J. Anim. Sci. 2004. 82:3662-3668
© 2004 American Society of Animal Science
Effects of increasing level of supplemental barley on forage intake, digestibility, and ruminal fermentation in steers fed medium-quality grass hay1
G. P. Lardy*,
D. N. Ulmer*,2,
V. L. Anderson
,3 and
J. S. Caton*,4
* Department of Animal and Range Sciences, North Dakota State University, Fargo 58105 and
and
Carrington 58421
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Abstract
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Objectives of this research were to evaluate effects of increasing level of barley supplementation on forage intake, digestibility, and ruminal fermentation in beef steers fed medium-quality forage. Four crossbred ruminally cannulated steers (average initial BW = 200 ± 10 kg) were used in a 4 x 4 Latin square design. Chopped (5 cm) grass hay (10% CP) was offered ad libitum with one of four supplements. Supplements included 0, 0.8, 1.6, or 2.4 kg of barley (DM basis) and were fed in two equal portions at 0700 and 1600. Supplements were fed at levels to provide for equal intake of supplemental protein with the addition of soybean meal. Forage intake (kg and g/kg BW) decreased linearly (P < 0.01), and total intake increased linearly (P < 0.03) with increasing level of barley supplementation. Digestible OM intake (g/kg BW) increased linearly (P < 0.01) with increasing level of barley supplementation; however, the majority of this response was observed with 0.8 kg of barley supplementation. Treatments had only minor effects on ruminal pH, with decreases occurring at 15 h after feeding in steers receiving 2.4 kg of barley supplementation. Total-tract digestibility of DM, OM, NDF, and CP were increased (P < 0.04) with barley supplementation; however, ADF digestibility was decreased by 1.6 and 2.4 kg of barley supplementation compared with controls. Ruminal ammonia concentrations decreased linearly (P < 0.01) at 1 through 15 h after feeding. Total ruminal VFA concentrations were not altered by dietary treatments. Ruminal proportions of acetate and butyrate decreased (P < 0.10) in response to supplementation. Rate, lag, and extent (72 h) of in situ forage degradability were unaffected by treatment. Generally, these data are interpreted to indicate that increasing levels of barley supplementation decrease forage intake, increase DM, OM, and NDF digestibility, and indicate alteration of the ruminal environment and fermentation patterns.
Key Words: Barley • Digestibility • Intake • Steers • Supplement
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Introduction
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Grazed and harvested forage provides a large proportion of nutrients for beef cattle in much of the Northern Plains. Diets based on mature forages often require supplementation to ensure optimal performance (Caton and Dhuyvetter, 1997
). A variety of supplements are available to beef cattle producers, including by-products, commercial supplements, and feeds raised on farms or ranches. Barley is widely grown in the Northern Plains and generally available at very reasonable costs. However, forage intake and digestibility may be negatively affected by the addition of barley, corn, or other cereal grains as a result of negative associative effects (Kartchner, 1980; Chase and Hibberd, 1987; Lusby and Wagner, 1987; Carey et al., 1993). The use of corn as a forage supplement is widely reported in the literature, and its use often results in decreased forage intake and lower forage digestibility, especially with lower-quality forages (Chase and Hibberd, 1987; Sanson et al., 1990; Pordomingo et al., 1991) and where degraded intake protein (DIP) concentration in the supplement is inadequate. Some work has been conducted with barley in this area as well with similar results (Kartchner, 1980; Boyles et al., 1998). However, barley contains less starch (57 vs. 72%; Huntington, 1997) and more DIP than corn (9.6 vs. 4.4%; NRC, 1996), which may lessen the negative associative effects commonly observed with cereal grain supplementation of forage-based diets (Bodine et al., 2000). Decreases in forage intake and digestibility resulting from these negative associative effects may result in no net improvement in energy status of the animal depending on the severity of depression in intake and digestibility. The objectives of this study were to determine the effect of feeding increasing levels of supplemental barley on intake and utilization of forage diets fed to beef cattle.
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Materials and Methods
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Four ruminally cannulated steers (average initial BW = 200 ± 10 kg; mean ± SD) were used in a 4 x 4 Latin square experiment designed to evaluate effects of increasing levels of barley supplementation on forage intake and nutrient utilization. Cannulation procedures and animal care throughout the experiment followed institutional Animal Care and Use guidelines. Ground (hammer type mill; 5.1-cm screen) medium-quality grass hay (predominately smooth brome, Bromus inerumus; 10.0% CP; DM basis) was available free choice as the basal diet. Supplements were formulated (Table 1) to meet NRC (1984) protein requirements for 0.45 kg gain/d (shrunk live weight basis). Supplement treatments were control or soybean meal (SBM + no barley), and SBM + 0.82, 1.66, or 2.44 kg (referred to as 0.8, 1.6, and 2.4 kg hereafter) of barley DM•steer–1•d–1 (Table 2). Supplements were fed to provide equal N from supplements with the addition of soybean meal in all four treatments to enhance the likelihood that any responses observed were due to increasing level of starch from the supplement, rather than differences in CP content.
Calculated ruminal DIP levels for supplement were 72, 76, 78, and 78% of supplemental CP for control, 0.8, 1.6, and 2.4 kg barley supplements respectively. Trace mineral salt blocks were provided free choice (minimum 98 g of MgCl, 350 mg of Zn, 280 mg of Mn, 175 mg of Fe, 35 mg of Cu, 7 mg of I, and 7 mg of Co/100 g of DM). Steers were given free access to water throughout the experiment and given a 1.5-mL i.m. injection of vitamins A (500,000 IU/mL), D (75,000 IU/mL), and E (7.5 IU/mL) at the beginning of the study.
Steers were housed in 3.9 x 3.9 m pens and adapted to diets for d 1 through 10 of each 21-d period. Then steers were moved to elevated metabolism cages for the duration of the experimental period. Supplement and fresh hay were fed in two equal portions at 0700 and 1600. Orts (approximately 8 to 15% of feed offered) were collected and weighed each morning before supplementation. Each period for the duration of the experiment consisted of 21 d, with 14 d of dietary adaptation (10 d in the pens and 4 d in metabolism cages) and 7 d for collection and subsampling of total fecal output.
On d 14 of each period, 200 mL of Co-EDTA (fluid-phase marker; Uden et al., 1980) was dosed intraruminally 2 h before supplementation, and ruminal fluid samples were collected at –2, 0, 1, 3, 6, 9, 12, 15, and 24 h after the 0700 supplementation. Whole ruminal contents (250 mL) were sampled by removing a composite sample from various locations within the rumen, and pH was determined immediately with a portable pH meter, fitted with a combination electrode (Orion SA230, Cambridge, MA). Contents were strained through four layers of cheesecloth, and the fluid portion was acidified with 7.2 N H2SO4 at the rate of 1 mL of acid/100 mL of strained ruminal fluid. Strained samples were stored frozen (–10°C).
At 0630 on d 16, 200 g of Yb-labeled hay (Teeter et al., 1984) was dosed intraruminally as a particulate phase marker. Rectal grab samples of feces were taken at 0, 4, 8, 12, 16, 21, 26, 30, 34, 38, 42, 47, 52, 60, 68, 78, 86, 94, 107, and 120 h after dosing. Fecal samples were stored frozen (–10°C).
In situ degradation measurements were initiated on d 18 of each period. Dacron bags (Ankom, Fairport, NY; 10 x 20 cm; 53 ± 10 µm pore size) that contained approximately 5 g (as-fed basis) of ground hay (2-mm screen) were placed in the rumen of each steer at incubation times of 0, 4, 8, 12, 16, 24, 36, 48, and 72 h. At each incubation time, three bags containing hay and one blank (empty) bag were placed in the rumen after soaking the bags for 15 min in tap water. Dacron bags were sealed with a No. 8 rubber stopper and two No. 19 rubber bands. An 18 x 24 cm lingerie bag fitted with a nylon zipper was used to suspend Dacron bags in the rumen. After incubation, all Dacron bags were washed with tap water until the rinse water was clear. Bags were then dried at 50°C for 48-h in a forced-air oven, desiccated until cool, weighed, and stored.
Laboratory Analyses
Dietary ort, fecal, and in situ samples were analyzed for DM, ash, and N (CP) by standard procedures (AOAC, 1990). Neutral and acid detergent fiber fractions were determined sequentially with crucibles on dietary and in situ samples by the method of Robertson and Van Soest (1982).
Ruminal fluid samples were thawed at room temperature and centrifuged at 10,000 x g for 10 min. Ruminal ammonia concentration was determined by the colorimetric method of Broderick and Kang (1980). Supernatant fluid from the initial centrifugation step was then mixed with 25% (wt/vol) metaphosphoric acid (5 mL of ruminal fluid plus 1 mL of metaphosphoric acid) and recentrifuged at 10,000 x g for 10 min. The fluid portion was taken for VFA analysis, and 2-ethylbutyric acid was used as the internal standard (Goetsch and Galyean, 1983). Determination of VFA was conducted by gas chromatography (Shimadzu Science Instruments, Columbia, MD; packed column, 140°C, N gas carrier). Cobalt concentration was determined in ruminal fluid samples by atomic absorption spectroscopy using an air-plus-acetylene flame.
In preparation for Yb analysis, fecal samples were extracted with 0.1 M EDTA (Hart and Polan, 1984). The concentration of Yb was determined by atomic absorption spectroscopy using a nitrous oxide-plus-acetylene flame.
Calculations
Intake and fecal output were determined by direct measurement. Rate of fluid passage was determined by regression of the natural log of the ruminal Co concentration (samples taken at –2, 0, and 1 h were omitted from the analysis) on time (Grovum and Williams, 1973). The absolute value of the slope was defined as fluid dilution rate. Fluid volume was determined by dividing the Co dose by the antilog of the marker concentration at time zero. Particulate passage rates were calculated using a one-compartment model (Ellis et al., 1979). Nonlinear procedures of SAS (SAS Inst., Inc., Cary, NC) were used (Marquardt method) to calculate particulate digesta kinetics.
Rates of DM, NDF, and ADF in situ degradation and lag times were determined by fitting the percentage of residue fraction (DM, NDF, or ADF) remaining to the nonlinear model of Mertens and Loften (1980). The model of Ørskov and McDonald (1979) was used to estimate in situ rate of forage CP degradability. This model also was used to divide total forage CP into rapidly (Fraction A) and slowly degraded (Fraction B) CP fractions. The calculated rate of CP degradation is associated with Fraction B because the degradation of Fraction A is assumed to be instantaneous. Computations associated with models used for in situ DM, NDF, and CP degradation rates were conducted using the nonlinear procedures (Marquardt method) of SAS. In situ CP residues were corrected for microbial contamination by using purines as a microbial marker (Messman et al., 1992; Johnson et al., 1998).
Statistical Analyses
Intake, digestibility, in situ, and digesta kinetics data were analyzed as a 4 x 4 Latin square (Steel and Torrie, 1980). The model contained effects for steer, period, and treatment. When significant F-statistics were noted, linear, quadratic, and cubic contrasts were used to evaluate treatment effects. Fermentation data were analyzed as a split-plot within a Latin square (Gill and Hafs, 1971). When treatment x sampling time interactions were absent (P > 0.10), data were pooled across time. All statistical computations were conducted using the GLM procedure of SAS.
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Results and Discussion
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Increasing levels of barley generally had a deleterious effect on forage DMI. Forage intake decreased linearly (P < 0.01) with increasing levels of barley; however, supplement amount increased, resulting in a linear increase (P < 0.03) for total intake (Table 3). Forage intake adjusted for BW (g/kg BW) decreased linearly (P < 0.10), but total intake (forage + supplement; g/kg BW) did not differ among treatments. Boyles et al. (1998) observed similar decreases in forage intake with increasing level of barley supplementation (without added SBM) on similar quality forage (9.5% CP). The decreases in forage intake observed in our study with twice-daily supplements are also similar to other research with corn-based supplements (Chase and Hibberd, 1987; Sanson et al., 1990; Pordomingo et al., 1991). Chase and Hibberd (1987) and Sanson et al. (1990) fed low-quality harvested forages (4% CP), whereas the observations of Pordomingo et al. (1991) were made under grazing conditions on summer native range. Our research was conducted using a harvested medium-quality forage (10% CP). Matejovsky and Sanson (1995) noted similar responses in forage intake for lambs fed increasing levels of corn (0.25, 0.50, and 0.75% BW) with low-, medium-, or high-quality hays. Boyles et al. (1998) reported lower forage intake with steers fed 2.4 kg barley DM•animal–1•d–1 compared with unsupplemented steers. Forage used in that study was of similar quality to the forage used in our study. Carey et al. (1993) compared barley, corn, or beet pulp as supplements for medium-quality grass hay. They noted no differences in forage intake (kg of DM) but reported decreased forage intake compared with unsupplemented steers when intake was expressed as a percentage of BW; no differences in forage intake were noted among the barley, corn, or beet pulp supplements. On closer scrutiny of our forage DMI, little difference was noted between 0.0 and 0.8 kg of barley; however, from 0.8 to 1.6 and 1.6 to 2.4 kg of supplementation, forage DMI (g/kg BW) decreased by approximately four times the standard error. Digestible OM intake (DOMI; Table 3) increased (linear, P < 0.01; cubic, P < 0.09) as supplemental barley increased. The cubic nature of this response resulted from control being the least, 0.8 and 1.6 intermediate, 1.6 numerically lower than 0.8, and 2.4 kg the highest. When expressed as g/kg BW, DOMI increased linearly (P < 0.01) with increasing level of barley. This response was present because of the large difference between control and 2.4 kg of barley supplementation, 15.8 vs. 18.1 g/kg BW, respectively. These data indicate that the largest change in DOMI was observed with 0.8 kg of barley, and no increase in DOMI occurred when the level was increased to 1.6 kg, with a smaller incremental increase observed at 2.4 kg of barley.
Dry matter, OM, and NDF digestion increased linearly (P < 0.03) in response to higher levels of barley supplementation (Table 4). Increases in DM and OM digestibilities are likely a result of the supplement being more digestible than the grass hay. There was also a cubic response (P < 0.07) in NDF digestibility, which resulted from steers fed CON and 1.6 treatments having lower digestibilities, with steers fed 0.8 kg being intermediate, and those fed 2.4 kg of barley having the highest values. Higher levels of NDF digestibility in steers fed 2.4 kg of barley are likely the result of consumption of greater amounts of a more highly digestible NDF from the barley. Digestibility of ADF was 56.3, 56.7, 52.9, and 53.9 ± 0.95% for Con, 0.08, 1.6, and 2.4 treatments, respectively. These values resulted in a linear decrease (P < 0.04) in total-tract ADF digestibility with increasing level of barley supplementation. In addition, ADF digestion responded cubically (P < 0.07), which, like the cubic response in NDF digestibility, likely reflects changes in ruminal microbial populations and increased intake of a more readily fermentable fiber source in the steers supplemented with 2.4 kg of barley. Crude protein digestion decreased linearly (P < 0.01) with increasing level of barley supplementation, presumably reflecting the lower quantity of soybean meal associated with the higher levels of barley supplements, which could have altered either ruminal or postruminal protein disappearance.
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Table 4. Influence of increasing level of barley supplementation on digestibility of grass hay-based diets by steers
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During analysis of ruminal pH over time (–2 to 24 h after the 0700 supplementation), treatment x sampling time interactions (P < 0.10) were detected. No differences in ruminal pH were observed, except at 15 h, when linear and quadratic effects (P < 0.03) were observed (5.28, 6.39, 6.29, and 5.94 ± 0.08 for CON, 0.8, 1.6, and 2.4 treatments, respectively). The only time that pH fell below 6.2 was for the 2.4-kg treatment at 15 h. Mertens (1977) suggested that ruminal pH less than 6.2 could inhibit ruminal fiber digestion. Boyles et al. (1998), who supplemented steers once daily, reported few differences in ruminal pH in steers fed increasing levels of barley, which agrees with our findings. Reynolds et al. (1993) noted lower ruminal pH at 0, 4, 16, and 20 h after feeding for corn- compared with barley-based supplements for steers fed wheat straw diets. They fed corn and barley at 30% of the diet; consequently, the cattle supplemented with corn received more starch, which may explain the differences between grain types. Leventini et al. (1990) reported a barley level x sampling time interaction for ruminal pH in steers fed 10, 30, or 50% barley in bromegrass hay-based diets. Hay was similar in quality to that used in our study. Leventini et al. (1990) noted lower ruminal pH for steers fed 30 or 50% barley at 9 h after feeding. In our study, supplementing twice daily likely may have diminished potential ruminal pH responses.
Treatment x time interactions were detected for ruminal ammonia data (P < 0.10). Ruminal ammonia concentrations decreased linearly with increasing level of barley (P < 0.01; Table 5) for all observed times, except at –2, 0, and 24 h. Sampling times –2, 0, and 24 are the three times that were farthest from time of supplementation, and would thus be least likely to demonstrate a treatment response. This finding is similar to other research with corn-based supplements (Chase and Hibberd, 1987; Pordomingo et al., 1991). Decreased ruminal ammonia concentrations may be expected with increasing level of cereal grain (starch) supplementation. If more OM were available for ruminal fermentation, more ammonia would be assimilated into microbial protein. Carey et al. (1993) reported decreased ruminal ammonia with supplemental barley, corn, or beet pulp compared with steers supplemented with soybean meal. In the present study, readily fermentable carbohydrates and DIP were not balanced in supplements. If they had been, differences in ruminal ammonia would likely not have been as pronounced.
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Table 5. Influence of increasing level of barley supplementation on ruminal ammonia concentrations (mg/100 mL) in steers fed grass hay-based diets
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Boyles et al. (1998) reported increased ruminal ammonia concentrations in steers fed 1.6 or 2.4 kg barley•steer–1•d–1 with forage of similar quality to that in our study. Reasons for these differences are not readily apparent, but they may reflect greater protein intake by barley-supplemented steers (protein levels among supplements were not equalized in the study of Boyles et al., 1998). Alternatively, the differing ruminal ammonia response between the work of Boyles et al. (1998) and the present study may be related to the forage-to-concentrate ratio differences. In our study, steers fed 0.82, 1.66, and 2.44 kg of barley DM/d had average concentrate inclusion rates of 22.3, 31.2, and 39.1% of the diet, respectively. Boyles et al. (1998) fed 0.8, 1.6, and 2.4 kg of barley, but the concentrate inclusion ratios were 8.8, 16.7, and 26.0% of the diet, respectively. The steers used by Boyles et al. (1998) were heavier than those in this study (329 vs. 200 kg), and consequently consumed more forage mass in relation to the quantity of supplement fed. Forage intake, expressed as a percentage of BW, was similar between the two studies. Another difference between the two studies is that we supplemented twice daily, whereas Boyles et al. (1998) fed supplement only once daily. Differences in frequency of supplementation could be expected to alter ruminal ammonia concentrations and other fermentation characteristics.
The absence of treatment x sampling time interactions (P < 0.10) allowed for pooling VFA data across time. Total VFA concentrations (mM) were not affected by treatment. Individual VFA proportions (mol/100 mol) responded to increasing levels of barley with cubic effects (P < 0.02) in acetate and butyrate (Table 6). In addition, butyrate increased with increasing level of supplemental barley (linear; P < 0.02). Boyles et al. (1998) noted similar changes in acetate and increases in butyrate and isovalerate with increasing level of barley supplementation. Pordomingo et al. (1991) reported a tendency toward decreased acetate proportions and similar increases in butyrate proportions in steers fed increasing levels of corn while grazing native rangeland in New Mexico, which is similar to the results of Chase and Hibberd (1987) in cattle fed low-quality hay and supplemental corn. Reynolds et al. (1993) noted no differences in acetate concentration with barley or corn supplementation and reported increased butyrate in grain supplemented steers compared with controls.
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Table 6. Influence of increasing level of barley supplementation on ruminal volatile fatty acid concentration in steers fed grass hay-based diets
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Ruminal fluid passage rate was unaffected by increasing level of barley supplementation (Table 7). Likewise, particulate passage was not changed in barley-supplemented vs. control steers (Table 7). In contrast, Leventini et al. (1990) reported increased fluid passage rate with increasing level of barley supplementation. Pordomingo et al. (1991) noted no differences in ruminal fluid kinetics with increasing level of corn supplementation, which generally agrees with our results.
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Table 7. Influence of increasing level of barley supplementation on ruminal fill and fluid passage rate in steers fed grass hay-based diets
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No differences were noted in rate or extent of digestion of DM, NDF, ADF, or corrected CP or lag time associated with bacterial colonization (Table 8). These findings agree with those of Boyles et al. (1998) and Pordomingo et al. (1991). Mertens and Loften (1980) concluded that the decrease in digestibility with the addition of starch in vitro was a result of increased lag time; however, lag time was unaffected in our study. In addition, the extent of digestion (72 h in situ) was not altered by the barley supplementation levels used in this study (Table 8).
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Table 8. Influence of increasing level of barley supplementation on rate, extent (72 h), and lag time of dry matter, neutral detergent fiber, acid detergent fiber, and corrected crude protein disappearance from in situ bags in steers fed grass hay-based diets
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In summary, decreases in forage intake resulting from barley supplementation seemed to be largely linear in steers consuming medium-quality hay and supplemented twice daily. Supplementing twice daily should have, at least theoretically, muted the effects of grain supplementation on forage intake and digestion. Although this may be the case with some measurements (ruminal pH, lag time, and digestion rate), increasing barley supplementation in this study nonetheless de creased forage use as measured through intake and ADF digestibility. Conversely, barley supplementation increased intakes of digestible OM and total DM, and both these responses were most pronounced at 0.8 kg of barley supplementation. Barley can be a low-cost, readily available, supplemental energy source for many farms and ranches in the northern Great Plains, but it should be limited to lower levels (0.8 kg or less, which represented 12.5% of the diet or 0.4% of BW) for optimum forage nutrient use. Ultimately, level of barley supplementation will be driven by production demands and the cost of barley relative to hay. Additional supplementation strategies that are effective in optimizing forage use, decreasing winter feeding costs, and maximizing net returns for beef cattle production systems are needed.
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Footnotes
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1 The authors thank T. Johnson, T. Gilbery, and T. Skunberg for their assistance with this project. 
2 Current address: Stockmen’s Supply, Inc., West Fargo, ND 58078.
3 Current address: Carrington Res. Ext. Ctr., Box 219, Carrington, ND 58421–0219.
4 Correspondence—phone: 701-231-7653; fax: 701-231-7590; e-mail: joel.caton{at}ndsu.nodak.edu.
Received for publication June 11, 2003.
Accepted for publication September 4, 2004.
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T. L. Lawler-Neville, S. M. Shellito, T. D. Maddock, M. L. Bauer, G. P. Lardy, T. C. Gilbery, and J. S. Caton
Effects of concentrated separator by-product (desugared molasses) on intake, site of digestion, microbial efficiency, and nitrogen balance in ruminants fed forage-based diets
J Anim Sci,
August 1, 2006;
84(8):
2232 - 2242.
[Abstract]
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Abstract
Introduction
