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ANIMAL PRODUCTION |
Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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0.03), peaking at 35 and 52% WCGF, respectively. The efficiency of gain was not affected (P 
0.42) by dietary treatment. Steers fed dry-rolled corn and 35% WCGF had heavier HCW, lower DMI, greater ADG, increased G:F, increased s.c. fat thickness at the 12th rib, and greater yield grades compared with steers fed dry-rolled barley and 35% WCGF (P 0.04). The apparent dietary NEg was similar among the barley and WCGF combinations (P 0.51); however, the corn and 35% WCGF diet was 25% more energy dense (P < 0.001) than was the barley and 35% WCGF diet. In Exp. 2, no grain x processing interactions (P 0.39) were observed. Particle size was 2.15 and 2.59 mm for fine- and coarse-rolled barley and was 1.90 and 3.23 mm for fine- and coarse-rolled corn. Steers fed a combination of corn and WCGF had increased ADG, greater G:F, heavier HCW, larger LM area, more s.c. fat thickness at the 12th rib, greater yield grades, increased marbling, and more KPH compared with steers fed a combination of barley and WCGF (P 0.03). Fine-rolling of the grain increased fat thickness (P = 0.04). The addition of WCGF to the barley-based diets increased DMI and gain. Decreasing grain particle size did not greatly affect performance of the steers fed the 50% WCGF diets; however, carcasses from the steers fed the fine-rolled grain contained more fat.
Key Words: barley • corn • finishing • processing • steer • wet corn gluten feed
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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) in high-grain diets. Dependent on inclusion level and diet, steer performance has not been affected (Green et al., 1987; Ham et al., 1995), has been enhanced (Firkins et al., 1985; Ham et al. 1995; Richards et al., 1998), or has decreased (Krehbiel et al., 1995) when WCGF replaced a portion of dry-rolled corn. Krehbiel et al. (1995) reported that steers ruminally dosed with 7.5 kg of WCGF or a 1:1 combination of WCGF to dry-rolled corn had reduced time of ruminal pH <6.0 compared with steers dosed with 7.5 kg of dry-rolled corn, which agrees with the results of Firkins et al. (1985), who reported greater ruminal pH in WCGF-fed ruminants.
Dry-rolled corn, compared with whole corn, results in increased ADG (Owens et al., 1997), and dry-rolled barley, compared with whole barley, results in increased ADG and G:F (Hunt, 1996; Owens et al., 1997). Decreased grain particle size increases ruminal starch disappearance in limit-fed cattle (Galyean et al., 1979), increases ruminal corn passage rate (Ewing et al., 1986), and improves performance (Turgeon et al., 1983). However, increased rates of ruminal starch digestion predispose grain-fed cattle to subacute acidosis (Owens et al., 1998).
Firkins et al. (1985) and Krehbiel et al. (1995) suggested that WCGF suppresses subacute acidosis, and the results of Ham et al. (1995) led us to hypothesize that addition of WCGF to dry-rolled, barley-based finishing diets will increase steer performance and the feeding value of barley relative to corn because dry-rolled barley ferments faster than dry-rolled corn (Odle and Schaefer, 1987; Herrera-Saldana et al., 1990). Our objectives were to determine the optimum combination of barley and WCGF and, in diets containing optimal WCGF, determine effects of barley or corn particle size reduction on finishing steer performance and carcass characteristics.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Exp. 1
Using a randomized complete block design, 144 crossbred steers (initial BW = 298.9 ± 1.4 kg) were fed finishing diets to evaluate the effect of replacing barley and concentrated separator by-product (CSB; desugared beet molasses) with WCGF on steer performance and carcass characteristics. Steers originated from south central North Dakota and were shipped approximately 300 km to the North Dakota State University Animal Research Center in Fargo. Before initiation of the finishing experiment, a 48-d receiving period was used to acclimate steers to bunk feeding and wet feedstuffs.
Steers were weighed on 3 consecutive mornings before feeding for determination of initial BW. For 3 d before initiation of the experiment and on the day of initial BW measurement, steers were fed a common diet at 1.8% of BW. Steers were blocked by BW (4 blocks) and were allotted randomly to treatment using mean BW from the first 2 d of initial weighing. After being weighed on d 3 of initial weighing, steers were sorted into feedlot pens where they received their dietary treatments for the duration of the experiment (4 pens per treatment; 6 steers per pen). Each pen (14.7 m2 of indoor pen space; 34.8 m2 of outdoor pen space) had a concrete surface, 3.0 m of bunk space, and a continual flow water fountain. Pen served as the experimental unit.
Dietary treatments (Table 1) contained 0, 17, 35, 52, and 69% WCGF, where WCGF replaced barley and CSB. A positive-control treatment (dry-rolled corn and 35% WCGF) was used to compare performance of steers fed barley or corn when diets contained 35% WCGF. The combination of WCGF and corn was based on the data of Ham et al. (1995), where the greatest DMI and gain were achieved when dry-rolled corn comprised 52.5% of dietary DM and WCGF comprised 35% of dietary DM.
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Wet corn gluten feed was delivered approximately every 10 d to the research center. Diets were mixed daily in a 2.55-m3 stationary paddle mixer (S20, H.C. Davis Sons Mfg. Co. Inc., Bonner Springs, KS); steers were fed once daily in the morning. Bunk assessments were made daily and were dependent on the amount of feed remaining in the bunk with the goal that only traces of feed would be present. Orts were measured weekly. A sample of the refused feed was taken, and DM was measured (55°C for 48 h).
Feedstuff samples were taken weekly or with each new feed delivery. All feedstuffs were dried at 55°C for 48 h and stored for nutrient analyses. A composite sample of each feedstuff and samples from each load of WCGF were analyzed for DM, CP, and ash (methods 930.15, 990.02, and 942.05, respectively; AOAC, 1997), NDF (Robertson and Van Soest, 1991; with 
-amylase and without sodium sulfite), and ADF (Goering and Van Soest, 1970); fibers were not adjusted for residual ash. Composite samples of whole barley and WCGF were analyzed for starch (Herrera-Saldana and Huber, 1989). Grain samples were taken weekly or with each load of grain and composited for density and particle size analysis. Particle size was analyzed following the procedure of ASAE (1993) with the following modifications: a Tyler Ro-Tap sieve shaker (W. S. Tyler, Mentor, OH) was substituted for the Tyler RX86 sieve shaker. To compensate for differences in sieve shakers, the wing nut supports were raised approximately 2.5 cm from the top of the sieves, allowing the sieves to rock back and forth. Thirteen sieves were used along with a bottom pan. The sieve sizes ranged from 3,360 to 53 µm. Particle size was calculated as the geometric mean diameter using the equations of Baker and Herrman (2002).
At the beginning of the experiment, steers were adapted to a 90% concentrate diet over 21 d using transition diets containing 55% (3 d), 65% (4 d), 75% (7 d), and 85% (7 d) concentrate. During the transition period, steers were offered feed ad libitum and consumed 2.5% of their BW. Finishing diets were formulated to contain a minimum of 12.5% CP, 0.70% Ca, 0.32% P, 0.20% S, 27.5 mg of monensin (Rumensin, Elanco Animal Health, Indianapolis, IN)/kg, and 11.0 mg of tylosin (Tylan, Elanco Animal Health)/kg. Thiamine was added to the diet to supply at least 5 mg of dietary thiamine/kg.
When steers were visually observed to be finished, they were shipped to a commercial slaughter facility. Hot carcass weight and incidence of liver abscess were measured on the day of slaughter. Trained personnel from North Dakota State University evaluated carcass measurements and characteristics following a 24-h chill. Characteristics and measurements recorded were s.c. fat thickness at the 12th rib, LM area, KPH, marbling, and liver score using the method of Brink et al. (1990).
Exp. 2
One hundred forty-four crossbred steers (initial BW = 315.0 ± 1.5 kg) originating from south central North Dakota were used to evaluate coarse and fine dry-rolled corn or barley on feedlot performance and carcass characteristics when diets contained 50% WCGF. Steers were vaccinated, implanted, given a parasiticide, dehorned, ear-tagged, and fed in the same facility as described for Exp. 1.
Initial BW was determined following the same procedure as described in Exp. 1. Steers were blocked by BW into 6 BW blocks and allotted randomly to 1 of 4 dietary treatments (6 pens per treatment; 6 steers per pen). Treatments were 1) coarse-rolled corn, 2) fine-rolled corn, 3) coarse-rolled barley, and 4) fine-rolled barley. The quality control for grain processing was set for coarse-rolled grain to be 85% of the density of whole grain and for fine-rolled grain to be 75% of the density of whole grain.
Based on results of Exp. 1, where we calculated the optimum inclusion level of WCGF in diets containing barley to be approximately 50% of dietary DM, we formulated diets in Exp. 2 to contain 50% WCGF, 42% processed grain (fine- or coarse-rolled corn or barley), 5% alfalfa hay, and 3% supplement (DM basis; Table 2). Our objectives were to determine whether finishing steer performance could be enhanced by processing grain to a finer particle size and to determine the feeding value of dry-rolled barley relative to dry-rolled corn when the diets contained 50% WCGF. The diet was formulated to contain a minimum (DM basis) of 14.4% CP, 0.80% Ca, 0.70% P, and 1.0% K. All diets contained 27.5 mg of monensin (Rumensin)/kg, 11.0 mg of tylosin (Tylan)/kg, and 5 mg of dietary thiamine/kg. All steers were reimplanted on d 56 with 120 mg of trenbolone acetate and 24 mg of estradiol (Revalor-S).
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The collection and analysis of feedstuff samples and orts were conducted as described for Exp. 1; however, particle size and density of the grains were determined weekly or with each new load of grain. Steers were shipped to a commercial slaughter facility when they had approximately 1.0 cm of s.c. fat thickness at the 12th rib. The heavy BW block was slaughtered on d 159, and the remaining 5 blocks were slaughtered on d 182. Hot carcass weight was measured immediately after slaughter. After carcasses were chilled for 24 h, trained personnel collected the following data: s.c. fat thickness at the 12th rib, LM area, KPH, and marbling.
Calculations
Final BW was calculated from HCW divided by a common dressing percentage of 62. Dry matter intake expressed relative to BW was calculated as DMI divided by the average of initial and final BW. Yield grade was calculated as 2.5 + [6.35 x 12th rib fat thickness (cm)] + [0.0017 x HCW (kg)] + [0.2 x KPH (%)] – [2.06 x LM area (cm2)] (Boggs and Merkel, 1993).
Apparent dietary NEg was calculated using the equations for large-framed steers (NRC, 1984) and the process outlined by Larson et al. (1993). The apparent NEg of barley and WCGF were determined by substitution using tabular NEg values (NRC, 1996) for other dietary ingredients. A NEg of 1.25 Mcal/kg for dry-rolled barley (calculated from the 0% WCGF diet) was used in Exp. 1 to calculate the NEg of WCGF, and a NEg of 1.47 Mcal/kg was used for WCGF (95% of dry-rolled corn value) when calculating the NEg of corn and barley in Exp. 2.
Statistics
Exp. 1.
The experiment was designed as a randomized complete block. Pen served as the experimental unit (4 pens per treatment). Performance and carcass data were analyzed with the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The model included block and dietary treatment. Orthogonal linear, quadratic, and cubic contrasts were used for WCGF concentration in barley diets. A preplanned, single df contrast was used to compare barley and corn fed with 35% WCGF.
Exp. 2.
Performance and carcass data were analyzed as a randomized complete block design with a 2 x 2 factorial arrangement of dietary treatments using the GLM procedure of SAS. Factors were grain (corn or barley) and dry processing (coarse or fine rolled). Pen was the experimental unit (6 pens per treatment). The model for analysis of performance and carcass characteristics included block, grain, processing, and grain x processing. We did not observe a grain x processing interaction (P 0.39); however, interactive means are presented.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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. The nutrient analysis of WCGF was very similar to the nutrient profile reported by NCRRP (1989) and Ham et al. (1994) with the exception of ash, which was 239% greater in this experiment compared with that of Ham et al. (1994). Stock et al. (2000) described the variability in nutrient composition of WCGF as affected by the ratio of steep to bran, which caused protein concentrations to range from 14 to 24% of the DM. Dry matter (±SD) of WCGF was 43.2 ± 2.9%. The barley used in this experiment was lower in CP than light barley (14% CP; NRC, 1996) but contained similar NDF to that of light barley (28% NDF; NRC, 1996). The nutrients in the corn used in this experiment were similar to values reported by NRC (1996). The density of dry-rolled barley was decreased 11% from whole barley density, and the density of dry-rolled corn was 9.5% less than whole corn. Particle size of dry-rolled barley was 19% less than the particle size of whole barley; dry-rolled corn was decreased 24% compared with whole corn. Relative to the minimum density requirement for U.S. No. 1 corn and barley, the corn and barley fed in this experiment were 0.8% heavier and 6.5% lighter, respectively. The density of barley is correlated with starch content (r = 0.47) and ADF content (r = –0.44; Reynolds et al., 1992). Engstrom et al. (1992) reported a negative correlation between NDF and ADF with barley density (r = 0.69 for both NDF and ADF); furthermore, those researchers found that the starch and ADF content of barley explain 69 and 90% of the variation in G:F. Grimson et al. (1987), Mathison et al. (1991), and Engstrom et al. (1992) reported a general improvement in G:F with an increase in density of barley.
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). However, gain efficiency was not affected (P 0.42) by replacement of barley and CSB with WCGF. These results are similar to the results reported in the literature with respect to replacement of dry-rolled corn with WCGF (Ham et al., 1995; Hussein and Berger, 1995; Richards et al., 1998). The design used by Ham et al. (1995) is similar to the design used in the current experiment. Ham et al. (1995) replaced 0, 20, 40, 60, 80, and 100% of the dry-rolled corn and molasses with WCGF in diets fed to finishing steers. Those researchers reported that maximum gains and DMI resulted when WCGF was included at 35% of dietary DM (40% replacement). In the current experiment, DMI peaked with the 35% WCGF diet, a 10% increase compared with the 0% WCGF diet, whereas ADG peaked at the 52% WCGF diet, an 11% improvement compared with the 0% WCGF diet. Using regression to calculate the optimum inclusion level of WCGF in barley-based diets suggested that the optimum level based on ADG would be 48% of dietary DM.
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) than barley-fed steers. Corn-fed steers gained faster (P = 0.04), consumed less DM (P = 0.001), and had heavier final BW (P = 0.04) than barley-fed steers.
Data comparing corn and barley have demonstrated variable results. In a review of grain processing, Owens et al. (1997) reported performance of cattle fed grain processed by various methods; the mean G:F for cattle fed dry-rolled corn was 5.1% greater than the mean G:F for cattle fed dry-rolled barley. Zinn (1993) compared steam-flaked corn and steam-rolled barley, reporting that steam-flaked corn improved G:F of cattle 6.2% compared with cattle fed steam-rolled barley; however, contrary to those results, Garret et al. (1971) reported a 9.0% increase in G:F for cattle fed dry-rolled barley compared with cattle fed dry-rolled corn. Furthermore, Gray and Stallknecht (1988) reported that steers fed dry-rolled barley had similar performance compared with steers fed whole corn (0.170 and 0.168 G:F for steers fed dry-rolled barley and whole corn, respectively). Combs and Hinman (1988) reported that G:F for steers were 0.160, 0.161, 0.148, and 0.149 when fed tempered whole barley, dry-rolled corn, tempered whole corn, or high-moisture corn, respectively. Combs and Hinman (1988) concluded that ADG and G:F were similar between steers fed tempered barley and dry-rolled corn; however, comparisons between tempered whole barley and tempered whole corn or between tempered whole barley and high-moisture corn were not made.
Apparent dietary NEg was not affected by replacement of dry-rolled barley and CSB with WCGF (P 0.51; Table 4); however, apparent dietary NEg was 25% greater (P < 0.001) for the dry-rolled corn diet compared with the dry-rolled barley diet. Using substitution, the apparent NEg for dry-rolled barley and WCGF was calculated (Table 4). The apparent NEg for dry-rolled barley was calculated to be very similar to the NEg for light barley (1.22 Mcal/kg; NRC, 1996). The difference in dietary NEg between the barley and corn diets containing 35% WCGF was primarily due to the quality of the barley compared with the corn used in this experiment. According to NRC (1996) values, light barley is 27% lower in NEg than cracked corn. The barley grain (before processing) fed in this experiment was less dense (0.57 vs. 0.61 kg/L) compared with the minimum density allowed for U.S. No. 1 Grade barley (USDA, 1995), contained less starch (51.4 vs. 57.5%) compared with values reported by Huntington (1997), and had less CP (11.9 vs. 13.2%) compared with NRC (1996). Based on the performance of the steers in this experiment, WCGF included in dry-rolled barley diets was calculated to have 101.8% the NEg of dry-rolled barley. Our results agree with the data summarized by Stock et al. (2000) in that WCGF has a similar energy value as the grain it replaces. Stock et al. (2000) reported that WCGF has 93 to 100% the NE of corn and that increasing the ratio of steep to bran increased the energy of WCGF. The NEg value given to WCGF from the treatments that contained combinations of barley and WCGF is far below the NEg of corn. This could, in part, be due to a low steep to bran ratio, but is more likely a function of the light density barley used in this experiment, which decreased the overall energy content of the diet. When the NEg value of WCGF was calculated in the diet containing dry-rolled corn, WCGF was estimated to have a NEg of 1.55 Mcal/kg, which is similar to the NRC (1996) value for cracked corn.
Hot carcass weight responded quadratically (P = 0.04) with inclusion of WCGF, peaking at the 52% WCGF treatment (Table 5). Ham et al. (1995) did not report HCW; however, based on ADG (calculated from HCW-adjusted final BW), which peaked when WCGF was included at 35% of the diet (DM basis), HCW would have responded quadratically, peaking at a lower level of WCGF inclusion than in our experiment. The levels of WCGF fed by Firkins et al. (1985) were 0, 50, 70, and 90% (DM basis); they reported that cattle fed WCGF had heavier carcasses compared with control cattle and that within the WCGF diets, there was a linear decrease in HCW as inclusion of WCGF increased. Krehbiel et al. (1995) reported similar HCW for control and cattle fed 35% WCGF with a lower HCW for cattle fed 94.5% WCGF; cattle fed 86.5% WCGF were intermediate. Calculated yield grade (linear, P = 0.04) increased with the inclusion of WCGF. Yield grade peaked at the 70% inclusion level in the experiment conducted by Firkins et al. (1985), was not affected by replacement of dry-rolled corn and molasses with WCGF (Ham et al., 1995), and was lower at 94.5% WCGF compared with control and 35% WCGF; 86.5% WCGF was intermediate (Krehbiel et al., 1995). No other carcass measurements were affected (P 0.16) by replacement of dry-rolled barley and CSB with WCGF.
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reported that barley-fed cattle had heavier carcass weights than corn-fed steers; no other carcass characteristics were affected. Comparing barley with whole corn, Gray and Stallknecht (1988) reported no effect on carcass characteristics. Discrepancies between our data and those reported in the literature could be due to differences in the quality of barley fed because of improved performance with heavier density barley (Mathison et al., 1991).
The optimum inclusion level of WCGF in barley-based diets was greater than the 20 to 30% (DM basis) optimum inclusion level of WCGF in dry-rolled, corn-based diets suggested by Milton (2001). Based on our data, a greater optimum inclusion level of WCGF in diets based on dry-rolled barley compared with diets based on dry-rolled corn is likely a function of dry-rolled barley containing less NE than dry-rolled corn, or alternatively, increased levels of WCGF were needed to circumvent increased cases of subacute acidosis in the diets containing dry-rolled barley. Grains that have fast rates of ruminal starch fermentation predispose cattle to acidosis (Owens et al., 1998). Britton and Stock (1987) categorized barley as having a faster rate of ruminal starch fermentation compared with corn, and Herrera-Saldana et al. (1990) reported that barley has a faster rate of ruminal starch digestion than corn.
To further elucidate whether subacute acidosis might have been involved in the reduction in performance of steers fed dry-rolled barley vs. dry-rolled corn, intake variance was calculated according to Stock et al. (1995a). Stock et al. (1995b) determined that increased intake variance is an indication of subacute acidosis for individually fed cattle and suggested that measuring intake variance on a pen basis is not a good measure of subacute acidosis because decreased intake with occurrence of subacute acidosis by individual animals would be masked by the average intake of the cattle within a pen. However, in the current experiment, there were 6 steers in each pen, fewer animals per pen than the number (n = 20) viewed by Owens et al. (1998), which would mask any intake fluctuations between individual animals. Daily DMI was calculated from weekly DMI by dividing dry refused feed evenly over the days between measurements of refused feed (7 d). The feeding period was broken up into periods based on visual appraisal of intake trends. The periods were d 0 to 28, d 29 to 84, d 85 to 118, and d 119 to 161.
Quadratic changes (P 0.03) in intake variance were detected from d 0 to 28 (1.52, 2.47, 2.44, 2.17, and 1.44 ± 0.35 kg2 for 0, 17, 35, 52, and 69% WCGF, respectively) and from d 29 to 84 (0.62, 0.83, 1.52, 0.90, and 0.85 ± 0.21 kg2 for 0, 17, 35, 52, and 69% WCGF, respectively). Also, when comparing barley-fed vs. corn-fed steers at 35% WCGF, barley-fed steers tended (P = 0.06) to have greater intake variance during d 0 to 28 (2.44 vs. 1.42 kg2) and d 29 to 84 (1.52 vs. 0.89 kg2) compared with corn-fed steers. Stock et al. (1995a) reported that performance has an inverse relationship with intake variance. Similarly, Fulton et al. (1979) reported overall reduction in intake with increased intake variance during the grain adaptation phase. Our data would support the inverse relationship of gain with intake variance when comparing barley with corn. However, in diets containing barley and WCGF, intake variance has a positive relationship with ADG and DMI.
The degree to which barley is processed affects performance. Hironaka et al. (1979) reported that performance peaked when barley was processed to a particle size of 0.87 mm compared with more coarsely processed barley (1.03 and 1.53 mm) and more finely processed barley (0.48 and 0.67 mm), all of which were smaller than barley fed in the current experiment. Furthermore, barley fed in the current experiment was processed to 89% (0.57 kg/L decreased to 0.50 kg/L) of whole kernel density, which was a smaller reduction in density than barley fed by Parrott et al. (1969; dry-rolled barley was 61% of whole kernel density), and a heavier density than fed by Zinn (1993; dry-rolled barley density was 0.39 kg/L). Hunt (1996) compared the results of research trials where corn and barley were fed and concluded that performance is generally similar between corn-fed and barley-fed cattle.
The performance results of the current experiment are similar to those reported by Ham et al. (1995), where replacement of dry-rolled grain with WCGF creates a positive associative effect resulting in increased feed intake and gain. In the current experiment, the associative effect would be, in part, due to replacing barley that is high in starch (51.4% starch; DM basis) with WCGF, which is lower in starch (11.8% starch; DM basis) and is higher in digestible fiber (DeHaan, 1983 as cited by Krehbiel et al., 1995). The optimum inclusion level of WCGF was greater in dry-rolled barley diets than in dry-rolled corn diets, which appears to be due to at least 2 factors 1) dry-rolled barley used in this experiment was lower in NE compared with dry-rolled corn and 2) the NDF fraction of the barley used in this experiment (23.5% NDF) was similar to the NDF level of the light barley (0.43 kg/L) fed by Mathison et al. (1991; 21.6% NDF), which decreased performance relative to barley varieties that contained less NDF.
Exp. 2
The nutrient concentrations of coarse-rolled corn, fine-rolled corn, coarse-rolled barley, fine-rolled barley, and WCGF are listed in Table 6. The difference between nutrient content of fine-rolled and coarse-rolled grain was either due to sampling differences or a change in recoverable nutrients after different degrees of processing. Whole barley contained 51.8% starch (DM basis). Wet corn gluten feed was greater in NDF and lower in starch (13.3%; DM basis) than data reported by NCRRP (1989) and Ham et al. (1994). Dry matter (±SD) of WCGF was 41.0 ± 1.8%.
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There were no grain source x processing interactions (P 0.41). In disagreement with the hypothesis that decreasing particle size would enhance feedlot performance; coarse- or fine-rolling grain did not affect any measure of feedlot performance (P 0.14; Table 7). The results of this study are in agreement with those of Turgeon et al. (1983), who reported no difference (statistical comparison was not reported) between steers fed cracked corn-based diets compared with steers fed finely rolled corn-based diets. Turgeon et al. (1983) reported that corn particle size did not affect ruminal or postruminal DM, OM, or starch digestion; however, total tract starch digestion increased in steers fed cracked corn compared with steers fed whole corn. Galyean et al. (1979) reported increased ruminal starch and DM digestibility in steers (feed intake was 1.3% of their BW) fed ground corn in comparison with whole corn; no differences in ruminal or postruminal DM, OM, or starch digestion were present between corn ground through 3.18-, 4.76-, or 7.94-mm screens. Level of intake in our study was similar to intakes (% of BW) reported by Turgeon et al. (1983). Our results are, however, in agreement with the hypothesis that fine-rolled grain included in WCGF-based diets would not cause subacute acidosis when measured as a reduction in performance. Stock et al. (1990) linked a decrease in performance to subacute acidosis, and because performance was similar between steers fed either coarse-rolled or fine-rolled grain, subacute acidosis presumably did not occur to an extent to negatively affect performance.
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) for steers fed the corn and WCGF combination compared with the barley and WCGF combination. The NRC (1996) value for NEg of heavy barley is 1.40 Mcal/kg. Based on steer performance, with the assumption that carcass composition was similar between dietary treatments, the calculated apparent NEg for coarse-rolled and fine-rolled corn were 105% of the NRC (1996) value for cracked corn (Table 7). The calculated apparent NEg for coarse-rolled and fine-rolled barley were 99 and 90% of the NRC (1996) value for heavy barley.
Using NRC (1984) equations to estimate dietary NEg, the assumption was made that retained energy was similar between treatments (not adjusted for differences in carcass composition). Because feedlot performance was similar between steers fed coarse-rolled and fine-rolled grain, apparent dietary NEg (Table 7) was not affected (P = 0.41) by processing. However, steers fed fine-rolled grain had increased amounts of s.c. fat thickness at the 12th rib (1.19 vs. 1.09 cm for fine-rolled compared with coarse-rolled, respectively), and consequently, would have increased retained energy and likely indicates dietary NEg was underestimated for grains finely rolled compared with coarsely rolled grains.
There were no processing x grain interactions for carcass characteristics (P 0.44; Table 8). Processing grain to a finer particle size increased (P = 0.04) s.c fat thickness at the 12th rib and tended to increase (P = 0.07) yield grade. No other carcass characteristics were affected by processing (P 0.22). For grain-fed cattle, the primary objective of processing grain is to enhance nutrient utilization by exposing a greater proportion of the starch to ruminal fermentation (Hale, 1973). Although G:F was not affected by grain processing, the increase in apparent carcass fat (fat thickness and yield grade) observed in steers fed fine-rolled grain indicates differences in either digestion site or nutrient utilization (Harmon and McLeod, 2001).
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IMPLICATIONS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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Footnotes |
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2 Corresponding author: Marc.Bauer{at}ndsu.edu
Received for publication August 23, 2005. Accepted for publication November 22, 2005.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONIMPLICATIONSLITERATURE CITED |
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