with transfer efficiencies calculated for trans-10-18:1 from data comparing duodenal contents and milk fat in cows fed a MFD diet (Piperova et al., 2002).

The apparent transfer efficiency of trans-10, cis-12-18:2 in this study (5%) was somewhat higher than the 2.4 to 4.4% and 3.4 % reported by Giesy et al. (2002) and Perfield II et al. (2002), respectively, for this isomer in milk of cows fed greater doses of rumen-protected CLA. The amount of trans-10, cis-12-18:2 in milk of the cows fed Ca-CLA (0.28 g/d) was similar to the 0.30 g/d observed in the study by Perfield II et al. (2002), resulting in a 23% decrease in milk fat yield in both studies. The apparent transfer efficiency of trans-10, cis-12-18:2 from Ca-CLA supplements was lower compared with that observed (10 to 21%) for this isomer during abomasal infusion of CLA supplements (Chouinard et al., 1999a, b). Nevertheless, the degree of milk fat reduction reported herein (23%) and by Perfield II et al. (2002) was almost identical (24%) to the MFD achieved in response to higher levels of trans-10, cis-12-18:2 (0.86 g/d) in milk provided by abomasal infusion of pure trans-10, cis-12 CLA (Baumgard et al., 2001). Thus, the MFD caused by the Ca-CLA diet was greater than expected based on the concentration of trans-10, cis-12-18:2 in milk.

Discrepancies between concentrations of trans-10, cis-12-18:2 in milk and degree of milk fat reduction have been observed previously (Loor et al., 2002; Peterson et al., 2003) during dietary-induced MFD, suggesting that other substances may also be involved. In this experiment, the cis-9, trans-11-18:2; the cis-11, trans-13-18:2; the trans, trans and the cis, cis CLA isomers were also increased in milk by the Ca-CLA supplement. However, it has been demonstrated that abomasal infusion of cis-9, trans-11-18:2 (Baumgard et al., 2000) or trans-8, cis-10 and cis-11, trans-13-18:2 (Perfield II et al., 2004) had no effect on milk fat synthesis, and Loor and Herbein (2003) did not observe MFD in feeding experiments in which the trans, trans and the cis, cis CLA isomers in milk were elevated. Perhaps, as Bauman and Griinari (2001, 2003) have suggested, other unidentified intermediates, produced in the rumen, may also be involved in MFD. Further research is required to investigate these discrepancies.

In this study, milk concentrations and yield of CLA were not different among cows fed the Ca-supplemented diets; however, changes in the CLA isomer profile were observed. It has been reported that formation of CLA in the rumen cannot account for the concentrations of CLA in milk (Piperova et al., 2002) and that ⁹-desaturation of ruminally derived trans-18:1 precursors is the primary source of cis-9 containing CLA in milk (Griinari et al., 2000; Corl et al., 2001, 2002). The increase in yield of cis-9 containing CLA observed in milk of cows fed Ca-tFA diets was in agreement with these findings. Compared with the control, milk secretion of trans-11-18:1 was increased by 15, 16, and 31%, respectively, with the Ca-tFA diets and resulted in a 19% (100 g Ca-tFA), 35% (200 g Ca-tFA), and 36% (400 g Ca-tFA) increase milk yield of cis-9, trans-11-18:2. Griinari et al. (2000) have shown that abomasal infusion of trans-11-18:1 in lactating cows resulted in a 31% increase in the yield of cis-9, trans-11-18:2, accounting for 12% of the infused trans monoene. Availability of trans-7-18:1 in milk was not determined in this experiment; however, milk yield of trans-7, cis-9-18:2 was increased by 30, 57, and 58%, respectively, with increasing doses of Ca-tFA, suggesting that a sufficient amount of trans-7-18:1 was delivered to the mammary gland to account for the increase.

The cis-9, trans-11-18:2 in milk of cows fed Ca-CLA originated from 3 sources: biohydrogenation of PUFA in the rumen, endogenous synthesis via ⁹-desaturation of trans-11-18:1, and the amount transferred from the supplement. Under normal rumen conditions, the portion of cis-9, trans-11-18:2 that escapes biohydrogenation is minor (Piperova et al., 2002; Corl et al., 2002). Thus, we assumed that all of the milk cis-9, trans-11-18:2 CLA was derived from the supplement and from endogenous synthesis. Furthermore, the amount derived from endogenous synthesis can be estimated from the quantity of this isomer in control milk, if ⁹-desaturation was not appreciably altered by the Ca-CLA supplement. Indeed, this appeared to be the case when we examined the values for the trans-7, cis-9-18:2, an isomer not present in the Ca-CLA supplement and known to be almost exclusively produced via ⁹-desatu-ration of trans-7-18:1 (Piperova et al., 2002; Corl et al., 2002). Because yields of trans-7, cis-9-18:2 and trans-6+7+8-18:1 in milk of cows fed Ca-CLA were not significantly different from the control values, we believe that ⁹-desaturation in the mammary gland was not altered by the Ca-CLA supplementation. This is consistent with data reported by Giesy et al. (2002) and Perfield II et al. (2002), showing that ratios of fatty acids representing product/substrate for ⁹-desaturase were not affected in milk of cows fed doses of Ca salts of CLA higher than those used in the present study. Hence, the apparent transfer efficiency of cis-9, trans-11-18:2 from the supplement to milk (11%) was calculated assuming that the difference in cis-9, trans-11-18:2, compared with the control, was derived from the Ca-CLA supplement. A similar transfer efficiency (9 to 10%) was reported for cis-9, trans-11-18:2 by Giesy et al. (2002) in lactating cows fed increasing doses of Ca-CLA-60. These transfer efficiencies were lower than the 22.5% observed for this isomer during abomasal infusion of a mixture of CLA isomers (Chouinard et al., 1999a). As suggested by Giesy et al. (2002), site of supplementation may be an important factor in the efficiency of CLA transfer into milk.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
We have shown that dietary Ca-tFA supplementation can reduce milk fat content and yield; however, the MFD was less pronounced, compared with Ca-CLA supplementation. The concentration and yield of cis-9 containing CLA were highest in milk of cows fed the Ca-tFA supplement, which provided the trans-7 and trans-11-18:1 precursors for the endogenous synthesis of CLA in the mammary gland. The decrease in milk fat in cows fed Ca-CLA was associated with the greater level of trans-10, cis-12-18:2 in milk. In contrast, concentrations of trans-10, cis-12-18:2 were not altered by supplementation with Ca-tFA, whereas the levels of trans-18:1, including the trans-10 isomer, were elevated in milk of cows fed the tFA supplements. These results provide evidence that an increase in trans-10, cis-12-18:2 is not required for MFD and suggest that other components, including the trans-10-18:1, could also be involved.

	ACKNOWLEDGEMENTS

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The authors thank Bioproducts, Inc. for providing the Ca supplements and the financial support for this study. The assistance of Emiko Yoshizumi with the milk fat analysis is greatly appreciated.

Received for publication February 2, 2004. Accepted for publication June 23, 2004.

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TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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