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Department of Animal Science, Cornell University, Ithaca, NY 14853
2 Corresponding author: tro2{at}cornell.edu
| ABSTRACT |
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that have been shown previously to reduce plasma nonesterified fatty acids and increase peripartal dry matter intake (DMI) in dairy cows. Data from Holstein cows (n = 36) entering their second or greater lactation were used to determine whether late prepartum administration of TZD would affect periparturient metabolism, milk production, and ovarian activity. Cows were administered 0, 2.0, or 4.0 mg of TZD/kg of BW by intrajugular infusion once daily from 21 d before expected parturition until parturition. Plasma samples were collected daily from 22 d before expected parturition through 21 d postpartum and twice weekly from wk 4 through 9 postpartum. In response to increasing TZD dosage, plasma nonesterified fatty acid concentrations decreased linearly during the postpartum period (d 0 to +21: 348, 331, 268 ± 31 µEq/L, respectively). Plasma concentrations of glucose were highest in cows administered 4.0 mg of TZD/kg of BW during the peripartum and postpartum periods (d –7 to +7: 57.9, 57.8, 61.1 ± 0.8 mg/dL and d 0 to +21: 51.6, 49.3, 54.7 ± 1.1 mg/dL, respectively). Plasma concentrations of β-hydroxybutyrate were increased during the peripartum period by TZD administration (9.6, 9.9, 10.2 ± 0.3 mg/dL) but were not affected during the postpartum period. Plasma insulin was not affected by treatment during any time period. Postpartum liver triglyceride content was decreased linearly (11.0, 10.4, 4.2 ± 1.6%) and glycogen content was increased linearly (2.16, 2.38, 2.79 ± 0.19%) by prepartum TZD administration. Prepartum TZD administration linearly increased DMI during the peripartum period (d –7 to +7: 16.1, 17.2, 17.3 ± 0.5 kg/d). Cows administered TZD prepartum maintained higher postpartum body condition scores than control cows (wk 1 through 9: 2.77, 2.89, 3.02 ± 0.05). There was no effect of prepartum TZD on milk yield; however, yields of 3.5% fat-corrected milk (52.2, 54.6, 48.0 ± 1.6 kg/d) and most other milk components were decreased in cows that received 4.0 mg of TZD/kg of BW prepartum. Prepartum TZD administration linearly decreased the number of days to first ovulation (29.3, 28.3, 19.0 ± 3.6 d). These results suggest that prepartum administration of TZD improves metabolic health and DMI of periparturient dairy cows and may decrease reliance on body fat reserves during early lactation.
Key Words: transition cow thiazolidinedione peroxisome proliferator-activated receptor-
| INTRODUCTION |
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Adipose tissue is a metabolically dynamic endocrine organ, and adipose tissue metabolism in the transition dairy cow has received some attention (as reviewed by Vernon, 2005), but most research has focused on the utilization of fatty acids (NEFA) that have already been mobilized and taken up by the liver (Drackley et al., 2001). In early lactation, adipose tissue is predisposed to catabolism through increased lipolysis and decreased lipogenesis (McNamara, 1991). Insulin resistance contributes to these processes to mitigate the period of negative energy balance that occurs because the postpartum increase in energy intake lags behind the increase in milk energy output. Recently, it was reported that insulin resistance can be induced by experimental hyperlipidemia, and the periparturient dairy cow that mobilizes excessive amounts of body fat is at greater risk for insulin resistance, leading to energy-related metabolic disorders (Pires et al. 2007).
Insulin resistance is likely mediated through the actions of peroxisome proliferator-activated receptor-
(PPAR-
) that is highly expressed in bovine adipose tissue (Sundvold et al., 1997; Harvatine and Bauman, 2007). Peroxisome proliferator-activated receptor-
belongs to a subfamily of the nuclear-receptor family that regulates gene expression in response to ligand binding (Hammarstedt et al., 2005). Activation of PPAR-
potentiates adipocyte differentiation, enhances insulin action, and decreases the release of FFA from the adipocytes (Houseknecht et al., 2002; Guo and Tabrizchi, 2006). The thiazolindinediones (TZD) are the most potent ligands of PPAR-
(Houseknecht et al., 2002). In addition to the effects of TZD on adipose tissue, there have been numerous reports on its beneficial effects on inflammation and its antiinflammatory properties (Hammarstedt et al., 2005).
Limited research has been conducted using TZD in ruminants. Kushibiki et al. (2001) reported that administering TZD to steers after a challenge with tumor necrosis factor-
(TNF-
) to induce insulin resistance resulted in decreased plasma NEFA. Recently, we demonstrated that administration of 2,4-thiazolidinedione during the late prepartum period in dairy cows tended to reduce the dramatic increase in plasma NEFA at the time of calving and during the immediate postpartum period and also tended to increase peripartal DMI (Smith et al., 2007). The objectives of this study were to study more comprehensively the role of TZD administration on metabolism and subsequent performance of transition dairy cows and to determine whether these responses of cows to prepartum administration of TZD are dose dependent.
| MATERIALS AND METHODS |
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Cows were fitted with an indwelling jugular catheter (Micro-Renathane Implantation Tubing, 2.03 mm o.d. x 1.02 mm i.d.; Braintree Scientific Inc., Braintree MA) on d 23 before expected parturition. Beginning on d 21 before expected parturition, cows were assigned to 1 of 3 treatments in a completely randomized design and were administered either TZD (2.0 or 4.0 mg/kg of BW) or saline (control) by intrajugular infusion once daily at 1200 h. Daily administration of treatments continued until parturition and actual days on treatment averaged 20 ± 4, 22 ± 5, and 20 ± 4 d, respectively, for the 3 increasing doses of TZD. The TZD was obtained as 2,4-thiazolidinedione from Sigma Chemical Co. (St. Louis, MO). All treatments were administered in 100 mL of sterile saline; the TZD was dissolved into sterile saline on a daily basis, left overnight in the dark at room temperature and allowed to dissolve, and gently mixed before drawing into sterile syringes. Cow assignment to treatments was balanced for BCS and calculated previous 305-d mature-equivalent milk yield.
Cows were fed a common TMR for ad libitum intake during the pre- and postpartum periods that was formulated to meet or exceed predicted requirements for energy, protein, minerals, and vitamins (NRC, 2001). Individual DMI was recorded from 32 d before expected parturition through 63 d postpartum. Ingredient and chemical compositions of the diets fed during the experiment are described in Table 1. All nonforage ingredients in both prepartum and postpartum TMR diets were blended by a commercial feed mill into separate concentrate mixtures and were mixed at the farm with the appropriate forage components for each diet. Fresh feed was provided each morning at 0900 h, orts were weighed and recorded daily, and water was made available at all times.
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Body weights and BCS of each animal were recorded once weekly beginning the week before treatment initiation and continuing throughout the study. Body condition scores were assigned using a 5-point system (Wildman et al., 1982) by 2 individuals blinded to treatment and the average of these 2 scores was the assigned value. Energy balance was calculated as net energy balance during both the prepartum and postpartum periods using NRC (2001) equations. Prepartum calculations of net energy requirements were based on BW, actual calf birth weight, and day of pregnancy. Postpartum calculations of net energy requirements were based on BW, milk yield, and milk composition (fat, true protein, and lactose). Daily observations, daily rectal temperatures, and general health records were maintained throughout the study.
After parturition, cows were milked 3 times daily (0800, 1600, and 2400 h) and yields were recorded at each milking for the first 63 d postpartum. During the 9-wk postpartum period, milk samples were collected from each milking on 1 d/wk and composited on an equal volume basis into a single sample for analysis. The composited samples were stored at 4°C with a preservative (Bronopol tablet; D&F Control System, San Ramon, CA) until analyzed (Dairy One Cooperative Inc., Ithaca, NY) within 24 h for fat, protein, and lactose using infrared analysis and SCC by an optical fluorescent method as described previously (Smith et al., 2007).
Plasma and Tissue Sampling and Analyses
Blood samples were collected immediately before treatment administration at 1200 h via the jugular catheter on d 22 (covariate) and then daily from d 21 before expected parturition until parturition. A sterile solution of sodium heparin (200 IU/mL of saline) and Naxcel (4 mg/mL of saline; Pfizer Inc., New York, NY) was injected into the catheter after sampling to prevent blood coagulation and bacterial growth. After parturition, blood samples were collected daily beginning at 1200 h via venipuncture of the coccygeal vessels until 21 d postpartum and then twice per week from wk 4 through 9 postpartum. Blood samples were transferred into glass test tubes containing sodium heparin (100 IU/mL of blood). Plasma was harvested after centrifugation (2,800 x g for 15 min at 4°C), snap-frozen in liquid N2, and stored at –20°C until analyses for metabolites. Plasma concentrations of glucose were determined by enzymatic analysis (glucose oxidase) using a commercial kit (kit no. 510-A; Sigma Chemical). Plasma concentrations of NEFA were analyzed by enzymatic analysis (NEFA-C; Wako Pure Chemical Industries, Osaka, Japan). Plasma concentrations of BHBA were determined by enzymatic analysis (BHBA dehydrogenase; kit no. 310, Sigma Chemical). All spectrophotometric measurements were conducted using a Versamax tunable microplate reader (Molecular Devices, Sunnyvale, CA).
Plasma was analyzed for concentrations of insulin by RIA (Ehrhardt et al., 2001) using bovine insulin (Elanco Animal Health, Greenfield, IN) for iodination and standards (the lowest standard was 0.05 ng/mL). Intra- and interassay CV for the insulin RIA were 12.5 and 13.3%, respectively. Finally, plasma was analyzed for concentrations of progesterone by RIA (Staigmiller et al., 1979; Nara and First, 1981). Intra- and interassay CV for the progesterone RIA were 8.5 and 8.1%, respectively. Plasma progesterone concentrations were used to determine days to first ovulation. Ovulation was assumed to have occurred 3 d before measured plasma progesterone was greater than or equal to 1 ng/mL.
Liver samples were obtained from each cow via percutaneous trochar biopsy on d 10 and 21 postpartum. Briefly, the biopsy site at the 11th intercostal space was clipped and scrubbed using surgical scrub [Betadine Surgical Scrub (7.5% povidone-iodine); Purdue Frederick, Stamford, CT]. Cows were administered 20 mg of the sedative xylazine hydrochloride (Rompun, 2%; Bayer Inc., Sarnia, Ontario, Canada) via venipuncture of the coccygeal vessels 10 min before the procedure. A local anesthetic (Lidocaine-HCl, 2%; Butler Animal Health, Dublin, OH) was administered percutaneously; an incision (approximately 3 cm) was made, and the liver was biopsied using a stainless steel biopsy tool (30 cm in length x 1 cm o.d.). After biopsy, the incision was closed using surgical staples (3M Precise Vista Disposable Skin Stapler; 3M, St. Paul, MN) and a topical antiseptic was applied (BluKote aerosol spray; H. W. Naylor Co., Morris, NY). Liver tissue was blotted to remove excess blood and connective tissue, snap-frozen in liquid N2, and stored at –80°C until analyzed for triglyceride (TG) and glycogen content as described previously (Smith et al., 2007).
The first milking after calving was defined as colostrum. The milk was weighed and subsampled. Subsamples were immediately frozen and stored at –20°C until analysis for total IgG using the Single Radial Immunodiffusion assay (Bethyl Laboratories Inc., Montgomery, TX). Samples were thawed at room temperature, thoroughly mixed by vortexing, diluted 1:4 with 0.05 M phosphate buffer (1 mL of colostrum, 3 mL of PBS), and mixed by vortexing before plating diluted samples for analysis.
Ovarian Ultrasonography
Ovarian follicular activity of all cows was examined by linear array ultrasonography (7.5-MHz transrectal transducer, Aloka 210; Corometrics Medical Systems Inc., Wallingford, CT) 3 times weekly (Monday, Wednesday, and Friday) beginning on d 8 to 10 postpartum and continuing through 21 d postpartum. Diameter of the dominant follicles and corpora lutea between ultrasound examinations was calculated by linear interpolation.
Statistical Analyses
Before statistical analysis, 4 cows were removed from the data set. One cow was removed from the control group because she gave birth to twins, 1 cow was removed from the group administered 2.0 mg of TZD/kg of BW because she suffered a severe uterine torsion before calving, and 2 cows were removed from the group administered 4.0 mg of TZD/kg of BW because they gave birth to twins.
Pretreatment values for plasma variables and DMI, BW, and BCS measured or assessed during the week before assignment to treatments were used as covariates during analysis of covariance applied to their corresponding measurements during the treatment period. Analysis of variance was conducted on measurements conducted over time (plasma variables, DMI, BW, BCS, milk yield, and liver composition) using the MIXED procedure (SAS Institute, 2001) for a completely randomized design with repeated measures. The model included the fixed effects of covariate, treatment, time, and the interaction of treatment and time. Cows were blocked by expected calving date and block was included as a random effect along with cow nested within treatment. For each variable, cow was subjected to 7 covariance structures (first-order autoregressive, heterogeneous first-order autoregressive, compound symmetry, heterogeneous compound symmetry, first-order antedependence, Toeplitz, and variance components). The structure yielding the smallest Akaikes information criterion was selected. The method of Kenward-Rogers was used to calculate denominator degrees of freedom. Covariates were dropped from the model if P > 0.20 and the data were reanalyzed. Prepartum (d –21 to –1 or wk –3 to –1), postpartum (d 0 to 21 or wk 1 to 9, depending on the variable), and peripartum (d –7 to +7) data were analyzed separately. Measurements that were not repeated over time (e.g., calf birth weight, colostrum yield, IgG concentration, and days to first ovulation) were subjected to ANOVA using the MIXED procedure of SAS. The model included the effects of treatment. The number of cows with days to first ovulation less than or equal to 21 d was evaluated by chi-square analysis.
Linear and quadratic effects of increasing doses of TZD were evaluated using orthogonal contrasts for all variables measured. Statistical significance was declared at P < 0.05 and trends were discussed at 0.05 < P < 0.10. Least squares means and SEM are reported throughout.
| RESULTS |
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Reproductive performance parameters are described in Table 5. Prepartum TZD administration linearly decreased (P = 0.02) days to first ovulation, but did not affect (P = 0.12) the proportion of cows ovulating by 21 d postpartum. There was no effect (P > 0.10) of prepartum treatment on peak plasma progesterone concentration, size of the dominant follicle, day postpartum of the peak dominant follicle size, or the size of the corpus luteum (CL).
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| DISCUSSION |
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We expect that some aspects of insulin resistance in adipose tissue are mediated through the action of PPAR-
in dairy cows during the transition period. Thiazolidinediones are potent synthetic ligands for PPAR-
that have been shown to reduce plasma NEFA and potentiate the action of insulin in peripheral tissues of several species (Houseknecht et al., 2002; Hammarstedt et al., 2005; Guo and Tabrizchi, 2006). Peroxisome proliferator-activated receptor-
is highly expressed in adipose tissue in both lactating (Harvatine and Bauman, 2007) and nonlactating (Sundvold et al., 1997) bovines, and we expect that TZD administration would directly activate PPAR-
in adipose tissue. Few studies have been published in which TZD was administered to ruminants. We recently demonstrated that TZD administration to late prepartum dairy cows tended to reduce plasma NEFA and tended to increase DMI during the peripartum (d –7 to d +7) period (Smith et al., 2007).
In this experiment, the effects of TZD administration on plasma NEFA concentrations were similar to those reported in our previous experiment (Smith et al., 2007). Daily administration of TZD during the prepartum period linearly decreased plasma NEFA concentrations from d 7 prepartum through d 7 postpartum. In the only other published experiment using TZD in ruminants, Kushibiki et al. (2001) administered recombinant TNF-
to steers for 9 d to induce insulin resistance and increase plasma NEFA. Similar to the current and previously reported results in transition dairy cows, administration of 2.0 mg of TZD/kg of BW to recombinant TNF-
-treated animals significantly reduced plasma NEFA after d 2 of treatment. Reduction of plasma NEFA concentrations is a consistent observation across many large-scale TZD clinical studies in humans or laboratory animals, and these results are consistent with PPAR-
activation (as reviewed by Sharma and Staels, 2007).
Tordjman et al. (2003) reported that TZD directly stimulates reesterification of fatty acids in adipocytes and lowers fatty acid release into the plasma by inducing phosphoenolpyruvate carboxykinase in adipose tissue, which increases glyceroneogenesis and promotes a futile cycle; however, the activity of phosphoenolpyruvate carboxykinase and its activation by TZD in bovine adipose is unknown. Most likely, the small increases in plasma glucose during the peripartum and postpartum periods in cows administered 4.0 mg of TZD/kg of BW in the late prepartum period can be explained by the downstream effects of TZD administration on liver TG concentrations. Accumulation of TG in the liver decreases the hepatic gluconeogenic capacity (Bobe et al., 2004; Overton and Waldron, 2004). Therefore, cows administered 4.0 mg of TZD/kg of BW may have had increased gluconeogenic capacity in the liver.
Consistent with the decrease in plasma NEFA concentrations during the peripartum and postpartum periods for cows treated with TZD during the prepartum period, liver TG content was linearly decreased by increasing TZD administration prepartum. It has been demonstrated that cows with decreased plasma NEFA concentrations typically have lower liver TG concentrations (Drackley et al., 2001). Thiazolidinediones such as pioglitazone and rosiglitazone have consistently been shown to reduce hepatic TG content in humans with type 2 diabetes (Mayerson et al., 2002; Bajaj et al., 2003). Higher uptake of fatty acids by adipose tissue might have reduced their delivery to the liver, thus decreasing hepatic TG content. In addition, in the current study TZD administration linearly increased liver glycogen stores. Although this increase is consistent with an increase in plasma glucose concentrations during the peripartum period, the small increase in liver glycogen content is confounded with the large decrease in liver TG content. This decrease in liver TG and increase in liver glycogen resulted in a decreased liver TG-to-glycogen ratio in cows administered TZD prepartum. This ratio has been suggested to be an indicator for the likelihood of a cow to develop ketosis (Drackley et al., 1992). In the current experiment, prepartum TZD tended to increase plasma BHBA concentrations during the prepartum period and increased peripartal BHBA concentrations, although the magnitude of the increase was small. We previously reported (Smith et al., 2007) that BHBA concentrations in cows administered TZD were decreased as parturition approached. Cows in our previous experiment were feed restricted to consume no more than 130% of calculated energy requirements during the prepartum period, whereas cows in the present experiment were fed for ad libitum intake during this time frame and consumed approximately 150% of the calculated energy requirements. These differences in energy intake likely were relatively minor; therefore, the reason for the differences in results between experiments is not clear.
Dry matter intake increased linearly with TZD dose during the peripartum period, consistent with results of our previous experiment (Smith et al., 2007). This could again have been attributed to the reduction in postpartum plasma NEFA concentrations (Allen et al., 2005); however, there could have been a direct or a carryover effect of prepartum TZD administration on peripartum DMI. Activation of PPAR-
by TZD administration has been shown to increase food intake in normal, aging, and Zucker diabetic rats (Wolden-Hanson et al., 2002; Larsen et al., 2003; Saitoh et al., 2007). Administration of TZD as rosiglitazone to healthy men housed in respiration chambers increased energy balance and energy intake (Joosen et al., 2006). Humans treated for type 2 diabetes with troglitazone have reported increases in hunger when compared with patients not administered TZD (Shimizu et al., 1998). In addition, TZD has been shown to reduce TNF-
mRNA expression and plasma TNF-
levels in humans (as reviewed by Hammarstedt et al., 2005). Expression of mRNA for TNF-
is elevated in liver (Loor et al., 2005) and possibly adipose tissue at the onset of parturition. Given that TNF-
administration has been reported to reduce feed intake in lactating dairy cows (Kushibiki et al., 2003), it is possible that TZD-induced positive changes in DMI during the peripartum period may have been mediated by decreased expression of TNF-
, but this was not measured in the present study. The increase in peripartum DMI was most likely due to a combination of the reduction in plasma NEFA and the direct effects of activation of PPAR-
.
One of the objectives of this experiment was to follow up our previous experiment with a larger scale study, in part to examine the effects of TZD administration on aspects of performance during the postpartum period. Previously, milk production was not affected by prepartum TZD administration (Smith et al., 2007). In the current experiment, milk production during the first 63 d postpartum tended to be decreased and yields of 3.5% FCM were reduced (P = 0.04) in cows administered 4.0 mg of TZD/kg of BW during the prepartum period. These results are consistent with the concurrent linear reduction in peripartum plasma NEFA concentrations that would be available for direct incorporation into milk fat. In general, yields of milk components were decreased for cows administered 4.0 mg of TZD/kg of BW during the prepartum period. Reasons for differences in results between the 2 experiments are uncertain; however, performance effects also should be evaluated in which TZD is able to be administered without chronic catheterization and intensive handling. There are no previous reports on the effects of TZD on milk yield in any species, and the experiments conducted in our laboratory are the first reported.
Although the limited replication in this experiment did not allow for comprehensive evaluation of the reproductive performance of cows administered TZD during the prepartum period, we evaluated days to first ovulation indirectly based on plasma progesterone and several aspects of follicular dynamics. Administration of prepartum TZD linearly decreased the number of days to first ovulation. Negative energy balance has been shown to have a negative impact on the timing of postpartum first ovulation (Butler, 2000; Jorritsma et al., 2003) and minimizing BCS loss has been shown to optimize reproductive efficiency (as reviewed by Roche, 2006). In this study, prepartum TZD administration tended to increase postpartum net energy balance quadratically and resulted in less loss (P < 0.01) of BCS postpartum. These results suggest that improved energy balance after TZD administration in dairy cows may improve reproductive performance. Furthermore, higher BCS during early lactation for cows administered TZD prepartum corroborates the positive effects of prepartum TZD administration on postpartum calculated net energy balance. Despite these effects on days to first ovulation, prepartum TZD administration did not affect the size or day of the dominant follicle or the size of the CL. Lucy et al. (1991) reported that the predicted energy balance before d 25 postpartum was not related to the frequency of class 4 (>15 mm) follicles. Beam and Butler (1997) determined that cows fed increasing amounts of added fat during early lactation had more class 4 follicles by d 14 postpartum; however, the number of large follicles was not correlated with energy balance in their study. Clearly, aspects of reproduction as potentially affected by prepartum TZD warrant more thorough investigation in a larger study.
There was no effect of prepartum TZD administration on calf birth weight in the present or previous (Smith et al., 2007) experiment. Sevillano et al. (2005) reported that newborn rats from mothers treated with TZD as englitazone had a lower body mass than control rats, but the size of the litter was not changed. In that study, mothers were treated with TZD for 4 out of the 20 d they were pregnant, or 20% of the pregnancy. Our cows were treated for 21 or 25 d (Smith et al., 2007) of the 280 d they were pregnant, or about 7.5 or 9% of their pregnancy, respectively. It is possible that the TZD was not administered to the cows long enough for there to be an effect on calf birth weight. However, a second experiment was recently published in which rosiglitazone was administered during the entire pregnancy and showed that postnatal growth and litter size in mice were unaffected by treatment; the authors concluded that prepartum TZD caused no phenotypic harm to the mouse fetus, suggesting potential safety of use during pregnancy (Klinkner et al., 2006). Finally, colostrum quantity was increased by prepartum administration of 2.0 mg of TZD/kg of BW; however, quality as assessed by IgG content appeared to be uniformly high and sufficient across all treatments (Davis and Drackley, 1998).
| CONCLUSIONS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Received for publication July 1, 2008. Accepted for publication March 31, 2009.
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