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J. Anim. Sci. 2005. 83:2815-2825
© 2005 American Society of Animal Science

ANIMAL NUTRITION

Effect of grain processing degree on intake, digestion, ruminal fermentation, and performance characteristics of steers fed medium-concentrate growing diets1

W. L. Bengochea, G. P. Lardy2, M. L. Bauer and S. A. Soto-Navarro3

Department of Animal and Range Sciences, North Dakota State University, Fargo 58105


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results and Discussion
 Literature Cited
 
Three trials were conducted to evaluate the effects of degree of barley and corn processing on performance and digestion characteristics of steers fed growing diets. Trial 1 used 14 (328 ± 43 kg initial BW) Holstein steers fitted with ruminal, duodenal, and ileal cannulas in a completely randomized design to evaluate intake, site of digestion, and ruminal fermentation. Treatments consisted of coarsely rolled barley (2,770 µm), moderately rolled barley (2,127 µm), and finely rolled barley (1,385 µm). Trial 2 used 141 crossbred beef steers (319 ± 5.5 kg initial BW; 441 ± 5.5 kg final BW) fed for 84 d in a 2 x 2 factorial arrangement to evaluate the effects of grain source (barley or corn) and extent of processing (coarse or fine) on steer performance. Trial 3 investigated four degrees of grain processing in barley-based growing diets and used 143 crossbred steers (277 ± 19 kg initial BW; 396 ± 19 kg final BW) fed for 93 d. Treatments were coarsely, moderately, and finely rolled barley and a mixture of coarsely and finely rolled barley to approximate moderately rolled barley. In Trial 1, total tract digestibilities of OM, CP, NDF, and ADF were not affected (P ≥ 0.10) by barley processing; however, total tract starch digestibility increased linearly (P < 0.05), and fecal starch output decreased linearly (P < 0.05) with finer barley processing. In situ DM, CP, starch disappearance rate, starch soluble fraction, and extent of starch digestion increased linearly (P < 0.05) with finer processing. In Trial 2, final BW and ADG were not affected by degree of processing or type of grain (P ≥ 0.13). Steers fed corn had greater DMI (P = 0.05) than those fed barley. In Trial 3, DMI decreased linearly with finer degree of processing (P = 0.003). Gain efficiency, apparent dietary NEm, and apparent dietary NEg increased (P < 0.001) with increased degree of processing. Finer processing of barley improved characteristics of starch digestion and feed efficiency, but finer processing of corn did not improve animal performance in medium-concentrate, growing diets.

Key Words: Barley • Corn • Digestion • Particle Size • Processing • Steer


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results and Discussion
 Literature Cited
 
Growing or backgrounding cattle is a tool to allow for moderate animal growth (Block et al., 2001Go). Basal forage diets contain a relatively low or moderate concentrate level and are fed for a variable period (Vaage et al., 1998Go). Feeding whole barley results in poor animal performance (Mathison, 1996Go). The degree of barley processing for optimal performance in diets for growing cattle has not been researched extensively. Reed et al. (2005)Go reported an improvement in steer performance with finer processing of sprout-damaged barley in growing diets. In high-barley finishing diets, starch digestibility increased with increased degree of temper-rolling (Beauchemin et al., 2001Go). Rapid fermentation rates increase the possibility of acidosis (Owens et al., 1998Go). When diets are adequate in effective fiber, Koenig et al. (2003)Go suggested barley grain can be more extensively rolled. In corn-based dairy diets, an improvement in N and starch use was noted with fine grinding (San Emeterio et al., 2000Go). Callison et al. (2001)Go reported increased ruminal digestion of nonstructural carbohydrates with increasing processing level in dairy cattle diets containing 50% roughage.

Little information is available on the effects of degree of processing of sound (nonsprouted) barley in growing diets. We hypothesized that finer dry-roll processing would increase ruminal fermentation, thereby increasing ADG and/or G:F, but that it might negatively affect ruminal fermentation of fiber. We also hypothesized that mixtures of coarsely and finely rolled barley may cause positive associative effects (Stock et al., 1987Go). Therefore, the objectives of this series of studies were to evaluate the effects of 1) barley processing degree on ruminal fermentation and digestibility, 2) corn and barley processing on performance of growing cattle, and 3) blending barley of differing particle sizes in diets for growing beef steers.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results and Discussion
 Literature Cited
 
All animal care, handling, and surgical procedures were approved by the North Dakota State University Institutional Animal Care and Use Committee before the start of the study.

Trial 1
Animals and Diets.
Fourteen ruminally, duodenally, and ileally cannulated Holstein steers (328 ± 43 kg initial BW) were used in a completely randomized design. Steers were weighed at the beginning and end of the trial. They were individually fed and housed in a climate-tempered (>8°C) room in individual tie stalls (1.2 m x 2.0 m and 1.5 m x 2.5 m) on rubber mats, which allowed for separation of urine and feces. Animals were allowed ad libitum access to water and were fed totally mixed diets at 0600 daily. Treatments consisted of 1) coarsely rolled barley (2,770 ± 1.46 µm particle size), 2) moderately rolled barley (2,127 ± 1.56 µm particle size), and 3) finely rolled barley (1,385 ± 1.33 µm particle size). Five steers were used for the coarsely and finely rolled barley treatments, whereas four steers were used for the moderately rolled barley treatment. Grain was dry rolled using a Roskamp Champion (Waterloo, IA) roller mill. Diets (Table 1Go) were formulated to contain a minimum of 12.5% CP, 0.6% Ca, 0.3% P, 0.6% K, and 27.5 mg of monensin/kg (Elanco Animal Health, Indianapolis, IN).


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  		Table 1. Dietary composition and analyzed nutrient content of diets fed in trials 1, 2, and 3 (DM basis)
 
Sampling Protocol.
The experimental period was 21 d in length, which included a 14-d adaptation period and a 7-d collection period. Grain was processed in a single batch, and samples were analyzed for density and particle size. Grain samples were collected during each experimental period and analyzed for particle size; the mean was then reported. Particle size was analyzed following the procedure of ASAE (1993)Go using a Tyler Ro-Tap sieve shaker (W. S. Tyler, Mentor, OH). Samples of diets were collected daily during the collection period (d 15 to 21), composited, dried (55°C, 48 h, forced-air Grieve SB-350 oven; The Grieve Corporation, Round Lake, IL), and ground to pass a 2-mm screen using a Wiley mill (Model #3; Arthur H. Thomas, Philadelphia, PA). Chromic oxide was used as an external marker to determine duodenal and ileal DM flow; it was mixed in the supplement and fed at 0.25% of the dietary DM. Orts were collected daily during the collection period (d 15 to 21), subsampled (10% by weight), dried, and ground in a Wiley mill. Fecal output was collected daily during the collection period (d 15 to 21) at 0500 using stainless-steel pans placed directly behind the stalls. Feces were sampled at 10% of total weight, composited, and stored (–20°C). The composited sample was mixed in a rotary mixer (Hobart H-600, Troy, OH), subsampled, and dried in a forced-air oven (55°C) for 48 h. Dried samples were ground in a Wiley mill to pass a 2-mm screen. Duodenal (approximately 200 g) and ileal (approximately 100 g) chyme samples were collected on d 17 to 19. Samples were collected in a manner that allowed a sample to be collected every other hour in a 24-h cycle. Samples were then stored frozen (–20°C), subsampled, lyophilized (Virtis Genesis 25LL; The Virtis Company, Inc., Gardiner, NY), and ground with a Wiley mill to pass a 2-mm screen. Ruminal fluid was collected through a suction-strainer on d 20 beginning at 0400, and continuing every other hour for 14 h. For fluid dilution rate and rumen fluid volume, CoEDTA (200 mL; 4.0 g of Co; Uden et al., 1980Go) was dosed intraruminally 2 h before feeding on d 20. Approximately 100 mL of ruminal fluid were collected; pH was measured (Model 2000 pH meter; Beckman, West Chester, PA), and the fluid was placed in a plastic bag (Whirlpak, Nasco U.S.A.) and stored (–20°C) for ammonia analysis. A 4-mL ruminal fluid sample also was drawn from the sample, 1 mL of 25% (wt/vol) m-phosphoric acid (HPO3) was added, and the sample was stored frozen (–20°C) until analysis of VFA.

In situ bags containing 5.0 g of processed barley were incubated intraruminally within nylon lingerie washing bags (30.5 cm x 25.4 cm) on d 18 through 21. Samples of coarsely, moderately, and finely rolled barley were incubated in steers fed the same barley processing treatment. Samples were placed in Dacron bags (10 cm x 20 cm; 50 ± 15 µm pore size; Ankom, Fairport, NY) and incubated ruminally in singlet for the 0-, 2-, 4-, 8-, and 12-h incubation times; in duplicate for the 16-, 24-, and 36-h incubation times; and in triplicate for the 48- and 72-h incubation times, along with a blank bag at each time. Bags were sealed with an impulse sealer (AIE-200; American International Electric, Whittier, CA) and inserted in reverse order. All bags were removed at 0 h and rinsed with tap water to remove large particulate matter. In situ bags were then rinsed in a top-loading washing machine (Model WJXR2080TSWW; General Electric, Louisville, KY). The machine was filled with 45 L of water, agitated for 1 min, drained, and spun for 2 min using the delicate cycle. This cycle was repeated six times; after such time, bags were placed in a forced-air oven for 48 h and stored at room temperature until analysis.

Ruminal contents were evacuated on d 21 to determine DM fill. Ruminal contents from each steer were removed, weighed, mixed, and sampled. Contents (4 kg) were mixed with 2 L of 3.7% formaldehyde/0.9% NaCl and stored in 4.5-L plastic buckets (Zinn and Owens, 1986Go). A separate sample of ruminal contents was collected for later analysis and weighed, dried, and ground. Samples were stored frozen (–20°C) until analysis.

Laboratory Analyses.
Diet, ort, duodenal, ileal, fecal, and ruminal content samples without formalin were analyzed for DM, OM, and CP (Methods 930.15, 942.05, and 990.02, respectively; AOAC, 1997Go). Concentrations of NDF (with heat-stable {alpha}-amylase and without sodium sulfite) and ADF were determined using a Fiber Analyzer (Model 200; Ankom Technology). Chromium was analyzed in duodenal and ileal samples by the spectrophotometric method (Fenton and Fenton, 1979Go). In situ residue was analyzed for DM, CP, and starch (Herrera-Saldana and Huber, 1989Go). Duodenal samples also were analyzed for purines to estimate microbial content based on DM:purine of isolated ruminal bacteria (see later description; Zinn and Owens, 1986Go), and duodenal, ileal, and fecal samples were analyzed for starch content (Herrera-Saldana and Huber, 1989Go).

Formalized ruminal contents were blended (Model 37B119; Waring, New Hartford, CT), and the mixture was strained through four layers of cheesecloth. Feed particles and protozoa were removed via centrifugation at 500 x g twice for 20 min each time. The particle-free supernatant fraction was then spun at 30,000 x g for 20 min to collect bacteria. Isolated bacteria were lyophilized and analyzed for DM, CP, starch, and purines (Zinn and Owens, 1986Go).

Ruminal fluid was thawed and centrifuged at 20,000 x g for 20 min, and the supernatant fraction was collected for analysis of ammonia (Broderick and Kang, 1980Go). Ruminal VFA concentrations were quantified by gas chromatography (5890A Series II GC; Hewlett Packard, Wilmington, DE) using a capillary column (15 m x 0.53 mm x 0.5 µm; Nukol; Supelco, Bellefonte, PA) and flame ionization detection. Cobalt was determined using air-acetylene flame atomic absorption spectroscopy (Model 3030B; Perkin Elmer, Inc., Wellesley, MA). In situ DM, CP, and starch disappearance were fitted to the following model (Ørskov and McDonald, 1979Go):


where a = soluble fraction (%), b = slowly degradable fraction (%), k = fractional rate constant at which b is degraded (h–1), and t = incubation time (h).

Trial 2
In a randomized complete block design with a 2 x 2 factorial arrangement of treatments, 144 crossbred beef steers (319.7 ± 5.5 kg of initial BW) were blocked by initial BW and used to evaluate the degree of processing (coarse or fine particle size) on two grains (corn or barley) in growing diets. Steers originated from south central North Dakota and were shipped approximately 300 km, where they were housed at the North Dakota State University Animal Research Center in concrete-floored pens with access to a barn (4.9 m x 3.0 m indoor and 11.6 m x 3.0 m outdoor; 3.0 m of bunk space per pen). Steers were fed in concrete fence-line bunks and had access to an automatic water supply. During the receiving period, all steers received a common transition diet consisting of hay, silage, supplement, and molasses or desugared molasses. Steers were administered a booster vaccination against bovine rhinotracheitis, viral diarrhea, parainfluenza-3, respiratory syncytial virus, and Haemophilus somnus and were treated with doramectin (Pfizer, Exton, PA) for control of internal and external parasites. The steers were dehorned, if needed, and ear-tagged. Steers were sorted into three weight blocks, stratified by BW within block, and allotted randomly to one of four treatments (six steers per pen; six pens per treatment). The main effects were grain type (barley or corn; 40% of diet DM) and processing (coarsely or finely rolled; Table 1Go). Coarsely and finely rolled grains were obtained by changing roll gap width in the mill. Diets were formulated to contain a minimum (DM basis) of 12.5% CP, 0.6% Ca, 0.3% P, 0.6% K, and 27.5 mg monensin/kg (Elanco Animal Health). Grain samples were collected weekly and composited for density and particle size analysis. Particle size was analyzed as previously mentioned. Steers were implanted with 200 mg of progesterone plus 20 mg of estradiol (Fort Dodge Animal Health, Fort Dodge, IA) before the start of the trial. Initial and final BW were the average of weights taken on three consecutive days and recorded in the morning before feeding. Steers were fed for 84 d. Feed offered was adjusted daily based on bunk assessment made before feeding. Orts were weighed weekly, and diet samples were composited and subsampled for analysis of particle size and laboratory analyses. Diets were analyzed for DM, OM, N, ADF, NDF, and starch using the same procedures as Trial 1.

Dietary NE (Mcal/kg) for each diet was calculated from estimates of energy gain (EG; Mcal/d) for large-framed steers based on BW and growth rate (NRC, 1984Go; EG = [0.0493BW0.75]ADG1.097, where BW = full weight x 0.96) and maintenance energy expended (EM, Mcal/d; EM = 0.077BW0.75) using the quadratic formula


where a = –0.41EM; b = 0.877EM + 0.41DMI + EG; and c = –0.877DMI, kg/d; dietary NEg = 0.877NEm – 0.41 (Zinn and Shen, 1998Go).

Trial 3
One hundred forty-three crossbred beef steers (277 ± 19 kg initial BW) were used in a randomized complete block design. Steers were blocked by BW and allotted randomly to dietary treatment (five or six animals per pen; six pens per treatment). Steers were received using methods similar to Trial 2. Treatments were 1) coarsely rolled barley, 2) moderately rolled barley, 3) finely rolled barley, and 4) a mixture of coarsely and finely rolled barley to simulate moderately rolled barley. Barley processing differences were obtained by changing roll gap width in the mill. Diets contained 41.18% barley (DM basis; Table 1Go). Wet beet pulp was used instead of corn silage in the previous experiments. Barley samples were sampled as previously mentioned for Trial 2.

Initial and final BW were the average of weights taken on three consecutive days and recorded in the morning before feeding. Steers were fed for 89 d. Feed offered was adjusted daily based on bunk assessment made before feeding. Orts were weighed weekly, and diet samples were composited and subsampled for analysis of particle size and laboratory analysis. Diets were analyzed for DM, OM, N, ADF, NDF, and starch using the same procedures described previously.

Statistical Analyses
Data for Trial 1 were analyzed as a completely randomized design using the Mixed procedure of SAS (SAS Inst., Inc., Cary, NC). The model included only the fixed effect of treatment (degree of processing) with no random effects because the experimental design was completely randomized. The Mixed procedure of SAS also was used to analyze ruminal data over time using a completely randomized design. The statistical model included fixed effects for degree of processing, time, and degree of processing x time; the repeated subject was animal nested within treatment. The covariance structure that best fit this dataset was type-1 autoregressive. Orthogonal contrasts were conducted for linear and quadratic effects of degree of processing. Contrast coefficients were based on unequal spacing of mean particle size between treatments (IML procedure of SAS).

Data for Trial 2 were analyzed as a randomized complete block experimental design with a 2 x 2 factorial arrangement of treatments using pen as the experimental unit. The Mixed procedure of SAS was used, and the model included terms for block, degree of processing (coarsely rolled or finely rolled), grain type (corn or barley), and the associated interaction. The model included treatment as a fixed effect and block as a random effect.

Data for Trial 3 were analyzed as a randomized complete block design using the Mixed procedure of SAS; pen was the experimental unit. The model included the fixed effect of treatment and block as random effect. Orthogonal contrasts were conducted for linear and quadratic effects of degree of processing. Contrast coefficients were based on unequal spacing of mean particle size between treatments (IML procedure). An additional preplanned contrast also was used to compare the mixed treatment to the medium treatment.


   Results and Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
Literature Cited
 
Trial 1
Coarsely rolled barley had a particle size of 2,770 ± 1.46 µm, moderately rolled barley had a particle size of 2,127 ± 1.56 µm, and finely rolled barley had a particle size of 1,385 ± 1.33 µm. Analyzed composition of the diets is presented in Table 1Go. Density of the barley before processing was 603 g/L (46.7 pounds/bushel), and composition of the barley was 12.8% CP, 17.5% NDF, 5.2% ADF, and 46.9% starch.

Dry matter intake (Table 2Go), when expressed on a kg/d basis, was not affected (P = 0.42) by treatments; however, when expressed on a g/kg of BW basis, DMI decreased linearly with the increasing degree of processing (P = 0.04). These results are in agreement with Hironaka et al. (1992)Go, who reported decreased intake from increased degree of processing of steam-rolled barley. However, these results are in contrast with reports by Beauchemin et al. (2001)Go and Koenig et al. (2003)Go, who reported no differences in feed intake with different degrees of barley processing. Koenig et al. (2003)Go also reported no differences in intake relative to BW (18 g/ kg of BW); however, both Beauchemin et al. (2001)Go and Koenig et al. (2003)Go indicated that intake by ruminally and duodenally cannulated cattle used in their research was less than would be expected in the commercial feedlot settings and much lower than intakes in the present experiment. Koenig et al. (2003)Go fed steam-rolled barley that was processed to a degree of coarsely or flatly processing indices (86 and 61% of original density). The barley was fed with silage at 5 or 20% of dietary DMI. Beauchemin et al. (2001)Go fed 86% temper-rolled barley diets at four degrees of processing indices (82, 75, 70, and 65% of original density) and found no effect of processing index on intake. Processing index was measured as the volume weight of the barley after processing expressed as a percentage of its volume weight before processing (DM basis; Beauchemin et al., 2001Go). Furthermore, the temper-rolled barley Beauchemin et al. (2001)Go fed was much larger (5.96, 5.28, 4.16, and 3.27 mm, respectively) than the dry-rolled barley in the present experiment. Temper-rolling would produce larger, flatter particles than dry-rolling barley, which also may affect how processing influences intake. In dairy diets, which contain levels of concentrate comparable with growing diets, there was no effect of degree of processing on DMI when corn was used as the grain source (San Emeterio et al., 2000Go; Callison et al., 2001Go; Dhiman et al., 2002Go). However, Yang et al. (2000)Go reported a quadratic change in intake from coarsely, moderately, moderately and flatly, and flatly steam-rolled barley, where the moderately steam-rolled barley treatment had the greatest intake in diets containing 53% barley (DM basis).


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  		Table 2. Effect of degree of barley processing on DMI, ruminal fill, and fluid dilution rate in trial 1
 
Neither ruminal fluid dilution rate (P = 0.17) nor ruminal DM fill were affected (P = 0.40) by treatment. Fluid dilution rate was also not affected by degree of processing in research reported by San Emeterio et al. (2000)Go, Yang et al. (2000)Go, or Beauchemin et al. (2001)Go. Boss and Bowman (1996)Go also reported no effect of treatment on fluid passage rate when comparing three varieties of barley to corn.

Organic matter intake expressed relative to BW (P = 0.04) linearly decreased with increased barley processing degree (Table 3Go). A quadratic effect occurred for apparent and true ruminal OM digestibility (P ≤ 0.04). There was a quadratic tendency for digestibility in the large intestine (P = 0.06). For the ruminal OM digestibility quadratic effect, the medium treatment had the greatest digestibility. The quadratic tendency in the large intestine resulted in the fine treatment having the greatest OM digestibility. Total OM flowing to the duodenum was not different (P = 0.60) nor was microbial OM flowing to the duodenum (P = 0.67). Callison et al. (2001)Go reported that total tract digestibility decreased linearly with increased degree of corn processing in diets for lactating dairy cows. These results contrast those of Zinn (1993)Go and Beauchemin et al. (2001)Go, who reported similar OM intakes but quadratic increases in total tract digestibilities as processing increased. Beauchemin et al. (2001)Go fed barley at 86% of the diet, and Zinn (1993)Go fed barley at 90% of the diet (DM basis). Koenig et al. (2003)Go fed barley at 68.8 and 83.8% of the diet and also reported similar intakes among treatments; however, there was no effect with grain processing.


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  		Table 3. Effect of degree of barley processing on characteristics of OM, CP, and starch digestion in steers fed a growing diet in trial 1
 
Crude protein intake as well as total duodenal CP flow and microbial and nonmicrobial flow were not affected (P ≥ 0.69) by degree of barley processing. Apparent digestion of CP in the rumen responded quadratically (P = 0.04), and CP digestibility in the small intestine tended to change quadratically (P = 0.06). The moderate treatment had the greatest CP apparent ruminal digestibility, and the fine treatment had the least. True ruminal CP digestion did not differ (P = 0.37) among treatments, indicating that recycling of N might have been affected. Nitrogen input and output from the stomach complex was similar (apparent N disappearance was not different than zero; P = 0.35) for the fine treatment, indicating that microbial capture of N was very efficient or that more N was being recycled than in the moderate treatment. In the small intestine, the moderate treatment had the lowest CP digestibility, and the fine treatment had the greatest. This result may indicate that finer processing of barley delivers more metabolizable AA to the animal than the moderate treatment. There was a tendency for a linear increase of CP digestibility in the large intestine (P = 0.08) with increasing degree of processing. Crude protein intakes reported by Beauchemin et al. (2001)Go and Koenig et al. (2003)Go also were similar among treatments. Beauchemin et al. (2001)Go fed barley temper-rolled to four extents (coarse, moderate, moderate and flat, and flat) at 86% of the diet. Koenig et al. (2003)Go fed steam-rolled barley at 68.8 and 83.8% of the diet at two processing indices of 86 and 61%. Beauchemin et al. (2001)Go reported CP flow to the duodenum increased with increased degree of barley processing.

Microbial efficiency responded quadratically (P = 0.02; Table 3Go); the finely rolled barley treatment had a greater efficiency than the moderately rolled barley treatment. This response was primarily a 1-kg/d decrease in OM truly fermented in the reticulorumen; none of the OM components (starch, NDF, or CP) measured were affected (P ≥ 0.31) by barley processing. This response may be due to negative effects associated with increased starch fermentation rates; however, we measured no differences in ruminal pH (see subsequent). In the study by Koenig et al. (2003)Go, microbial protein synthesis efficiency was not affected by degree of barley steam rolling. Others (Yang et al., 2000Go; Beauchemin et al., 2001Go; and Callison et al., 2001Go) reported no effects of degree of processing on microbial efficiency; however, their numerical trends followed the quadratic response observed in this trial.

Increased degree of processing did not affect starch intake (P = 0.69; Table 3Go) or starch reaching the small intestine (P = 0.31). Starch ({alpha}-linked glucose) of microbial origin decreased (P = 0.03) with degree of processing. This was primarily because of increased starch (linear; P = 0.04) in the isolated bacteria (3.55, 3.57, and 1.77 ± 0.58% starch for coarse, moderate, and fine, respectively). Apparent or true ruminal starch digestion also did not differ (P ≥ 0.31) among treatments. Increasing degree of processing linearly decreased fecal starch output (P < 0.01) and linearly increased total tract starch digestibility (P < 0.001). Starch intake also was not affected by processing in other studies (Zinn, 1993Go; Yang et al., 2000Go; Beauchemin et al., 2001Go). Total tract starch digestibilities reported by Beauchemin et al. (2001)Go, Callison et al. (2001)Go, and Koenig et al. (2003)Go all followed patterns similar to those found in the current study. Yang et al. (2000)Go reported a linear increase in total tract starch digestion with increasing degree of processing to the moderate and flat treatment with no improvement after that. Zinn (1993)Go reported no effect of steam-flaked barley flake thickness on total tract starch digestibility. In the current study, no treatment effects were observed for ruminal (P = 0.17), small intestinal (P = 0.14), or large intestinal starch digestion (P = 0.26). Total tract starch digestion increased linearly (P < 0.001) with finer processing without increases (P ≥ 0.17) in digestion along the digestive tract. More than 90% of starch intake and >92% of total tract starch disappearance truly disappeared in the stomach complex. The magnitude of change in percentage of total tract digestibility was similar to the change in the stomach complex; however, variance was much greater, thereby precluding detection of differences if they existed.

Intake of NDF (P = 0.76) and ADF (P = 0.78), as well as total tract NDF (P = 0.54) and ADF (P = 0.55) digestibility, were unaffected by degree of processing (data not shown). Total tract NDF and ADF digestibilities averaged 60.08 ± 6.50% and 35.69 ± 3.70%, respectively, across treatments. Zinn (1993)Go and Yang et al. (2000)Go reported no differences in total tract digestibilities of ADF. The total tract digestibilities of NDF (Koenig et al., 2003Go) were similar to our findings; however, ADF total tract digestibility decreased with greater extent of processing.

The effect of degree of processing on ruminal fermentation characteristics is shown in Table 4Go. Ruminal pH responded quadratically (P = 0.01); moderately rolled barley had the greatest pH. There was no time x treatment interaction (P = 0.16), and mean pH did not fall below 6.0. These results are in contrast to findings by Beauchemin et al. (2001)Go, who reported a quadratic increase in ruminal pH by processing barley more finely. Koenig et al. (2003)Go compared two degrees of steam-rolled barley at 68.6 and 83.8% processing indices, and Yang et al. (2000)Go fed steam-rolled barley at processing indices of 81.0, 72.5, 64.0, and 55.5% and reported no differences in ruminal pH among treatments.


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  		Table 4. Effect of degree of barley processing (Proc) on ruminal pH, ammonia, and VFA molar proportion in steers consuming feedlot growing diets in trial 1
 
Ruminal ammonia was not affected by treatment (P = 0.16), and there was no time x treatment interaction (P = 0.26; Table 4Go) for ruminal ammonia concentrations. Beauchemin et al. (2001)Go reported similar results for ruminal ammonia. Yang et al. (2000)Go reported that ammonia concentration increased when coarsely rolled barley was replaced by moderatly rolled barley but decreased with replacement by moderate, flatly rolled barley or flatly rolled barley.

There was a time x treatment interaction (P = 0.06) observed for total VFA concentration (data not shown). At 2 h after feeding, the finely processed barley treatment had a greater total VFA concentration with no other time periods affected. This result might have been caused by a faster fermentation of the more finely processed barley. Main effect means for barley processing are presented for VFA concentrations (Table 4Go). Beauchemin et al. (2001)Go indicated no differences for total VFA among the coarse, moderate, moderate-flat, and flat temper-rolled barley treatments. There was no treatment (P ≥ 0.30) or time x treatment interaction (P ≥ 0.62) for ruminal acetate, propionate, or butyrate molar proportion or for acetate:propionate. Ruminal isobutyrate, valerate, and isovalerate also were unaffected (P ≥ 0.14) by treatment (data not shown). Yang et al. (2000)Go reported a significant decrease in acetate, while increasing the propionate and decreasing the acetate:propionate when feeding moderate, flatly rolled barley compared with coarsely or moderately rolled barley.

The effect of degree of processing on rate of in situ DM, CP, and starch ruminal disappearance of barley is shown in Table 5Go. Rate of DM disappearance linearly and quadratically increased with increased degree of processing (P ≤ 0.02). In situ rate of CP and starch degradability also increased linearly (P < 0.001) from increasing degree of processing. The in situ extent of degradability linearly increased for CP (P = 0.05) and for starch (P = 0.003) with increased degree of processing. These results agree with those of Yang et al. (2000)Go and Beauchemin et al. (2001)Go.


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  		Table 5. Effect of degree of barley processing on in situ disappearance rates in steers fed a growing diet in trial 1
 
Trial 2
The nutrient content of corn and barley diets is shown in Table 1Go. Test weight of the barley was 603 g/L (46.7 pounds/bushel), and that of the corn was 742 g/L (57.5 pounds/bushel). The corn and barley treatments were formulated to contain 12.5% CP; however, the corn treatments averaged 11.1% CP, and the barley averaged 12.3% CP. This lower CP concentration might have limited responses in the corn treatment. Particle size of the treatments was 2,740 ± 1.73 µm and 968 ± 2.11 µm for coarsely and finely rolled corn and was 2,132 ± 1.51 µm and 1,307 ± 1.69 µm for coarsely and finely rolled barley, respectively. Barley (12.8% CP, 17.5% NDF, 5.2% ADF, and 50.6% starch) and corn (9.6% CP, 8.5% NDF, 2.1% ADF, 62.8% starch) nutrient content (DM basis) was similar to those data reported by the NRC (1996)Go.

The effect of grain processing on performance by steers fed growing diets is shown in Table 6Go. Final BW was not affected by degree of processing (P = 0.21) or grain type (P = 0.57). In addition, ADG was not affected by degree of processing (P = 0.92) or grain type (P = 0.91). Steers fed corn had greater DMI when expressed as kg/d or g/kg of BW (P = 0.05 and 0.009, respectively) than did steers fed barley. In a similar study by Reed et al. (2005)Go that compared corn with sprout-damaged barley processed to different degrees, DMI did not differ among treatments; however, finely rolled sprouted barley treatment had greater ADG than did the corn and coarsely rolled barley treatment. Gray and Stallknecht (1988)Go found no differences between dry-rolled barley and whole shelled corn treatments for ADG, DMI, or G:F.


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  		Table 6. Effect of grain processing for growing diets on performance of beef steers in trial 2
 
There was a tendency for a grain type x processing degree interaction for G:F and apparent dietary NE (P ≤ 0.08). Steers fed finely rolled barley had an improved G:F and dietary NEm and NEg compared with steers fed the finely rolled corn, whereas coarsely rolled corn and coarsely rolled barley did not differ. This result is in agreement with Reed et al. (2005)Go. Wang et al. (2003)Go compared dry-rolled barley processed to a coarse and fine degree in growing diets. They reported lower DMI and ADG in cattle fed finely rolled compared with coarsely rolled barley with no effect on gain efficiency. The low dietary protein of the corn-based diets might have contributed to this interaction as well. The diets were formulated to contain 12.5% CP; however, the corn-based diets contained only 11.1% CP. This might have limited microbial and/or animal responses to the finely rolled corn treatment, whereas the finely rolled barley treatment, containing 12.3% CP, had increased gain efficiency compared with finely rolled corn. Furthermore, apparent dietary NE also was low for the finely rolled corn treatment, which might also be an indication of lower dietary CP (Zinn and Shen, 1998Go).

Milner et al. (1995Go, 1996)Go conducted two trials comparing corn and three varieties of barley in feedlot diets. Corn-fed steers had increased DMI and greater ADG than barley-fed steers; however, barley-fed steers had a greater G:F. Other high-grain finishing diets comparing barley and corn also reported similar results for DMI, ADG, and G:F (Mathison and Engstrom, 1995Go; Kincheloe et al., 2003Go)

Trial 3
The nutrient content of the diets fed in Trial 3 is shown in Table 1Go. The density of the barley before processing was 596 g/L (46 pounds/bushel), and average composition of composited barley was 13.3% CP, 18.3% NDF, 5.7% ADF, and 51.4% starch (DM basis). There were small differences between analytical results of different particle sizes, indicating little segregation took place during handling and storage. Resulting particle size was 2,569 ± 1.32 µm for coarsely rolled barley, 1,980 ± 1.43 µm for moderatly rolled barley, 1,324 ± 1.54 µm for finely rolled barley, and 1,762 ± 1.73 µm for the mixed barley treatment.

The effect of increasing degree of processing on performance of beef steers fed growing diets is shown in Table 7Go. There were no differences among treatments for final BW (P = 0.51) or ADG (P = 0.43). This finding contrasts that of Reed et al. (2005)Go, who reported an increase in ADG with increased degree of processing. Reed et al. (2005)Go fed barley with average particle sizes of 2,628 and 1,998 µm, which is similar to the coarse and moderate treatments in the present trial.


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  		Table 7. Effect of particle size processing barley for growing diets of beef steers in trial 3
 
Dry matter intake decreased linearly (P < 0.001) with increasing degree of processing, and DMI tended to be greater (P = 0.09) for the mixed treatment than for the moderate treatment. Callison et al. (2001)Go reported no differences for DMI among finely, moderately, and coarsely ground corn treatments in lactating dairy diets. Bradshaw et al. (1996)Go reported no differences in DMI when increasing processing of barley for growing as well as finishing phases of feedlot diets. Reed et al. (2005)Go reported similar intakes between moderately and coarsely rolled sprout-damaged barley.

Gain efficiency increased linearly with increasing degree of processing (P < 0.001); the fine treatment had the greatest gain efficiency, and the coarse treatment had the least. The moderate treatment tended to have a greater (P = 0.07) G:F than did the mixed treatment. Apparent NEm and NEg (P < 0.001) linearly increased with increased degree of processing. The moderate treatment had a greater (P = 0.03) NEm and NEg than did the mixed treatment. In Trial 3, the fine treatment resulted in a 13% improvement in G:F above the coarse treatment and a 9% improvement in G:F from the coarse to the moderate treatment. Bradshaw et al. (1996)Go reported no differences in ADG or G:F with increased processing of barley. Reed et al. (2005)Go reported an increase in gain efficiency with a decrease in particle size of sprout-damaged barley. Zinn (1993)Go compared steam-flaked corn, dry-rolled barley, thin steam-rolled barley, and coarse steam-rolled barley and reported no differences for ADG or G:F among barley treatments. Apparent dietary NE was greater for the steam-rolled barley than for the dry-rolled barley. Feed intake was less for steam-rolled barley than for dry-rolled barley.

There was no benefit to mixing barley of different particle sizes, which is similar to findings of Callison et al. (2001)Go. In that study, the mixing of coarse-ground and steam-rolled corn for lactating dairy cattle was investigated. Intake and gain efficiency of the mixed treatment was similar to the coarse-rolled treatment, although the mean particle size was smaller than the moderate treatment (1,762 vs. 1,946 µm). We hypothesized that mixing finely and coarsely rolled barley would cause positive associative effects (Stock et al., 1987Go), but there was no apparent improvement by mixing finely and coarsely rolled barleys vs. the coarsely rolled treatment.

In summary, digestibilities of OM, CP, NDF, and ADF were not affected by degree of barley processing, but total tract starch digestibility increased with the finer processing. In situ DM, CP, and starch disappearance rate increased with decreased particle size of barley. In performance trials, DMI decreased with finer processing barley. Dry matter intake was greater by corn-fed steers than by barley-fed steers. Finer processing of corn did not result in improved growth or gain efficiency, which might have been due to low dietary CP rather than to barely. Gain efficiency and apparent dietary NE was greater with increased degree of barley processing. There was no benefit of mixing coarsely and finely rolled barley.


   Footnotes
 
1 This material is based on work supported by the Cooperative State Research, Education, and Extension Service, USDA, "Feed Barley for Rangeland Cattle" Grant No. 2002-34403-12790. Gratitude is expressed to Animal and Range Sciences personnel for assistance with laboratory analysis, animal care, and data collection. Back

3 Current address: 224 Knox Hall, Dep. Anim. Range Sci., New Mexico State University, Las Cruces 88003. Back

2 Correspondence: 100 Hultz Hall (phone: 701-231-7660; fax: 701-231-7590; e-mail: glardy{at}ndsuext.nodak.edu).

Received for publication November 9, 2004. Accepted for publication August 11, 2005.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Literature Cited
 


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