HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Frank, N. Articles by Latour, M. A. Search for Related Content PubMed PubMed Citation Articles by Frank, N. Articles by Latour, M. A.

Effect of hypothyroidism on the blood lipid response to higher dietary fat intake in mares^1,2

N. Frank^*,3, J. E. Sojka^* and M. A. Latour

^* Department of Veterinary Clinical Sciences, and and Department of Animal Sciences, Purdue University, West Lafayette, IN 47907

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Blood lipid and lipoprotein concentrations were measured and compared between euthyroid and thyroidectomized mares on low-fat or high-fat diets to test the hypothesis that hypothyroidism alters the blood lipid response to higher dietary fat intake. Four healthy adult mares and four adult mares that had been thyroidectomized 3 to 6 mo earlier were placed on low-fat or high-fat diets according to a replicated 2 x 2 Latin square design consisting of two 5-wk feeding periods separated by a 2-wk washout interval. Plasma lipid concentrations were measured at 0, 3, 4, and 5 wk, and plasma lipase activities were measured at the end of each 5-wk feeding period. Compared with euthyroid mares (0.46 ng/mL [range 0.34 to 0.68 ng/mL T₃], and 21.5 ng/mL [range 18.1 to 25.1 ng/mL T₄], respectively), median serum concentrations of T₃ and T₄ were lower (P = 0.029 and P = 0.021, respectively) in thyroidectomized mares (0.26 ng/mL [range 0.23 to 0.26 ng/mL T₃], and undetectable T₄). Serum T₄ concentrations were below the limits of detection in thyroidectomized horses. Alterations in body weight over 5 wk did not differ between groups. Mean plasma very low density lipoprotein (VLDL) and triglyceride (TG) concentrations were higher (P = 0.045 and 0.034, respectively) in hypothyroid mares (55.42 ± 35.05 mg/dL and 52.83 ± 34.46 mg/dL, respectively) compared with euthyroid mares (28.28 ± 13.76 mg/dL and 23.53 ± 9.84 mg/dL, respectively). Mean plasma total cholesterol (TC) concentrations increased from 88.73 ± 25.49 mg/dL at baseline to 103.93 ± 24.42 mg/dL after 5 wk on the low-fat diet, but increased by a greater magnitude (P = 0.006 diet ± time interaction) in mares that were on the high-fat diet (81.05 ± 17.24 mg/dL and 123.84 ± 32.27 mg/dL, respectively). Mean plasma TC concentrations were higher (P = 0.099) in hypothyroid mares (116.16 ± 32.89 mg/dL) than in euthyroid mares (89.56 ± 14.45 mg/dL). Higher post-heparin plasma lipoprotein lipase and hepatic lipase activities (P = 0.012 and P = 0.017, respectively) were detected in mares that were on the high-fat diet (2.66 ± 0.91 µmol FA•mL^–1•h^–1 and 2.95 ± 0.49 µmol FA•mL^–1•h^–1, respectively) vs. a low-fat diet (1.75 ± 0.55 µmol FA•mL^–1•h^–1 and 2.27 ± 0.59 µmol FA•mL^–1•h^–1, respectively). We conclude that plasma VLDL and TG concentrations are elevated in hypothyroid mares, but the blood lipid response to higher dietary fat intake is not influenced by hypothyroidism.

Key Words: Cholesterol • Hypothyroidism • Lipase • Thyroidectomy • Very Low Density Lipoprotein

	Introduction

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
We have previously reported that higher plasma triglyceride (TG), very low-density lipoprotein (VLDL), and low-density lipoprotein (LDL) concentrations are detected following thyroidectomy in horses (Frank et al., 1999). Results from our initial study suggest that thyroid hormones play an important role in equine lipoprotein metabolism. However, in subsequent studies, we determined that kinetic parameters of VLDL metabolism are not affected by thyroidectomy, and hypothyroidism does not affect the plasma VLDL response to feed deprivation (Frank et al., 2003a,b). Results of the latter study suggest that, although higher plasma VLDL concentrations are detected in thyroidectomized horses, hypothyroidism does not impair the animal’s ability to respond to different physiological stresses.

Lower plasma TG concentrations, higher plasma total cholesterol (TC) concentrations, and increased lipoprotein lipase activity are associated with consumption of high-fat diets in horses (Orme et al., 1997; Geelen et al., 1999, 2001a). Development of this characteristic blood lipid profile reflects an adaptation in blood lipoprotein metabolism. We hypothesized that hypothyroidism would significantly impair the horse’s ability to adapt to a high-fat diet and, therefore, result in a blood lipid profile that differs from that of euthyroid horses that are on the same diet. Specifically, we aimed to compare plasma density <1.006 g/mL lipoprotein, TG, TC, and NEFA concentrations, and plasma lipase activities in euthyroid and hypothyroid mares placed on low-fat and high-fat diets.

	Materials and Methods

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Experimental Subjects and Diets

Four thyroidectomized and four healthy mares were selected. Thyroid glands had been surgically removed 3 mo (n = 2) or 6 mo (n = 2) earlier using a previously described procedure (Frank et al., 1999). Subjects were of the Quarter Horse breed. Mean ± SD ages were 10 ± 6 yr (range, 4 to 19 yr) and 10 ± 7 yr (range, 4 to 16 yr) for euthyroid and hypothyroid mares, respectively. Body condition scores ranged between 6 and 7 for all mares (Henneke et al., 1983). Mares were weighed at the beginning and end of each feeding period.

Beginning 2 wk before sample collection, mares were enclosed in treatment pens measuring 5 m ± 15 m with two mares housed in each pen. Mixed grass-alfalfa hay containing 2.1% DM as fat (crude ether extract) and water were provided for ad libitum intake during this acclimatization period. Pelleted feeds containing 3.2% (low fat) or 7.3% (high fat) of DM crude fat were supplied by Purina Mills Inc. (St. Louis, MO). Composition of feeds is outlined in Table 1 based on information provided by the manufacturer and from independent analysis of feeds by the Dairy One DHIA Forage Testing Laboratory (Ithaca, NY). Daily amounts of feed provided to mares were calculated according to NRC (1989) guidelines. Amounts were calculated to provide 1.5 times the DE requirements for maintenance with the aim of providing enough feed for ad libitum intake. Pelleted feeds were fed exclusively. Mares were separated from each other for 2 h at feeding times (0600 and 1600) by closing a gate to divide each pen. Unconsumed feed was removed from the pens, but some feed was spilled onto the pen floor and trampled making determination of amounts left uneaten imprecise.

The study protocol was approved by the Purdue University Animal Care and Use Committee. A replicated 2 ± 2 Latin square design comprised two 5-wk feeding periods separated by a 2-wk washout interval. Mixed grass-alfalfa hay was provided for ad libitum intake during the washout period. Four mares were assigned to receive either low-fat or high-fat diets and each treatment group contained two euthyroid mares and two hypothyroid mares. Mares were randomly assigned to each group. Water was provided for ad libitum intake. Blood samples (50 mL) were collected at the beginning of the feeding period and at wk 3, 4, and 5 via jugular venipuncture into EDTA-coated tubes. Blood was collected between 0830 and 0930 and stored immediately in ice for transport to the laboratory. Post-heparin plasma lipase activities were measured in blood samples collected at the end of each 5-wk period. Serum T₃ and T₄ concentrations were measured 10 d after surgery (3 to 6 mo prior) in thyroidectomized horses and 7 d before the study started in euthyroid mares.

Thyroid Hormone Measurements

Serum T₃ and T₄ concentrations were measured using RIA (Diagnostic Products Corp., Los Angeles, CA) previously validated for use with equine sera (Sojka et al., 1993). Samples were analyzed in duplicate with standards provided by the manufacturer. Results of duplicate analyses were examined, and an intraassay coefficient of variability of <5% was required for acceptance of results. Interassay variability was assessed using two canine serum controls (Diagnostic Products Corp.) containing known concentrations of canine T₃ and T₄. Values for these control samples were compared between runs and variability of <10 % was required for acceptance of results.

Isolation and Quantification of Very Low density Lipoprotein

Low-speed centrifugation (1,000 x g) at 4°C for 20 min was used to separate plasma from chilled blood samples. Six-milliliter plasma samples were placed in a fixed-angle rotor (Beckman Instruments Inc., Fullerton, CA) for ultracentrifugation at 112,000 x g for 18 h at 10°C. A 1-mL fraction of density <1.006 g/mL plasma was isolated from each tube. This fraction is referred to as VLDL. Triglyceride, phospholipid (PL), and total cholesterol (TC) components of VLDL were measured using enzymatic colorimetric reagents (Wako Chemicals USA, Richmond, VA) in an automated discrete analyzer (Cobas Mira, Roche Diagnostic Systems Inc., Somerville, NJ). Lipoprotein lipase, phospholipase D, and cholesterol oxidase, respectively, were the principal reagents of the TG, PL, and TC assays used. Protein content of VLDL was analyzed, using bovine serum albumin standards and spectrophotometer (DU640 spectrophotometer, Beckman Instruments Inc.) in accordance with a modified method of the Lowry et al. (1951) procedure (Markwell et al., 1978). Plasma VLDL concentrations were calculated by summing concentrations of lipid (TG, TC, and PL) and protein components.

Analysis of Other Plasma Lipids

Concentrations of plasma TG and TC were measured using the enzymatic colorimetric reagents and instrumentation already described. Plasma NEFA concentrations were measured using an in vitro enzymatic colorimetric test kit (Wako Chemicals USA, Richmond, VA) employing acyl CoA synthetase, acyl CoA oxidase, and ascorbate oxidase reactions.

Measurement of Post-Heparin Plasma Lipase Activities

Lipoprotein lipase (LPL) and hepatic lipase (HL) activities were measured in post-heparin plasma (PHP) according to the method of Watson et al. (1992). Briefly, 70 IU/kg sodium heparin was injected i.v., and blood samples were collected via jugular venipuncture 10 min later. Samples were placed on ice and plasma subsequently isolated as described above. Aliquots of PHP (250 µL) were stored at –70°C until further analysis. Lipase substrate containing 50 µCi glycerol tri[1-¹⁴ C]oleate (Amersham Pharmacia Biotech, Piscataway, NJ) and 500 mg of triolein was prepared in toluene, dried under nitrogen, and stored at –20°C. On the day of use, buffered solutions of gum arabic and bovine serum albumin were added and the mixture sonicated to create a substrate emulsion. Ten microliters of PHP was added to 200 µL of substrate emulsion. A 250-µL volume of Tris buffer containing 0.1 M or 1.0 M sodium chloride was added to tubes for LPL or HL activity measurements respectively. After addition of 50 µL serum activator (LPL) or 0.15 M NaCl (HL) tubes were incubated at 28°C for 60 min. Reactions were terminated and fatty acids extracted by addition of methanol-chloroform-heptane mixture according to the method of Belfrage and Vaughan (1969). Radioactivity was counted in 0.5-mL aliquots of upper phase using a scintillation counter (1600TR liquid scintillation analyzer, Packard Instrument Company Inc., Meriden, CT). Lipase activity is reported as micromoles of fatty acids released per 1 mL of PHP in 1 h of incubation (µmol FA•mL^–1•h^–1). Duplicate assays were performed for each sample collected.

Statistical Analyses

Body weights and mean serum thyroid hormone concentrations were compared using the Wilcoxon rank sum test because data were not normally distributed. Thyroid hormone status, diet, time, and period effects and their interaction terms were examined for blood lipid and lipoprotein concentrations at t = 0, 3, 4, and 5 wk by ANOVA for repeated measures using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Thyroid hormone status, diet, and thyroid x diet effects were examined for LPL and HL activities by ANOVA using the MIXED procedure of SAS. Where significance was established, differences of least squares means among the four groups of horses at each time point were compared using t-tests. An alpha level of P < 0.05 was used for determination of significance.

	Results

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Serum concentrations of T₃ and T₄ were lower (P = 0.029 and P = 0.021, respectively) in thyroidectomized compared with euthyroid horses (Table 2). Alterations in body weight over 5 wk did not differ between groups (Table 2). Horses consumed experimental feeds without health complications. Although formulated with the intent of being isocaloric, diets differed slightly with respect to DE (Table 1).

View larger version (16K): [in this window] [in a new window]   Figure 1. Very low density lipoprotein (VLDL) concentrations in a) euthyroid mares on low-fat diet (n = 4; black bars), b) euthyroid mares on high-fat diet (n = 4; white bars), c) hypothyroid mares on low-fat diet (n = 4; gray bars), and d) hypothyroid mares on high-fat diet (n = 4; bars with diagonal lines). Mean VLDL concentrations were higher (P = 0.045) in hypothyroid mares. Data are summarized as means ± standard errors. Within a time point, means that do not have a common superscript differ (P < 0.10).

View larger version (17K): [in this window] [in a new window]   Figure 2. Plasma triglyceride (TG) concentrations in a) euthyroid mares on low-fat diet (n = 4; black bars), b) euthyroid mares on high-fat diet (n = 4; white bars), c) hypothyroid mares on low-fat diet (n = 4; gray bars), and d) hypothyroid mares on high-fat diet (n = 4; bars with diagonal lines). Mean TG concentrations were higher (P = 0.034) in hypothyroid mares. Data are summarized as means ± SEM. Within a time point, means that do not have a common superscript differ (P < 0.10).

View larger version (20K): [in this window] [in a new window]   Figure 3. Plasma total cholesterol (TC) concentrations in a) euthyroid mares on low-fat diet (n = 4; black bars), b) euthyroid mares on high-fat diet (n = 4; white bars), c) hypothyroid mares on low-fat diet (n = 4; gray bars), and d) hypothyroid mares on high-fat diet (n = 4; bars with diagonal lines). Mean plasma TC concentrations rose when mares were placed on experimental diets, and increased by a greater magnitude in mares that were on the high-fat diet (P = 0.006 diet x time interaction). Mean plasma TC concentrations were higher (P = 0.099) in hypothyroid mares. Data are summarized as means ± SEM. Within a time point, means that do not have a common superscript differ (P < 0.10).

View larger version (18K): [in this window] [in a new window]   Figure 4. Post-heparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities in a) euthyroid mares on low-fat diet (n = 4; black bars), b) euthyroid mares on high-fat diet (n = 4; white bars), c) hypothyroid mares on low-fat diet (n = 4; gray bars), and d) hypothyroid mares on high-fat diet (n = 4; bars with diagonal lines). Higher LPL and HL activities (P = 0.012 and P = 0.017, respectively) were detected in mares that were on the high-fat diet. Data are summarized as means ± SEM. Within an enzyme, means that do not have a common superscript differ (P < 0.10).

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

Higher plasma TC concentrations may be associated with high-fat diets in horses because high-density lipoprotein (HDL) concentrations increase. This class of lipoproteins predominates in horses and constitutes approximately 60% of total plasma lipoprotein mass (Watson et al., 1991). Significantly higher HDL cholesterol (HDL-C) concentrations have been detected in horses on high-fat diets (Geelen et al., 1999, 2001a; Marchello et al., 2000). Geelen et al. (1999) reported that plasma HDL-C concentrations increased by 54% in horses that were on a diet containing 11.8 % of DM soybean oil for 6 wk. An explanation for the observed increase in HDL-C has not been established. It has been suggested that elevated HDL-C concentrations result from increased LPL activity and enhanced transfer of cholesterol from VLDL to HDL during lipolysis (Geelen et al., 2001a).

Dietary fat intake, but not hypothyroidism, was associated with significantly higher LPL and HL activities in this study. Increased plasma lipase activities have been previously detected in horses (Orme et al., 1997; Geelen et al., 2000, 2001a) and ponies (Schmidt et al., 2001) on high-fat diets. A positive linear correlation (R² = 0.819; P =0.001) between LPL activity and dietary fat intake has been reported (Geelen et al., 2001a). Lipoprotein lipase and HL activities are thought to increase in response to tissues that are adapting to fatty acid use as dietary fat intake increases (Geelen et al., 2001b).

Lower plasma TG concentrations have been associated with high-fat diets in horses (Duren et al., 1987; Orme et al., 1997; Geelen et al., 2000). It was noted in this study that euthyroid mares that were on either experimental diet tended to have lower plasma VLDL and TG concentrations when compared with baseline values. This finding was attributed to the higher fat and lower CF content of both diets relative to the hay being consumed before each feeding period. However, plasma VLDL and TG concentrations did not appear to decrease by the same magnitude in hypothyroid mares (Figures 1 and 2), suggesting that differences between groups were accentuated by feeding experimental diets. Although differences in feed intake could not be assessed precisely because measurements of unconsumed feed were unobtainable, the dietary differences (3.2 vs. 7.3% fat) were sufficiently separated that any imprecision in feed intake would be inconsequential with regard to their effects between the treatment groups.

Significant effects of hypothyroidism on plasma VLDL and TG concentrations were detected in this study, but the baseline concentrations detected in thyroidectomized horses were only 1.25- to 1.4-fold higher, respectively than euthyroid values. We have previously reported a marked ninefold increase in mean plasma VLDL concentration following thyroidectomy (Frank et al., 1999). However, in subsequent studies, including the one reported here, plasma VLDL concentrations were only moderately higher when compared with euthyroid values (Frank et al., 2003a,b). Reasons for these discrepancies are not readily evident, but variation between horses with respect their lipoprotein metabolism is likely to have been a contributing factor. Other factors, such as stress associated with surgery, may have magnified the previously reported response (Frank et al., 1999). In the study reported here, serum thyroid hormone concentrations were not measured at the same time in both groups of mares. However, thyroid glands were completely removed during the surgery, and it has previously been shown that serum T₄ concentrations remain undetectable in thyroidectomized horses, even when measured 16 mo after surgery (Lowe et al., 1974).

Plasma VLDL and TG concentrations reflect each other because VLDL carries the majority of TG within equine plasma (Watson et al., 1993; Geelen et al., 1999). Geelen et al. (1999) reported that 54% of plasma TG was associated with VLDL in horses fed low-fat and high-fat diets for 6 wk. Both concentrations were elevated in the thyroidectomized horses of this study, suggesting that VLDL was either being produced at a faster rate by the liver or cleared from circulation more slowly. Lipase activities did not, however, differ between hypothyroid and euthyroid mares, indicating that hypothyroidism did not affect VLDL clearance.

Lipoprotein isolated from the density < 1.006 g/mL plasma fraction has been previously identified as VLDL in horses and is referred to that way here (Watson et al., 1991, 1993). It must be stated, however, that VLDL isolated from blood samples collected from mares in this study may also have contained chylomicrons because sampling occurred approximately 3 h after feeding. Our results do not, however, support the existence of chylomicrons in equine plasma, a conclusion in accordance with observations made by others (Watson et al., 1991, 1993). If chylomicrons were being formed, higher plasma VLDL concentrations might be expected in mares that were on the high-fat diet. In this study, plasma VLDL concentrations tended to be lower in this group. Chylomicron concentrations can be easily measured in humans by quantifying apolipoprotein B-48 (apoB-48), because this apolipoprotein is found exclusively within chylomicrons. Unfortunately, similar techniques cannot be used in horses because apoB-48 is found in both VLDL and chylomicrons (Greeve et al., 1993).

In conclusion, higher plasma VLDL and TG concentrations were detected in hypothyroid horses, but the blood lipid response to higher dietary fat intake was not influenced by hypothyroidism.

	Implications

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 
Higher plasma very low density lipoprotein concentrations were detected in thyroidectomized mares, but hypothyroid horses did not differ in their ability to adapt to a high-fat diet. Results of this study support our assertion that hypothyroidism has little effect on very low density lipoprotein metabolism in horses; however, long-term effects of hypothyroidism on very low density lipoprotein metabolism have yet to be determined and warrant further study.

	Footnotes

 
¹ Supported by the State of Indiana and Purdue Univ. School of Vet. Med. Research Account funded by the Total Wagers Tax.

² The authors thank Purina Mills Inc., St. Louis, MO, for providing experimental feeds used in this study.

³ Correspondence: Dept. of Large Anim. Clin. Sci., Univ. of Tennessee, Knoxville 37996-4545 (e-mail: nfrank{at}utk.edu).

Received for publication June 30, 2003. Accepted for publication May 25, 2004.

	Literature Cited

Top Abstract Introduction Materials and Methods Results Discussion Implications Literature Cited

 


Belfrage, P., and M. Vaughan. 1969. Simple liquid-liquid partition system for isolation of labeled oleic acid from mixtures with glycerides. J. Lipid Res. 10:341–344.[Abstract]

Dietschy, J. M. 1998. Dietary fatty acids and the regulation of plasma low density lipoprotein cholesterol concentrations. J. Nutr. 128:444S–448S.

Duren, S. E., S. G. Jackson, J. P. Baker, and D. K. Aaron. 1987. Effect of dietary fat on blood parameters in exercised Thoroughbred horses. Pages 674–685 in Equine Exercise Physiology. 2nd ed. J. R. Gillespie and N. E. Robinson, ed. ICEEP Publ., Davis, CA.

Frank, N., J. E. Sojka, M. A. Latour, S. R. McClure, and L. Polazzi. 1999. Effect of hypothyroidism on blood lipid concentrations in horses. Am. J. Vet. Res. 60:730–733.[Medline]

Frank, N., J. E. Sojka, and M. A. Latour. 2003a. Effects of hypothyroidism and withholding of feed on plasma lipid concentrations, concentration and composition of very-low-density lipoprotein, and plasma lipase activity in horses. Am. J. Vet. Res. 64:823–828.[Medline]

Frank, N., J. E. Sojka, B. W. Patterson, K. V. Wood, C. C. Bonham, and M. A. Latour. 2003b. Effect of hypothyroidism on kinetics of metabolism of very-low-density lipoprotein in mares. Am. J. Vet. Res. 64:1052–1058.[Medline]

Geelen, S. N. J, M. M. Sloet van Oldruitenborgh-Oosterbaan, and A. C. Beynen. 1999. Dietary fat supplementation and equine plasma lipid metabolism. Equine Vet. J. Suppl. 30:475–478.[Medline]

Geelen, S. N. J., W. L. Jansen, M. J. H. Geelen, M. M. Sloet van Oldruitenborgh-Oosterbaan, and A. C. Beynen. 2000. Lipid Metabolism in equines fed a fat-rich diet. Int. J. Vitam. Nutr. Res. 70:148–152.[Medline]

Geelen, S. N. J., W. L. Jansen, M. M. Sloet van Oldruitenborgh-Oosterbaan, H. J. Breukink, and A. C. Beynen. 2001a. Fat feeding increases equine heparin-released lipoprotein lipase activity. J. Vet. Intern. Med. 15:478–481.[Medline]

Geelen, S. N. J., C. Blázquez, M. J. H. Geelen, M. M. Sloet van Oldruitenborgh-Oosterbaan, and A. C. Beynen. 2001b. High fat intake lowers hepatic fatty acid synthesis and raises fatty acid oxidation in aerobic muscle in Shetland ponies. Br. J. Nutr. 86:31–36.[Medline]

Greeve, J., I. Altkemper, J-H. Dieterich, H. Greten, and E. Windler. 1993. Apolipoprotein B mRNA editing in 12 different mammalian species: Hepatic expression is reflected in low concentrations of apoB-containing plasma lipoproteins. J. Lipid Res. 34:1367–1383.[Abstract]

Henneke, D. R., G. D. Potter, and J. L. Kreider. 1983. Relationship between condition score, physical measurements and body fat percentage in mares. Equine Vet. J. 15:371–372.[Medline]

Lowe, J. E., B. H. Baldwin, R. H. Foote, R. B. Hillman, and F. A. Kallfelz. 1974 Equine hypothyroidism: The long term effects of thyroidectomy on metabolism and growth in mares and stallions. Cornell Vet. 64:276–295.[Medline]

Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Randall. 1951. Protein measurement with the Folin phenol reagent. J. Biol. Chem. 193:265–275.[Free Full Text]

Marchello, E. V., W. A. Schurg, J. A. Marchello, and S. P. Cuneo. 2000. Changes in lipoprotein composition in horses fed a fat-supplemented diet. J. Equine Vet. Sci. 20:453–458.

Markwell, M. K., S. M. Haas, L. L. Bieber, and N. E. Tolbert. 1978. A modification of the Lowry procedure to simplify protein determination in membrane and lipoprotein. Anal. Biochem. 87:206–210.[Medline]

NRC. 1989. Pages 2–31 in Nutrient Requirements of Horses. 5th ed. Natl. Acad. Press, Washington, DC.

Orme, C. E., R. C. Harris, D. J. Marlin, and J. Hurley. 1997. Metabolic adaptations to a fat supplemented diet by the thoroughbred horse. Br. J. Nutr. 78:443–458.[Medline]

Schmidt, O., E. Deegen, H. Fuhrmann, R. Dühlmeier, and H-P. Sallmann. 2001. Effects of fat feeding and energy level on plasma metabolites and hormones in Shetland ponies. J. Vet. Med. 48:39–49.

Sojka, J. E., M. A. Johnson, and G. D. Bottoms. 1993. Serum triiodothyronine, total thyroxine, and free thyroxine concentrations in horses. Am. J. Vet. Res. 54:52–55.[Medline]

Watson, T. D. G., L. Burns, S. Love, C. J. Packard, and J. Shepherd. 1991. The isolation, characterization and quantification of the equine plasma lipoproteins. Equine Vet. J. 23:353–359.[Medline]

Watson, T. D. G., L. Burns, C. J. Packard, and J. Shepherd. 1992. Selective measurement of lipoprotein lipase and hepatic triglyceride lipase in heparinized plasma from horses. Am. J. Vet. Res. 53:771–775.[Medline]

Watson, T. D. G., C. J. Packard, and J. Shepherd. 1993. Plasma lipid transport in the horse (Equus caballus). Comp. Biochem. Physiol. 106B:27–34.

This article has been cited by other articles:

				N. Frank, F. M. Andrews, S. B. Elliott, J. Lew, and R. C. Boston Effects of rice bran oil on plasma lipid concentrations, lipoprotein composition, and glucose dynamics in mares J Anim Sci, November 1, 2005; 83(11): 2509 - 2518. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Frank, N. Articles by Latour, M. A. Search for Related Content PubMed PubMed Citation Articles by Frank, N. Articles by Latour, M. A.