Feed Intake and Digestibility by Cattle Consuming

Feed intake and digestibility by cattle consuming bermudagrass or orchardgrass hay supplemented with soybean hulls and(or) corn Sr. Galloway DL, A. L. Goetsch, L. A. Forster, Jr, A. R. Patil, W. Sun and Z. B. Johnson J ANIM SCI 1993, 71:3087-3095.

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Feed Intake and Digestibility by Cattle Consuming Bermudagrass or Orchardgrass Hay Supplemented with Soybean Hulls and(or) Corn D. L. Galloway, Sr., A. L. Goetschl, L. A. Forster, Jr., A. R. Patil, W. Sun, and Z. B. Johnson Department of Animal Science, University of Arkansas, Fayetteville 72701

ABSTRACT: Effects of supplementing cattle consuming tropical or temperate grass with corn and(or) soybean hulls on feed intake and digestibility were determined. In Exp. 1, eight Holstein steer calves (210 rf: 9.2 and 269 k 9.4 kg initial and final BW, respectively), in two simultaneous Latin squares, were given ad libitum access to bermudagrass ( B ) or orchardgrass ( 0 hay without supplementation or with (DM basis) 5%of BW of ground corn ( C ) , .7%of BW of soybean hulls ( H ) , or .25% of BW of corn plus .35% of BW of soybean hulls (CH). Total OM intake was greater ( P < .05) with than without supplementation (5.05, 6.04, 5.95, 6.06, 6.04, 6.81, 6.61, and 6.69 kg/d), and digestible OM intake was affected by forage source ( P < . 0 5 ) , mixing of supplement types (CH versus the mean of C and H; P < .09), and the forage source x supplementation interaction ( P < .09; 2.65, 3.40, 3.33, 3.46, 3.71, 4.14, 3.98, and 4.30 kg/d for B, B-C, B-H, B-CH, 0, 0-C, O-H, and O-CH, respective-

ly). Total tract NDF digestibility was greater ( P < . 0 5 ) for 0 than for B diets and for H than for C (56.4, 53.9, 58.1, 56.9, 68.5, 64.9, 67.7, and 69.6%for B, B-C, B-H, B-CH, 0, 0-C, O-H, and O-CH, respectively). In Exp. 2, mature cannulated beef cattle (524 k 1.6 kg BW) were used in a design similar to Exp. 1 with comparable dietary supplement levels. The concentration of total VFA and acetate:propionate in ruminal fluid did not differ between C and H. Duodenal microbial N also did not differ among supplement treatments, but postruminal OM digestibility was greater ( P < .06) for C than for H with both forages. In conclusion, digestible OM intake was improved similarly by supplementing growing steers consuming moderate-quality, temperate, or tropical grass hay with .5% of BW of corn or .7% of BW of soybean hulls. A mixture of corn and soybean hulls increased digestible OM intake with both forage sources relative to the mean of C and H.

Key Words: Cattle, Feed Intake, Digestion, Soybean Hulls

J. Anim. Sci. 1993. 71:3087-3095

Introduction Ruminants derive most nutrients from forage in typical production systems, although desired levels of performance are not always achieved when forage is consumed alone. Hence, to enhance energy and(or) protein status, concentrates are often used to supplement ruminants ingesting forage. However, high dietary levels of the most common type of energy supplement, cereal grains high in starch, can decrease forage digestibility (Hoover, 1986). Byproduct feedstuffs such as soybean hulls offer an alternative to high-starch supplements. Supplementation with soybean hulls, which have a high concentration of degradable fiber, affects ruminal pH relatively less than supplementation with cereal grains (Klop-

'To whom correspondence should be addressed. Received April 8, 1993. Accepted June 16, 1993.

fenstein and Owen, 1987). Furthermore, the absence of starch in soybean hulls may avert decreased fibrolytic activity that results from preferential starch utilization by fiber-digesting microbes (Hoover, 1986). Comparisons between supplemental corn and soybean hulls generally have entailed similar quantities of DM, yielding different levels of supplemental DE. Mixes of soybean hulls and corn have not been investigated thoroughly, even though adverse effects of grain on fiber digestibility typically increase as level of supplementation increases. Forage characteristics influence ruminal conditions and nutrient absorption by ruminants (Minson, 1990); therefore, optimal supplement composition may vary among forage sources. Our objective was to compare effects of supplementation with a low to moderate level of DE from corn, soybean hulls, or a mixture of the two feedstuffs on feed intake and digestibility by cattle consuming moderate-quality, tropical or temperate grass hays.

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Materials and Methods Experiment 1 Eight Holstein steer calves (210 k 9.2 and 269 k 9.4 kg initial and final BW, respectively) were used in a split-plot experiment with two simultaneous 4 x 4 Latin squares and 14-d periods. Animals in this and the subsequent experiment were handled in accordance with guidelines recommended by Consortium (1988). Steers were placed in tie stalls (1.2 m x 2.4 m ) in an enclosed barn with free access to water. Steers were weighed (unshrunk) at the beginning of the study and at 1300 on d 14 of each period. Steers were assigned to squares to yield similar average BW and variation in BW within each square. Steers of one square were fed long-stemmed bermudagrass hay ( B; Cynodon dactylon), whereas those of the other square were fed long-stemmed orchardgrass hay ( 0;Dactylis glomerata), a t 105 to 110% of consumption on the preceding few days. Orchardgrass hay consisted mostly of leaf, being cut at early anthesis; B was primarily vegetative growth, with most tillers between growth stages 14 and 17 (West, 1990). Hay was preserved in rectangular bales (approximately 23 kg, air-dry basis) stored in a covered barn. Steers were not supplemented (Control) or were offered (DM basis) .5% of BW of ground corn ( C), .7% of BW of soybean hulls ( H), or .25% of BW of corn plus .35% of BW of soybean hulls ( C H ) . Supplements provided a similar quantity of DE; total supplemented DE was approximately 20 kcaVkg of BW (NRC, 1984). Hay and supplements were fed at 0800 and 1600 in equal amounts. Supplement was placed in buckets and fed before hay was offered; hay was placed in feeders along with the buckets that contained supplement. All steers were given 12 g (airdry) of a 3:l mixture of NaCl and trace minerals2 and 9 g of dicalcium phosphate. Hay refusals were collected and weighed immediately before the 0800 meal. To estimate particulate passage rate, 100 g of ytterbium-labeled (Goetsch and Galyean, 1983a; 24-h soak) hay (unground) was mixed with 127 g of unlabeled hay of the 0800 meal on d 9 and fed. Consumption was complete in < 30 min; remaining hay was offered thereafter. Fecal grab samples were taken on d 11 to 14 at 12-h intervals, advancing 3 h daily, and frozen. Composites constructed on a freshweight basis were formed within steer and period, dried a t 55"C, and ground to pass a 1-mm screen. Hay and supplement composites were constructed from

2Contained > 129%Zn, 10% Mn, 5% K, 2.5% Mg, 1.5% Cu, .3% I, .1% Co, and .02% Se. 3Contained 96 t o 98% NaCl and 2 .5% Fe, .04% %In, .002% Cu, and .0007% Co.

samples taken on d 9 to 14 and ground to pass a l-mm screen. Feed and fecal composites were analyzed for DM, ash, N (AOAC, 1984), NDF (Goering and Van Soest, 1970; without decalin, ethoxyethanol, or sodium sulfite), and AIA (Van Keulen and Young, 1977; 2 N HC1). Amylase was used to determine NDF in supplements (Cherney et al., 1989). Hay and soybean hulls were analyzed for ADF and ADL sequentially (Goering and Van Soest, 1970). Cellulose was determined as the loss in weight after treatment with H2SO4, and ADF was subtracted from NDF to yield an estimate of hemicellulose. Individual fecal samples were ashed, dissolved in a 3 N HC1:3 N HNO3 solution (Ellis et al., 19821, and analyzed for ytterbium by atomic absorption spectrophotometry with a nitrous oxide-plus-acetylene flame. Digestibilities of OM, NDF, and N were determined with AIA as an internal marker. Particulate passage rate was estimated by regressing the natural logarithm of ytterbium concentration against time after dosing in the decay portion of the fecal marker excretion curve. Voluntary hay intake on d 10 to 14 was analyzed as a split-plot in time using the GLM procedure of SAS (1985). Hay intake was not affected by day or the day x treatment interaction ( P > . l o ) and was, therefore, averaged over days. Data were analyzed with the following sources of variation: forage source o r square, steer within square, period, supplement treatment, and the forage source x supplement treatment interaction. Steer within square variation was used to test for the effect of forage source. Orthogonal contrasts were conducted for effects of supplementation (Control versus other treatments), supplement type (C versus H ) , mixing of supplement types (CH versus the mean of C and HI, and interactions between forage source and supplementation, supplement type, and mixing of supplement types.

Experiment 2 Eight beef cattle (British breeds; 501 +. 20.0 and 550 f 22.4 kg initial and final unshrunk BW, respectively), four cows ( 8 yr old) and four steers ( 7 y r old), with cannulas in the rumen and duodenum (T-type) were used in an experiment with two simultaneous 4 x 4 Latin squares. Two steers and two cows were assigned to each square to yield similar mean BW and variation in BW within each square. Animals were housed in an enclosed barn in 3.1-m x 4.6-m pens with free access to water and trace mineral salt3. Animals of one square were fed B and others received 0; hay sources were those used in Exp. 1. Supplement treatments were the same as in Exp. 1, with similar dietary levels of supplement, except that total intake was less than ad libitum. In a 14-d preliminary period, average ad libitum intake of B was determined without supplementation, and Control intake during the experiment was set at 85 to


SOYBEAN HULLS AND CORN FOR CATTLE

90% of this level (1.38% of BW; DM basis). Hay intake was 1.10% of BW for C, H, and CH supplement treatments. Levels of supplementation were (DM basis) .28% of BW of ground corn ( C ) , .39% of BW of soybean hulls ( H ) , and .14% of BW of corn plus .19% of BW of soybean hulls (CHI. Equal meals were fed at 0700 and 1600 on d 1to 7 and at 0700 and 1900 on d 8 to 14. Hay was offered after consumption of supplement. Hay and supplement composite samples were taken on d 9 to 14 and ground to pass a l-mm screen. Digesta were sampled on the last 5 d of each period. On d 9 at the 0700 meal, 100 g (air-dry) of ytterbiumlabeled hay (unground) was mixed with 200 g of unlabeled hay and fed to each animal; remaining hay was fed after consumption of labeled hay. On d 11, 100 mL of CoEDTA (Uden et al., 1980) was dosed into the rumen before the 0700 meal. Ruminal fluid was sampled (400 mL) at 0700, 0900, 1100, 1300, 1600, 1900, and 2300 on d 11; at 0830, 1430, and 2100 on d 12; and at 1000 and 1600 on d 13. Ruminal fluid pH was measured with a pH electrode immediately after collection at 0700, 0900, 1100, 1300, and 1600 on d 11. Samples were strained through eight layers of cheesecloth. One aliquot (200 mL) of ruminal fluid was composited for each animal in a saline (.9%; wt/vol)-formalin (3.7%; wt/vol) solution, and another 200-mL portion was frozen after adding 2 mL of a 7.2 N HzS04. Duodenal (200 mL) and fecal samples were obtained at 0700 and 1300 on d 11; at 0830 and 1430 on d 12; at 1000 and 1600 on d 13; and at 1130 and 1730 on d 14, representing 90-min intervals between morning and evening meals. Composites of duodenal samples were formed for each animal and stored frozen. Fecal samples were stored frozen before compositing. One portion of duodenal digesta was lyophilized and ground t o pass a l-mm screen. A second portion was centrifuged at 10,000 x g for 10 min, and the supernatant fluid was later analyzed for ammonia N concentration (Broderick and Kang, 1980). The DM content of whole duodenal digesta also was measured. Fecal samples were thawed and subsampled to form a composite, which was lyophilized and ground ( l - m m screen). Remaining feces were dried for 48 h in a forced-air oven at 55°C and ground to pass a 2-mm screen. Composite samples of feed, duodenal digesta, and feces were analyzed for DM, ash, N, NDF, ADF, and AIA; ADF and ADL concentrations in hay were determined. Dry duodenal composites were analyzed for nucleic acids (Zinn and Owens. 1986). Individual fecal samples were analyzed for ytterbium to estimate particulate passage rate. Bacterial cells were isolated by differential centrifugation (Merchen and Satter, 1983) of ruminal fluid stored in sa1ine:formalin solution and analyzed for DM, ash, N, and nucleic acids. Frozen ruminal fluid samples were thawed at

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room temperature, and an aliquot was centrifuged at 10,000 x g for 10 min. Supernatant fluid was analyzed for cobalt by atomic absorption spectrophotometry with an air-plus-acetylene flame. Ruminal fluid passage rate was estimated by regressing the natural logarithm of cobalt concentration against time after administration. Ruminal fluid volume was calculated by dividing the cobalt dose by the extrapolated concentration at the time of dosing, and outflow rate was estimated by multiplying volume by passage rate. Centrifuged ruminal fluid at 0700, 0900, 1100, 1300, and 1600 on d 11 was analyzed for ammonia N, and VFA in ruminal fluid at 1300 and 1900 were quantified (Goetsch and Galyean, 1983b). Acid insoluble ash was used as an internal marker to estimate digestibility. Flows of OM, NDF, and N were calculated by multiplying DM flow by their digesta concentrations of OM, NDF, and N, respectively. The percentage of microbial N in duodenal digesta was obtained by dividing nucleic acid concentration in duodenal digesta by the ratio of nucleic acid: total N in bacterial cells, and microbial OM was derived by use of bacterial cell N and OM concentrations. Data were analyzed as described for Exp. 1. In addition, ruminal pH and ammonia N and VFA concentrations were analyzed as a split-plot in time. Because interactions between sampling time and forage source and supplement treatments were not significant ( P > .lo), values averaged over time were analyzed in a reduced model.

Results and Discussion Experiment 1 The NDF concentration in B was greater than that in 0 (Table 11, which was expected based on different photosynthetic pathways and similar maturity of the two forages at harvest. The concentration of NDF in soybean hulls was similar t o that of 0, although the ADL concentration in soybean hulls was much less. Supplement made up 18, 25, 21, 16, 23, and 19% of total DMI for B-C, B-H, B-CH, 0-C, O-H, and O-CH, respectively. Total OM intake was increased ( P < .05) by supplementation and not different among supplement treatments (Table 2 ) ; thus, hay OM intake was less ( P< .05) for H than for C and was not affected by mixing supplement types. Decreases in hay OM intake were 14, 39, 23, 36, 65, and 55% of supplement OM intake for B-C, B-H, B-CH, 0-C, O-H, and O-CH, respectively. In contrast, Martin and Hibberd ( 1990) reported that intake of low-quality native range grass was decreased by only .64 kg when 3 kg of soybean hulls (DM basis) was supplemented to beef cows. This small decrease in hay intake by soybean hulls relative to the larger decrease in our experiment may partially relate to lower dietary C P levels in the former study.


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Table 1. Feed composition (percentage of dry matter) Exp. 1 Item

Ash CP NDF ADF ADL Cellulose Hemicellulose

aB = bermudagrass hay; 0

Exp. 2

Ba

0

C

H

B

0

C

H

7.0 11.4 77.7 35.4 5.2 29.0 42.3

9.5 15.4 65.3 35.7 4.8 29.5 29.7

1.7 10.6 13.9 -

6.7 14.0 66.0 48.6 2.1 46.6 17.4

7.1 12.2 75.7 33.7 5.7 26.8 42.0

9.3 14.7 63.6 37.3 5.7 30.3 26.2

1.4 9.3 9.0

6.4 14.4 62.2 -

-

-

-

-

-

= orchardgrass hay; C = corn; H = soybean hulls.

Sarwar et al. (1992) did not alter total DMI by lactating dairy cows by replacing dietary forage or corn with soybean hulls. Chan et al. (1991) supplemented mature beef cows consuming low-quality native grass hay ad libitum with two levels of corn or soybean hulls (approximately .25 or .50% of BW; DM basis). Total OM intake did not differ between supplement types with the high level of supplementation, but with the low level, total OM intake tended to be greater for the diet with soybean hulls than with corn. Organic matter digestibility was greater ( P < .05) for 0 than for B diets and not different among supplement treatments (Table 2 1. Assuming that

total tract supplement OM digestibility is similar to TDN concentration (90% for corn and 64% for soybean hulls; NRC, 19841, hay OM digestibility was 48.5, 53.3, 52.1, 54.9, 59.0, and 61.6% for B-C, B-H, B-CH, 0 - C , 0-H, and 0-CH, respectively. Thus, C seemed t o decrease hay OM digestibility slightly, and mixing corn and soybean hulls yielded somewhat greater hay OM digestibility than expected based on additive effects of each supplement type; however, effects of mixing supplement types on digestibilities of OM and NDF were significant only a t P < .19 and .E, respectively. Soybean hulls OM digestibility, by assuming similar hay OM digestibility for H and Control treatments, was 66 and 56% for B and 0, respectively.

Table 2. Intake, digestibility, and particulate passage rate in Holstein steer calves consuming bermudagrass or orchardgrass hay supplemented with corn and(or) soybean hulls (Exp. 1) Bermudagrass Item

OM Intake, kgld Supplement Hay Total Digestion %

kg/d

NDF Intake, kgld Digestion %

kg/d Nitrogen Intake, gld Disappearance %

g/d Particulate passage rate, %/h

Orchardgrass

C

H

6.04 6.04

1.14 5.66 6.81

1.54 5.08 6.61

1.35 5.34 6.69

,123 .142

57.1 3.46

61.6 3.71

61.1 4.14

61.3 3.98

64.4 4.30

1.71 ,105

4.78

4.56

4.35

4.24

4.75

4.48

,089

58.1 2.77

56.9 2.60

68.5 2.97

64.9 2.74

67.7 3.17

69.6 3.11

1.60 ,083

C

H

5.05 5.05

1.14 4.90 6.04

1.49 4.46 5.95

1.31 4.75 6.06

52.7 2.65

56.3 3.40

56.2 3.33

4.21

4.25

56.4 2.36

53.9 2.29

Conta

-

CH

Cont

-

CH

SE

99.2

115.7

123.1

120.9

165.0

173.8

175.1

174.0

4.05

55.2 54.7

53.2 61.6

55.9 68.6

55.4 66.9

62.5 103.1

56.2 96.7

56.3 96.7

60.3 105.2

2.48 4.06

4.18

4.80

4.71

4.62

4.60

4.69

4.67

4.86

.126

Effectb

F F,S,m,Ps

F,T f.T

F F,F*S S,PS

aCont = control; C = corn; H = soybean hulls. bEffect: F and f = forage source ( P < .05 and .lo, respectively); S and s = supplementation ( P < .05and .lo, respectively); T = supplement type ( C versus H; P < .05); m = mixing of supplement types (CH versus C and H; P < . l o ) ; F*S and P s = forage source x supplementation interaction ( P < .05 and .lo, respectively). Downloaded from jas.fass.org by guest on December 31, 2011


Similarly, Martin and Hibberd (1990) observed 61% total tract digestibility of soybean hulls OM. Total tract NDF digestibility was greater ( P < .05) for 0 than for B, and greater for H than for C (Table 2). In other instances, replacing forage with soybean hulls has increased NDF digestibility (Sarwar et al., 1991, 1992; Grigsby et al., 1993). Lower digestibility of NDF for C than for H coincides with predicted hay OM digestibilities listed earlier. Similarly, Highfill et al. (1987) observed a negative associative effect in digestibility when a low-quality fescue hay was supplemented with a corn-soybean meal mix, but this effect did not occur with soybean hulls. Moreover, Anderson et al. (1988) sequentially increased NDF digestibility by beef steers when corn stover was replaced by 12.5, 25, and 50% soybean hulls. Neutral detergent fiber digestibility was not affected by substitution of 12.5 or 25% corn for corn stover, whereas NDF digestibility decreased markedly when the level of corn was increased to 50%. Slightly greater NDF digestibility for H than for Control with B, and a slightly lesser value with 0, suggest that digestibility of soybean hulls NDF was intermediate t o that of B and 0. Quicke et al. (1959) reported 54% cellulose digestibility for soybean hulls. In the current experiment, by assuming that H did not affect hay NDF digestibility, soybean hulls NDF was 64 and 61% digestible with B and 0, respectively. The slightly greater value with B than with 0 may reflect a true difference in digestibility of soybean hulls NDF, or that effects of H on hay NDF digestibility varied slightly with forage source. The former possibility seems unlikely, in part because particulate passage rate was similar for B-H and O-H. With regards to the latter factor, 0rskov and Ryle (1990) indicated that supplementation of low-quality forage with readily degraded fiber can increase fiber digestibility by enhancing microbial attachment and colonization. The potential effect of such an increase in fiber digestibility would be greater for B than for 0 because of lower Control NDF digestibility with B. Digestible OM intake (Table 2 ) was greater ( P < .05) for 0 than for B. Separate supplementation with corn and soybean hulls increased ( P < .05) digestible OM intake similarly regardless of forage source. Mixing corn and soybean hulls increased ( P < .09) digestible OM intake compared with the mean of C and H, reflecting similar differences (nonsignificant) in digestibilities of OM ( P < .19) and NDF ( P < .15). Factors responsible for the positive associative effect of mixing corn and soybean hulls on digestible OM intake may involve the lower level of starch in the CH than in the C supplement. High levels of starch added t o forage diets can decrease fibrolytic activity of microbes via decreased pH and preferential starch use by fiber-digesting microbes (0rskov and Ryle, 1990). However, because the level of supplemental starch with C was not very high, substantial adverse effects

309 1

on fiber digestion would not be expected (Klopfenstein et al., 1985). Supplementation increased digestible OM intake (Table 2 ) more with B than with 0 (forage source x supplementation interaction; P < ,091. This interaction resulted from similar, nonsignificant, interactions in OM intake ( P < .20) and digestibility ( P < .28). In experiments similar t o ours, supplementation increased digestible OM intake more with tropical than with temperate grass (Jones et al., 1988; Lagasse et al., 1990; Sun et al., 1991). Total N digestibility was greater for 0 than for B diets, but not different among supplement treatments (Table 2). Likewise, the quantity of N digested daily was greater ( P < .05) for 0 than B diets. Supplementation of B increased digestible N intake, but supplementation of 0 did not (Forage source x supplementation interaction; P < .05), presumably because of the lower level of N in B than 0, and a numerically greater increase in OM intake with supplementation of B (forage source x supplementation interaction; P < .20). Supplementation increased particulate passage rate more with B than with 0 (forage source x supplementation interaction; P < .08). Likewise, concentrate supplementation of forage diets in similar experiments has increased particulate passage rate (Brake et al., 1989; Hall et al., 1990; Galloway et al., 1993). Factors responsible for increased particulate passage rate with supplementation in our study are unclear.

Experiment 2 Dietary levels of supplement OM were 21, 26, 23, 21, 26, and 24% for C, H, and CH with B and 0, respectively. Ruminal pH did not differ among diets (Table 3 ) probably because of the moderate level of feed intake and supplement levels less than 30% of the diet. Effects of a corn-based supplement on NDF digestibility did not seem to be caused by decreased pH with low-quality fescue (Highfill et al., 1987) or bromegrass hay (Grigsby et al., 1993). In our experiment, ruminal ammonia N concentration was greater ( P < .08) for 0 than for B diets, and was not affected by supplement treatments (Table 31; however, supplementation numerically decreased ammonia N concentration with 0 (forage source x supplementation interaction; P < .13). Highfill et al. ( 1987 ) observed lower ruminal concentrations of ammonia N at most sampling times in cattle consuming low-quality fescue hay supplemented with approximately 26% soybean hulls than that in cattle consuming a corn-based concentrate. The disparity between these results may involve greater concentrations of CP in the forage used in our experiment. The concentration of total VFA in ruminal fluid (Table 3 ) did not differ among diets, although it tended to be greater for H than for C with 0 (forage source x supplement type interaction; P < .12).


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Table 3. Ruminal digesta characteristics of beef cattle consuming bermudagrass or orchardgrass hay supplemented with corn and(or) soybean hulls (Exp. 2) Bermudagrass Item PH Ammonia N, mg/dL VFA Total, mM MoVlOO mol Acetate Propionate Isobutyrate Butyrate Isovalerate Valerate Acetate:propionate

Orchardgrass

Conta

C

H

CH

Cont

C

H

CH

SE

Effectb

6.64 7.3

6.55 7.6

6.54 7.1

6.49 7.8

6.56 10.5

6.58 8.5

6.62 8.8

6.59 8.6

,054 .78

f

-

80.3

84.2

82.7

86.7

79.1

77.0

87.2

85.3

69.5 20.5 7.4 1.2 .8 3.40

68.8 19.1 1.0 8.8 1.5 .8 3.62

68.6 20.6 .9 8.1 1.3 .7 3.35

68.2 19.3 1.1 9.4 1.3 .8 3.55

69.0 19.7 1.3 7.7 1.6 .7 3.53

68.4 18.4 1.5 9.2 1.8

67.5 19.9 1.3 9.0 1.6

3.76

70.1 18.1 1.6 8.0 1.5 .8 3.89

3.40

.62 .54 .22 .33 .ll .05 .118

7.38 74.9

6.38 91.0

6.78 99.4

7.28 77.2

6.52 82.5

7.27 84.0

6.55 82.8

6.91 93.5

.328 8.60

5.34

5.59

6.67

5.58

5.30

5.94

5.93

6.43

.297

S,t,f*t,Pm

3.93

3.64

4.50

3.53

3.53

4.09

4.00

3.93

,228

Pt

.6

.8

.a

3.58

m f,s,F*M

F S,T,M F,T

-

m,F*M

Fluid passage rate, %/h

Fluid volume, L Fluid outflow rate, L/h

Particulate passage rate. %/h

Ps

-

aCont = control; C = corn; H = soybean hulls. bEffect F and f = forage source ( P < .05 and .lo, respectively); S and s = supplementation ( P < .05 and .lo, respectively); T and t = supplement type ( C versus H; P < .05 and .lo, respectively); M and m = mixing of supplement types (CH versus C and H; P < .05 and .lo, respectively); Ps = forage source x supplementation interaction ( P < . l o ) ; Pt = forage source x supplement type interaction ( P < .lo); F*M and P m = forage source x mixing of supplement types interaction ( P < .05 and .lo, respectively).

Highfill et al. ( 198 7 supplemented cattle consuming low-quality fescue hay with approximately 26% soybean hulls or a corn-based concentrate, fed in one meal per day. The concentration of total VFA in ruminal fluid was either not different or was greater for soybean hulls than for corn at various sampling times. Grigsby et al. (1993) reported no differences in the concentration of total VFA in steers consuming bromegrass hay supplemented with different proportions of soybean hulls and corn at 40% of the diet. The molar proportion of acetate was less ( P < . O S ) for CH than for the mean of C and H (Table 3 ) . Supplementation decreased ( P < .06) the molar proportion of propionate. The proportion of propionate and acetate:propionate ratio were less for CH than for the mean of C and H with B, but greater with 0 (forage source x mixing of supplement types interaction; P < . 0 5 ) . Factors responsible for these interactions are unclear. Highfill et al. (1987) supplemented beef cows consuming low-quality fescue hay with soybean hulls or a corn-soybean meal mix a t 25 or 27% of DMI in two experiments. At all but one sampling time in one experiment, the acetate:propionate ratio was similar for both supplement treatments. Conversely, different mixes of soybean hulls and corn at 40% of the diet did not affect acetate:propionate ratio with a bromegrass hay diet (Grigsby et al., 1993). Supplementation decreased ruminal fluid passage rate (Table 3 ) with B and caused an increase with 0 (forage source x supplementation interaction; P < .lo). Ruminal fluid volume was increased ( P < . 0 5 ) by

supplementation, being greater for H than for C with B (forage source x supplement type interaction; P < .07),and less for CH than for the mean of C and H with B, but greater with 0 (forage source x mixing of supplement type interaction; P < .06). Particulate passage rate was greater for H than for C with B, but not different with 0 (forage source x supplement type interaction; P < .06). Fluid and particulate passage rates were not affected in beef steers consuming corn stalks by substituting 12.5, 25, or 50% soybean hulls for corn (Anderson et al., 1988), or in steers consuming bromegrass alone or with different proportions of soybean hulls and corn at 40% of the diet (Grigsby et al., 1993). Total OM flow at the duodenum (Table 4) did not differ among diets. Microbial OM flow at the duodenum was increased ( P < . 0 5 ) by supplementation, but not different among supplement treatments. Feed OM flow at the duodenum did not differ among diets, and neither apparent nor true ruminal OM digestibilities differed among diets, Ruminal NDF digestibility was increased ( P < .05 by supplementation, coincident with no effect of supplementation on NDF digestibility in Exp. 1 and lower feed intake and particulate passage rate in Exp. 2 than in Exp. 1. Postruminal OM digestibility was greater for C than for H ( P < .06), and the difference was numerically greater with B than with 0 (forage source x supplement type interaction; P < .15). These results indicate that the high-starch supplement, C, resulted in greater postruminal OM digestibility than did the supplemental


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Table 4. Organic matter and neutral detergent fiber intakes and digestibilities by beef cattle consuming bermudagrass or orchardgrass hay supplemented with corn and(or) soybean hulls (Exp. 2) Bermudagrass Item OM Intake, kgid Duodenal, kgid Total Microbial Feed Fecal, kgid Digestibility, % Apparent ruminal True ruminal Postruminal Total tract

NDF Intake, kgid Duodenal, kg/d Fecal, kg/d Digestibility, c/o Ruminal Total tract

Orchardgrass

Conta

C

H

CH

Cont

C

6.71

6.76

7.22

6.99

6.57

3.28 .38 2.90

3.34 .47 2.86

2.76 .43 2.33

2.52

2.14

2.26

3.31 .52 2.79 2.14

3.10 .45 2.65 2.44

51.7 57.3 10.8 62.5 5.47 2.24 1.89 59.8 65.5

50.7 57.8 17.3 68.0 4.50 1.60 1.56 64.3 64.9

61.9 67.9 6.5 68.4 5.61 1.66 1.70 70.7 69.4

53.6 60.9 16.1 69.6 5.05 1.64 1.60 68.3 68.6

52.9 59.7 9.9 62.8 4.60 1.62 1.55 64.9 66.3

H

CH

SE

Effectb

6.69

7.15

6.92

.020

S,T,f*s

3.04 .49 2.56 2.10

3.25 .55 2.70

3.26 .55 2.71

,258 ,041 ,227

-

2.37

2.12

,206

s

54.4 61.7 14.0 68.4 3.83 1.18 1.24 69.0 67.6

54.6 62.3 12.4 67.0 4.95 1.47 1.49 70.4 69.8

52.8 60.7 16.5 69.3 4.39 1.37 1.32 69.0 69.8

3.72 3.26 2.98 2.97

S -

-

t S

_

-

,172 ,143

S f,s

3.48 2.88

S -

aCont = control; C = corn; H = soybean hulls. bEffect: f = forage source ( P < . l o ) ; S and s = supplementation ( P < .05 and .lo, respectively!; T and t = supplement type ( C versus H; P < .05 and .lo, respectively); Ps = forage source x supplementation interaction ( P c ,101.

feedstuff high in potentially degraded fiber, H. Whether sites of digestion varied similarly in Exp. 1 is unknown, although with ad libitum intake and faster particulate passage rate than in Exp. 2, greater differences between C and H might be expected in Exp. 1. Mixing corn and soybean hulls yielded sites of digestion that did not differ from the mean of C and H. Total tract OM digestibility was greater ( P < .05) with than without supplementation. In Exp. 1, compensatory differences in OM intake and digestibility between C and H resulted in similar digestible OM intake. This implies that energy intake with a fixed, restricted level of forage intake might be greater for H than for C. However, digestible OM intake in Exp. 2 (data not shown) was not greater ( P < .20) for H than for C, perhaps because of fewer adverse effects of C on fiber digestibility with the lower level of feed intake than in Exp. 1. Total duodenal N flow was less than N intake for all diets (Table 51, reflecting a net loss of N in the stomach. The range in differences between supplement treatments in N loss was greater for B than for 0 diets. For B, the least value was with C (7% of N intake), and the greatest was with H (31%). Total duodenal N flow was greater for C than for H with B, but less for C than for H with 0 (forage source x supplement type interaction; P < .lo). Similar, nonsignificant interactions were observed for duodenal flow of microbial ( P < .18) and feed N ( P < .12). Overall, with B, the C supplement promoted the most complete capture of fed N at the duodenum, whereas

recovery with 0 was greatest for H. The effect of supplementation ( P < .05) on duodenal microbial N flow resulted from the greater quantity of OM fermented with than without supplementation because microbial efficiency did not differ among diets. Our estimates of microbial efficiency are slightly less than those typically observed with high-forage diets. Factors that may have contributed to this finding include low feed intake and the ruminal digesta fraction from which bacterial cells were isolated. Broderick and Merchen ( 1992) summarized that estimates of duodenal flow of microbial N based on the ratio of nucleic acids:total N in bacterial cells isolated from ruminal fluid are lower than those based on the ratio in particle-associated cells. Furthermore, microbial N flow may be underestimated by use of the nucleic acid:total N ratio in bacterial cells when ruminal outflow of protozoa is significant (Broderick and Merchen, 1992). In contrast to no effect of supplement type or mixing of supplement types on duodenal microbial N flow in our experiment, microbial N flow at the abomasum in beef cows consuming low-quality fescue hay tended to be greater for supplementation with soybean hulls than with a corn-soybean meal mix (25% of the diet), and efficiency of microbial growth was slightly greater for the diet with soybean hulls (Highfill et al., 1987). That DMI tended to be less for the corn than for the soybean hulls diet in that study may partially explain the disagreement with results from our experiment. With 60% dietary bromegrass, a


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GALLOWAY ET AL.

Table 5. Nitrogen intake and disappearance and microbial efficiency for beef cattle consuming bermudagrass or orchardgrass hay supplemented with corn and(or) soybean hulls (Exp. 2) Bermudagrass

Orchardgrass

Item

Conta

C

H

CH

Cont

C

H

CH

SE

Effectb

Intake, gld Duodenal, g/d Total Microbial Ammonia Feed Fecal, g/d Disappearance, 570 Apparent ruminal True ruminal Postruminal Total tract

141.5

133.8

158.5

146.1

170.7

159.0

182.8

171.0

2.96

-

116.0 49.3 5.3 61.5 48.2

124.2 59.3 4.0 60.9

109.8 55.0 3.8 51.1

128.6 64.4 4.6 59.7

134.0 54.1 6.7 73.3

131.9 60.1 4.7 67.1

157.7 69.7 5.6 82.4

11.58 4.84 .78 7.60

Pt S

45.1

49.8

47.2

57.3

57.8

65.8

140.3 68.1 4.4 67.8 57.2

4.87

F

18.4 56.3 47.6 66.0

6.4 54.4 59.8 66.2

30.7 67.9 37.7 68.4

13.2 59.8 54.9 68.1

21.2 56.8 44.8 66.0

16.6 57.3 46.6 63.2

13.9 55.0 50.2 64.1

17.9 60.2 48.2 66.0

8.59 5.35 7.11 3.56

-

12.8

15.5

11.3

15.9

13.9

15.4

15.8

16.2

1.91

-

Microbial efficiencyC

S -

-

f*t

aCont = control; C = corn; H = soybean hulls. bEffect: F = forage source ( P e .05); S = supplementation ( P e .05); Pt = forage source x supplement type interaction ( P < ,101. CGrams of microbial nitrogenkilogram of OM truly fermented.

2 : l mixture of soybean hulls and corn resulted in greater duodenal flow of microbial N and lower apparent feed N flow than did soybean hulls or corn given separately or in a 1:2 mixture (Grigsby et al., 1993). The higher level of supplementation in that experiment than in our study may explain the difference in associative effects when soybean hulls and corn were supplemented together. Postruminal N digestibility was greater for C than for H with B, but less with 0 (forage source x supplement type interaction; P < . l o ) , at least partially because of coincident differences in duodenal flow of total N (Table 5 ) . Total tract N disappearance did not differ among diets. In contrast, Nakamura and Owen ( 1 9 8 9 ) observed lower CP digestibility for diets with soybean hulls versus corn, and suggested that rapid ruminal passage rate of soybean hulls increased hindgut microbial fermentation and fecal excretion of microbial N. In summary, our results suggest that with a moderate level of supplemental DE ( 2 0 kcaVkg of BW), corn and soybean hulls will elicit a similar increase in energy intake by growing ruminants consuming either moderate-quality, temperate or tropical grass forage because of compensatory differences in forage intake and fiber digestibility. The positive associative effect in digestible OM intake when corn and soybean hulls were mixed occurred with a level of corn that would not be expected to markedly decrease fiber digestibility. Thus, further research should be conducted to determine whether such changes resulted from decreasing the adverse effects of corn on fiber digestibility, or whether other factors, such as increased microbial colonization of newly ingested fiber, occurred when potentially degraded fiber was supplemented.

Implications These results suggest that supplementation of growing cattle consuming moderate-quality, tropical or temperate grass to appetite with a low to moderate level of digestible energy from corn or soybean hulls will increase digestible organic matter intake to the same extent. Greater changes may occur relative to no supplementation with tropical than with temperate grass. Mixing corn and soybean hulls may slightly increase digestible organic matter intake relative to the mean of each feedstuff supplemented separately. Differences between supplement types in acetate: propionate ratio in ruminal fluid seem unlikely with a moderate level of supplementation, and postruminal organic matter digestibility may be greater for supplementation with corn versus soybean hulls. Literature Cited Anderson, S. J., J. K. Merrill, M. L. McDonnell, and T. J. Klopfenstein. 1988. Digestibility and utilization of mechanically processed soybean hulls by lambs and steers. J. Anim. Sci. 66: 2965. AOAC. 1984. Official Methods of Analysis (14th Ed.). Association of Official Analytical Chemists, Arlington, VA. Brake, A. C., A. L. Goetsch, D. S. Hubbell, K. L. Hall, K. M. Landis, and K. F. Harrison. 1989. Intake, digestion and daily gain by cattle consuming bermudagrass hay and receiving concentrate supplements. Livest. Prod. Sci. 22:255. Broderick, G. A,, and J. H. Kang. 1980. Automated simultaneous determination of ammonia and total amino acids in ruminal fluid and in vitro media. J. Dairy Sci. 63:64. Broderick, G . A., and N. R. Merchen. 1992. Markers for quantifying microbial protein synthesis in the rumen. J. Dairy Sci. 75:2618. Chan, W. W., C. A. Hibberd, R. R. Scott, and K. Swenson. 1991. Corn LIS soybean hull supplements for beef cows fed low quality native range grass hay. p 172. Oklahoma Agric. Exp. Sta. MP134.


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