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Thirty-eight multiparous Holstein cows were utilized in a completely randomized design to examine the effect of feeding calcium salts of conjugated linoleic acid (CLA) and trans-octadecenoic acids (trans-C18:1) on animal performance and lipid and glucose metabolism during the transition to lactation. Dietary treatments were initiated approximately 28 d prior to expected calving dates and continued through d 49 postpartum. Prepartum treatments consisted of 1) a basal diet (Control), 2) basal diet + 150 g/d of CLA mix (CLA), and 3) basal diet + 150 g/d of trans-C18:1 mix (TRANS). Amounts of calcium salts of CLA and trans-C18:1 mixes were adjusted to 225 g/d during the 49-d postpartum treatment period. All diets were offered as a total mixed ration. Prepartum fat supplementation had no detectable effects on dry matter intake, body weight, or body condition score. After parturition, cows in the TRANS group consumed less dry matter at wk 4, 5, and 6 of lactation than did cows in the control group. Cows fed the trans-C18:1 supplement were in a more severe negative energy balance than those fed the control diet at 1 wk of lactation. Periparturient fat supplementation had no detectable effects on milk yield during wk 1 to 7 of lactation. Milk fat was not affected during wk 1 to 4, but was reduced after wk 4 of lactation by dietary CLA. Feeding calcium salts of CLA decreased short- to medium-chain fatty acid (C4 to C14) concentrations and increased both linoleic and linolenic acid concentrations in milk fat. Concentrations of nonesterified fatty acids and β-hydroxybutyric acid in blood were greater in cows fed the CLA-supplemented diet than in those fed the control diet at 1 wk of lactation. In spite of small numerical tendencies, hepatic lipid and triacylglycerol concentrations did not vary significantly among dietary treatments. Periparturient fat supplementation had no detectable effects on plasma glucose and insulin concentrations. Steady-state concentrations of hepatic mRNA encoding pyruvate carboxylase and phosphoenolpyruvate carboxykinase were greater for the TRANS treatment group than the control and CLA groups. Results indicate that dietary CLA and trans-C18:1 fatty acids may affect lipid and glucose metabolism in early postpartum Holstein cows through distinct mechanisms.
Conjugated linoleic acid (CLA) refers to a mixture of positional and geometric isomers of octadecadienoic acids found predominantly in ruminant-derived products (
Review of the effects of trans fatty acids, oleic acid, n-3 polyunsaturated fatty acids, and conjugated linoleic acid on mammary carcinogenesis in animals.
). The finding that milk fat depression generally corresponds to an increase in milk fat content of the trans-10 octadecenoic isomer has led to the conclusion that the trans-10 fatty acid isomer or its metabolites may be responsible for milk fat depression (
). Recent studies have provided evidence that the polyunsaturated fatty acids containing trans-10 double bonds likely decrease milk fat percentage through a reduction in de novo fatty acid synthesis (
recently reported that calcium-protected CLA supplements were more effective at reducing milk fat content than were calcium salts of trans fatty acids. This observation led us to hypothesize that calcium salts of CLA and trans fatty acids may affect production and metabolic responses of transition dairy cows through different mechanisms.
The inability of high-producing dairy cows to maintain a positive energy balance imposes considerable metabolic stress on the lactating animal (
). Failure of the periparturient cow to adequately adjust her metabolism to support the increased nutrient requirements of early lactation may lead to metabolic disorders, suboptimal milk production, and compromised liver function (
). The objective of this study was to examine the effect of dietary supplementation of calcium salts of CLA and trans-C18:1 isomers on production and metabolic responses of periparturient Holstein cows.
Materials and Methods
Animals, Treatments, and Sampling
Thirty-eight multiparous Holstein cows were utilized in a completely randomized design to examine the effect of feeding calcium salts of CLA and trans-C18:1 fatty acids on animal performance and metabolism during the transition to lactation. All experimental animals were managed according to the guidelines approved by the University of Florida Animal Care and Use Committee. Dietary treatments were initiated approximately 28 d prior to calculated calving dates and continued through d 49 postpartum. Prepartum treatments consisted of 1) a basal diet (control; n = 17), 2) basal diet + CLA mix (bCLA; Bioproducts Inc., Fairlawn, OH; n = 10), and 3) basal diet + trans-C18:1 fatty acid mix (TRANS; Bioproducts Inc.; n = 11). Fat-supplemented diets were formulated for intakes of approximately 150 g/d prepartum and 225 g/d postpartum of calcium salts of CLA or trans-C18:1 mixtures. Each of these salts contains 85.0% lipids and 10.7% calcium (Bioproducts Inc.). Fat supplements were mixed with the concentrates and offered as part of the TMR to experimental animals. As a result of adding calcium salts of fatty acids to two of the three diets, experimental diets were not isoenergetic. Detailed fatty acid composition of calcium salts of fat supplements are presented in Table 1 (Bioproducts Inc.).
Table 1Fatty acid profile of calcium salts of conjugated linoleic acid (CLA) and trans-octadecenoic isomers (TRANS).
Prepartum cows were housed in pens with a sod base and equipped with shaded Calan gates (American Calan Inc., Northwood, NH). Postpartum cows were housed in a free-stall barn equipped with fans, sprinklers, and Calan gates. Intake of DM was measured daily. All experimental cows were offered ad libitum amounts of TMR to allow for 5 to 10% refusals (Table 2). Corn silage was the major forage component and ground corn was the primary concentrate. Dry matter of corn silage was determined weekly (55°C for 48 h), and the rations were adjusted accordingly to maintain a constant forage:concentrate ratio on a DM basis. Samples of forages and concentrate mixes were collected weekly and composited monthly and analyzed by wet chemistry methods for CP, ADF, NDF, and minerals (Dairy One, Ithaca, NY; Table 2).
Table 2Ingredient and chemical composition of experimental diets.
Diets contained 0 or 1.44% of calcium salts of conjugated linoleic acids (CLA), or 1.44% of calcium salts of trans-octadecenoic fatty acid mixture (DM basis). The calcium salt products partially replaced cornmeal.
Diets contained 0 or 1.29% of calcium salts of CLA, or 1.29% of calcium salts of trans-octadecenoic fatty acid mixture (DM basis). The calcium salt products partially replaced cornmeal.
Mineral and vitamin mix contained 22.8% CP, 2.1% fat, 22.89% Ca, 0.16% P, 2.77% Mg, 0.75% Na, 0.20% K, 2.42% S, 8.03% Cl, 146.7 mg/kg of Mn, 95.0 mg/kg of Zn, 26.6 mg/kg of Fe, 112.5 mg/kg of Cu, 10.7 mg/kg of Co, 7.9 mg/kg of I, 6.9 mg/kg of Se, 268,130 IU/kg of vitamin A, 40,000 IU/kg of vitamin D, and 1129 IU/kg of vitamin E (DM basis).
Mineral and vitamin mix contained 26.4% CP, 1.74% fat, 10.15%Ca, 0.90% P, 3.1% Mg, 8.6% Na, 5.1% K, 1.5% S, 4.1% Cl, 2231 mg/kg of Mn, 1698 mg/kg of Zn, 339 mg/kg of Fe, 512 mg/kg of Cu, 31 mg/kg of Co, 26 mg/kg of I, 7.9 mg/kg of Se, 147,756 IU/kg of vitamin A, 43,750 IU/kg of vitamin D, and 787 IU/kg of Vitamin E (DM basis).
Minimum concentrations of 40% Na, 55% Cl, 0.25% Mn, 0.2% Fe, 0.033% Cu, 0.007% I, 0.005% Zn, and 0.0025% Co (DM basis). Manufactured by Flint River Mills, Inc., Bainbridge, GA.
NEL values for prepartum and postpartum diets containing calcium salts were 1.58 and 1.69 Mcal/kg of dietary DM, respectively.
1.54
1.65
Ca, % of DM
1.75
0.35
Mg, % of DM
0.30
0.32
K, % of DM
1.12
1.36
Na, % of DM
0.25
0.40
S, % of DM
0.22
0.20
Fe, mg/kg of DM
402
406
Zn, mg/kg of DM
92
106
Cu, mg/kg of DM
18
29
Mn, mg/kg of DM
63
76
Mo, mg/kg of DM
1
1
1 Diets contained 0 or 1.44% of calcium salts of conjugated linoleic acids (CLA), or 1.44% of calcium salts of trans-octadecenoic fatty acid mixture (DM basis). The calcium salt products partially replaced cornmeal.
2 Diets contained 0 or 1.29% of calcium salts of CLA, or 1.29% of calcium salts of trans-octadecenoic fatty acid mixture (DM basis). The calcium salt products partially replaced cornmeal.
3 A marine and animal protein supplement containing 68% RUP (H. J. Baker & Bro., Inc., Stamford, CT).
4 Mineral and vitamin mix contained 22.8% CP, 2.1% fat, 22.89% Ca, 0.16% P, 2.77% Mg, 0.75% Na, 0.20% K, 2.42% S, 8.03% Cl, 146.7 mg/kg of Mn, 95.0 mg/kg of Zn, 26.6 mg/kg of Fe, 112.5 mg/kg of Cu, 10.7 mg/kg of Co, 7.9 mg/kg of I, 6.9 mg/kg of Se, 268,130 IU/kg of vitamin A, 40,000 IU/kg of vitamin D, and 1129 IU/kg of vitamin E (DM basis).
5 Mineral and vitamin mix contained 26.4% CP, 1.74% fat, 10.15%Ca, 0.90% P, 3.1% Mg, 8.6% Na, 5.1% K, 1.5% S, 4.1% Cl, 2231 mg/kg of Mn, 1698 mg/kg of Zn, 339 mg/kg of Fe, 512 mg/kg of Cu, 31 mg/kg of Co, 26 mg/kg of I, 7.9 mg/kg of Se, 147,756 IU/kg of vitamin A, 43,750 IU/kg of vitamin D, and 787 IU/kg of Vitamin E (DM basis).
6 Minimum concentrations of 40% Na, 55% Cl, 0.25% Mn, 0.2% Fe, 0.033% Cu, 0.007% I, 0.005% Zn, and 0.0025% Co (DM basis). Manufactured by Flint River Mills, Inc., Bainbridge, GA.
7 Contains 21% P and 15 to 18% Ca. Manufactured by Southeastern Minerals, Inc., Bainbridge, GA.
8 NEL values for prepartum and postpartum diets containing calcium salts were 1.58 and 1.69 Mcal/kg of dietary DM, respectively.
Postpartum cows were milked 3 times per day and milk weights were recorded at each milking. For each experimental cow, samples of milk from 2 consecutive morning (1000 h) and evening (1800 h) milkings were collected weekly at 5, 12, 19, 26, 33, 40, and 47 ± 2 DIM and analyzed for fat, protein, and SCC. Milk samples were analyzed for fat and protein concentration using a mid-infrared spectrophotometer equipped with an A and B filter (Bentley Instruments, model B2000, Chaska, MN). Two milk samples collected at 8-h intervals provide good estimates of milk fat content of the full day's production for herds milked 3 times per day (Wiggan, 1986). Daily values were calculated by averaging morning and evening milk values. At wk 2, 4, and 7 postpartum, additional milk samples were taken and composited for fatty acid profile determination. Body weights were measured and BCS assigned weekly by the same 2 individuals.
Blood (∼20 mL) was collected weekly at 4, 11, 18, 25, 32, 39, and 46 ± 2 DIM via coccygeal arterio-venipuncture into potassium oxalate- and sodium fluoride-coated tubes (Vacutainer, Becton Dickinson, Franklin Lakes, NJ) just before the morning feeding (0700 h). Samples were placed immediately in ice and centrifuged at 3000 × g for 30 min. Plasma was harvested and stored at −20°C for subsequent metabolite and hormone analyses. On d 2, 14 ± 2, and 28 ± 2 postpartum, liver samples were collected via biopsy, rinsed with sterile saline, snap-frozen in liquid nitrogen, and stored at −80°C until analyzed for lipid metabolites and mRNA abundance.
Prepartum energy balance was calculated using the following equation:
Net energy of intake was calculated by multiplying the weekly DMI by the calculated energy value of the diet. Energy requirement for body maintenance was computed using the following equation (
. Briefly, fatty acid profile was determined by split injection (20:1) onto a CP-Sil 88 fused-silica capillary column (100 m × 0.25 mm; Chrompack, Raritan, NJ) using a programmed temperature gradient method. The hydrogen carrier gas pressure was constant and the injector and detector temperatures were 255°C. Initial oven temperature was 70°C. Following injection of sample, the oven temperature was increased by 4°C/min to 175°C and held for 3 min. Oven temperature was then raised by 1°C/min to 185°C and held for 20 min. Oven temperature was then increased by 3°C/min to 215°C followed by an increase by 10°C/min to 240°C and held for 5 min. Oven temperature was subsequently returned to 70°C. Individual fatty acids were identified by comparison of retention times to those of pure standards (Matreya, Inc., Pleasant Gap, PA). A response correction factor for each fatty acid methyl ester was used to convert peak area percentage to weight percentage. Correction factors were determined by analyzing butter oil of a known fatty acid profile with certified values (CRM 164; European Community Bureau of Reference, Brussels, Belgium;
Concentrations of NEFA (NEFA-C kit; Wako Fine Chemical Industries USA, Inc., Dallas TX), glucose (Sigma procedure no. 510; Sigma Chemical Co., St. Louis, MO), and BHBA (Sigma procedure No. 319; Sigma Chemical Co., St. Louis, MO) in plasma were measured enzymatically with commercially available kits. Intraassay coefficients of variation were 4.8, 2.4, and 3.5% for plasma NEFA, glucose, and BHBA, respectively. Hepatic lipid was extracted from finely homogenized liver with a 2:1 (vol/vol) mixture of chloroform and methanol, and concentrations of total lipids were determined gravimetrically after drying under N2 (
). The lipid extract was redissolved in 3:2 (vol/vol) mixture of hexane and isopropanol, and concentrations of triacylglycerol (TAG) were measured colorimetrically as described by
. Sensitivity of the assay was 1 ng/ml, and intra- and interassay coefficients of variation were 2.7 and 6.9%, respectively.
Total liver cellular RNA was isolated from a subset of 5 animals per treatment group using TRIzol reagent (Life Technologies, Grand Island, NY). Total RNA (30 μg) was fractionated in a 1.0% agarose-formaldehyde gel and blotted to a Biotrans nylon membrane (ICN, Irvine, CA) via capillary action. The RNA was crosslinked to the membrane by UV irradiation and baked at 80°C for 1 h. The RNA blots were prehybridized with Rapid-Hyb buffer (Amersham-Pharmacia Biotechnology, Piscataway, NJ) at 60°C for 30 min. The filters were then hybridized with random primer-labeled pyruvate carboxylase (PC) and phosphoenol pyruvate carboxykinase (PEPCK) cDNA probes (
). After hybridization, RNA filters were washed for 20 min in 50 ml of 2× saline sodium citrate, 0.1% SDS at room temperature, followed by two 15-min washes in 0.1× saline sodium citrate and 0.1% sodium dodecyl sulfate at 42°C. The filters were blotted dry and exposed to x-ray film (X-OMAT, Eastman Kodak, Rochester, NY) for 24 to 48 h at −80°C. Hybridization signals for each target gene were quantified by densitometric analysis. Equal loading of RNA samples and specificity of treatment effects were verified by subsequent rehybridization of filter membranes with glyceraldehyde 3-phosphate dehydrogenase probe.
Statistical Analyses
Performance and intake responses were reduced to weekly means before statistical analysis. Production and metabolic responses were evaluated using the MIXED procedure for repeated measurement of the SAS software package (SAS Inst., Inc., Cary, NC). Fixed effects included treatment, week relative to calving, and treatment × week interaction. The variance for cow, nested within treatment, was used as random error term to test the main effect of treatment. Effects of CLA or trans-C18:1 supplementation were examined by single degree of freedom contrasts (control vs. CLA or control vs. TRANS). Differential temporal responses to dietary treatments were further examined using the SLICE option of the MIXED procedure. Liver metabolite and mRNA responses were analyzed using the MIXED procedure with mathematical models that included effects of treatment, sampling day, and treatment × day interaction. The cow variance was considered random and was utilized as the error term to test the main effect of treatment. Mean treatment and week effects are reported as least squares means.
Results
Production Responses
Dry matter intakes (15.8 ± 0.7 kg/d), BW (695.7 ± 21 kg), and BCS (3.10 ± 0.10) were similar for all 3 dietary treatment groups during the prepartum period. Average intakes of calcium salts of CLA and trans-C18:1 isomers were 231 and 214 g/d, respectively, during the prepartum period. Corresponding values were 258 and 261 g/d for the CLA and trans-C18:1 mixes, respectively, during the 49-d postpartum treatment period.
Postpartum DMI increased (P < 0.01) from 2.4% of BW at wk 1 to 3.9% of BW at wk 7 of lactation (Figure 1A). Compared with the control group, cows in the TRANS treatment group consumed less DM at wk 4 (0.5% BW, P < 0.01), 5 (0.6% BW, P < 0.01) and 6 (0.4% BW, P < 0.02) of lactation (Figure 1A). On average, cows in the bCLA treatment group consumed less DM (P < 0.02) than control cows at wk 6 of lactation (Figure 1A). Although cows in the TRANS group tended to have greater BW than cows in the other two treatment groups, patterns of BW response did not vary among dietary groups (Figure 1B). Cows fed the trans-C18:1-supplemented diet were in a more negative energy balance (P < 0.01) at wk 1 of lactation than cows in the control group (Figure 2).
Figure 1Average DMI (A) and BW (B) of postpartum Holstein cows fed a control (○), conjugated linoleic acids (CLA)-supplemented (▿), or trans-C18:1 (TRANS)-supplemented (□) diet. See Table 1for composition of fat supplements. Asterisks indicate significant treatment differences at wk 4 (P < 0.01), 5 (P < 0.01), and 6 (P < 0.02) of lactation for DMI.
Figure 2Calculated energy balance by week relative to parturition for Holstein cows fed a control (○), conjugated linoleic acids-supplemented (▿), or trans-C18:1 (TRANS)-supplemented (□) diet. The asterisk indicates significant treatment differences (P < 0.01) at wk 1 of lactation.
Average milk production during the 7-wk postpartum treatment period did not differ among the dietary groups (Table 3). Milk production pattern for cows in the TRANS treatment group was different (treatment × week interaction, third-order polynomial, P < 0.02) than those for cows in the control and bCLA groups (Figure 3A). Average 3.5% FCM weights were unaffected by dietary treatment during the first 7 wk of lactation (Figure 3B). Mean milk protein production and concentration and SCC were similar among dietary treatment groups (Table 3).
Table 3Least squares means for performance of lactating Holstein cows fed diets containing calcium salts of conjugated linoleic acid (CLA) or trans-octadecenoic acid isomers (TRANS) during wk 1 through 7 of lactation.
Figure 3Temporal patterns of milk yield (A) and 3.5% FCM (B) by postpartum Holstein cows fed a control (○), conjugated linoleic acids-supplemented (▿), or trans-C18:1 (TRANS)-supplemented (□) diet. See Table 1 for composition of fat supplements. There was a treatment × week interaction (third-order polynomial, P < 0.02) for milk yield.
Mean milk fat concentration was reduced (P < 0.01) in cows fed CLA (3.49 vs. 2.99, Table 3). Dietary CLA supplementation decreased (P < 0.05) milk fat content by 23, 26, and 25% at wk 5, 6, and 7 of lactation, respectively (Figure 4A). In spite of small numerical tendencies, trans-C18:1 supplementation had no detectable effect on milk fat percentage (Table 3; Figure 4A). Dietary CLA, but not trans-C18:1 mix, reduced (P < 0.02) milk fat yield by wk 7 of lactation (Figure 4B).
Figure 4Temporal patterns of milk fat percentage (A) and yield (B) in postpartum Holstein cows fed a control (○), conjugated linoleic acids-supplemented (▿), or trans-C18:1 (TRANS)-supplemented (□) diet. See Table 1 for composition of fat supplements. Asterisks indicate significant treatment differences at wk 5 (P < 0.03), 6 (P < 0.01), and 7 (P < 0.01) for milk fat percentage, and at wk 7 (P < 0.03) for milk fat yield.
As expected, higher concentrations of CLA (namely the trans-10, cis-12 isomer) and trans-C18:1 fatty acids were detected in milk from cows receiving the bCLA and TRANS diets, respectively (Table 4). In addition, supplementation of CLA decreased (P < 0.01) short- to medium-chain fatty acid (C4:0 to C14:0) concentrations and increased (P < 0.01) both linoleic and linolenic acid concentrations in milk fat (Table 4). There was a tendency (P < 0.06) for less cis-9,trans-11 CLA isomer in milk fats from CLA-supplemented than control cows (Table 4). The fatty acid profiles were derived from composite milk samples for wk 2, 4, and 7, and therefore may not reflect precise temporal changes in milk fatty acid composition.
Table 4Least squares means of fatty acids in milk fat from Holstein cows fed diets containing calcium salts of conjugated linoleic acid (CLA) or trans-octadecenoic acid isomers (TRANS).
Week × treatment interactions were detected for plasma NEFA (P < 0.01) and BHBA (P < 0.02) concentrations (Figure 5). At wk 1 postpartum, cows fed the CLA-supplemented diet had greater plasma NEFA and BHBA concentrations than those in the control group.
Figure 5Plasma NEFA (A) and BHBA (B) concentrations by week relative to parturition in Holstein cows fed a control (○), conjugated linoleic acids-supplemented (▿), or trans-C18:1 (TRANS)-supplemented (□) diet. Asterisks indicate significant treatment differences at wk 1 for plasma NEFA (P < 0.01) and BHBA (P < 0.02).
Mean liver lipid and TAG concentrations increased (P < 0.01) between d 2 and 14 postpartum, and then decreased by d 28 postpartum (Figure 6). In spite of numerical tendencies, mean hepatic lipid and TAG concentrations did not differ among the diets. Concentrations of glucose in plasma were unaffected by dietary treatment (Figure 7A). Plasma insulin concentration decreased (P < 0.01) from 0.41 ± 0.02 ng/mL at wk −1 to 0.32 ± 0.02 ng/mL at wk 1 postpartum (Figure 7B) and was greater (P < 0.05) in cows fed the TRANS diet than those fed the control diet at 6 wk of lactation.
Figure 6Liver lipid (A) and triacylglycerol (B) concentrations by day of lactation in Holstein cows fed a control (□)), conjugated linoleic acids-supplemented (diagonal line), or trans-C18:1 (TRANS)-supplemented (cross hatch) diet.
Figure 7Plasma glucose (A) and insulin (B) concentrations by week relative to parturition in Holstein cows fed a control (○), conjugated linoleic acids-supplemented (▿), or trans-C18:1 (TRANS)-supplemented (□) diet. A treatment effect was detected (P < 0.02) for plasma insulin at wk 6 of lactation.
Steady-state concentration of hepatic mRNA encoding PC was greater (P < 0.01) for the TRANS treatment group than for the control group at d 2, 14, and 28 postpartum (Figure 8A). The abundance of liver PEPCK mRNA transcript was greater (P < 0.01) in cows fed the TRANS diet than those fed the control diet at d 14 postpartum (Figure 8B).
Figure 8Steady-state concentrations of hepatic mRNA encoding pyruvate carboxylase (PC; A) and phosphoenolpyruvate carboxykinase (PEPCK; B) by day of lactation in Holstein cows fed a control (□), conjugated linoleic acids-supplemented (diagonal line), or trans-C18:1 (TRANS)-supplemented (cross hatch) diet. Asterisks indicate significant treatment differences at d 2 (P < 0.01) and 28 (P < 0.01) for PC mRNA, and at d 14 (P < 0.01) for PEPCK mRNA.
In the present study, 10-wk fat supplementation did not appear to have an adverse effect on the cow's health or production performance. Between wk 4 and 6 of lactation, DMI was lower in cows fed the TRANS diet compared with those fed the control diet. Results are consistent with other studies that have shown a decrease in DMI when cows were infused with trans (
) fatty acids. The mechanism by which dietary fat supplements alter DMI in dairy cows is unclear and may vary depending upon the profile of long-chain fatty acids that are available for intestinal absorption. In a recent cattle study (
). Unlike CLA, dietary supplementation of trans-C18:1 isomers had no detectable effect on milk fat percentage and yield during the first 7 wk of lactation. This is consistent with a recent report that calcium-protected CLA supplements were more effective at reducing milk fat content than were calcium salts of trans fatty acids (
). Available evidence indicates that supplemental CLA likely decreases milk fat content through inhibition of de novo fatty acid synthesis in the mammary gland, as reflected by decreased short-chain fatty acid concentrations in milk (
Concentrations of NEFA and BHBA in plasma were greater in cows fed the CLA-supplemented diet than those fed the control diet at 1 wk of lactation. Results are consistent with rodent studies (
). This discrepancy between the present study and previous reports in cattle may be due to differences in the duration or stage of lactation when those studies were conducted. Because plasma NEFA concentration is a reliable index of the magnitude of adipose fat mobilization (
Effect of bovine somatotropin on metabolism of lactating dairy cows: Influence on rates of irreversible loss and oxidation of glucose and nonesterified fatty acids.
), the current finding on plasma NEFA concentration would indicate that periparturient CLA supplementation might transiently enhance lipolysis shortly after calving in postpartum Holstein cows.
The observation that periparturient CLA supplementation failed to alter peripheral glucose concentration is consistent with previous cattle (
) data. However, the finding that supplemental trans-C18:1 monoenes failed to increase plasma glucose concentration is difficult to interpret in light of the induction of PC and PEPCK mRNA transcripts by dietary trans fatty acids. At any given time, plasma glucose concentration represents a steady-state level of blood glucose, which may not be indicative of how much glucose is being produced de novo and how much of it is being cleared from circulation. On the other hand, Northern blot analysis detects steady-state levels of a target gene, but does not provide adequate information as to how the enzymatic activity may be altered by a given treatment. Consequently, the apparent discrepancy between the amount of an enzyme and the concentration of its metabolic product may reflect the combined differences between peripheral processing of the metabolite and the enzymatic activity due to treatment.
Conclusion
Feeding calcium salts of CLA to early lactation Holstein cows depressed milk fat concentration after wk 4 of lactation, whereas supplementation of calcium salts of trans-octadecenoic fatty acids did not induce detectable alteration in milk fat content during the first 7 wk of lactation. Concentrations of NEFA and BHBA in blood were greater in cows fed the CLA-supplemented diet than those fed a control diet at wk 1 of lactation. Steady-state concentrations of hepatic mRNA encoding PC and PEPCK were upregulated by dietary trans fatty acids. Results indicate that feeding calcium salts of CLA and trans octadecenoic acids to postpartum Holstein cows may alter lipid and glucose metabolism through distinct mechanisms.
Acknowledgments
The authors express their appreciation to Bioproducts Inc. for partial financial support and the generous gift of calcium salts of CLA and trans-C18:1 isomers, and to the University of Florida Dairy Research Unit staff for management of the cows.
References
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Effect of bovine somatotropin on metabolism of lactating dairy cows: Influence on rates of irreversible loss and oxidation of glucose and nonesterified fatty acids.
Review of the effects of trans fatty acids, oleic acid, n-3 polyunsaturated fatty acids, and conjugated linoleic acid on mammary carcinogenesis in animals.
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