J. Anim Sci.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J. Anim Sci. 2008. 86:3062-3068. doi:10.2527/jas.2007-0372
© 2008 American Society of Animal Science
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
jas.2007-0372v1
86/11/3062    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Taugbøl, O.
Right arrow Articles by Harstad, O. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Taugbøl, O.
Right arrow Articles by Harstad, O. M.

ANIMAL NUTRITION

Cobalt supplied per os reduces the mammary {Delta}9-desaturase index of bovine milk1

O. Taugbøl*,2, I. J. Karlengen*, T. Bolstad*, A. H. Aastveit{dagger} and O. M. Harstad*

* Department of Animal and Aquaculture Sciences, and {dagger} Department of Chemistry, Biotechnology and Food Science, Section for Bioinformatics and Analytical Methods, Norwegian University of Life Sciences, 1432 Ås, Norway


   Abstract
Top
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Results indicated that the dual marker system of Yb-acetate and Co-EDTA supplied per os reduced the proportion of fatty acids in bovine milk that were products of {Delta} 9-desaturase. To verify this effect and identify the responsible marker component, 18 cows (3 cows per treatment) were administered per os a 0.25-L solution of either Co-acetate, Co-EDTA, Co-EDTA + Yb-acetate, EDTA, Yb-acetate, or water twice daily for 5 d. The daily amounts of Co, Yb, and EDTA were, respectively, 3.50, 3.44, and 21.00 g per cow. Milk and blood were sampled and analyzed for content of fatty acids, and blood was sampled and analyzed for Co and cobalamin. Only solutions containing Co had a reducing effect (P ≤ 0.01) on fatty acids that were products of {Delta}9-desaturase in milk—cis-9 10:1, cis-9 14:1, cis-9 16:1, cis-9, trans-11 18:2, and cis-9 18:1—with the exception of the solution containing Co-EDTA + Yb-acetate for cis-9 18:1. Of the substrate fatty acids of {Delta} 9-desaturase, only 18:0 increased (P < 0.001) in all groups supplied with Co-containing solutions. Thus, Co had a reducing effect (P ≤ 0.004) on the {Delta} 9-desaturase indices [(product of {Delta}9-desaturase)/(product of {Delta}9-desaturase + substrate of {Delta}9-desaturase)] of milk for cis-9 14:1, cis-9 16:1, cis-9 18:1, and cis-9, trans-11 18:2. There were no differences in {Delta}9-desaturase indices between Co-EDTA and Co-acetate. None of the marker solutions influenced the fatty acid composition of blood plasma, and Co was detected only in the blood samples from cows treated with solutions containing Co. On the basis of these results, we concluded that Co given per os decreased the {Delta}9-desaturase indices of bovine milk.

Key Words: bovine milk • cobalt • {Delta}9-desaturase • oleic acid • rumenic acid • stearoyl-coenzyme A desaturase


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Bovine milk fat contains a relatively high fraction of oleic acid (cis-9 18:1) and trans fatty acids, especially rumenic acid (cis-9, trans-11 18:2). Milk content of cis-9 18:1 and cis-9, trans-11 18:2 are, in principle, determined by their supply to the udder by the blood from the small intestine and mobilized adipose tissue, and endogenously by action of 9-desaturase on stearic (18:0) and trans-vaccenic acid (trans-11 18:1), respectively, in the mammary gland (Grummer, 1991Go; Griinari et al., 2000Go; Mosley et al., 2006Go). Endogenously synthesized cis-9 18:1 and cis-9, trans-11 18:2 may contribute more than 50 and 90%, respectively, of their total content in bovine milk (Kay et al., 2004Go; Shorten et al., 2004Go; Mosley and McGuire, 2007Go). Results obtained in our laboratory (Taugbøl et al., 2004Go) indicated that use of the marker system of Co-EDTA and Yb-acetate, supplied into the rumen, reduced the proportions of cis-9 16:1, cis-9 18:1, and cis-9, trans-11 18:2 in bovine milk. Shingfield et al. (2006)Go published results indicating the same effect of using a triple marker system with Co-EDTA, Yb-acetate, and chromium-mordanted straw. The objectives of this study were to verify the effect of the marker system of Co-EDTA and Yb-acetate on MUFA and cis-9, trans-11 18:2 in bovine milk, and to identify the responsible marker component.


   MATERIALS AND METHODS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
Animals and Treatment

The care and handling of the cows conformed to the laws and regulations controlling experiments with animals in Norway (The Animal Protection Act of December 20, 1974, and the Animal Protection Ordinance Concerning Experiments in Animals of January 15, 1996).

Experimental animals were 6 multiparous and 12 primiparous cows of the Norwegian Cattle breed, averaging 70 ± 37 d in milk and 31 ± 6 kg/d of milk at the start of the experiment. They were housed in a tie-stall barn and had free access to water. The cows were divided into 3 groups, 1 including multiparous cows and 2 groups with primiparous cows, graded according to milk yield. Within each group, cows were assigned randomly to 6 treatments: per os administration of 0.25 L of either Co-acetate, Co-EDTA, Co-EDTA + Yb-acetate, EDTA, Yb-acetate, or water twice daily for 5 d. The Co-EDTA was prepared as Na salt of the monovalent Co-EDTA anion according to Udén et al. (1980)Go. After crystallization, the marker was washed until the wash solution was clear (usually 4 times) with 75% (vol/vol) ethanol. Thereafter, the marker was washed 3 times with 96% (vol/vol) ethanol. Cobalt-EDTA, Co-acetate (Honeywell Specialty Chemicals, Seelze, Germany), Yb-acetate (Dasico a/s, Birkerød, Denmark), and EDTA (Na2EDTA·2H2O; Prolabo, Leuven, Belgium) were dissolved in distilled water. The daily amounts of Co, Yb, and EDTA were 3.50, 3.44, and 21.00 g per cow, respectively. The experimental design was a changeover, consisting of a pretreatment period of 2 wk and a treatment period of 5 d. The diet during the pretreatment and the treatment period consisted of the same prewilted grass silage (553 g of NDF and 135 g of CP per kg of DM) offered for ad libitum intake, supplemented with a commercial concentrate mixture according to the energy requirements of the cows. The main ingredients in the concentrate mixture were (per kg of DM) 326 g of oats, 220 g of barley, 99 g of rye, 69 g of molasses, 59 g of peas, 50 g of wheat bran, 40 g of maize gluten meal, and 30 g of rapeseed; and the composition was 217 g of NDF, 402 g of starch, 174 g of CP, and 42 g of crude fat. The daily amount of the concentrate mixture was divided into 4 portions and offered by an automatic feeder at 0400, 0600, 1200, and 1500 h.

Milk Recording and Sampling

The cows were milked and yield was recorded daily at 0630 and 1630 h. Individual samples of morning milk were collected immediately before the markers were administered and after 5 d in the treatment period. All milk samples were kept frozen (–20°C) until analysis for fatty acid composition.

Blood Sampling

Blood samples (10-mL heparin-containing tubes) from a jugular vein were collected 3 d before the treatment period at 0730 h and at 0730 h after 5 d of treatment. Blood was centrifuged at 500 x g for 20 min and plasma was stored at –20°C until analysis. Plasma samples were analyzed for fatty acid composition, co-balamin, and Co.

Analysis of Milk Fatty Acids

Milk fat was separated by using the rapid method described by Feng et al. (2004)Go. Of the separated lipid, 40 mg was transesterified by the method of Christie (1982)Go, as modified by Chouinard et al. (1999)Go by use of sodium methoxide. Fatty acid methyl esters (FAME) were quantified by a GLC instrument (6890N, Agilent Technologies, Palo Alto, CA) with a split-splitless injector, an automatic liquid sampler (7683B), and a flame-ionization detector. Separation was performed with a CP-select CB for FAME (200 m x 0.25 mm i.d. x 0.25 µm film thickness) fused-silica capillary column (Varian Inc., Palo Alto, CA). Initially, the oven temperature was 70°C with a 4-min hold, increased at 20°C/min to 160°C, and held for 80 min. The oven temperature was then increased to 220°C at 3°C/min and held for 28 min. Carrier gas was H2 with a pressure of 314 kPa. Fatty acid analysis was performed by autoinjection of 1 µL of each sample at a split ratio of 70:1, a H2 flow of 151 mL/min, and an injector temperature of 280°C. The flame-ionization detector temperature was 290°C with H2, air, and N2 makeup gas flow rates of 40, 450, and 45 mL/min, respectively. The sampling frequency was 10 Hz. The run time for a single sample was 136 min. Fatty acid peaks were identified by using a 37-component FAME mix and trans-11 18:1 from Supelco (Bellefonte, PA). Additional standards for CLA isomers were obtained from Natural ASA (Oslo, Norway).

Analysis of Blood Plasma

Fatty Acid Profile in Plasma Total Lipids. Plasma (200 µL) was added to 2 mL of methanolic HCl, mixed, and heated at 90°C for 120 min. The resulting FAME were added to 3 mL of distilled water and extracted twice with 1 mL of hexane, and the extracts were pooled. Plasma FAME analyses were performed with the same equipment as the milk FAME. Separations were performed with a DB-23 (60 m x 0.25 mm i.d. x 0.25 µm film thickness) column (Agilent Technologies). The temperature program was initially 120°C for 1 min, increased at 7°C/min to 230°C, and held for 12 min. Carrier gas was H2 with a pressure of 95.1 kPa. Fatty acid analysis was performed by autoinjection of 1 µL of each sample at a split ratio of 0.1:1, constant flow mode, and average velocity of 28 cm/s. The flame-ionization detector temperature was 260°C, with H2, air, and N2 makeup gas flow rates of 40, 450, and 45 mL/min, respectively. The sampling frequency was 10 Hz, and the run time for a single sample was 28.71 min. Fatty acids were identified by matching retention times with pure FAME standards (Supelco, and Sigma, St. Louis, MO) and CLA standards from Natural ASA.

Determination of Co. Instrumental neutron activation analysis was used for the determination of Co in plasma. Plasma (1 mL) was weighed into acid-cleaned polyethylene ampoules, then dried at 60°C overnight and sealed. The samples, together with standards and blank samples, were then irradiated for 13.5 h at a thermal neutron flux of 9.4 x 1012 neutrons·s–1·cm–2 at the reactor Jeep II (Kjeller, Norway). Standard reference materials [Community Bureau of Reference (BCR) No. 186, 1986, and National Institute of Standards and Technology No. 1575a, 2002] were used. The dry standard materials (approximately 1.0 g) were weighed into acid-cleaned ampoules and sealed. Empty ampoules were irradiated as blank samples. Measurement of the gamma spectra was performed with an HPGe detector (20% efficiency, 1.9 keV resolution of the 1,332.5-keV peak; Canberra, Meriden, CT), and the quantitative measurements were based on Genie 2k gamma spectrum analysis software (Canberra). All samples were counted for approximately 30 min 3 to 4 wk after irradiation. The concentration of the elements is given by


Formula

where m is the mass of trace element (µg/g of plasma) and D is the number of disintegrations/s (Bq) at the end of irradiation. The half-life of 60Co is 5 yr. The detection limit was defined as 10 x standard deviation of blank samples (0.00605 µg/g of plasma).

Determination of Cobalamin. Cobalamin in blood plasma of cows was determined by a Lactobacillus leichmannii microbiological assay (Kelleher and Broin, 1991Go; Molloy and Scott, 1997Go). The sensitivity of the assay was 30 pmol/L; within-assay CV was 4% and between-assay CV was 5%.

Calculation of the Desaturase Index

In the absence of direct measurements, milk fat product-to-substrate ratios have been used to estimate the activity of the {Delta} 9-desaturase enzyme in the mammary gland (Griinari et al., 2000Go), and later studies have shown that these milk fatty acid ratios are related positively to mammary {Delta}9-desaturase activity (Singh et al., 2004Go; Bernard et al., 2005Go). In the present experiment, the {Delta}9-desaturase index was defined as (product of {Delta}9-desaturase)/(product of {Delta}9-desaturase + substrate of {Delta}9-desaturase) (Kelsey et al., 2003Go). The desaturase index was calculated for 4 pairs of fatty acids: cis-9 14:1–14:0, cis-9 16:1–16:0, cis-9 18:1–18:0, and cis-9, trans-11 18:2–trans-11 18:1.

Statistical Analysis

The effect of treatments on fatty acid composition and the {Delta}9-desaturase indices in milk and on fatty acids and cobalamin in blood plasma were analyzed by using a mixed model (Wang and Goonewardene, 2004Go). Treatment was used as the main factor, cows as the subject, and sampling day (0 and 5) as the time factor. The results are given in tables with means and SEM. The SEM for Co in plasma was calculated based on the observed values above the detection limit. The P-values reported in the tables are for testing the interactions between treatments and time.


   RESULTS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
The effects of the marker solutions on milk fatty acid composition and {Delta}9-desaturase indices are shown in Table 1Go. Of the solutions supplied, only those containing Co (Co-acetate, Co-EDTA, Co-EDTA + Yb-acetate) consistently decreased the {Delta}9-desaturase indices of those calculated in milk: cis-9 14:1 (P < 0.001), cis-9 16:1 (P = 0.004), cis-9 18:1 (P < 0.001), and cis-9, trans-11 18:2 (P = 0.001; Table 1Go). There was no systematic difference on {Delta}9-desaturase indices whether Co was given as Co-EDTA or Co-acetate (Table 1Go). All solutions containing Co reduced the proportions of the product fatty acids of {Delta}9-desaturase—cis-9 10:1 (P < 0.001), cis-9 14:1 (P < 0.001), cis-9 16:1 (P = 0.01), cis-9 18:1 (P = 0.001), and cis-9, trans-11 18:2 (P < 0.001)—with the exception (P = 0.07) of Co-EDTA + Yb-acetate on cis-9 18:1. As a result, the sum of MUFA also decreased (P < 0.001; Table 1Go). Among the substrate fatty acids, only 18:0 increased (P < 0.001) after treatment with solutions containing Co. Cobalt-EDTA apparently increased (P ≤ 0.03) the proportion of 14:0 and 16:0 as well as the sum of SFA. That particular effect is explained by a rather decreased quantity of SFA in the milk of 1 cow on d 0, comparable with that typically found in milk from cows with fat depression; that is, a low proportion of de novo-synthesized fatty acids and a large proportion of trans-10 18:1 (5.0 g/100 g of fatty acid) was found in the milk from this cow on d 0 (Griinari et al., 1998Go). Thus, Co-EDTA probably does not deviate from the other solutions containing Co.


View this table:
[in this window]
[in a new window]

  		Table 1. Proportion of milk fatty acids and calculated desaturase indices before (d 0) and after 5 d of per os supplementation of marker components and water (control)1
 
In contrast to the effects of the solutions containing Co on milk fatty acids (Table 1Go), none influenced (P ≥ 0.08) blood content of fatty acids or cobalamin (Table 2Go). However, Co was detected only in blood samples from cows treated with solutions containing Co, and the concentration was nearly 3 times greater for Co-acetate compared with Co-EDTA.


View this table:
[in this window]
[in a new window]

  		Table 2. Cobalt, cobalamin, and fatty acids in blood plasma collected before (d 0) and after 5 d of per os supplementation of marker components and water (control)1
 

   DISCUSSION
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
Shingfield et al. (2006)Go published results suggesting that one or more of the triple marker system with Co-EDTA, Yb-acetate, or chromium reduced mammary {Delta}9-desaturase indices. A follow-up study showed that this effect was related to Co-EDTA, and that Co probably was the active component (Shingfield et al., 2008Go). The present results demonstrate that Co alone is the element responsible for the decreased {Delta}9-desaturase indices of bovine milk.

Cobalt might influence the fat metabolism in the rumen and thereby the supply to the udder of individual fatty acids, or affect the desaturation of saturated fatty acids within the mammary gland, or both. In this study, there were no observed effects of marker components on the fatty acid composition in blood plasma. In lactating dairy cows, mammary epithelial cells have a great activity of {Delta}9-desaturase (Christie, 1981Go; Grummer, 1991Go). Although we have not proved that {Delta}9-desaturase activity was influenced negatively, there are several indications that strongly support that hypothesis. The milk fatty acids with a chain length up to 14 carbon atoms are almost exclusively synthesized in the mammary gland (Palmquist et al., 1969Go; Kinsella, 1970Go). Consequently, the synthesis of cis-9 10:1 and cis-9 14:1 are dependent on mammary {Delta}9-desaturase activity (Bauman and Davis, 1974Go). Thus, the reduction of cis-9 10:1, cis-9 14:1, and the {Delta}9-desaturase index for cis-9 14:1 strongly indicates that the observed changes in the proportion of MUFA were caused by a decreased {Delta}9-desaturase activity in the mammary gland. A parallel argument can be used based on decreased cis-9, trans-11 18:2, because desaturated trans-11 18:1 is considered to be the major source of cis-9, trans-11 18:2 in milk fat (Griinari et al., 2000Go, Mosley et al., 2006Go). The {Delta}9-desaturase is known to be regulated by many dietary factors, including different fatty acids (Ntambi and Miyazaki, 2004Go). In fact, trans-10, cis-12 18:2 (Baumgard et al., 2000Go), trans-10, trans-12 18:2 (Sæbø et al., 2005Go), and trans-9, trans-11 18:2 (Perfield et al., 2007Go) infused postruminally induced a decrease in the desaturase indices of milk fat in lactating cows. Thus, the present effect of Co on the {Delta}9-desaturase indices might be an indirect effect of fatty acid biohydrogenation in the rumen, resulting in intermediates that affect the enzyme system of {Delta}9-desaturase. In the present experiment, trans-9, trans-11 18:2 was not separated from trans-10, trans-12 18:2 in blood plasma. However, their proportion and the amounts of trans-10, cis-12 18:2 in blood plasma did not differ among the treatments. Moreover, blood content of cobalamin and the proportions of odd- and branched-chain fatty acids in milk were not affected by Co, suggesting that there was no change of microbial metabolism in the rumen (Vlaeminck et al., 2005Go). These results, and the fact that solutions containing Co also increased Co concentrations in blood plasma, support the hypothesis that the effects obtained on {Delta}9-desaturase indices are most probably related to Co. Large amounts of Co might affect a wide range of functions, including {Delta}9-desaturase activity, its synthesis, or both. To determine the effect of Co on mammary {Delta}9-desaturase conclusively, studies using biopsied mammary tissue, labeled fatty acid substrates, and mammary mRNA expression of {Delta}9-desaturase should be realized.

Cobalt-EDTA, as prepared in the present experiment, allowed Co to be absorbed from the digestive tract, and most probably induced the decreased {Delta}9-desaturase indices in bovine milk. In other experiments conducted in our laboratory in which the same procedure as in the present experiment was used for preparing Co-EDTA, 1.6 to 2.5% of the Co supplied was recovered in the urine (Prestløkken and Harstad, 2001Go; H. Volden, unpublished results; A. Stevnebø, unpublished results). This was greater than the corresponding value of 0.8% found by Teeter and Owens (1983)Go, but less than the value of 3% reported by Udén et al. (1980)Go. Therefore, the procedure used for preparing Co-EDTA in the present experiment probably does not differ from others. However, further studies to elucidate the role of the procedure for preparation of Co-EDTA are necessary before conclusions about Co-EDTA as a marker for digesta flow measurements can be drawn.


   Footnotes
 
1 The authors thank Reidar Øvstegard, Kathrine Vestøl, Håvard Tveit, Øyvind Carlsen, Per Lindstad, Nina Asper, and Marit Nan-drup Pettersen at the Norwegian University of Life Sciences for their technical assistance. Back

2 Corresponding author: ole.taugbol{at}umb.no

Received for publication June 20, 2007. Accepted for publication April 26, 2008.


   LITERATURE CITED
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 


Bauman, D. E., and C. L. Davis. 1974. Biosynthesis of milk fat. Pages 31–75 in Lactation: A Comprehensive Treatise. B. L. Larson and V. R. Smith, ed. Academic Press, New York, NY.

Baumgard, L. H., B. A. Corl, D. A. Dwyer, A. Sæbø, and D. E. Bauman. 2000. Identification of the conjugated linoleic acid isomer that inhibits milk fat synthesis. Am. J. Physiol. Regul. Integr. Comp. Physiol. 278:R179–R184.[Abstract/Free Full Text]

Bernard, L., J. Rouel, C. Leroux, A. Ferlay, Y. Faulconnier, P. Legrand, and Y. Chilliard. 2005. Mammary lipid metabolism and milk fatty acid secretion in alpine goats fed vegetable lipids. J. Dairy Sci. 88:1478–1489.[Abstract/Free Full Text]

Chouinard, P. Y., L. Corneau, A. Sæbø, and D. E. Bauman. 1999. Milk yield and composition during abomasal infusion of conjugated linoleic acids in dairy cows. J. Dairy Sci. 82:2737–2745.[Abstract]

Christie, W. W. 1981. Effects of diet and other factors on the lipid composition of ruminant tissues and milk. Pages 193–226 in Lipid Metabolism in Ruminant Animals. W. W. Christie, ed. Pergamon Press, Oxford, UK.

Christie, W. W. 1982. A simple procedure for rapid transmethylation of glycerolipids and cholesteryl esters. J. Lipid Res. 23:1072–1075.[Abstract]

Feng, S., A. L. Lock, and P. C. Garnsworthy. 2004. Technical note: A rapid lipid separation method for determining fatty acid composition of milk. J. Dairy Sci. 87:3785–3788.[Abstract/Free Full Text]

Griinari, J. M., B. A. Corl, S. H. Lacy, P. Y. Chouinard, K. V. V. Nurmela, and D. E. Bauman. 2000. Conjugated linoleic acid is synthesized endogenously in lactating dairy cows by delta(9)-desaturase. J. Nutr. 130:2285–2291.[Abstract/Free Full Text]

Griinari, J. M., D. A. Dwyer, M. A. McGuire, D. E. Bauman, D. L. Palmquist, and K. V. V. Nurmela. 1998. Trans-octadecenoic acids and milk fat depression in lactating cows. J. Dairy Sci. 81:1251–1261.[Abstract]

Grummer, R. R. 1991. Effect of feed on the composition of milk-fat. J. Dairy Sci. 74:3244–3257.[Abstract/Free Full Text]

Kay, J. K., T. R. Mackle, M. J. Auldist, N. A. Thomson, and D. E. Bauman. 2004. Endogenous synthesis of cis-9, trans-11 conjugated linoleic acid in dairy cows fed fresh pasture. J. Dairy Sci. 87:369–378.[Abstract/Free Full Text]

Kelleher, B. P., and S. D. O. Broin. 1991. Microbiological assay for vitamin B12 performed in 96-well microtitre plates. J. Clin. Pathol. 44:592–595.[Abstract/Free Full Text]

Kelsey, J. A., B. A. Corl, R. J. Collier, and D. E. Bauman. 2003. The effect of breed, parity, and stage of lactation on conjugated linoleic acid (CLA) in milk fat from dairy cows. J. Dairy Sci. 86:2588–2597.[Abstract/Free Full Text]

Kinsella, J. E. 1970. Biosynthesis of lipids from (2-14C)acetate and D (–)-beta-hydroxy(1,3-14C)butyrate by mammary cells from bovine and rat. Biochim. Biophys. Acta 210:28–38.[Medline]

Molloy, A. M., and J. M. Scott. 1997. Microbiological assay for serum, plasma, and red cell folate using cryopreserved, microtiter plate method. Methods Enzymol. 281:43–53.[CrossRef][Medline]

Mosley, E. E., and M. A. McGuire. 2007. Methodology for the in vivo measurement of the delta(9)-desaturation of myristic, palmitic, and stearic acids in lactating dairy cattle. Lipids 42:939–945.[CrossRef][Medline]

Mosley, E. E., B. Shafii, P. J. Moate, and M. A. McGuire. 2006. Cis-9, trans-11 conjugated linoleic acid is synthesized directly from vaccenic acid in lactating dairy cattle. J. Nutr. 136:570–575.[Abstract/Free Full Text]

Ntambi, J. M., and M. Miyazaki. 2004. Regulation of stearoyl-CoA desaturases and role in metabolism. Prog. Lipid Res. 43:91–104.[CrossRef][Medline]

Palmquist, D., C. L. Davis, R. E. Brown, and D. S. Sachan. 1969. Availability and metabolism of various substrates in ruminants. V. Entry rate into body and incorporation into milk fat of D(–) beta-hydroxybutyrate. J. Dairy Sci. 52:633–638.[Abstract/Free Full Text]

Perfield, J. W., A. L. Lock, J. M. Griinari, A. Sæbø, P. Delmonte, D. A. Dwyer, and D. E. Bauman. 2007. Trans-9, cis-11 conjugated linoleic acid reduces milk fat synthesis in lactating dairy cows. J. Dairy Sci. 90:2211–2218.[Abstract/Free Full Text]

Prestløkken, E., and O. M. Harstad. 2001. Effects of expander-treating a barley-based concentrate on ruminal fermentation, bacterial N synthesis, escape of dietary N, and performance of dairy cows. Anim. Feed Sci. Technol. 90:227–246.[CrossRef]

Sæbø, A., P. C. Sæbø, J. M. Griinari, and K. J. Shingfield. 2005. Effect of abomasal infusions of geometric isomers of 10,12 conjugated linoleic acid on milk fat synthesis in dairy cows. Lipids 40:823–832.[CrossRef][Medline]

Shingfield, K. J., A. Arölä, S. Ahvenjärvi, A. Vanhatalo, V. Toivonen, J. M. Griinari, and P. Huhtanen. 2008. Ruminal infusions of cobalt-EDTA reduce mammary {Delta}9-desaturase index and alter milk fatty acid composition in lactating cows. J. Nutr. 138:710–717.[Abstract/Free Full Text]

Shingfield, K. J., V. Toivonen, A. Vanhatalo, P. Huhtanen, and J. M. Griinari. 2006. Short communication: Indigestible markers reduce the mammary {Delta}9-desaturase index and alter the milk fatty acid composition in cows. J. Dairy Sci. 89:3006–3010.[Abstract/Free Full Text]

Shorten, P. R., T. B. Pleasants, and G. C. Upreti. 2004. A mathematical model for mammary fatty acid synthesis and triglyceride assembly: The role of stearoyl CoA desaturase (SCD). J. Dairy Res. 71:385–397.[CrossRef][Medline]

Singh, K., D. G. Hartley, T. B. McFadden, and D. D. S. Mackenzie. 2004. Dietary fat regulates mammary stearoyl CoA desaturase expression and activity in lactating mice. J. Dairy Res. 71:1–6.[CrossRef][Medline]

Taugbøl, O., I. J. Karlengen, and O. M. Harstad. 2004. May cobalt-ethylene-diamine-tetraacetic acid (Co-EDTA) influence {Delta}9-desaturase activity and milk fatty acid composition in dairy cows. Page 239 in Proc. 8th Int. Conf. Eur. Soc. Vet. & Comp. Nutr., Budapest, Hungary.

Teeter, R. G., and F. N. Owens. 1983. Characteristics of water-soluble markers for measuring rumen liquid volume and dilution rate. J. Anim. Sci. 56:717–728.[Abstract/Free Full Text]

Udén, P., P. E. Colucci, and P. J. Van Soest. 1980. Investigation of chromium, cerium and cobalt as markers in digesta. Rate of passage studies. J. Sci. Food Agric. 31:625–632.[Medline]

Vlaeminck, B., C. Dufour, A. M. van Vuuren, A. R. J. Cabrita, R. J. Dewhurst, D. Demeyer, and V. Fievez. 2005. Use of odd and branched-chain fatty acids in rumen contents and milk as a potential microbial marker. J. Dairy Sci. 88:1031–1042.[Abstract/Free Full Text]

Wang, Z., and L. A. Goonewardene. 2004. The use of MIXED models in the analysis of animal experiments with repeated measures data. Can. J. Anim. Sci. 84:1–11.



This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
jas.2007-0372v1
86/11/3062    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Taugbøl, O.
Right arrow Articles by Harstad, O. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Taugbøl, O.
Right arrow Articles by Harstad, O. M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS