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Effects of moisture, roller setting, and saponin-based surfactant on barley processing, ruminal degradation of barley, and growth performance by feedlot steers¹

Y. Wang^*,2, D. Greer and T. A. McAllister^*

^* Research Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada T1J 4B1and and Agrichem Inc., Anoka, MN 55303-0845

	Abstract

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Two experiments were conducted to study the effects of six processing techniques for barley grain in a 3 x 2 factorial arrangement of grain conditions and roller settings on ruminal degradation of the grain (Exp. 1) and on growth performance by 138 feedlot steers (n = 23 per treatment; Exp. 2). Dry barley (11% moisture, D barley), barley tempered to 20% moisture (M barley), and barley tempered with 60 mL/t of surfactant-based tempering agent (GrainPrep, Agrichem, Inc., Anoka, MN; MS barley), were each rolled at two roller settings selected from preliminary tests. The settings selected for the study were RD, the roller position that had yielded optimally processed D barley, and RMS, the setting that had yielded optimally processed MS barley. Setting RMS was tighter than RD. Barley rolled at the RMS setting was more extensively processed (i.e., had a lower [P < 0.001] processing index, PI), had lighter (P < 0.001) volume weight, thinner (P < 0.001) kernels, and fewer (P < 0.001) whole kernels compared with setting RD. Tempering did not affect (P > 0.05) PI, percentage of whole kernels, or kernel thickness at either roller setting. The processing characteristics of tempered barley were unaffected (P > 0.05) by surfactant. The extent of in situ DM disappearance (ISDMD) was higher (P < 0.01) in grain rolled at setting RMS compared with RD. At both roller settings, tempering reduced (P < 0.05) ISDMD between 4 and 24 h of ruminal incubation. Steers fed RMS-rolled barley had lower (P < 0.001) DMI, slightly lower (P = 0.084) ADG, but increased (P < 0.05) gain:feed (G:F) compared with steers fed RD-rolled barley. Tempering did not affect (P > 0.05) ADG, DMI, or G:F during backgrounding, but improved (P < 0.01) these variables during finishing. Surfactant improved (P < 0.05) G:F but not DMI or ADG. The improvement in G:F was most pronounced when setting RMS was used. The optimal PI values calculated from performance data were numerically greater for the backgrounding diet than for the finishing diet. Steers fed M or MS barley had heavier (P < 0.01) hot carcasses and thicker (P < 0.05) fat cover but lower (P < 0.05) dressing percentages than steers fed D. When the feed barley was rolled at setting RMS, steers fed MS barley produced heavier (P < 0.05) carcasses than those fed M. Tempering with or without surfactant increased performance by feedlot steers compared with not tempering. Diet composition and degree of barley processing mediated this effect.

Key Words: Barley • Feedlots • Growth • Processing • Rumen Digestion • Surfactants

	Introduction

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Barley grain must be processed before feeding to cattle so that endosperm encased within indigestible pericarp and hull layers can be utilized (Wang and McAllister, 2000). Excessive processing, however, promotes grain digestion that is too rapid and often causes digestive disturbances, such as acidosis and bloat (Owens et al., 1997) and a concurrent decline in gain:feed (G:F). Also, energy costs increase with extent of processing. Therefore, ideal grain processing depends on striking a balance between optimizing grain utilization and minimizing expenditures associated with processing. Many factors, such as moisture, kernel uniformity, kernel hardness, and roller setting, can affect barley processing, and these factors often vary substantially in barley purchased from commercial sources. Consequently, achieving optimal processing of this highly variable grain represents a significant challenge to producers. Tempering grain before rolling has been used to standardize this inherent variation and to reduce mechanical wear on processing equipment (Mathison et al., 1997). The effects of tempering on animal performance, however, have been inconsistent (Hinman and Combs, 1983; Combs and Hinman, 1989; Mathison et al., 1997). Some of these discrepancies may have arisen from variations in the rate and extent of moisture uptake by the kernels during tempering. Surfactants have been used in a number of areas to enhance water penetration (Cairns, 1972; Aksenova et al., 1993; Coret and Chamel, 1993). However, there is little information on the effects of these compounds on the processing and utilization of barley grain. Our earlier research showed that saponin-based surfactant improved ruminal fermentation of barley grain (Wang et al., 2000b); thus, this study was conducted to evaluate the effects of tempering and of surfactant applied during tempering on the processing characteristics, ruminal degradation, and utilization of barley grain by feedlot cattle.

	Materials and Methods

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Grain Processing
The barley grain used in this study was from a single commercial source, consisted of a mixture of varieties, was stored in a hay shed, and was screened to remove small kernels and contaminants before being processed. Average DM content and volume weight were 89.69% and 642 g/L, respectively. Treatments were arranged as a 3 x 2 factorial, with three prerolling barley conditions—dry (D; nontempered, 11% moisture), tempered to 20% moisture (M), and tempered to 20% moisture with surfactant (MS)—and two roller settings (RD and RMS, described below). The surfactant was GrainPrep (AgriChem, Inc., Anoka, MN) applied at 60 mL/t (as treated). The two roller settings were determined from preliminary experiments with barley grain from the same source, and once selected, were employed consistently throughout the study. Setting RD produced visually optimal particle sizes from D barley, and yielded a volume weight of 516 g/L and a kernel thickness of 2.23 mm; setting RMS, which was tighter than RD, produced visually optimal particle sizes from MS barley, and yielded a volume weight of 450 g/L and kernel thickness of 2.00 mm. Moisture content of the grain was determined automatically before tempering by an Auto Delivery System (AgriChem, Inc.) that applied cold tap water to each batch of grain as required to attain a moisture content of 20%. To prepare MS barley, surfactant was incorporated into the volume of water calculated to be necessary to raise moisture content to 20%, in quantities that yielded a final surfactant concentration of 60 mL/t of barley. The barley at the elevated moisture level (±surfactant) was held in a steel bin for 4 h before being rolled. The nontempered barley was rolled directly after retrieval from storage. After rolling, the grain was air dried at room temperature and stored in separate steel bins. Each barley treatment (D, M, and MS, each rolled at RD or RMS) was prepared in 1.0-t batches, and 5-kg subsamples were collected from each batch for further evaluation. Eleven batches of each treatment were prepared over the course of this study.

Experiment 1—In situ Incubation
Three previously cannulated 3-yr-old heifers (initial BW approximately 725 kg) were used in a nylon bag experiment to assess the ruminal degradability of the barley grain processed by each of the six treatments described above. The heifers were fed a steamrolled barley grain-based finishing diet (Table 1) for 14 d before placement of the nylon bags. Each of the substrates (5.0 g, air-dried) was weighed into one of 72 monofilament nylon bags (12 x 15 cm; 50 µm pore size). The bags were ruminally incubated in each heifer for 0, 1, 2, 4, 8, 12, 24, and 48 h (triplicates for each time point). The incubation and subsequent sample preparations were conducted as described by Wang et al. (1998b).

Animals used in this study were cared for according to the guidelines set by the Canadian Council on Animal Care (CCAC, 1993).

Laboratory Analyses
Processing Characteristics.
All measurements were made on triplicate subsamples from each batch of processed grain after oven drying at 70°C for 48 h. Volume weight was measured on 500-mL samples of barley or processed barley. Particle size distribution of the processed barley was determined by dry sieving with an oscillating sieve shaker (W. S. Tyler, Inc., Mentor, OH) equipped with four sieves, arranged in descending mesh size (4.75, 3.35, 2.36, and 1.70 mm), and a collection pan (for particles <1.70 mm). Kernel thickness of the rolled barley samples was estimated by measuring 20 kernels from each subsample with an electronic digital caliper (Allied Tools Inc., Louisville, KY). Intact whole kernels were manually separated from 200-g subsamples from each batch of rolled grain, weighed, and expressed as a percentage of the entire sample.

Feed, Orts, and Nylon Bag Residues.
Freeze-dried feed samples and orts, and oven-dried nylon bag residues were ground to pass through a 1.0-mm screen using a Thomas Wiley Cutting Mill (model 4, Arthur H. Thomas Co., Philadelphia, PA) before chemical analysis. Dry matter content was determined by oven drying (105°C for 48 h), NDF by the procedure of Van Soest et al. (1991), starch by the method of Herrera-Saldana et al. (1990), total N by flash combustion (NA1500, Carlo Erba Instruments, Rodano, MI, Italy) followed by chromatographic separation and thermal conductivity, and OM by ashing (550°C for 16 h).

Calculations and Statistical Analyses
All calculations related to composition of the feed, characteristics of the grain, and parameters of ruminal degradation were calculated on a DM basis. Volume weights are expressed as g/L of grain or processed grain. Processing index (PI) was calculated according to the following equation:

[1]

Means of triplicate measurements from each of the 11 batches of rolled grain were used in the statistical analysis of processing characteristics.

Ruminal degradation parameters from Exp.1 were calculated using the following equations (McDonald, 1981):

[2]

[3]

where P = DM degraded at time t (%), a = the soluble fraction (%), b = the degradable fraction (%), c = the rate at which b is degraded (h^-1), t = time (h) spent in the rumen, L = lag time (h), k is the ruminal outflow rate (h^-1), which was set arbitrarily at 0.02, 0.04, and 0.06, and ED is the effective degradability. The constants a, b, c, and L for each animal were calculated using the nonlinear regression (NLIN) procedures of SAS (SAS Inst., Inc., Cary, NC).

Intake of feed DM, ADG, and G:F (expressed as ADG/DMI) were calculated with individual animal as the experimental unit. Data from the transition period were not included in the calculation. Optimal PI values of processed barley, identified on the basis of animal performance, were calculated by integration of the binomial regression equation between PI values and DMI, ADG or G:F. Ultrasound data were subject to ANOVA with repeated measurement; other data were statistically analyzed by the ANOVA. All statistical analyses were conducted with individual animal as the experimental unit using the GLM procedure of SAS. Differences between treatments were determined using least square means with the PDIFF procedure of SAS.

	Results

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Characterization of the Processed Grain
With rollers at setting RMS, the tempered barleys (M and MS) were flattened, but dry grain (D) was fractured into small particles, whereas at setting RD, barley D was fractured into an "optimum" size of particles, and M and MS kernels were completely flattened.

No interactive effects (P > 0.05) of prerolling conditions (D, M, MS) and roller settings (RD, RMS) on percentage of whole kernels, kernel thickness, or PI of the processed grain were observed, but there was a trend (P = 0.09) toward interactive effects on volume weight. The MS barley tended (P = 0.06) to have lower volume weight compared with D when rolled at RMS, whereas volume weights of D, M, and MS were similar (P > 0.05) when rolled at RD. On average, barley rolled at RMS produced lighter (P < 0.001) volume weight (453.8 vs. 502.6 g/L), lower (P < 0.001) PI (70.1 vs. 79.3%), fewer (P < 0.001) whole kernels (4.46 vs. 8.48%), and thinner (P < 0.001) kernel thickness (1.99 vs. 2.24 mm) compared with barley rolled at RD (Table 2). Unlike the roller setting, tempering the barley with or without surfactant did not affect (P > 0.05) volume weight, PI, percentages of intact kernels or thickness of the kernels processed at either roller setting.

Experiment 1
In accordance with the observed characteristics of the processed grains, barley rolled at RMS had higher (P < 0.01) in situ DM disappearance (ISDMD) compared to that rolled at RD (Figure 1). Tempering reduced (P < 0.05) ISDMD between 4 and 24 h of ruminal incubation of barley rolled at either setting. An interactive effect (P < 0.05) of pre-rolling conditioning and roller setting on ISDMD was observed between 8 and 24 h of ruminal incubation. In situ DM disappearance from MS barley was lower (P < 0.05) than from M when the grain was rolled at RD but not (P > 0.05) when rolled at RMS.

View larger version (26K): [in this window] [in a new window]   Figure 1. Disappearance of DM from six treatments of barley during 0, 1, 2, 4, 8, 12, 24, and 48 h of in situ incubation. Dry barley grain (barley D), barley tempered to 20% moisture (barley M), and barley tempered to 20% moisture with application (60 mL/t) of a saponin-based surfactant (barley MS) were each rolled at two roller settings: 1) RD, which had yielded visually optimal processing of the dry barley during preliminary investigation, and 2) RMS, which had yielded visually optimal processing of the MS barley. Setting RMS was tighter than setting RD.

View larger version (36K): [in this window] [in a new window]   Figure 2. Growth of feedlot steers consuming diets prepared with barley grain processed by six techniques. Barley that was untempered, (i.e., dry, D); tempered to 20% moisture (M), or tempered with saponin-based surfactant applied at 60 mL/t (MS) was rolled at two roller settings: RD, which had been determined in preliminary testing to yield optimal processing of barley D, and RMS, the setting at which MS barley was optimally processed. The backgrounding and finishing diets comprised 47 and 85% (DM basis) barley grain, respectively. Days 85 to 112 were used for adaptation of the steers to the finishing diet.

	Discussion

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Roller Settings
In this study, roller setting RMS produced particles with kernel thicknesses of 1.98 to 2.00 mm and PI between 67 and 72%, whereas setting RD produced barley with thicknesses of 2.21 to 2.24 mm and PI between 78 and 81%. Thus, the degree of processing was greater with RMS than with RD. Growth responses observed in steers on RMS diets compared with RD are consistent with the general trend that more extensively processed grain for feedlot cattle reduced ADG and DMI but improved G:F (Owens et al., 1997). Given that setting RMS produced smaller grain particles than did setting RD, however, this study also demonstrates that the performance response of feedlot cattle to temper- or dry-rolled barley is strongly dependent on the degree of processing. Animal response to tempering is likely more positive if the grain is more extensively processed. Adding moisture through tempering significantly reduced the percentage of fine particles; this reduction was more obvious when the roller was set to produce smaller particles. These tempering-mediated changes in particle size may have reduced the occurrence of subclinical acidosis and consequently improved animal performance. Hironaka et al. (1979) reported that cattle fed diets containing more finely ground barley had lower ruminal pH, more rumenitis, and more clumping of papillae compared to cattle fed coarser diets. Improved performance by steers fed temper-rolled barley compared with dry-rolled barley grain has been well documented (Hinman and Combs, 1983; Combs and Hinman, 1989; Bradshaw et al., 1996).

Grain Tempering
Animal responses to tempering differed between the backgrounding and finishing periods. Whereas tempering had no effect in the backgrounding period, it improved animal performance in the finishing period. This may reflect a relationship between diet composition and the effect of tempering. The finishing diet contained more concentrate than the backgrounding diet, thus ruminal passage rate would generally have been higher during finishing than during backgrounding. Calculated values indicate that the effect of tempering grain on effective ruminal degradability is likely to be more pronounced when the rumen passage rate (k) is higher than when it is lower. Thus, temper-rolling barley may be more likely to affect performance by feedlot cattle during finishing (concentrate-based diets) than during backgrounding (forage-based), given the differences in feed passage rate between the two diets. In addition, the higher proportion of forage in the backgrounding diet would reduce the challenge of ruminal acidosis in these cattle compared to those on a finishing diet, and therefore the presence of more fine particles in the backgrounding diet would be less detrimental to intake. This likely contributes to the differences in ADG, DMI, and G:F observed during finishing when comparing D to M, irrespective of roller setting.

Performance by feedlot cattle in this study was improved by tempering to increase prerolling moisture content of the whole grain from approximately 10 to 20%. In contrast, however, Bradshaw et al. (1996) and Mathison et al. (1997) compared dry-rolled grain (at 11 and 13% moisture, respectively) to tempered grain for feedlot cattle and found no effect on performance by cattle during growing and finishing phases. It could be that the effectiveness of tempering on animal performance is also influenced by the amount of moisture present in the original whole grain. Higher moisture in the grain would probably reduce the proportion of fine particles and therefore reduce the effect of the moisture added during tempering. Collectively, it appears that positive responses of animal performance to tempering are most likely to occur when barley grain contains less than 10% moisture, rollers are set to produce a fine particle size, and the animals are fed a concentrated diet. Further study is needed to refine this relationship.

Processing Indices
This study demonstrated that the roller setting and the moisture content of the grain affected the extent to which barley was processed, which in turn influenced animal performance. Definition of the degree of processing optimal for maximum animal performance, therefore, would be a valuable tool for selecting appropriate roller settings for use with different lots of barley grain. In this study, however, estimations of optimal PI for maximal animal performance varied with the performance parameter (i.e., DMI, ADG, or G:F) from which they were calculated. The range in optimal PI estimated from the three growth performance parameters was narrower for the finishing diet than for the backgrounding diet, thus it may be possible with a finishing diet to select one target PI to maximize all three performance parameters.

Optimal PI values calculated in this study are similar to the 75% reported by Beauchemin et al. (2001) for a feedlot beef finishing diet but higher than the 64% reported by Yang et al. (2000) for dairy cows. Differences in diet composition between beef and dairy rations would likely affect optimal PI, as was seen between backgrounding and finishing diets in the present study. A higher degree of processing (lower PI) was optimal when proportion of barley was greater. Differences in digestive physiology between the two types of cattle may also contribute to these differing optima. It is generally believed that dairy cows have higher feed intake and rumen passage rates than beef cattle. The faster rumen passage rate (k) is associated with lower ruminal effective degradability, and theoretically, a higher degree of processing (lower PI) of the diet would be required to attain a similar extent of digestion as would be accomplished by an animal with a lower ruminal passage rate. Therefore, dairy cows may be more tolerant of extensive processing than beef cattle. The concept that the optimal PI for maximal animal performance may be a function of rumen passage rate requires further evaluation.

Surfactant Applied During Tempering
The surfactant used in this study contains steroidal saponins from Yucca schidigera. This preparation has been shown in commercial trials to reduce the time required to temper corn grain from 3 to 4 h to approximately 30 min (Johnson and Greer, 1996). It is suggested that this effect is related to reduced water surface tension and improved interaction of water with the waxy surface of corn grain due to the surfactant nature of the saponins. In a related study, we found that applying the same product during tempering increased uptake of water by barley kernels in the early stage of tempering (for approximately 2 h), but not if the grain was tempered longer than 4 h, due to the natural water absorption (our unpublished observations). The present study revealed no effects of surfactant on the physical characteristics of barley grain (volume weight, PI, kernel thickness or particle distribution) tempered at 20% moisture for 4 h. This may indicate that the surface of barley grain is less repellent to water than is corn, and consequently the effect of a surfactant on water absorption during 4 h of tempering was not as great with barley as with corn.

The common practice is to temper grain to approximately 20% moisture, and both in vivo and in vitro studies have shown that the optimal time for cold tempering (room temperature) was about 12 h (Hinman and Combs, 1984; Bradshaw et al., 1992). In that situation, applying a surfactant to barley grain is unlikely to have a major effect on particle size distribution as measured by dry sieving. In the present study, however, observations made during dry sieving (i.e., independent of effect of surfactant) were not reflected in animal performance, which was enhanced by applying the surfactant during tempering. This discrepancy suggests that the performance response to the surfactant during the backgrounding period is due more to a direct effect on digestive and metabolic physiology than to alteration of the processing characteristics of the barley grain.

Our earlier research with steroidal saponins from Y. schidigera has revealed that they promote growth of ruminal bacteria that digest starch, enhance in vitro digestion of barley grain, increase microbial protein synthesis and the ratio of propionic:acetic acid in the rumen, decrease protozoal numbers and reduce protein degradation in the rumen (Wang et al., 1998a; 2000a,b), and increase ruminal pH (A. N. Hristov, personal communication). Zinn et al. (1998) also reported increased rumen microbial efficiency caused by the same saponin surfactant. These findings suggest that the saponin in the tempering agent may have improved rumen microbial fermentation, thereby enhancing animal performance. The fact that this surfactant enhanced the growth performance and feed efficiency of the backgrounding steers when the barley was processed at the tighter setting (RMS) indicates that regulating ruminal fermentation of finely processed barley may be an important aspect of improving barley grain digestion.

It is generally accepted that grain processed to too fine a particle size can cause bloat and acidosis or other subclinical diseases because of its rapid fermentation (McAllister et al., 1994). Wang et al. (2000a) found that saponins from Y. schidigera reduced the activity of the lactate-producing bacterium, Streptococcus bovis, whereas it increases the activity of the lactate-utilizing Selenomonas ruminantium. In the present study, the effectiveness of surfactant in regulating digestion of small particles was more distinct in the backgrounding than in the finishing phase, in terms of improved growth rate and feed efficiency. Collectively, the results of this study suggest that surfactant could play a role in regulating utilization of properly processed barley grain. The observed response demonstrates the critical nature of proper roller settings during the processing of barley grain and suggests maximal results could be achieved by a combination of proper roller setting and including surfactant when tempering grain to 20% moisture.

In conclusion, feedlot steers fed dry or tempered barley rolled at setting RMS ate less during backgrounding and finishing and grew more slowly during backgrounding, but utilized feed more efficiently (those fed D during backgrounding; those fed M during finishing) than did steers fed these respective barleys rolled at the looser RD setting. Tempering the barley before rolling increased the steers’ DMI, ADG, and G:F during finishing but not during backgrounding, irrespective of roller setting, with G:F enhanced further if surfactant was included during tempering. The effects of tempering and surfactant on parameters of animal performance (tempering on DMI and G:F during finishing, and surfactant on DMI and ADG during backgrounding) were influenced by the roller setting at which the barley was processed; specifically, they were enhanced when barley was processed to a greater degree. The mechanisms by which roller setting, tempering, and inclusion of surfactant affected animal performance differ, however, in that both roller setting and tempering act mainly through altering feed particle size, whereas surfactant may act directly upon rumen microbial activity to regulate digestion and utilization of the feed by the ruminant animal.

	Implications

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This study demonstrated that the effects of tempering on animal performance are mediated by roller setting, moisture content of the whole grain, and composition of the diet. To achieve maximal animal performance, more extensive processing of barley is required for finishing diets than for backgrounding diets. Application of a surfactant-based tempering agent during tempering did not affect processing characteristics but improved animal performance. The most efficient utilization of barley grain by feedlot cattle may be realized by tempering the barley with surfactant to 20% moisture and rolling to yield a processing index (i.e., the ratio of postrolling vs. prerolling volume weights) of approximately 80% for the backgrounding period and about 74% for the finishing period.

	Footnotes

 
¹ This study was conducted with financial support from Agrichem, Inc., and the Matching Investment Initiative of Agriculture and Agri-Food Canada. The authors gratefully acknowledge the assistance of W. Smart, R. Wilde, R. Coleman, K. Jakober, and the feedlot staff at the Lethbridge Research Centre. This is Lethbridge Research Centre contribution No. 38702081.

² Correspondence: P.O. Box 3000 (phone: 403 317-3340; fax: 403 382-3156; E-mail: wangy{at}agr.gc.ca).

Received for publication November 22, 2002. Accepted for publication June 6, 2003.

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