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ANIMAL PRODUCTION |
Department of Animal Science, University of Wyoming, Laramie 82071
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: beef cattle • body condition score • hormone • lipid supplementation • metabolite
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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) by partitioning nutrients for energy use from one metabolic process to another (Hess et al., 2005). For example, Bottger et al. (2002) attributed maintenance of greater BCS during lactation in beef cows to supplementation with linoleic acid, whereas dietary oleic acid increased milk fat synthesis. Increasing the BCS of thin lactating beef cows as a result of partitioning nutrients toward adipose tissue reserves rather than milk fat synthesis could lead to improved reproduction (Houghton et al., 1990) and decreased maintenance requirements (Wagner et al., 1988). Metabolic hormones play a major role in coordinating nutrient partitioning among milk synthesis, adipose tissue storage and mobilization, as well as oxidation in different tissues (Brockman and Laarveld, 1986). Lipid supplementation in lactating dairy cows, associated with increased plasma glucose and decreased ketone body concentrations, effectively increased substrate availability for milk fat synthesis and concurrently reduced the demand for mobilized substrate from energy reserves (Kronfeld et al., 1980). We hypothesized that the effects of dietary lipids on nutrient partitioning may be associated with changes in the concentrations of metabolites and metabolic hormones. Therefore, our objective was to evaluate the interaction of BCS at parturition and postpartum supplementation with cracked high-oleic acid or high-linoleic acid safflower seeds on the circulating concentrations of metabolites and hormones associated with nutrient use.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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. Briefly, in a 2-yr experiment (n = 36/yr), 3-yr-old Angus x Gelbvieh beef cows (n = 72) were managed nutritionally to achieve a BCS (1 = emaciated, 9 = obese; Wagner et al., 1988) of 4 ± 0.07 (479.3 ± 36.3 kg of initial BW) or 6 ± 0.07 (579.6 ± 53.1 kg of initial BW) at parturition. To ensure that postpartum cow and calf performance was not affected by prepartum energy deficit, cows achieving a BCS of 4 at parturition were managed to be in energy deficit during the second trimester of pregnancy, and then were fed to meet maintenance requirements throughout the third trimester. The cows were randomly assigned within BCS group to postpartum dietary treatment as they calved. Beginning 3 d postpartum, cows were placed into 1 of 6 pens (6 cows/pen) with individual feeding stanchions, and were fed twice daily. Diets were hay (2.13% of BW during yr 1 and 2.03% of BW during yr 2) plus a low-fat control supplement (0.57% of BW during yr 1 and 0.30% of BW during yr 2) or a supplement with either cracked high-linoleate safflower seeds (hay at 2.32% of BW and supplement at 0.39% of BW during yr 1; hay at 2.03% of BW and supplement at 0.23% of BW during yr 2) or cracked high-oleate safflower seeds (hay at 2.32% of BW and supplement at 0.40% of BW during yr 1; hay at 2.03% of BW and supplement at 0.24% of BW during yr 2) until d 61 of lactation. Each treatment (BCS 4 or 6 at parturition and dietary treatment) was represented in every pen with an average calving interval not greater than 7 d within each pen.
Previous research at the University of Wyoming indicated that cows with similar genetics produced 9 kg of milk during peak lactation (Bottger et al., 2002). Therefore, the diets (Table 1) were formulated to meet the energy requirements of a 544-kg beef cow producing 9 kg of milk at peak lactation. Within each year, the diets were also formulated to be isonitrogenous and isocaloric. The dietary CP was greater in yr 2 due to differences in the hay [bromegrass hay (8.5% CP) in yr 1 vs. foxtail millet hay (10.6% CP) in yr 2]. The dietary TDN was similar between the years, and lipid-supplemented diets were formulated to be isolipidic, with 5% DMI as fat. The dietary ingredients were analyzed for CP (Leco FP-528, Leco Corp., St. Joseph, MO), IVDMD (Daisy II Incubator; Ankom Tech. Corp., Fairport, NY), crude fat (2050 Soxtec Avanti Auto Control Unit; Foss Tecator, Eden Prairie, MN), and fatty acids via direct transesterification with methanolic HCl (Whitney et al., 1999; Kucuk et al., 2001).
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Beginning at 0500 on d 31 and 61 (i.e., 1 d after the sample collection procedure involving the calves), blood samples were collected from the cows via indwelling jugular catheters. Two preprandial blood samples (10 mL each) were collected immediately before feeding. The cows were allowed 1 h 45 min to consume feed and water, and then postprandial blood samples were collected beginning at 2 h from the onset of feeding (0 h) and continuing every 15 min for 4 h. The blood samples were immediately refrigerated for 12 h at 4°C and centrifuged at 1,300 x g for 30 min. Aliquots of serum (4 mL) and plasma (4 mL) were stored at 20°C until the metabolite and hormone assays were conducted.
Laboratory Analyses
Cow and calf preprandial serum samples were analyzed for IGF-I concentration (Echternkamp et al., 1990) by RIA with intra- and interassay CV of 12 and 16%, respectively. Cow preprandial, 0-h, and 4-h postprandial plasma samples were analyzed for NEFA (inter- and intraassay CV of 7.6 and 8.3%, respectively) and ß-hydroxybutyrate (inter- and intraassay CV of 4.3 and 11.9%, respectively) using commercially available kits (NEFA-C and Autokit 3-HB, respectively; Wako Chemicals, Richmond, VA). Calf preprandial and postprandial plasma samples also were analyzed for NEFA (inter- and intraassay CV of 5.0 and 4.1%, respectively).
Aliquots of cow and calf serum were analyzed for IGFBP using one-dimensional SDS-PAGE (Laemmli, 1970) and Western ligand-blot analysis (Clapper et al., 1998). Briefly, 1 µL of serum was mixed with 19.0 µL of loading buffer and electrophoresed through a 4% stacking gel and a 12% resolving gel. Proteins were electrophoretically transferred to nitrocellulose membranes and relative quantities of IGFBP were determined by incubation with [125I]IGF [400,000 cpm/mL, 0.1% BSA (A-7888; Sigma Chemical Co., St. Louis, MO), and 0.10 Tween-20]. The intensity of binding was determined with a BioRad Molecular Imager (VersaDoc Imaging System 3000, Bio-Rad Laboratories, Hercules, CA) using Quantity One software (version 4 image analysis software, BioRad Laboratories). Insulin-like growth factor binding proteins detected in serum included a 40- to 43-kDa doublet (presumed to be IGFBP-3; Echternkamp et al., 1990); a 34-kDa protein (presumed to be IGFBP-2; Echternkamp et al., 1990); and a 25-kDa protein (presumed to be IGFBP-4; Roberts et al., 1997).
Cow and calf preprandial and hourly postprandial serum samples were analyzed for insulin (Reimers et al., 1982; inter- and intraassay CV of 8.5 and 5%, respectively) and glucose (Infinity Glucose Hexokinase kit; Thermo Trace, Louisville, CO; inter- and intraassay CV of 6 and 7.5%, respectively). Cow preprandial and postprandial serum samples obtained every 15 min were also analyzed for GH concentrations (Hoefler and Hallford, 1987; inter- and intraassay CV of 7 and 7%, respectively).
Statistical Analyses
All data were analyzed as repeated measures with a 2 x 3 arrangement of treatments in a randomized complete block design using the MIXED procedures of SAS (SAS Institute, Inc., Cary, NC). Year was used as a block and the model included the effects of BCS at parturition, dietary treatment, day of sampling, time of sampling, and all possible interactions. The effects of BCS at parturition, dietary treatment, and day of lactation were tested using cow within BCS at parturition x dietary treatment x day of lactation as the subject, and time of sampling as the REPEATED statement. Using likelihood ratio testing, an autoregressive-1 structure was deemed most appropriate for the within-subjects effects. During the first year of the study, 1 calf died; however, the cow was mechanically milked twice daily and retained on the experiment. Observations from this cow were tested for normality (PROC UNIVARIATE) to ensure that her observations were not outliers. During the second year, 1 cow was removed from the study due to death of the calf. Necropsies performed at the Wyoming State Veterinary Laboratory revealed that the calves from both years died from complications not attributed to the study; consequently, least squares means were reported. The univariate procedure of SAS was used to test the BLUP estimates for normal distribution of the data, and all data were determined to be normally distributed. Pearson correlations were computed to evaluate the relationships between concentrations of metabolites, hormones, and variables for previously reported production traits.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). Relative quantities of IGFBP-2 in serum from BCS 6 cows supplemented with cracked high-oleate safflower seeds were greater (P = 0.01) than BCS 6 cows supplemented with linoleate and tended (P = 0.07) to be greater than BCS 6 control cows at d 6 of lactation. Additionally, BCS 6 cows supplemented with oleate had greater relative quantities of IGFBP-2 in serum than BCS 4 cows fed control (P = 0.02) or linoleate (P = 0.01) supplements at d 6. Insulin-like growth factor binding proteins may potentiate or inhibit the bioavailability of IGF-I (Roberts et al., 1997). Generally, IGFBP-2 is believed to inhibit the actions of IGF-I (Murphy, 1998). Roberts et al. (1997) noted that serum from cows that failed to resume estrus after parturition contained greater relative quantities of IGFBP-2 and less IGFBP-3 than cows that resumed cyclicity. Therefore, the decreased pregnancy rate of BCS 6 cows supplemented with oleate noted by Lake et al. (2005) may be associated with perturbations in the IGF system including increases of IGFBP-2. Main effects of BCS at parturition were not noted for serum IGFBP-3 (P = 0.16) and IGFBP-4 (P = 0.34; Table 2).
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). Preprandial (P = 0.23) and 0-h postprandial (P = 0.60) serum NEFA concentrations did not differ between cows in BCS 4 or 6; however, 4-h postprandial NEFA concentrations were greater (P = 0.02) in BCS 6 cows than BCS 4 cows. Mean concentrations of NEFA (P = 0.08) and ß-hydroxybutyrate (P = 0.08) tended to be greater in cows nutritionally managed to achieve a BCS of 6 at parturition (Table 2
). Similarly, greater levels of circulating NEFA were found in beef (Vizcarra et al., 1998) and dairy cows (Busato et al., 2002) maintained in optimal BCS during early lactation compared with cows managed in suboptimal condition. Increased concentrations of NEFA and ß-hydroxybutyrate most likely reflect greater fatty acid mobilization from adipocytes, which is consistent with a decrease in BCS in cows managed to achieve a BCS of 6 at parturition (Lake et al., 2005).
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. Preprandial glucose concentrations were greater (P < 0.001) compared with all postprandial samples because circulating insulin concentrations were greatest (P < 0.001) 1 h postprandially and least (P < 0.001) preprandially (Figure 3). In agreement with Blum et al. (2000), postprandial insulin concentrations returned to preprandial levels approximately 4 h after feeding. Although a sharp increase in circulating glucose concentration is associated with postprandial serum samples, greater concentration of serum glucose preprandially in the current study corresponds to lower serum insulin concentrations. Because insulin stimulates cellular glucose uptake, lower levels of circulating insulin lead to greater levels of circulating glucose. The increase in glucose and gluconeogenic precursors following feeding likely led to increased postprandial circulating insulin concentrations, thereby decreasing postprandial glucose concentrations.
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). Changes in insulin usually correspond to changes in circulating glucose concentrations (Busato et al., 2002). Therefore, the lack of change in serum insulin concentrations was most likely due to the lack of a BCS effect on glucose concentration. Mean serum concentrations of IGF-I (P < 0.001) were greater in BCS 6 than BCS 4 cows, which is consistent with the hypothesis that serum IGF-I concentrations may be indicative of nutritional status (Lalman et al., 2000; Zulu et al., 2002). Conversely, GH concentrations were greater (P = 0.003) in BCS 4 than BCS 6 cows. In addition, serum IGF-I concentrations and BCS at d 30 of lactation were positively correlated (P = 0.01; r = 0.38), whereas GH and BCS at d 30 were negatively correlated (P < 0.001; r = –0.43). Under conditions of adequate nutrient intake, GH regulates hepatic secretion of IGF-I (Thissen et al., 1994; Roberts et al., 1997). However, during periods of negative energy balance, the secretion of GH increases (Breier et al., 1988; Zulu et al., 2002), whereas concentrations of circulating IGF-I decrease (Thissen et al., 1994; Busato et al., 2002; Meikle et al., 2004). Reasons for this apparent uncoupling of the GH-controlled regulation of IGF-I are not clear; however, reduced hepatic binding of GH may explain decreased secretion of IGF-I (Breier et al., 1988). In addition, increased synthesis and secretion of GH may occur as a result of decreased levels of circulating IGF-I, reducing the negative feedback on the hypothalamic-pituitary regulation of GH synthesis (McGuire et al., 1992). Results from the current study support the contention of an uncoupling of the somatotropic axis.
Lalman et al. (2000) concluded that increased circulating IGF-I and decreased concentrations of GH were indicative of animals maintained in superior nutritional status. Meikle et al. (2004) reported improved reproductive performance in dairy cows with greater circulating IGF-I concentrations. Likewise, Roberts et al. (1997) indicated that circulating IGF-I concentrations were associated with the capacity of beef cows to resume cyclicity after parturition. In the current study, cows with a BCS of 6 at parturition had greater circulating IGF-I concentrations and greater overall pregnancy rates (Lake et al., 2005) than BCS 4 cows. The apparent uncoupling of the GH/IGF-I axis for cows with a BCS of 4 at parturition may have resulted in circulating IGF-I concentrations insufficient to achieve desirable reproductive performance (Hess et al., 2005).
No differences (P = 0.16 to 0.92) were noted for hormone or metabolite concentrations in the calf that could be related to maternal BCS at parturition (Table 2). Previously, Lake et al. (2005) reported that maternal BCS at parturition did not influence calf birth weight or ADG. Therefore, differences in metabolic nutritional indices would not be expected.
Dietary Treatment Effects on Cow Circulating Metabolite and Hormone Concentrations
Data presented in Table 3 illustrate that dietary supplementation did not influence plasma NEFA (P = 0.94) or serum concentrations of glucose (P = 0.15), IGF-I (P = 0.33), GH (P = 0.62), IGFBP-2 (P = 0.35), IGFBP-3 (P = 0.61), or IGFBP-4 (P = 0.41). The absence of an effect on NEFA supports earlier studies (Baumgard et al., 2002; Selberg et al., 2004) demonstrating that dietary lipid supplementation exerts little or no effect on lipolysis. A primary response to lipid supplementation by cows in midlactation may be increased availability of glucose for lactose synthesis, or for purposes other than milk fat synthesis (Kronfeld et al., 1980). The premise for increased lactose synthesis, or glucose sparing, is that fatty acid oxidation would be expected to increase relative to glucose oxidation. The lack of differences in circulating concentrations of glucose among dietary treatments is consistent with the lack of differences in milk lactose or total milk yield (Lake et al., 2005). Additionally, lipid supplementation occurred when the nutrient demands of early lactation may have superseded any potential effect on glucose metabolism.
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). In cell culture models, oleic acid has been shown to increase ß-cell mass and prevent cellular apoptosis (Maedler et al., 2003). Although fatty acids may impair ß-cell secretion during long-term exposure, such as conditions of type 2 diabetes, short-term exposure to fatty acids can stimulate insulin secretion in rats (Gravena et al., 2002). Therefore, increased insulin concentrations in the current study might be attributed to proliferative and protective properties associated with oleic acid on pancreatic ß-cells as well as stimulatory effects of unsaturated fatty acid on insulin secretion. Decreased plasma ß-hydroxybutyrate concentrations were reported in lipid-supplemented dairy cows (Blum et al., 1985). Concentrations of ß-hydroxybutyrate in plasma can be affected by rumen epithelial metabolism of butyrate, or ketone body formation in animals experiencing negative energy balance. Previous research from our laboratory demonstrated decreased ruminal molar proportions of butyrate in linoleate- and oleate-supplemented beef heifers fed supplements similar to those used in the current study (Scholljegerdes et al., 2004). Plasma concentrations of ß-hydroxybutyrate were greater (P < 0.001) 0 and 4 h postprandially compared with the preprandial sample. Because lipid supplementation did not affect production measures or change in energy balance (Lake et al., 2005), the postprandial increase in ß-hydroxybutyrate most likely originated from ruminal fermentation rather than ketogenesis.
Effects of lipid supplementation on circulating IGF-I and IGFBP concentrations were not evident in the current study probably because nutritional status was similar among cows fed different postpartum diets (Roberts et al., 1997).
Calf serum concentrations of insulin (P = 0.78), IGF-I (P = 0.92), IGFBP-2 (P = 0.15), IGFBP-3 (P = 0.21), IGFBP-4 (P = 0.81), or plasma concentrations of NEFA (P = 0.88) did not differ due to maternal lipid supplementation (Table 3). However, concentrations of serum glucose were greater (P = 0.004) in calves nursing lipid-supplemented cows than control-fed cows. Piot et al. (1999) also reported greater circulating glucose concentrations in preruminant calves supplemented with tallow (high in long-chain fatty acids) in a milk replacer. Total milk fat output was not different in the current study due to lipid supplementation (Lake et al., 2005); therefore, metabolic adaptation resulting in increased circulating glucose concentrations is likely attributed to increased long-chain fatty acid content of milk from lipid-supplemented cows (Lake et al., 2004). Greater mean glucose concentrations, coupled with similar insulin concentrations, in calves nursing lipid-supplemented dams compared with control calves is indicative of decreased insulin-stimulated uptake of glucose. Exogenously derived fatty acids may influence lipogenic activity such that fatty acid synthesis is downregulated, thereby decreasing the use of glucose for fatty acid synthesis.
Day of Lactation Effects on Cow Circulating Metabolite and Hormone Concentrations
A day of lactation x time of sampling interaction (P = 0.001; Figure 4) occurred for plasma ß-hydroxybutyrate concentration. No difference between preprandial (P = 0.54) and 4-h postprandial (P = 0.26) concentrations of ß-hydroxybutyrate in plasma were detected between d 3 and 6. However, 0-h plasma concentrations of ß-hydroxybutyrate were greater (P < 0.001) at d 3 than 6. As shown in Table 4, no effects of day of sampling were noted in cows for serum concentrations of insulin (P = 0.62), IGFBP-2 (P = 0.12), IGFBP-3 (P = 0.97), and GH (P = 0.34). Although circulating concentrations of insulin did not differ by day of lactation, a positive correlation (P = 0.01; r = 0.30) was observed between circulating insulin and acetyl-CoA carboxylase activity (data not shown) at d 30 of lactation. Because insulin is indicative of nutritional status and acetyl-CoA car-boxylase is regulated by insulin (Witters et al., 1988), an increase in acetyl-CoA carboxylase would be expected in animals with greater levels of circulating insulin. Furthermore, a correlation (P = 0.04; r = 0.25) existed between circulating concentrations of insulin and rate of palmitate incorporation into lipid (data not shown) at d 30 of lactation.
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). Plasma concentrations of NEFA are indicative of adipose tissue mobilization because of negative energy balance associated with increased nutrient demand, inadequate nutrition, or a combination of both. Further evidence for this relationship is supported by the negative correlation between circulating concentrations of NEFA and insulin at d 6 of lactation (P = 0.004; r = –0.27) as well as NEFA and total milk yield at d 30 of lactation (P = 0.04; r = –0.25). The increased circulating concentration of ß-hydroxybutyrate observed concomitantly with NEFA is indicative of enhanced ketogenesis as a consequence of negative energy balance. Greater loss of BCS at d 30 compared with d 60 of lactation (Lake et al., 2005) likely resulted in the increased NEFA at d 3 rather than at d 6, the anticipated time of peak lactation.
Metabolic actions of IGFBP-4 are predominantly inhibitory to IGF-I (Murphy, 1998). Roberts et al. (1997) reported no differences in serum IGFBP-4 due to energy restriction or week of sampling in cows. In the current study, circulating IGFBP-4 was greatest at d 3 of lactation, which corresponds to when BW loss was greatest (Lake et al., 2005). Generally, levels of circulating IGF-I concentrations increase as lactation progresses (Busato et al., 2002). Increased (P = 0.003) circulation of IGF-I from d 3 to 6 was consistent with the decrease in NEFA and increase in BCS at d 60 (Lake et al., 2005). Backfat accretion is due to excess substrate availability for fat deposition to subcutaneous adipocytes. Therefore, a positive correlation (P = 0.003; r = 0.65) between ultrasonic 12th rib fat measurements (Lake et al., 2005) and circulating IGF-I concentration at d 3 was not surprising.
Calf serum glucose (P = 0.73), insulin (P = 0.34), IGFBP-2 (P = 0.75), IGFBP-3 (P = 0.73), and IGFBP-4 (P = 0.99) were not influenced by day of lactation (Table 3). However, calf plasma NEFA was greater (P = 0.01) at d 30 compared with d 60 of age whereas serum IGF-I was greater (P < 0.001) at d 60. A decrease in plasma NEFA concentration has been reported as calves increase age and BW (Quigley and Bernard, 1992; Quigley et al., 1994). The increase in serum IGF-I from d 30 to 60 is in agreement with Govoni et al. (2003) who reported increased serum IGF-I in calves until 17 wk of age. Likewise, Kerr et al. (1991) noted a correlation (r = 0.74) between IGF-I and BW from birth to 18 mo in Holstein calves. Therefore, the increase in serum IGF-I in the current study would be expected due to the greater BW of calves at d 60 (Lake et al., 2005).
Calf serum glucose (P < 0.001) and plasma NEFA (P < 0.001) were greater preprandially, whereas serum insulin (P < 0.001) was greater postprandially (Table 5). The finding of decreased NEFA concentration postprandially is consistent with results from veal calves (Kaufhold et al., 2000) and Holstein calves (Quigley and Bernard, 1991) and is likely attributed to the effect of increasing insulin (Kaufhold et al., 2000). Greater glucose concentration preprandially is a consequence of decreased insulin in the preprandial state. As glucose concentrations increase after feeding, stimulated increases in insulin concentrations initiate cellular uptake of glucose and result in lower circulating glucose for several hours after feeding. Postprandial clearance of glucose to levels equal to or less than preprandial concentrations within several hours is consistent with previous reports (Quigley et al., 1992; Kaufhold et al., 2000).
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Cows with a BCS of 4 at parturition had a decrease in circulating NEFA and an increase in serum GH; however, an uncoupling of the IGF/GH axis in cows with a BCS of 4 at parturition may have detrimental impacts on subsequent reproductive performance.
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Footnotes |
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2 Current address: Department of Animal Science, Purdue University, West Lafayette, IN 47907.
3 Current address: USDA-ARS, NGPRL, Mandan, ND 58554.
4 Current address: Department of Animal and Range Science, New Mexico State University, Las Cruces, NM.
5 Corresponding author: brethess{at}uwyo.edu
Received for publication August 25, 2005. Accepted for publication November 21, 2005.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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