Steer responses to increasing proportions of legume when fed switchgrass hay1

The Professional Animal Scientist 29 (2013):383–394

©2013 American Registry of Professional Animal Scientists

Steer responses to increasing proportions of legume when fed switchgrass hay1

J. C. Burns*2 and D. S. Fisher† *USDA-ARS and Department of Crop Science and Department of Animal Science, North Carolina State University, Raleigh 27695; and †USDA-ARS (Retired), Watkinsville, GA 30677

ABSTRACT Switchgrass (Panicum virgatum L.; SG) may have CP below recommended concentrations for feeding ruminants that limit animal performance when cut as hay and fed as the sole diet. Three experiments were conducted to determine the influence of white clover (Trifolium repens. L.) at 0, 15, and 30% of DM (Exp. 1), or alfalfa (Medicago sativa L.) at 0, 25, and 50% of DM with either headed SG (Exp. 2) or vegetative SG (Exp. 3) on steer DMI (kg/100 kg of BW) and DM digestion (g/kg). Eating behavior (Exp. 1) and masticated feed characteristics (Exp. 2 and 3) were also examined. Steer (Bos taurus L.) DM digestion of SG (Exp. 1) increased linearly (P < 0.01) from 544 g/kg on SG to 584 g/kg when clover composed 30% of the offered diet. However, steer DMI of headed SG (Exp. 2) was 1.61 kg/100 kg of BW with a DM digestion of 480 g/kg when fed alone, and both increased linearly (P < 0.01)

1 Cooperative investigation of the USDAARS and the North Carolina ARS, Raleigh 27695-7642. The use of trade names does not imply endorsement by USDA-ARS or by the North Carolina ARS of the products named or criticism of similar ones not mentioned. 2 Corresponding author: joe_burns@ncsu. edu

to 2.68 kg/100 kg of BW and 578 g/kg, respectively, when alfalfa composed 50% of the offered diet. The DM digestion of vegetative SG (Exp. 3) increased linearly (P = 0.09) from 541 when fed alone to 575 g/kg when alfalfa composed 50% of the offered diet. The CP of masticated feed (Exp. 2 and 3) increased linearly (P < 0.01) and NDF decreased linearly (P < 0.01) with increasing alfalfa. Perennial legumes can be a useful source of CP in SG hay diets. Key words: switchgrass, white clover, alfalfa, hay, intake and digestion

INTRODUCTION Switchgrass (SG; Panicum virgatum L.), a native, warm-season perennial, has potential as a multipurpose forage crop for the mid-Atlantic region of the United States. It has potential as pasture (Burns et al., 1984, 1991, 2011), hay (Burns et al., 1985; Burns, 2011), or when conserved as either baleage (Huntington and Burns, 2007) or silage (Burns et al., 1993), as well as being an energy crop for biomass production (North Carolina ARS, 2009; Yang et al., 2009; Xu et al., 2010). As noted for most grasses, CP concentrations of SG decline with advancing maturity (Buxton et al., 1996; Burns et al., 1997; Coleman et al., 2004). This decline becomes of

major importance when SG comprises the major portion of the diet of the ruminant. For example, Kanlow SG averaged about 11.3% CP when vegetative (1.3-m tall), but by haying stage (mid-boot) it had declined to about 4.0% CP, with a decline in CP digestibility from about 62.0 to 24.0% (Burns et al., 1997). The diet of growing cattle averaging 270 kg in BW requires CP concentrations of 10.0 to 12.7% of DM to support gains of 0.9 to 1.3 kg/d. For a mature beef cow during peak lactation, the diet should contain a CP concentration of at least 11.0% of DM (NRC, 2000). These CP requirements alone make it necessary for SG to be harvested at an earlier maturity (vegetative stage) sacrificing DM production or, alternatively, to add a costly CP supplement. Another option for supplementing CP is through the feeding of legume hay. Generally, legumes such as white clover (Trifolium repens L.) and alfalfa (Medicago sativa L.), when fed as the sole diet, provide CP in excess of animal requirements (NRC, 2000). The objective of this study was to determine the effect of feeding legumes as a proportion of a SG hay diet on steer DMI, apparent wholetract DM digestibility, and diet and fecal particle size and composition. Three separate experiments were conducted with white clover serving

384 as the legume component in Exp. 1 and alfalfa as the legume components in Exp. 2 and 3.

MATERIALS AND METHODS Experimental Hays Experimental hays were produced in 3 consecutive yr for Exp. 1, 2, and 3, respectively. The hays were obtained from well-established stands of SG, ladino white clover, and alfalfa grown in the Piedmont on a Cecil clay loam (fine, Kaolinitic, thermic Typic Kanhapludult) soil at the North Carolina State University Field Laboratories, Raleigh, North Carolina (35°52′N, 78°47′W, 132 m elevation). Each year, residue from the previous fall was removed from the Kanlow SG stand by burning in mid-February. This provided the grass for all 3 experiments. The residues from the legume stands were removed by clipping. All stands were fertilized and limed according to soil test (North Carolina Department of Agriculture, Soil Test Laboratory, Agronomic Division, Raleigh, NC). Soil pH was maintained above 6.0 for SG and above 6.5 for the legumes. The SG stand was top-dressed with 56 to 96 kg of N/ ha, depending on the year, in preparation for the growth of the subsequent experimental hay. The experimental forage was either artificially dried (Exp. 1) or field cured (Exp. 2 and 3). Forage that was artificially dried was harvested with a conventional flail harvester (cut into 8- to 15-cm lengths), blown into a self-unloading wagon, unloaded into a metal bulk drying barn (Burns et al., 1997), and dried overnight (~18 h) by forced air (88°C at inlet). After drying (about 90% DM), the forage was baled from the dryer with a conventional square baler. When hay was field cured, the forage was cut with a conventional mower conditioner, tedded daily to aid drying, windrowed when dry (about 88% DM), and baled with a conventional square baler. To promote stand longevity, the mower conditioner or flail harvester was set to leave stubble of 15 cm for SG, 10 cm

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for alfalfa, and 5 cm for Ladino white clover. The hay was transported from the field or dryer and stored on wooden pallets in a well-ventilated building designed for hay storage until use in each respective experiment. Treatments in each experiment included 100% SG, as well as increasing proportions of either Ladino white clover (Exp. 1) or alfalfa (Exp. 2 and 3). In preparation for feeding, the field-cured hays were passed through a hydraulic bale press (Van Dale 5600, J. Starr Industries, Fort Atkins, WI) with stationary knives spaced at 10 cm. This process reduces hay into 7- to 13-cm lengths with essentially no leaf loss. The artificially dried hay, having been flail harvested, required no further processing before mixing. These methods of preparation aided mixing and feeding, and minimized the amount of hay that was tossed out of the manger during feeding. The increasing proportions of legume were based on weight, with the appropriate amounts of SG and legume combined and mixed in a Davis Precision horizontal batch mixer (H.C. Davis Sons Manu. Co. Inc., Bonner Spring, KS). The mixture was then stored in feed carts until feeding.

Intake and Digestion Forages were evaluated in an animal facility consisting of an intake area fitted with electronic gates (American Calan Inc., Northwood, NH) and a digestion area equipped with digestion crates previously described by Burns and Fisher (2007). The intake phase of each experiment consisted of a 21-d period with the first 7 d used for adjustment and the last 14 d used to estimate daily DMI (Burns et al., 1994). Animals were moved into digestion crates immediately following the intake period. The digestion phase consisted of a 7-d adjustment period followed by a 5-d total collection period (12 d total; Cochran and Galyean, 1994). Total collections consisted of feces and urine in Exp. 1 and feces only in Exp. 2 and 3. A recorded weight of hay was

fed twice daily allowing an excess based on the previous day’s intake. The mean weight of the as-fed diet in excess of ad-libitum intake was 11.5% in Exp. 1, 16.0% in Exp. 2, and 15.3% in Exp. 3. The unconsumed hay (orts) was weighed daily. A daily sample of the hay and orts was obtained for each animal and composites made on a weekly basis for the intake phase and for the 5-d collection period in the digestion phase. In the digestion phase, urine (Exp. 1 only) was collected in containers placed under the crates and feces (all 3 experiments) were collected on a plastic sheet placed on the floor immediately in back of each digestion crate. Total urine was collected daily, acidified with 6 M HCl to ensure pH <6.0, thoroughly mixed, and a 5% aliquot retained in a freezer (−15°C). Feces were removed periodically throughout the day and weighed for 5 consecutive days for DM digestion estimates. Feces were thoroughly mixed each day, and 5% of the fresh weight was placed in a freezer (−15°C) for subsequent analyses. At completion of experiments, the urine samples were thawed, thoroughly mixed, and a subsample retained for analysis. Feces were thawed, thoroughly mixed, and 2 subsamples obtained. One subsample was used for chemical analysis and the second subsample retained for determination of particle sizes (see below). The weekly hay samples, orts, and fecal samples (for composition analysis) were oven dried at 55°C and weighed for DM determination. Samples were thoroughly mixed, and approximately 500 g of sample was ground in a Wiley mill to pass a 1-mm screen and stored at room temperature until analysis.

Masticate Phase Mature, esophageally fistulated steers were used to determine the characteristics of masticated feed in Exp. 2 and Exp. 3. The steers were fed a common hay not used in the experiment before initiation of the mastication phase. During each mastication experiment, steers were fed

Legumes as a protein source for switchgrass hay

meals of the experimental hays before masticate collection. At sampling the esophageal cannula was removed and each bolus collected by hand, to ensure a complete sample. The first 3 to 4 boluses were discarded, and the following 12 were collected. The boluses were placed on a large plastic tray, gently mixed together, placed into plastic bags, immediately quickfrozen in liquid nitrogen (−195°C), stored in a freezer (−15°C) until being freeze-dried, and then returned to the freezer until analysis. Particle-size estimates of the freeze-dried boluses were obtained by passing two 15-g samples through a Fritsch Vibrator system (Fritsch Analysette, the Tekmor Co., Cincinnati, OH). Nine particle sizes were obtained consisting of DM retained on 5.60-, 4.00-, 2.80-, 1.70-, 1.00-, 0.50-, 0.25-, and 0.125-mm sieves and that which passed through the 0.125-mm sieve (<0.125 mm). The dry weight was recorded for material retained on each sieve, as well as that which passed through the 0.125-mm sieve, and percentages of cumulative particle weight oversize were determined and used to calculate mean and median particle sizes (Fisher et al., 1988). Median particle size was compared statistically among hays (within experiment) and, when differences were significant, the cumulative particle weight distributions are presented as supplementary data. Before grinding, the duplicate sieved samples of each hay were composited to form 3 particle-size classes consisting of large (≥1.7 mm), medium (<1.70 and ≥0.50 mm), and small (<0.50 mm). An additional 10-g sample was retained for estimating composition of the whole masticates. Composite and whole samples were ground in a cyclone mill (Udy Corp., Fort Collins, CO) to pass a 1-mm screen and then stored in a freezer until further laboratory analyses.

Fecal Particle-Size Distribution The second fecal sample obtained from animals in Exp. 1 for particlesize determination remained in a

freezer before freeze drying and then returned to the freezer until it was dry sieved using a Fritsch vibrator system. Eight particle sizes were obtained consisting of DM retained on 4.00-, 2.80-, 1.70-, 1.00-, 0.50-, 0.25-, and 0.125-mm sieves and that which passed through the 0.125-mm sieve (<0.125 mm). As in the case of the masticate samples, fecal particle-size data were also expressed in percentages of cumulative particle weight oversize and were used to determine mean and median particle sizes (Fisher et al., 1988). Fecal particle-size classes were also determined and expressed as large, medium, and small.

Eating Behavior Eating behavior was monitored for the 3 hay treatments in Exp. 3 during the last 5 d of the digestion phase with an electronic system that continuously recorded jaw movements (chews: Luginbuhl et al., 1987). Data were categorized into the activities of chews during eating, rumination chews, and resting chews. From these data the total chews were determined and expressed as number per day. The time devoted to each activity during 24 h was determined, as were bolus number per day and chews per bolus.

Experimental Description All 3 intake and digestion experiments described below were conducted with Angus steers (Bos taurus L.). The masticate experiments (Exp. 2 and 3) were conducted with Hereford steers. All animals were handled under procedures approved by the North Carolina State University Institutional Animal Care and Use Committee. Exp. 1. The initial spring growth of Kanlow SG in yr 1 was removed May 18 and the field top-dressed with 90 kg of N/ha. The subsequent regrowth was cut July 26 in the late-vegetative stage (1.1-m canopy height) and was artificially dried as described above. A regrowth of Regal Ladino white clover served as the legume component and was cut August 27 near full bloom

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and was also artificially dried. Three treatments were evaluated and consisted of 1) 100% SG, 2) 85% SG and 15% clover, and 3) 70% SG and 30% clover. The hays were fed to 9 Angus steers in a randomized complete block design with 3 animal replicates. Steers were grouped in threes based on BW (avg = 265 ± 12 kg) and assigned at random within replicate to the 3 hay treatments. Exp. 2. Kanlow SG was top-dressed with 56 kg of N/ha in late March of yr 2. The initial growth was harvested August 19 with heads emerged and field cured. The initial growth of Cimarron alfalfa, harvested at approximately one tenth bloom, was also field cured. Three treatments were evaluated for intake and digestibility and consisted of 1) 100% SG, 2) 75% SG and 25% alfalfa, and 3) 50% SG and 50% alfalfa. The hays were fed to 9 Angus steers in a randomized complete block design with 3 animal replicates. Steers were grouped in threes based on BW (avg = 283 ± 19 kg) and assigned within replicate to the 3 hay treatments. A separate mastication experiment was conducted using the former 3 treatments plus a treatment of 100% alfalfa. Consequently, 4 esophageally fistulated steers (avg BW = 795 ± 76 kg) were used in a 4 × 4 Latin-square design. Each day constituted a period. Exp. 3. The same stand of Kanlow SG was top-dressed with 56 kg of N/ha in late March. The initial growth was removed May 5, the field top-dressed again with 56 kg of N/ ha, and regrowth was harvested in yr 3 on July 28 and field cured. Spring growth of Cimarron alfalfa was harvested at full bloom and field cured. The same 3 treatments as tested in Exp. 2 were evaluated using the same protocols and a similar design. Nine Angus steers were grouped in threes on the basis of BW (avg = 252 ± 28 kg) and randomly assigned within replicate to the 3 hay treatments. A separate mastication experiment with 4 treatments, as described in Exp. 2, was also conducted with 4 esophageally fistulated steers (avg BW = 798 ± 106 kg).

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Laboratory Analysis Exp. 1. All hays, orts, and fecal and urine samples were analyzed for total N colorimetrically (AOAC, 1990) with a Technicon autoanalyzer (Bran and Luebbe, Buffalo, IL), and CP was estimated as N × 6.25. The hay, orts, and fecal samples were also analyzed for concentrations of NDF, ADF, and lignin (permanganate), which was determined according to Van Soest and Robertson (1980). Hemicellulose and cellulose were determined by difference, and CP was estimated as N × 6.25. In vitro DM disappearance was determined by a modified Tilley and Terry (1963) 2-stage procedure (Burns and Cope, 1974). Ruminal inoculum was obtained from a mature Hereford steer fed a mixed alfalfa-orchardgrass (Dactylis glomerata L.) hay. A difference value (DV) was calculated (hay concentration minus orts concentration) as an index to selective consumption. Exp. 2 and 3. Nutritive value for all hay, orts, and fecal samples from the intake and digestion experiments were predicted from spectra obtained

with a Model 5000 near-infrared reflectance spectrophotometer with WinISI, Version 1.5, software (Foss North America Inc., Eden Prairie, MN). The Mahalanobis distance (H statistic = 0.6) was used to identify samples with different spectra. These samples were subsequently analyzed by wet chemistry and used to create a library for the SG:alfalfa mixtures of hay and orts or added to an existing library (fecal). Equations were developed and predictions obtained of the various estimates of nutritive value (Table 1). Estimates of DM disappearance were determined by fermenting samples for 48 h in a batch fermentation vessel (Ankom Technology Corp., Fairport, NY) with artificial saliva and rumen inoculum according to Burns and Cope (1974). Fermentation was terminated with neutral detergent solution in an Ankom 200 fiber analyzer (Ankom Technology Corp.) to remove the residual microbial DM, and results were reported as in vitro true DM disappearance (IVTD). Inoculum was obtained from the rumen of a mature Hereford steer fed a

mixed alfalfa–orchardgrass hay. Total N was determined colorimetrically as noted in Exp. 1, and CP was estimated as N × 6.25. Fiber fractions were determined using reagents according to Van Soest and Robertson (1980) to estimate NDF and ADF using an Ankom 200 fiber analyzer. Lignin was determined by the sulfuric acid procedure, hemicellulose was determined by difference (NDF − ADF) as was cellulose [ADF − (lignin + ash)]. All whole masticate samples and each particle-size class of large, medium, and small were analyzed by wet chemistry. The whole masticate was analyzed for IVTD, CP, and NDF, whereas the 3 particle sizes were not analyzed for CP. As noted for Exp. 1 a DV was determined as an index of selective consumption.

Statistical Analysis The intake and digestion data for all 3 experiments were analyzed as randomized complete block designs. A mixed model was used for all 3 experiments and included a random effect for replication and a fixed ef-

Table 1. Characteristics of the near-infrared reflectance spectrophotometric1 prediction equations (Exp. 2 and 3)2

Item3 Hay (as fed and orts)  IVTD  CP  NDF  ADF  Cellulose  Lignin Fecal  CP  NDF  ADF  Cellulose  Lignin

Mean (%)

No.  

90 86 87 87 88 88   372 371 375 367 363

 

58.8 9.7 72.6 40.8 34.6 6.0   10.9 64.7 36.3 26.3 9.3

Calibration

Range (%)  

38.9–72.0 3.3–15.9 51.3–84.2 32.2–50.7 25.3–43.6 3.9–8.8   5.2–17.4 43.9–77.4 28.8–43.5 18.5–33.9 5.5–15.7

SE (%)  

2.44 0.33 0.75 0.52 0.52 0.20   0.29 1.18 0.99 0.56 0.49

Cross validation

R2  

0.91 0.99 0.99 0.99 0.99 0.96   0.99 0.97 0.90 0.97 0.96

SE (%)  

2.83 0.37 0.93 0.65 0.60 0.26   0.33 1.36 1.08 0.60 0.55

R2  

0.88 0.99 0.99 0.98 0.98 0.94   0.98 0.96 0.88 0.96 0.95

As fed and orts include only selected samples from switchgrass (SG) and SG–legume mixtures. Fecal library includes samples from multiple experiments. 2 Consists of number of samples (No.), mean, range, and associated calibration and cross validation standard errors (SE) and correlation coefficients (R2) for SG and SG–legume mixed diets (as fed and weighback), and fecal constituents. 3 IVTD = in vitro true DM disappearance. 1

Legumes as a protein source for switchgrass hay

fect for treatments. Masticate data for Exp. 2 and Exp. 3 were analyzed as 4 × 4 Latin squares. The mixed model for the Latin-square analysis included terms for animal, period, and treatment. Animal and period were random effects, and treatments were fixed effects (Steel and Torrie, 1980; MIXED procedure, SAS Institute Inc., Cary, NC). Means, when significant differences existed, were compared using orthogonal contrasts to test the effect of increasing proportion of legume within the ANOVA. The sum of squares was partitioned into 2 df for linear and lack of fit (or quadratic) responses to legume in the diet. However, in the masticate experiments (Exp. 2 and 3), a fourth treatment consisting of 100% alfalfa was evaluated and a single df contrast was used to compare it with the other 3 treatments. Differences in animal response and hay chemical composition were considered significant at P ≤ 0.10. The associations among animal responses (n = 9), hay nutritive value (n = 9), and masticate characteristics (n = 6) for the 3 experiments were examined using simple correlation (r) analysis (SAS Institute Inc.) based on treatment means, with statistical significance tested at P ≤ 0.10.

RESULTS AND DISCUSSION Exp. 1 DMI and Digestibility. Steers fed 100% SG hay consumed 1.81 kg/100 kg of BW with DM digestion of 544 g/kg (Table 2). This is within the range previously reported (Vona et al., 1984; Burns et al., 1997). Increasing the proportion of white clover to 30% of the DM fed did not improve DMI but did increase DM digestion linearly (P = 0.05) from 544 to 584 g/ kg. The digestibility of NDF and its constituent fiber fractions was generally not altered by increasing white clover. The exception was hemicellulose digestion, which increased linearly (P = 0.09) from 599 to 629 g/kg with increasing proportions of white clover. Digestible DMI also reflects

the increase in DM digestion increasing linearly (P = 0.08) from 0.99 to 1.22 kg/100 kg of BW. The nutritive value of the SG averaged 42.9% IVDMD, 8.3% CP with an NDF concentration of 73.2% (Table 3). Such hay is inadequate to support desirable steer (272 kg) gains of about 0.9 kg/d, which requires a DMI of about 2.86 kg/100 kg of BW with apparent DM digestion of 600 g/kg and a CP concentration of 10% (NRC, 2000). Increasing the white clover component in the SG diet to 30% of DM linearly increased (P < 0.01) IVDMD and CP and reduced NDF and hemicellulose quadratically (P < 0.05). The other constituent fiber fractions of the diet were reduced linearly (P < 0.01; Table 3). The noted exception was lignin, which increased linearly (P = 0.06) with increasing white clover. These changes are consistent with greater concentrations of CP and lignin in legumes and lesser concentrations of NDF compared with grasses (Frame et al., 1998a). These shifts were reflected in increased DM digestion but not in DMI. When white clover was fed as 30% of the dietary DM, the CP concentrations of the hay was adequate to meet NRC requirements for daily gains of 0.9 kg, whereas both DMI and DM digestion were inadequate (NRC, 2000). The difference in composition between the hays and the orts (DV, Table 3) reveals that on the 100% SG diet, some selective consumption was evident because the orts were lesser in IVDMD and CP and greater in NDF. This is consistent with the literature regarding selective intake (Forbes, 2007; Burns, 2011). However, with increasing white clover, none of the changes diminished and were not of sufficient scope at 30% white clover to be significant. Urine and Fecal Characteristics. Adding clover to the SG diet increased the CP of the hay (Table 3) and also resulted in a linear (P = 0.04) increase in steer daily N intake (Table 4). Although total urine was not altered by increasing the clover component, N excreted in the urine

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increased linearly (P = 0.01) to 0.026 kg/d. Examination of fecal composition also showed a linear (P = 0.05) increase in CP concentration as did the daily excretion of N in the feces (Table 4). It is noteworthy that some reduction in N availability may have occurred in these forages through artificial drying (heating). However, the increase in CP of the hays (with increasing white clover), and resulting increase in N excretion in urine and in feces, indicates that any loss of N availability is probably of limited biological importance. Neutral detergent fiber and its constituents hemicellulose and cellulose decreased linearly (P ≤ 0.04), whereas ADF and lignin were not altered by increasing clover in the diet. Particle-size distributions of the fecal DM were similar among the 3 treatments (data not shown). Subsequent calculation of the particle-size classes of large, medium, and small were also similar among treatments. Large particles composed 0.7% (SE = 0.10) of the fecal DM, medium particles 28.8% (SE = 3.40), and small particles 70.5% (SE = 3.39).

Exp. 2 DMI and Digestion. Steers consumed 1.61 kg/100 kg of BW of the mature SG diet with a DM digestion of 480 g/kg (Table 2). These responses are within the range previously reported (Vona et al., 1984; Burns et al., 1997). Replacing SG with alfalfa up to 50% of the diet resulted in a linear increase (P < 0.01) in both DMI and DM digestion. This resulted also in linear increases (P ≤ 0.03) in digestible DMI and digestible intakes of NDF and its fiber constituents. Nutritive value of the SG hay was consistent with the moderate DMI with IVTD and CP averaging 51.9 and 7.1%, respectively, and NDF at 79.1% (Table 3). Such CP and NDF concentrations are also consistent with mature SG (Vona et al., 1984; Burns et al., 1997). Adding alfalfa up to 50% of the DM linearly increased (P < 0.01) IVTD and CP and decreased (P < 0.01) NDF and its fiber

 

 

 

 

   

2

1

HEMI = hemicellulose; CELL = cellulose. Values are the mean of 3 steers. 3 LOF = lack of fit.

Exp. 1   SG (% DM) WC (% DM)  —   100   85  15   70  30  SE   Significance (P-value)   Treatment   Linear   LOF3 Exp. 2 (headed SG)   SG (% DM) AL (% DM)   100  —   75  25   50  50  SE     Significance (P-value)   Treatment   Linear   LOF Exp. 3 (vegetative SG)   SG (% DM) AL (% DM)   100  —   75  25   50  50  SE     Significance (P-value)   Treatment   Linear   LOF

Item

0.11 0.12 0.12

1.77 2.20 2.09 0.13

<0.01 <0.01 0.15

1.61 1.89 2.68 0.14

0.22 0.18 0.25

1.812 2.14 2.08 0.12

Intake (kg/100 kg of BW)

 

 

 

 

   

0.14 0.09 0.27

541 574 575 11.2

0.02 <0.01 0.91

480 531 578 16.8

0.11 0.05 0.62

544 571 584 11.3

DM

 

 

 

 

   

0.63 0.99 0.35

586 598 586 9.4

0.52 0.27 0.99

519 543 568 28.4

0.24 0.11 0.88

539 551 567 13.0

NDF

 

 

 

 

   

0.93 0.82 0.79

568 570 565 10.4

0.77 0.49 0.93

516 533 545 28.1

0.41 0.24 0.62

482 508 513 17.2

ADF

 

 

 

 

   

0.32 0.58 0.17

604 627 612 10.1

0.43 0.22 0.91

524 555 598 30.1

0.13 0.09 0.24

599 599 629 12.6

HEMI

Apparent digestion1 (g/kg)

 

 

 

         

            0.97   0.90   0.86   643 644 641 7.4

0.71   0.42   0.94  

581 601 616 28.7

    587   610   621   18.5       0.31   0.15   0.74  

   

CELL

 

 

 

 

   

0.12 0.11 0.14

0.96 1.26 1.20 0.070

<0.01 <0.01 0.17

0.77 1.01 1.55 0.079

0.13 0.08 0.26

0.99 1.22 1.22 0.078

DM

 

 

 

 

   

0.12 0.19 0.10

0.75 0.95 0.87 0.057

0.04 0.02 0.50

0.65 0.75 0.99 0.073

0.54 0.60 0.35

0.71 0.81 0.75 0.050

NDF

 

 

 

 

   

0.06 0.04 0.13

0.36 0.47 0.46 0.029

0.03 0.01 0.47

0.34 0.41 0.55 0.039

0.43 0.40 0.34

0.32 0.39 0.37 0.027

ADF

 

 

 

 

   

0.16 0.69 0.07

0.39 0.48 0.41 0.028

0.08 0.03 0.55

0.31 0.35 0.44 0.034

0.62 0.91 0.36

0.38 0.42 0.39 0.024

HEMI

 

 

 

 

   

0.07 0.07 0.13

0.36 0.46 0.45 0.027

0.04 0.02 0.52

0.34 0.40 0.52 0.037

0.48 0.56 0.31

0.33 0.39 0.36 0.026

CELL

Digestible intake (kg/100 kg of BW)

Table 2. Dry matter intake, apparent digestion, and digestible intakes of a switchgrass (SG) hay diet with increasing proportions of either white clover (WC; Exp. 1) or alfalfa (AL; Exp. 2 and 3) hays (DM basis)

388 Burns and Fisher

 

 

 

 

 

   

0.80 0.53 0.87

64.5 63.8 63.6 0.99

<0.01 <0.01 0.39

51.9 55.9 61.9 0.84

<0.01 <0.01 0.17

42.93 49.4 52.0 1.09

AF

 

   

 

   

 

   

0.19 0.08 0.88

6.9 4.4 2.4 1.50

0.13 0.07 0.33

7.4 10.7 11.0 1.16

0.35 0.29 0.32

4.1 5.3 −0.2 2.56

DV                                                              

   

 

   

 

   

0.16 0.11 0.25

11.7 11.6 12.3 0.27

<0.01 <0.01 0.08

7.1 8.4 11.3 0.32

0.02 <0.01 0.80

8.3 9.6 11.1 0.44

AF

 

   

 

   

 

   

0.21 0.09 0.98

3.5 4.2 4.9 0.51

0.22 0.12 0.41

4.2 3.8 0.0 1.58

DV

0.05 0.02 0.68

3.5 1.8 −0.6 0.67

CP (%)

                                                             

   

 

   

 

   

<0.01 <0.01 0.72

73.9 72.4 70.5 0.54

<0.01 <0.01 0.14

79.1 74.6 66.8 0.70

<0.01 <0.01 0.05

73.2 69.5 64.1 0.62

AF

 

   

 

   

 

   

DV

0.13 <0.01 0.66

−5.9 −1.7 4.0 1.51

<0.01 <0.01 0.50

−5.0 −9.4 −12.0 1.04

0.50 0.31 0.60

−7.6 −7.2 −1.2 4.01

NDF (%)

2

1

HEMI = hemicellulose; CELL = cellulose; AF = as fed; DV = difference value (hay concentration minus orts concentration). IVDMD in Exp. 1; IVTD = in vitro true DM disappearance in Exp. 2 and 3. 3 Values are the mean of 3 steers. 4 LOF = lack of fit.

  Exp. 1   SG (% DM) WC (% DM)   100  —   85  15   70  30  SE       Significance (P-value)    Treatment     Linear     LOF4   Exp. 2 (headed SG)   SG (% DM) AL (% DM)   100  —   75  25   50  50  SE       Significance (P-value)    Treatment     Linear     LOF     Exp. 3 (vegetative SG)   SG (% DM) AL (% DM)   100  —   75  25   50  50  SE       Significance (P-value)      Treatment   Linear     LOF  

Item

IVDMD or IVTD2 (%)

                                                             

   

 

   

 

   

0.01 <0.01 0.79

36.9 38.2 39.7 0.40

<0.01 <0.01 0.30

42.9 41.7 38.8 0.57

<0.01 <0.01 0.80

37.9 36.3 34.6 0.54

ADF

 

   

 

   

 

   

<0.01 <0.01 0.28

36.9 34.2 30.8 0.25

<0.01 <0.01 <0.01

36.2 32.9 28.0 0.17

<0.01 <0.01 0.02

35.3 33.2 29.5 0.16

HEMI

 

   

 

   

 

   

0.18 0.07 0.97

32.6 33.1 33.5 0.29

<0.01 <0.01 0.22

37.7 36.0 32.6 0.51

<0.01 <0.01 0.18

31.8 30.5 27.9 0.37

CELL

Fiber fraction (%)

 

   

 

   

 

   

<0.01 <0.01 0.93

4.2 5.2 6.1 0.09

<0.01 <0.01 0.66

5.0 5.5 6.1 0.06

0.08 0.06 0.14

5.3 5.2 5.9 0.22

Lignin

Table 3. In vitro DM disappearance and nutritive value of a switchgrass (SG) hay diet with increasing proportions of either white clover (WC; Exp. 1) or alfalfa (AL; Exp. 2 and 3) hays (DM basis)1

Legumes as a protein source for switchgrass hay

389

390

0.09 0.04 0.40 0.21 0.14 0.29 0.10 0.04 0.92 0.01 0.01 0.25 0.24 0.17 0.31 0.02 0.01 0.69 0.12 0.05 0.81 0.02 0.01 0.16 0.10 0.11 0.12 2

1

HEMI = hemicellulose; CELL = cellulose. Values are the mean of 3 steers. 3 LOF = lack of fit.

0.08 0.04 0.29

SG (% DM) WC (% DM)  100  —  85  15  70  30 SE     Significance (P-value)   Treatment    Linear      LOF3

Item

 

0.0492 0.071 0.074 0.0073

N intake (kg/d)

 

2.6 5.1 4.5 0.71

Total excreted

 

0.011 0.024 0.026 0.0030

N excreted

 

8.3 9.2 10.5 0.62

CP

 

72.3 70.7 68.0 0.76

NDF

 

41.8 40.7 40.9 0.45

 

30.9 30.0 27.1 0.64

 

28.0 26.9 26.0 0.74

 

11.6 11.6 12.4 0.33

 

0.023 0.029 0.030 0.0027

N excreted (kg/d) Lignin CELL HEMI ADF

Composition1 (%)

Feces Urine (kg/d)

Table 4. Daily nitrogen intake and excretion in urine and feces and composition of feces of a switchgrass (SG) hay diet with increasing proportion of white clover (WC), Exp. 1 (DM basis)

Burns and Fisher

constituents. The exception was lignin concentration, which was linearly increased (P < 0.01). These shifts are consistent with greater concentrations of CP and lignin and lesser concentration of NDF found in alfalfa versus grasses (Frame et al., 1998b). Examination of the DV further indicated selective consumption of the offered diet. Both IVTD (P = 0.07) and CP (P = 0.09) averaged greater, and NDF lesser (P < 0.01), in the as-fed hay compared with the concentration of the orts (Table 3). Diet Characteristics. In the mastication experiment a fourth treatment consisting of 100% alfalfa hay was added and provides a contrast between the composition of mature SG alone and the alfalfa source that was added to the SG hay. Note that the mature SG had an IVTD of 61.7%, CP of 7.3%, and NDF of 73.7%. These nutritive values are in contrast to alfalfa, which had an IVTD of 78.8%, CP of 17.4%, and NDF of 46.1% (Table 5). Examining the whole masticate reveals a linear increase (P < 0.01) in masticate DM through the 50% alfalfa contribution, indicating reduced incorporation of saliva with increasing proportions of alfalfa. Also, IVTD and CP gave linear increases (P < 0.01), with NDF decreased (P < 0.01). These changes reflect the addition of alfalfa having greater concentrations of IVTD and CP and a lesser concentration of NDF (100% of DM, Table 5). Even though the quantity of salvia incorporated in the bolus differed, particle size of the masticate was not altered by increasing the proportion of alfalfa in the SG diet nor was the particle size of alfalfa alone different from the hay mixtures. Steers masticated all hay diets similarly, and the proportions of large, medium, and small particles were not altered by increasing the contribution of alfalfa to the SG diet. Furthermore, alfalfa hay alone did not differ from the SG– alfalfa combinations (Table 5). The IVTD of the large and medium particle-size classes was not altered by increasing proportions of alfalfa in the SG diet averaging 61.5 and

 

 

0.02 0.72 0.02 0.01

18.7 20.3 19.0 20.9

<0.01 <0.01 <0.01 <0.01

15.24 16.8 16.6 20.9

DM (%)

 

 

 

0.57 0.44 0.86 0.26

1.9 1.9 1.9 1.8

0.60 0.39 0.79 0.32

2.0 1.9 1.9 1.8

PS (mm)

 

 

 

0.07 0.13 0.06 0.12

72.9 70.7 71.6 72.9

<0.01 <0.01 0.68 <0.01

61.7 64.7 66.6 78.8

IVTD (%)

 

 

 

<0.01 0.03 0.52 <0.01

10.7 11.0 11.9 13.7

<0.01 <0.01 0.57 <0.01

7.3 9.1 10.2 17.4

CP (%)

2

1

IVTD = in vitro true DM disappearance. Large = ≥1.7 mm; Medium = <1.7 mm and ≥0.50 mm; Small = <0.50 mm. 3 Prop. = proportion of masticate DM. 4 Values are the mean of 4 steers. 5 LOF = lack of fit.

Exp. 2 (headed SG) AL (% DM)   SG (% DM)   100  —   75  25   50  50   —  100   Significance (P-value)    Treatment     Linear       LOF5    100 AL vs. others  Exp. 3 (vegetative SG)   SG (% DM) AL (% DM)   100  —   75  25   50  50   —  100   Significance (P-value)    Treatment     Linear     LOF      100 AL vs. others 

Item

Whole masticate

 

 

 

<0.01 <0.01 0.76 <0.01

70.2 68.6 66.4 59.0

<0.01 <0.01 0.99 <0.01

73.7 68.5 63.2 46.1

NDF (%)  

IVTD  

NDF    

Prop.  

IVTD  

Medium NDF    

Prop.  

IVTD

Small

 

NDF

                    0.30 0.34 0.58 0.12

57.1 57.1 54.8 53.1  

0.01 0.12 0.11 <0.01

70.8 69.1 69.6 72.1

 

<0.01 <0.01 0.55 <0.01

71.7 69.6 68.5 60.4

  37.2 75.7 67.6   5.7 79.8 62.1   37.8 73.3 66.4   5.1 79.0 60.6   38.7 72.4 64.0   6.5 82.0 56.4   41.6 71.0 57.0   5.6 84.8 49.6                   0.17 0.18 <0.01   0.47 <0.01 <0.01   0.41 0.04 <0.01   0.35 0.03 0.04   0.89 0.56 0.51   0.23 0.04 0.55   0.04 0.82 <0.01   0.87 <0.01 <0.01

  59.0 60.7 73.9   33.7 67.3 69.9   7.3 73.1 62.5   56.6 61.5 71.1   36.4 68.5 65.5   7.1 76.6 56.5   54.7 62.2 68.1   37.7 69.9 59.7   7.5 80.5 48.9   50.7 74.0 49.1   40.9 80.9 42.9   8.3 90.4 31.1                           0.46 <0.01 <0.01   0.32 <0.01 <0.01   0.76 <0.01 <0.01   0.42 0.36 <0.01   0.29 0.12 <0.01   0.88 <0.01 <0.01   0.95 0.94 0.90   0.83 0.93 0.67   0.74 0.88 0.70   0.19 <0.01 <0.01   0.14 <0.01 <0.01   0.33 <0.01 <0.01

   

Prop.3

Large

Particle-size class2 (%)

Table 5. Dry matter, median particle size (PS), and nutritive value1 of whole masticate and particle-size classes of a switchgrass (SG) diet with increasing proportions of alfalfa (AL) hay (DM basis)

Legumes as a protein source for switchgrass hay

391

392 68.6%, respectively (Table 5). However, IVTD of the small particle-size class increased linearly (P < 0.01) from 73.1% for only SG to 80.5% with 50% alfalfa. On the other hand, NDF showed a linear decline for all 3 particle-size classes with increasing proportions of alfalfa. As expected, alfalfa alone was greatest (P < 0.01) in IVTD and least (P < 0.01) in NDF for all 3 particle-size classes compared with the other 3 treatments.

Exp. 3 DMI and Digestion. Steers consumed 1.77 kg/100 kg of BW of the immature SG hay, and no increase in DMI was noted with alfalfa even when fed at 50% of the diet DM (Table 2). However, DM digestion increased linearly (P = 0.09) from 541 to 575 g/kg when alfalfa increased up to 50% of the diet DM. Digestible DMI was not altered by increasing alfalfa in the hay; however, digestible ADF and cellulose increased linearly (P ≤ 0.07). Digestible intake of NDF and hemicellulose both increased as alfalfa increased to 25% of the DM and then decreased at 50% alfalfa (lack of fit; P = 0.10 and 0.07, respectively). The nutritive value of the immature SG hay averaged 64.5% IVTD, 11.7% CP, and 73.9% NDF (Table 3). The addition of alfalfa did not alter IVTD or CP but linearly reduced (P ≤ 0.01) NDF and its constituent hemicellulose. In contrast, ADF, cellulose, and lignin linearly increased (P ≤ 0.01). When animals were fed 100% SG, the DV indicated selective consumption with positive IVTD and CP and negative NDF. However, increasing the proportion of alfalfa in the mixtures linearly reduced the magnitude of the DV for IVTD, CP, and NDF, indicating that selectivity played less of a role when alfalfa was fed. Diet Characteristics. As noted for masticate in Exp. 2, a fourth treatment consisting of 100% alfalfa hay was also included in this experiment. This provided a contrast between the composition of the immature SG and the alfalfa source

Burns and Fisher

that was added to the SG hay. Note the similarity in IVTD between the immature SG and the alfalfa (72.9%) but differences in CP and NDF. Alfalfa had greater CP (13.7 vs. 10.7%) and lesser NDF (59.0 vs. 70.2%), and this is consistent with reports in the literature (Frame et al., 1998b). Increasing the proportion of alfalfa mixed with the SG hay increased DM (reduced incorporation of saliva), resulting in a lack of fit (quadratic response) and a reduction in DM with either a 25 or 50% mixture of alfalfa with the SG hay (Table 5). However, particle size of the masticate was not altered. Although the effect was small, the IVTD decreased with inclusion of 25% alfalfa and then increased at 50% inclusion, resulting in a lack of fit compared with a linear effect. The CP increased linearly and NDF decreased linearly with the increased proportions of alfalfa. The latter 2 changes are consistent with the CP and NDF composition of alfalfa and expected when added to SG. The proportion of large, medium, and small particles of the masticate DM averaged 56.3, 37.9 and 5.8%, respectively, and were not altered by increasing the proportion of alfalfa mixed with the SG hay (Table 5). Within the large particle-size class, IVTD was not altered by increasing the proportion of alfalfa, whereas NDF declined linearly. Within the medium and small particle-size classes, IVTD declined linearly in medium particles but with a lack of fit in small particles. The latter was associated with a small reduction in IVTD at 25% alfalfa but an increase at 50% alfalfa. In both medium and small particle-size classes, NDF concentrations declined linearly, reflecting the lesser concentrations of NDF in alfalfa (Frame et al., 1998b). In comparing alfalfa with the other treatments, alfalfa whole masticate had greater CP and lesser NDF concentrations with a greater proportion of medium particles (41.6 vs. 37.9%) in the masticated forage. Within each particle-size class, alfalfa had greater IVTD and lesser NDF. The noted exception was IVTD for the medium

particle size, which was similar to the mean of the other treatments (71.0 vs.73.8%). Eating Behavior. Steers readily consumed all diets, with chews per day (24 h) averaging 47.9 × 103 with no difference noted among the 3 treatments (data not shown). Chews devoted to eating, ruminating, and resting averaged 24.0, 19.6, and 4.1 × 103, respectively. These results are similar to those reported for SG baleage (Huntington and Burns, 2007). Increasing the alfalfa component of mixture with SG did not alter eating or ruminating chews, but a lack of fit (P = 0.10) was evident for resting chews. These averaged 4.0 × 103 for SG, 5.3 × 103 for 25% alfalfa, and 3.3 × 103 for the 50% mixture (data not shown). Chews devoted to eating averaged 59/min and were not altered by the proportion of alfalfa in the mixture. Chews while ruminating averaged 56/ min, and small differences resulted in a lack of fit (P = 0.04) averaging 56/min for SG, decreased to 53/min when hay was 25% alfalfa and then increased to 59/min at 50% alfalfa. The increase in resting chews per minute and decline in ruminating chews for the 25% alfalfa treatment is difficult to explain, but may be associated with preference for, and availability of, specific components in the hay mixture. Steers devoted similar time among treatments to daily activities, averaging 6.8 h eating, 5.8 h ruminating, and 11.4 h resting. Furthermore, the total boluses per day were similar among treatments, averaging 379 boluses/d and 128 chews/bolus. These activities are similar in magnitude to those reported by Huntington and Burns (2007). The animal responses from the 3 experiments were integrated using correlation analysis. Dry matter intake (kg/100 kg of BW) of steers was well correlated (r = 0.79; P = 0.01) with the proportion of legume hay added to the SG, regardless of legume species or SG maturity. This demonstrates the generally positive influence of legumes on animal response. In general, DMI was negatively cor-

Legumes as a protein source for switchgrass hay

related (r = −0.73; P = 0.03) with the NDF concentration of the diet. Furthermore, DMI was related to masticate characteristics (alfalfa–SG treatments only) being positively correlated (r = 0.82; P = 0.08) with whole masticate IVTD and CP concentrations (r = 0.81; P = 0.05) but negatively correlated (r = −0.82; P = 0.05) with masticate NDF. Also, DMI was negatively associated with the proportion of masticate DM composed of large particles (r = −0.82; P = 0.05) but positively correlated with the proportion of medium particles (r = 0.81; P = 0.05), and no correlation was noted with the proportion of small particles (r = 0.33; P = 0.51). The relationship between DMI and DM digestion of the hay diets was positive (r = 0.76; P = 0.02), as expected. Dry matter digestion of the hays, as noted for DMI, was well correlated (r = 0.66; P = 0.05) with the proportion of legume and consequently with the CP concentration of the diet (r = 0.78; P = 0.01). On the other hand, DM digestion was negatively correlated (r = −0.89; P < 0.01) with NDF concentrations of the hay. This was also reflected in whole masticate with DM digestion being positively correlated with masticate in vitro estimates of DM disappearance (r = 0.75; P = 0.05) and CP (r = 0.79; P = 0.07) and negatively associated (r = −0.77; P = 0.07) with NDF. Dry matter digestion was also related to the extent that steers masticated the forage and reduced the particle size. The proportion of large particles composing the masticate DM (55 to 59%) was negatively correlated (r = −0.78; P = 0.07) with DM digestion, whereas medium particles (34 to 39% of DM) were positively correlated (r = 0.78; P = 0.07), with no relationship (r = 0.21; P = 0.68) noted for small particles (5 to 8% of DM). However, DM digestion was positively correlated with in vitro estimates of DM disappearance and negatively correlated with NDF concentrations within each particle-size class as noted above for the whole masticate. These

associations are consistent with those reported by Pond et al. (1990). Integration of DMI and DM digestion in the digestible DMI calculation reflects the relationships noted for DMI and DM digestion above and were well correlated (r = 0.80; P < 0.01) with the proportion of legume in the hay mixtures. It is noteworthy that NDF digestion was only well correlated with estimates of DM disappearance (r = 0.78; P = 0.01) and CP concentrations (r = 0.95; P < 0.01) of the hays.

IMPLICATIONS Switchgrass is a productive, warmseason, perennial grass with yield potential greater than most warm-season forage species. A major concern for its use as hay, however, is its limited nutritive value, especially CP, even when harvested by the late-vegetative stage. Data from these experiments support the use by producers of either white clover or alfalfa in mixture with SG to remove this limiting factor. The use of one of these perennial legumes in mixture with SG is practical. In addition, it provides the grassland farmer an on-farm option of a source of both supplemental protein with reduced NDF concentrations when using a warm-season, grass-based diet for ruminants.

393

Burns, J. C., D. S. Fisher, and K. R. Pond. 2011. Steer performance, intake, and digesta kinetics of switchgrass at three forage masses. Agron. J. 103:337–350. Burns, J. C., R. D. Mochrie, and D. H. Timothy. 1984. Steer performance from two Pennisetum species, switchgrass, and a fescue‘Coastal’ bermudagrass system. Agron. J. 76:795–800. Burns, J. C., R. D. Mochrie, and D. H. Timothy. 1985. Intake and digestibility of dry matter and fiber of flaccidgrass and switchgrass. Agron. J. 77:933–936. Burns, J. C., K. R. Pond, and D. S. Fisher. 1991. Effects of grass species on grazing steers: II. Dry matter intake and digesta kinetics. J. Anim. Sci. 69:1199–1204. Burns, J. C., K. R. Pond, and D. S. Fisher. 1994. Measurement of intake. Pages 494–532 in Forage Quality, Evaluation and Utilization. G. C. Fahey Jr., ed. Am. Soc. Agron., Crop Sci. Soc. Am., Soil Sci. Soc. Am., Madison, WI. Burns, J. C., K. R. Pond, D. S. Fisher, and J.-M. Luginbuhl. 1997. Changes in forage quality, ingestive mastication, and digesta kinetics resulting from switchgrass maturity. J. Anim. Sci. 75:1368–1379. Buxton, D. R., D. R. Mertens, and D. S. Fisher. 1996. Forage quality and ruminant utilization. Pages 229–266 in Cool-Season Forage Grasses. L. E. Moser, D. R. Buxton, and M. D. Casler, ed. Agron. Monogr. 34. ASA, CSSA, and SSSA, Madison, WI. Cochran, R. C., and M. L. Galyean. 1994. Measurements of in vivo forage digestion by ruminants. Pages 613–643 in Forage Quality, Evaluation and Utilization. G. C. Fahey Jr., ed. Am. Soc. Agron., Crop Sci. Soc. Am., Soil Sci. Soc. Am., Madison, WI.

AOAC. 1990. Official Methods of Analysis. 15th ed. AOAC, Arlington, VA.

Coleman, S. W., J. E. Moore, and J. R. Wilson. 2004. Quality and utilization. Pages 267–308 in Warm-Season (C4) Grasses. L. E. Moser, B. L. Burson, and L. E. Sollenberger, ed. Agron. Monogr. 45. Am. Soc. Agron., Crop Sci. Soc. Am., Soil Sci. Soc. Am., Madison, WI.

Burns, J. C. 2011. Intake and digestibility among Caucasian bluestem, big bluestem, and switchgrass compared with bermudagrass. Crop Sci. 51:2262–2275.

Fisher, D. S., J. C. Burns, and K. R. Pond. 1988. Estimation of mean and median particle size of ruminant diets. J. Dairy Sci. 71:518–524.

Burns, J. C., and W. A. Cope. 1974. Nutritive value of crownvetch forage as influence by structural constituents and phenolic and tannin compounds. Agron. J. 66:195–200.

Forbes, J. M. 2007. Diet selection: Principles. Pages 144–187 in Voluntary Food Intake and Diet Selection in Farm Animals. 2nd ed. CAB Int., Cambridge, MA.

Burns, J. C., and D. S. Fisher. 2007. Dry matter intake and digestibility of ‘Coastal’, ‘Tifton 44’ and ‘Tifton 85’ bermudagrass hays grown in the U.S. upper south. Crop Sci. 47:795–810.

Frame, J., J. F. L. Charlton, and A. S. Laidlaw. 1998a. White clover. Pages 15–106 in Temperature Forage Legumes. CAB Int., New York, NY.

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Burns, J. C., D. S. Fisher, and K. R. Pond. 1993. Ensiling characteristics and utilization of switchgrass preserved as silage. Postharvest Biol. Technol. 3:349–359.

Frame, J., J. F. L. Charlton, and A. S. Laidlaw. 1998b. Lucerne (Syn. Alfalfa). Pages 107–179 in Temperate Forage Legumes. CAB Int., New York, NY.

394 Huntington, G. B., and J. C. Burns. 2007. Afternoon harvest increases readily fermentable carbohydrate concentration and voluntary intake of gamagrass and switchgrass baleage by beef steers. J. Anim. Sci. 85:276–284. Luginbuhl, J.-M., K. R. Pond, J. C. Russ, and J. C. Burns. 1987. A simple electronic device and computer interface system for monitoring chewing behavior of stall-fed ruminants. J. Dairy Sci. 70:1307–1312. North Carolina ARS. 2009. Switchgrass: Establishment, management, yield, nutritive value, and utilization. Tech. Bull. 326. North Carolina Agric. Res. Serv., Raleigh, NC. NRC. 2000. Nutritional Requirements of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC. Pond, K. R., J.-M. Luginbuhl, J. C. Burns, and D. S. Fisher. 1990. Mastication of lig-

Burns and Fisher nocellulose during ingestion and rumination. Pages 23–32 in Microbial and Plant Opportunities to Improve Lignocellulose Utilization by Ruminants. D. E. Akin, L. G. Ljundhal, J. R. Wilson, and P. J. Harris, ed. Elsevier Publ. Co., New York, NY. Steel, R. G. D., and J. H. Torrie. 1980. Principal and Procedures of Statistics: A Biometrical Approach. McGraw-Hill Publ. Co., New York, NY. Tilley, J. M., and R. A. Terry. 1963. A twostage technique for in vitro digestion of forage crops. J. Br. Grassl. Soc. 18:104–111. Van Soest, R. J., and J. B. Robertson. 1980. Systems of analysis for evaluating fibrous feeds. Pages 49–60 in Standardization of Analytical Methodology for Feeds. W. J. Pigden, C. C. Balch, and M. Graham, ed. Int. Dev. Res. Center, Ottawa, Canada.

Vona, L. C., G. A. Jung, R. L. Reid, and W. C. Sharp. 1984. Nutritive value of warmseason grass hays for beef cattle and sheep: Digestibility, intake and mineral utilization. J. Anim. Sci. 59:1582–1593. Xu, J., J. J. Cheng, R. R. Sharma-Shivappa, and J. C. Burns. 2010. Lime pretreatment of switchgrass at mild temperatures for ethanol production. Bioresour. Technol. 101:2900– 2903. Yang, Y., R. R. Sharma-Shivappa, J. C. Burns, and J. Cheng. 2009. Saccharification and fermentation of dilute-acid-pretreated freeze-dried switchgrass. Energy Fuels 23:5626–5635.