Roughage Source and Level in Beef Cattle Finishing Diets1

The Professional Animal Scientist 12:192-198

Roughage Source and Level in Beef Cattle Finishing Diets1 M. J. GUTHRIE2, M. L. GALYEAN3, PAS, K. J. MALCOLM-CALLIS, and G. C. DUFF, PAS Clayton Livestock Research Center, Department of Animal and Range Sciences, New Mexico State University, Clayton, NM 88415-9501

Abstract Three experiments were conducted to evaluate the effects of roughage level and source in beef cattle finishing diets. In Exp. 1, 228 crossbred beef heifers (initial BW = 346 kg) were fed diets containing 7.5 or 15% roughage (DM basis), with alfalfa hay, sudangrass hay, or cottonseed hulls as roughage sources. Daily gain was not affected (1)>0.10) by roughage level, but DMI was increased (p<0.10) with 15 vs 7.5% roughage. Among roughage sources, daily gain was less (p<0.05) with alfalfa than with cottonseed hulls or sUdangrass. Dry matter intake was greater (p<0.05) with sudangrass than with alfalfa and intermediate with cottonseed hulls. Feed:gain did not differ (p>0.1O) among roughage sources, but heifers fed alfalfa were least efficient. In Exp. 2, 224 crossbred beef steers (initial BW = 308

' The authors were supported by funds from the New Mexico Agric. Exp. Sta., Las Cruces. 2Present address: East Texas State Univ., Dept. of Agric. Sci., Commerce, TX 754293011 .

3To whom reprint requests should be addressed. Present address: Div. of Agric., West Texas A &: M Univ., WTAMU Box 998, Canyon, TX 79016-0001 . Reviewed by D. C. Anderson and Sarah Northcutt.

kg) were fed 90% concentrate diets with either whole-shelled or steam-flaked com as grain sources and either alfalfa hay or sudangrass hay as roughage sources. Daily gain was not affected by grain source, but DMI and feed:gain were greater (p<0.0l) with whole-shelled than with steam-flaked com. Similarly, gain did not differ (1)>0.10) between sudangrass and alfalfa, but steers fed sudangrass had greater (p<0.02) DMI and were less efficient (p<0.03) than those fed alfalfa as the roughage source. In Exp. 3, 132 crossbred steers (initial BW = 313 kg) were used in a randomized block design with different roughage sources and levels, including: alfalfa hay at 10% of dietary DM or sudangrass hay at 5, 7.5, and 10% of dietary DM. Daily gain was greater (p<0.06) with diets containing sudangrass than with the alfalfa diet, but level of sudangrass did not affect (1)>0.10) daily gain. Daily DMI was increased (p<0.03) for diets with sudangrass vs alfalfa, and responded quadratically (p<0.11) to sudangrass level, with maximum DMI at 7.5% sudangrass. Feed:gain did not differ between the roughage sources but increased linearly (p<0.11) with increasing level of sudangrass. These results indicate that roughage level and source alter DMI and performance by finishing beef cattle. Sudangrass hay consistently increased DMI relative to alfalfa hay in high-concentrate beef cattle finishing

diets, but responses in daily gain and feed efficiency were not consistent between these two roughages. Further research is needed to characterize the relationship between chemical and physical characteristics of roughages and finishing beef cattle performance. (Key Words: Beef Cattle, Roughage, Grain Processing, Feed Intake .)

Introduction High-concentrate, beef cattle finishing diets typically contain small amounts of roughage. Roughage is often added to decrease the incidence of digestive upsets like acidosis and liver abscesses, but roughage level can affect performance by finishing beef cattle. Kreikemeier et a1. (4) noted faster, more efficient gains by cattle fed either 5 or 10% roughage than by those fed 0 or 15% roughage in steam-rolled wheat diets. Stock et a1. (10) fed roughage (50:50 mixture of alfalfa and corn silage) levels of 0, 3, 6, and 9% in high moisture corn and dry rolled sorghum diets to yearling steers and reported a quadratic effect of roughage level on DMI and daily gain. Gain was maximized at 9% roughage, but cattle were less efficient as roughage

Roughage Source and Level for Finishing Beef Cattle

level increased from 0 to 9%. Similarly, with diets based on a combination of dry rolled wheat and dry rolled corn (75:25), increasing roughage level (0, 3.75, and 7.5%) increased DMI but linearly decreased gain:feed. Adding roughage to dry rolled wheat, but not to dry rolled corn or sorghum diets (0 vs 7.5%), was beneficial to gain efficiency (10). With whole-shelled corn diets, daily DMI increased linearly as alfalfa level increased from 0 to 8% (n but gain did not increase sufficiently to counterbalance the increased feed intake, leading to decreased gain efficiency with increased roughage level. Nonetheless, cattle fed 8% roughage had heavier carcass weights than those fed 0 or 4% roughage, leading to greater profitability with the higher roughage level (7). Roughage source may be as important in beef cattle finishing diets as roughage level. Mader et al. (6) reported that effects of roughage source on performance by cattle fed high-concentrate diets depended on corn processing method. Steers fed ground high moisture or dry rolled corn diets with 9.2% alfalfa silage had greater DMI and improved feed:gain compared with those fed 11.5% corn silage diets. Moreover, DMI and feed:gain were increased with 9.2% alfalfa hay vs 11.5% corn silage as roughage sources in ground high moisture corn diets, but roughage source did not markedly affect performance with dry rolled corn diets. In two other trials, roughage source did not affect performance by cattle fed whole dry corn diets, but feed:gain was improved with alfalfa silage vs hay in whole high moisture corn diets (6). Because of the effects of roughage source and level on performance, and the need for a greater understanding of these effects, we conducted three experiments. The objective of the first experiment (Exp. 1) was to evaluate effects of three roughage sources (alfalfa, cottonseed hulls, and sudangrass hay) fed at two levels (7.5 and 15% of DM) on performance by growing-finishing beef heifers fed

whole-shelled corn diets. The second experiment (Exp. 2) was designed to evaluate the possible interaction of roughage source (alfalfa and sudangrass hays) and grain processing method (whole-shelled or steamflaked corn). The third experiment (Exp. 3) was designed to determine the equivalency of roughage sources by comparing sudangrass hay and alfalfa, with sudangrass fed at three levels.

Materials and Methods Experiment 1. Two hundred twenty-eight crossbred (British x Brahman) heifers were used in a completely random design with a 2 x 3 factorial arrangement of treatments. Factors were roughage level (either 7.5 or 15% of DM) and roughage source (alfalfa, sorghum sudangrass hay, or cottonseed hulls). Ingredient composition of the six

193

treatment diets is shown in Table L Alfalfa (field cubes) and sorghum sudangrass (large round bales) were ground to pass a 2.5-cm screen before mixing into diets. All heifers were implanted with Synovex H (Fort Dodge Animal Health, Overland Park, KS) and weighed (unshrunk) on d O. Heifers were stratified by body weight and assigned randomly to pens so as to equalize body weight among treatments. Final un shrunk body weights were obtained after 70 d on feed. Feed was offered once daily in quantities sufficient to allow freechoice consumption. Diet samples were taken weekly to determine DM content (100 DC forced-air oven for 24 h), ground to pass a 2-mm screen, and analyzed for ash, Cp, and ADF by AOAC (1) procedures (Table 1). Performance data (daily gain, DMI, and feed:gain) were analyzed as a completely random design with a statistical model that included the

TABLE 1. Ingredient and chemical composition of whole-shelled corn diets (OM basis) fed to beef heifers (Exp. 1). 15% Roughage

7.5% Roughage

Item

Alfalfa

Hulls

Sudangrass

Alfalfa

Hulls

Sudangrass

Ingredient, % Corn Roughage Soybean meal Molasses Limestone Dicalcium phosphate Salt Urea Premixa

82.96 7.31 2.07 4.84 1.03 0.67 0.51 0.51 0.10

79.62 7.43 5.15 4.83 1.23 0.62 0.51 0.51 0.10

80.95 7.67 3.60 4.82 1.23 0.61 0.51 0.51 0.10

77.86 14.67 0.0 4.86 0.82 0.67 0.51 0.51 0.10

69.26 14.85 8.24 4.83 1.03 0.67 0.51 0.51 0.10

71.95 15.30 5.14 4.81 1.02 0.66 0.51 0.51 0.10

77.0 4.4 11.8 10.7

76.1 5.5 11.8 9.2

75.2 5.9 11.2 11.7

77.3 5.1 13.0 13.9

77.1 6.6 12.7 1l.8

Chemical composition, %b DM 75.0 Ash 5.6 CP 11.9 ADF 9.5

aSupplied through a Micro-Ingredient Machine. Included trace mineral at 0.1 % of the diet, monensin (200 mg per heifer, daily), tylosin (75 mg per heifer, daily), vitamin A (2,205 IU/kg of diet), and vitamin E (200 IU per heifer, daily). Trace mineral contained 4.4% Mn, 0.30% Co, 6.6% Fe, 1.3% Cu, 12.0% In, and 20.0% Mg. bAverage of samples collected throughout the experiment.

194

Guthrie et al.

TABLE 2. Ingredient composition of the 90% concentrate diets (OM basis) fed to beef steers (Exp. 2). Steam-flaked corn Item

Ingredient, % Sudangrass hay Alfalfa hay Whole-shelled corn Steam-flaked corn Soybean meal Molasses Fat (yellow grease) Limestone Dicalcium phosphate Salt Urea Ammonium sulfate Premix a Chemical composition, %b DM Ash CP ADF

Alfalfa

Sudangrass

Whole-shelled corn Alfalfa

10.19 10.19 77.49 5.07 2.00 1.02 0.66 0.51 0.51 0.51 2.04

83.7 5.4 11.1 6.0

10.13 10.11 77.64

75.49 2.00 5.07 2.00 1.02 0.66 0.51

5.04 2.00 1.02 0.65 0.51

0.51

0.50

0.51 2.04

0.51 2.02

84.3 5.7 11.5 6.5

Sudangrass

87.4 5.4 11.1 5.7

75.64 1.98 5.04 1.99 1.02 0.65 0.51 0.51 0.51 2.02

86.9 5.3 11 .2 5.9

aHominy feed-based premix consisted of 0.42% vitamin A (30,000 USP units/g), 0.15% vitamin E (500,000 IU/kg), 5% trace mineral (4.40/0 Mn, 0.30% I, 0.200/0 Co, 6.60/0 Fe, 1.30/0 Cu, 12.0% In, and 20.0% Mg), 1.160/0 monensin (132 g/kg), and 0.280/0 tylosin (220 g/ kg). bAverage of samples collected throughout the experiment.

effects of roughage level, roughage source, roughage level x source, and residual error. Pen (two pens of 19 heifers for each roughage level x source combination) was considered the experimental unit for all statistical analyses. Experiment 2. TWo hundred twenty-four mixed breed (British x Continental) steers were used. All steers had been adapted to an 85% concentrate diet before starting the experiment. Steers were weighed (unshrunk) on 2 consecutive d at the start of the trial and assigned randomly to one of four treatments within light and heavy weight blocks. Each steer was implanted with Synovex S (Fort Dodge Animal Health) and vaccinated with a sevenway clostridial on the first of the 2 initial weigh d. The 90% concentrate treatment diets (Table 2) were ar-

ranged in a 2 x 2 factorial and consisted of: 1) a whole-shelled corn-based diet with alfalfa (tubground field cubes as in Exp. 1) as the roughage; 2) whole-shelled corn with sudangrass (tub-ground large, round bales as in Exp. 1) as the roughage; 3) steam-flaked corn with alfalfa; and 4) steam-flaked corn with sudangrass. Steers were fed once daily in quantities sufficient to ensure ad libitum access to feed and were weighed at 28-d intervals throughout the trial. Each steer was revaccinated with a seven-way clostridial on d 56 and reimplanted with Synovex Son d 84 of the trial. The heavy block of steers was slaughtered after 126 d on feed, and the light block was slaughtered after 154 d on feed. Carcass data were collected only for steers in the light block. Details of carcass data collection procedures were

provided by Galyean et a1. (3) . Samples of diets were collected at weekly intervals throughout the experiment and analyzed for chemical constituents (Table 2) as described for Exp. 1. Performance data were analyzed as a randomized complete block design with a 2 x 2 factorial arrangement of treatments. The statistical model included effects for block, block x treatment, corn processing method, roughage source, corn processing method x roughage source, and residual error. Pen (two pens of 14 steers for each roughage source x corn processing method combination within weight block) was the experimental unit for all analyses. Experiment 3. One hundred thirty-two crossbred (British x Continental) steers were used. All steers had been adapted to a 90% concentrate diet before starting the experiment. Steers were weighed (unshrunk) on 2 consecutive d at the start of the trial and assigned randomly to one of four treatments within light, medium, and heavy weight blocks. Steers were sorted into 12 pens with 11 steers per pen (three pens per treatment). Each steer was implanted with Synovex S and vaccinated with a seven-way clostridial on the first of the 2 initial weigh d. Ingredient composition of the four treatment diets is shown in Table 3. Diets were formulated (DM basis) to contain 1) 5% sudangrass, 2) 7.5% sudangrass, 3) 10% sudangrass, and 4) 10% alfalfa as the roughage levels and sources. As in Exp. 1 and 2, large round bales of sudangrass hay were tub-ground before inclusion in the diets; however, unlike these previous experiments, ground alfalfa hay purchased in bulk was used rather than tub-ground field cubes. Steers were fed once daily in quantities sufficient to allow ad libitum consumption and weighed at 28-d intervals throughout the trial. Steers in the light and medium weight blocks were reimplanted with Synovex S on d 84. The heavy-block steers were taken off trial after 84 d on feed, the medium-block steers

Roughage SOUTce and Level faT Finishing Beef Cattle

195

reflected differences in DMli heifers fed alfalfa consumed approximately 0.9 kg less (P<0.05) DM/d than those fed sudangrass, with intermediate Treatmenta intake by heifers fed cottonseed hulls. Feed:gain means did not differ Item S-5 S-7.5 S-10 A-l0 (P>0.1O) among roughage sources, although heifers fed alfalfa were the Ingredient, % least efficient. Sudangrass hay 4.86 7.27 9.70 Experiment 2. Performance data Alfalfa hay 10.08 during various segments of the Whole-shelled corn 16.31 15.82 15.33 15.67 experiment are shown in Table 5. Steam-flaked milo 62.67 64.61 60.73 62.06 Source of dietary roughage did not 1.98 Soybean meal 1.98 1.98 interact with corn processing method Molasses 5.06 5.07 5.04 5.07 for any variable measured; hence, Fat (yellow grease) 2.00 1.99 2.00 2.00 main effect means (roughage source Limestone 1.01 1.02 1.01 1.02 averaged over corn processing Dicalcium phosphate 0.65 0.65 0.65 0.65 Salt 0.51 0.51 0.51 0.51 method and vice versa) are preUrea 0.49 0.49 0.48 0.49 sented. Daily gain did not differ Ammonium sulfate 0.51 0.50 0.51 0.51 (P>0.1O) during the first 56 d bePremix b 2.01 2.01 2.01 2.01 tween steers fed whole-shelled corn and those fed steam-flaked corn. Chemical composition, % However, from d 0 to 112, gain was DM 84.5 84.6 84.4 84.6 less (P<0.08) with whole-shelled than Ash 4.5 4.8 5.5 5.4 with steam-flaked corn. For the CP 11.5 12.0 12.2 12.5 entire experiment, daily gain was the ADF 8.4 9.6 8.6 9.3 Ca 0.58 0.62 0.76 0.77 same for the two types of corn. Daily p 0.36 0.39 0.40 0.38 DMI was greater (P0.10) 0.28% tylosin (220 g/kg). ' between cattle fed sudangrass hay as the dietary roughage and those fed alfalfa, but DMI was consistently greater (P<0.02) with sudangrass than with alfalfa. As a result of similar after 112 d on feed, and the lightResults daily gain and increased DMI, feed block steers after 140 d on feed. Experiment 1. No interactions of required per unit of gain for the Carcass data were not collected for overall experiment was greater roughage level and roughage source this experiment. Diet samples were (P<0.03) for cattle fed sudangrass vs were detected. Daily gain was not taken weekly to determine DM alfalfa as the dietary roughage. different for the two roughage levels content, ground, and analyzed for Hot carcass weights were heavier (Table 4), but heifers fed 15% roughchemical constituents as described (P<0.03) for light-block steers fed age diets consumed approximately for Exp. 1 (Table 3). sudangrass than for those fed alfalfa Performance data were analyzed as 7% more (P0.1O) by treatment. Only 3.6% of (p<0.05) per day (Table 4) than those alfalfa vs sudangrass hay, and linear the light-block cattle had liver fed either cottonseed hulls or and quadratic effects of sudangrass abscesses. sudangrass hay. Differences in gain hay level. T~BLE

3. Ingredient and chemical composition (OM basis) of concentrate diets fed to beef steers (Exp. 3).

196

Guthrie et al.

TABLE 4. Influence of roughage source and level on performance by beef heifers fed whole-shelled corn-based diets for 70 d (Exp. 1). Roughage level Item

7.5%

15%

Initial wt., kg Final wt., kg Daily gain, kg Daily DMI, kg Feed :gain, kg:kg

345.6 345.6 427.7 427.3 1.17 1.17 7.94d 8.48 e 6.78 7.30

Roughage source SEa

Alfalfa

Sudangrass SEa

Hulls

345.6 345.2 9.5 346.1 10.0 419.6 430.0 433.2 1.20c 0.02 1.05 b 1.26C 8.22bc 0.19 7.74 b 8.66c 0.20 7.38 6.84 6.90

11.3 12.2 0.03 0.23 0.24

astandard error of main effect means, n = 6 pens per treatment for roughage level, and n = 4 pens per treatment for roughage source. b,cMeans within roughage source with no common superscript differ significantly (P<0.05). d,eMeans within roughage level with no common superscript differ significantly (P<0.10).

TABLE 5. Performance by finishing steers fed steam-flaked or wholeshelled corn diets with either alfalfa or sudangrass as the dietary roughage source (Exp. 2). Corn

Roughage

Steam- Wholeflaked shelled

SudanOSla grass

Discussion SEb

OSla

Alfalfa

No. of steers (pens) 112 (8) 112 (8) Initial wt., kg 308.4 308.4 Final wt., kg 518.0 518.0

NS NS

112 (8) 112 (8) NS 308.4 308.4 515.3 520.3 NS

dO to 56 Daily gain, kg Daily DMI, kg Feed:gain, kg:kg

1.69 7.89 4.66

1.76 8.80 5.03

NS 0.Q1 0.01

1.69 7.98 4.72

1.76 8.71 4.96

NS 0.01 0.05

0.03 0.10 0.07

dO to 112 Daily gain, kg Daily DMI, kg Feed:gain, kg:kg

1.66 8.35 5.01

1.61 9.12 5.68

0.08 0.Q1 0.01

1.62 8.39 5.18

1.65 9.03 5.51

ND 0.02 0.02

0.02 0.15 0.07

dO to finish Daily gain, kg Daily DMI, kg Feed:gain, kg:kg

1.50 8.26 5.49

1.50 9.21 6.13

NS 0.01 0.01

1.49 8.39 5.67

1.52 9.03 5.96

NS 0.02 0.03

0.02 0.14 0.07

Item

Experiment 3. Performance data throughout the experiment are shown in Table 6. During the first 84 d, steers fed sudangrass hay as the dietary roughage gained more rapidly (P<0.02) than those fed alfalfa. This difference in gain between alfalfa vs the three levels of sudangrass was evident for the overall feeding period (P<0.06) . Final body weights of cattle fed sudangrass were greater (P<0 .06) than of those fed alfalfa. Dry matter intake was consistently greater throughout the trial with sudangrass than with alfalfa (P<0.03) . Within levels of sudangrass, daily DMI increased quadratically (P<0 .04 fVi d 0 to 84; P
0.31 2.45

aObserved significance level for main effects; probability of a difference is less than the value indicated. NS = nonsignificant (1'>0.10). bPooled SE of main effect means.

Differences in feed intake by cattle fed the different roughage sources in our three experiments are generally consistent with other reports in the literature. White and Reynolds (11) compared effects of diets containing 20 or 40% rice straw, 20 or 40 % alfalfa hay, 20% rice hulls, 40% dehydrated sudangrass pellets, and 20% polyethylene pellets on performance by finishing steers. Diets with lower quality (higher crude fiber) roughage sources like straw, hulls, and sudangrass pellets resulted in greater DMI than diets with higher quality (lower crude fiber) alfalfa hay, and increasing the level of dietary roughage increased DMI. Intake of diets containing roughage was greater than with an all-concentrate diet (11). Similarly, Loerch (5) noted increased intake and daily gain by

Roughage Source and Level for Finishing Beef Cattle

TABLE 6. Influence of roughage source and level on performance by beef steers (Exp. 3). Treatmenta Item

S-5

No. steers (pens) 33 (3) Initial wt., kg 313.1 Final wt., kg 469.1 Daily gain, kg dOt084 dO to end

Contrast b

S-7.5

S-10

33 (3) 312.8 472.5

31304

467.5

A vs SSH SSH level

SEc

33 (3) 312.8 458.1

NS 0.06

NS NS

9042

1.52

1045

1046 lAO

1.32 1.30

0.02 0.06

NS NS

0.09 0.10

Daily DMI, kg/steer dO to 84 7.22 dO to end 7040

7.79 7.89

7.55 7.71

6.94 7.19

0.01 0.03

Q, 0.04

Q,O.11

0.28 0.32

Feed:gain, kg:kg dOt084 dO to end

5.15 5045

5.17 5.52

5.25 5.52

NS NS

NS L,O.l1

0.11 0.11

1045 1042

4.96 5.21

1.51

33 (3)

A-10

as-5 = 5% sudangrass hay; S-7.5 = 7.5% sudangrass hay; S-' 0 = '0% sudangrass hay; A-10 = 10% alfalfa hay. bProbability level for contrasts: A vs SSH = alfalfa vs sudangrass hay; SSH level = linear (L) or quadratic (Q) effect of sudangrass hay. NS = nonsignificant (I» 0.12). cPooled SE of treatment means.

crossbred steers fed 15% corn silage diets vs all-concentrate high moisture corn-based diets. Bartle et al. (2) fed three roughage levels (10, 20, and 30%) from two sources (alfalfa and cottonseed hulls) to finishing steers. Averaged over roughage source, diets with 20% roughage resulted in similar gain to diets with 10% roughage, but decreased gain efficiency. Diets with 30% roughage decreased both gain and efficiency. Dry matter intake was greater when cottonseed hulls was the roughage source, but gain and gain efficiency were less with cottonseed hulls than with alfalfa (2). The consistent increase in DMI in our experiments, which varied in grain processing method and grain type, with sudangrass vs alfalfa as the dietary roughage source does not suggest an interaction between these two roughage sources and grain processing method as reported by Mader et al. (6) for alfalfa hay, alfalfa silage, and corn silage. The three roughages we used may have different effects on the flow of

digesta (grain or hay) from the rumen, which could alter feed intake. Owens and Goetsch (9) and Wylie et al. (12) reported that increasing dietary roughage decreased residence time of grain in the rumen. In 35% roughage diets, DMI was greater and passage of steam-flaked milo from the rumen tended to be greater when cottonseed hulls replaced half the alfalfa hay than with all alfalfa hay or replacement of half the alfalfa by wheat straw (8) . Replacing alfalfa by cottonseed hulls increased dietary NDF content compared with all alfalfa and wheat straw:alfalfa. Moreover, digestibility of DM and NDF was less with cottonseed hulls:alfalfa than with all alfalfa and wheat straw:alfalfa (8). The effects on DMI noted with sudangrass in our experiments may have been related to differences in the chemical and physical characteristics of dietary fiber, which might have impacted digesta passage, rumination, or ruminal contractions. Further studies are needed to determine the ruminal

197

changes associated with beef cattle finishing diets based on various roughage sources. Daily gain followed responses in DMI, with less gain by heifers fed alfalfa than by those fed sudangrass hay in whole-shelled corn-based diets (Exp. 1) and a similar difference in gain in favor of sudangrass over alfalfa for steers in Exp. 2 and 3. Bartle et al. (2) reported lower and less efficient gain when cottonseed hulls was the dietary roughage vs alfalfa; however, roughage source interacted with roughage leveL At 10% dietary roughage, differences in daily gain and gain efficiency between cottonseed hulls and alfalfa were small, with the advantage for alfalfa over cottonseed hulls increasing as roughage level increased to 20 and 30% of the diet (2). Perhaps differences in daily gain between roughage sources were minimized in our experiments by the use of 10% or less roughage; however, daily gain was increased with whole-shelled corn diets in Exp. 1 for sudangrass vs alfalfa even at 15% dietary roughage. Feed:gain responses in our studies depended on the experiment. The findings in Exp. 1 and 3 that cattle fed sudangrass hay were equal in efficiency or more efficient than those fed alfalfa hay contrasts results with corn-based diets in Exp. 2, in which steers fed sudangrass as the roughage were less efficient than those fed alfalfa. As noted previously, at the same percentage of roughage in the dietary DM, diets with sudangrass resulted in greater DMI than those with alfalfa; this effect was consistent with milo- and corn-based diets. Based on the similar (1'>0.10) feed intake by cattle fed 10% alfalfa and those fed 5% sudangrass in Exp. 3., it seems that sudangrass has approximately two times the roughage value of alfalfa in high-concentrate finishing diets . As noted with DMI responses, differences in feed efficiency between sudangrass and alfalfa may reflect differences in the chemical and physical characteristics of dietary fiber. Although ADF content may

198

Guthrie et ai.

not be the most effective basis for comparison, at the same dietary roughage level total dietary ADF was approximately three percentage units greater in Exp. 3 than in Exp. 2. In Exp. 2, ADF content was greater for sudangrass diets than for alfalfa diets, whereas the alfalfa diet in Exp. 3 had a slightly higher ADF content than the sudangrass diet. In Exp. I, within the two roughage levels fed, dietary ADF content was similar for alfalfa- and sudangrass-based diets. Different lots of alfalfa and sudangrass, with associated differences in quality, probably account for the differences in ADF content between these two roughage sources in our experiments. Further characterization of the fiber in high concentrate diets might aid our understanding of differences among various roughage sources.

sudangrass than with alfalfa translated to greater gain and equal or improved feed efficiency. Based on responses in dry matter intake, sudangrass hay seems to have approximately twice the roughage value of alfalfa hay. Reasons for differences in roughage value between sudangrass and alfalfa are not known, but differences may be related to physical and chemical characteristics of dietary fiber. Further research is needed to develop practical methods for determining the equivalency among roughage sources.

Implications

1. AOAC. 1990. Official Methods of Analysis. (15th Ed.). Association of Official Analytical Chemists, Arlington, VA.

Increasing the level from 7.5 to 15% of various dry roughages in high-concentrate beef cattle finishing diets increased dry matter intake, with little effect on daily gain. Dry matter intake was consistently greater with ground sudangrass hay as the dietary roughage than with ground alfalfa hay. In two of three experiments, greater dry matter intake with

Literature Cited

2. Bartle, S. J., R. L. Preston, and M. F. Miller. 1994. Dietary energy source and density: Effects of roughage source, roughage equivalent, tallow level, and steer type on feedlot performance and carcass characteristics. J. Anim. Sci. 72:1943. 3. Galyean, M. L., K. J. Malcolm-Callis, S. A. Gunter, and R. A. Berrie. 1995. Effects of zinc source and level and added copper lysine in the receiving diet on performance by growing and finishing steers. Prof. Anim. Sci. 11:139.

4. Kreikemeier, K. K., D. L. Harmon, R. T. Brandt, Jr., T. G. Nagaraja, and R. C. Cochran. 1990. Steam-rolled wheat diets for finishing cattle: Effects of dietary roughage and feed intake on finishing steer performance and ruminal metabolism . J. Anim. Sci. 68:2310. 5. Loerch, S. C. 1991. Efficacy of plastic pot scrubbers as a replacement for roughage in high-concentrate cattle diets. ] . Anim. Sct 69:2321. 6. Mader, T. L., J. M. Dahlquist, and L. D. Schmidt. 199L Roughage sources in beef cattle finishing diets. J. Anim. Sci. 69:462. 7. Milton, C. T., R. T. Brandt, Jr., and S. A Shuey. 1994. Roughage levels in whole shelled corn finishing diets: feed lot performance and carcass traits. J. Anim. Sci. 72(Suppl. 2):79. (Abs.) . 8. Moore, J. A., M. H. Poore, and R. S. Swingle. 1990. Influence of roughage source on kinetics of digestion and passage, and on calculated extents of ruminal digestion in beef steers fed 650/0 concentrate diets. ] . Anlm. ScI. 68:3412. 9. Owens, F. N., and A. L. Goetsch. 1986. Digesta passage and microbial protein synthesis. In : Control of Digestion and Metabolism in Ruminants. p 196. L. P. Milligan, W. L. Grovum, and A. Dobson (Eds.). Prentice-Hall, Englewood Cliffs, NJ. 10. Stock, R. A., M. H. Sindt, J.

c. Parrott, and

F. K. Goedeken. 1990. Effects of grain type,

roughage level and monensin level on finishing cattle performance. J. Anim. Sci. 68:3441. 11. White, T. W., and W. L. Reynolds.' 1969. Various sources and levels of roughage in steer rations. ]. Anim. Sci. 28:705. ' 12. Wylie, M. J" T. W. White, W. C. Ellis, and ] . H. Matis. 1990. The flow of undigested corn residues through the gastrointestinal tract of cattle. J. Anim. Sci. 68:3843.

\