Effects of whole or ground corn with different forms of hay in 85% concentrate diets on digestion and passage rate in beef heifers

Animal Feed Science and Technology, 18 (1987) 151-164 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

151

Effects of Whole or Ground Corn w i t h D i f f e r e n t Forms of Hay in 85% C o n c e n t r a t e Diets on D i g e s t i o n and P a s s a g e Rate in B e e f Heifers* A.L. GOETSCH 2, F.N. OWENS', M.A. FUNK** and B.E. DORAN 1

'Oklahoma Agricultural Experiment Station, Oklahoma State University, StiUwater 74078 (U.S.A.) 2Arkansas Agricultural Experiment Station, University o[ Arkansas, Fayetteville 72701 (U.S.A.) (Received 12 August 1986; accepted for publication 24 February 1987)

ABSTRACT Goetsch, A.L., Owens, F.N., Funk, M.A. and Doran, B.E., 1987. Effects of whole or ground corn with different forms of hay in 85% concentrate diets on digestion and passage rate in beef heifers. A nim. Feed Sci. Technol. , 18: 151-164. Effects of physical forms of corn (whole or ground through a 3-mm screen) and prairie hay (coarsely chopped, long; ground through a 3.8-cm screen, medium; ground through a 4-mm screen, short) on digestion and passage rate in cannulated beef heifers (320.5 kg) fed 85% concentrate were determined. A 6 ><6 Latin-square experiment with 14-day feeding periods was conducted. Heifers were fed completely mixed diets at 12-h intervals at a rate of 70 g of dry matter per kg of body weight °'75 daily. Ruminal buffering capacity between pH 7.0 and 5.5 was higher (P < 0.05) for whole than for ground corn at 2 h after feeding, but roughage form did not affect buffering capacity. Ruminal organic matter digestion was lower and post-ruminal digestion was higher for whole than for ground corn with short and medium hays (corn- and hay-form interaction, P < 0.05). Long hay tended to lessen ruminal and elevate post-ruminal disappearance of organic matter with ground corn, but caused the opposite changes with whole corn. Ruminal starch disappearance tended to increase with increasing length of hay in whole-corn diets, while starch digestion in the rumen with ground corn tended to be higher with short than with medium or long hays. Postruminal starch digestion varied inversely with ruminal disappearance, maintaining constant total tract digestion within corn form. Total tract starch digestion was lower for whole than for groundcorn diets ( P < 0.05), because of similar trends for less digestion in the rumen and post-ruminal tract with whole corn. The physical form of roughage in diets with 85% concentrate altered the site of digestion in a different way with processed than with unprocessed corn. Inclusion of long hay in whole-corn-based diets presumably increased particle breakdown as compared with shorter forms of hay, resulting in less efficient digestion because of higher ruminal but constant total tract digestion. Conversely, increasing roughage length in ground-corn-based diets improved digestive *Journal article number 5032 of the Oklahoma Agricultural Experiment Station, Stillwater 72078. Approved for publication by the Director of the Arkansas Agricultural Experiment Station. **Present address: Department of Animal Sciences, University of Illinois, Urbana 61801.

0377-8401/87/$03.50

© 1987 Elsevier Science Publishers B.V.

152 efficiencyby decreasingruminal and increasingpost-ruminal digestion,possiblybecausepotentially digestiblesubstrate passed through the tureen more quickly.

INTRODUCTION

Forms of feed grains requiring little or no processing are of interest to minimize monetary, managerial and equipment inputs for the preparation of finishing-cattle diets. The form chosen is likely to be dictated by factors such as digestive efficiency, processing costs and accompanying management considerations. To evaluate these items properly attributes of the entire diet, not just those of grain, are required. The chemical and physical properties of different grain forms affect the relative dietary value by such factors as susceptibility to microbial attack, gut motility, saliva flow, eating time, re-mastication and ruminal digesta outflow rate. The quantity and characteristics, both physical and chemical, of dietary roughages moderate these conditions. Digestive function interactions between physical properties of roughage and grain are therefore likely. Whole corn is fermented in the rumen more slowly than processed corn (Galyean et al., 1979; Aguirre et al., 1984), so that rapid outflow of particles of grain from the rumen should decrease digestion more with whole than with processed corn ( Owens and Goetsch, 1986). Furthermore, large grain particles entering the intestines may not be digested completely (Kim and Owens, 1985; Ledoux et al., 1985). Whole corn promotes more mastication than processed corn (Galyean et al., 1979; Aguirre et al., 1984) though this is not sufficient for maximum ruminal or complete intestinal digestion. Processing corn increases total digestion of diets containing more than 20% roughage (NRC, 1984) with most of the increase occurring in the rumen (Galyean et al., 1979; Aguirre et al., 1984). However, concurrent increases in heat and gas losses ( NRC, 1985) and in rumen acidosis (Vance et al., 1972) occur. For best use of processed corn diets, the ruminal outflow rate of digesta with potential for intestinal digestion should be increased, but without sacrifice of total digestion. Increasing total tract digestion of whole-corn diets, either in the rumen or preferably in the small intestine, would improve animal performance. Therefore, the objectives of this study were to investigate the effects of hay form on digestive function in beef heifers fed 85% concentrate diets consisting mainly of ground or whole corn. MATERIALSAND METHODS Animals and diets

Six Hereford x Angus heifers (320.5 kg initial weight), cannulated in the rumen and duodenum, were used in a 6 X 6 Latin-square with a 2 X 3 factorial

153 TABLEI Composition of diets fed to beef heifers Ingredient

% dry matter

Corn (IFN 4-02-931) 1 Prairie hay (IFN 1-03-191 ) 2 Soybean meal ( IFN 5-20-637) Molasses ( IFN 4-04-696) Limestone (IFN 6-01-069) Trace mineralizedsalt3 Chromic oxide

72.00 15.00 10.00 1.45 0.75 0.50 0.30

Composition

Diet''2

Dry matter ( % air-dry) Ash ( % dry matter) Starch (% dry matter) Crude protein (% dry matter) Acid detergent fiber ( % dry matter)

GS

GM

GL

WS

WM

WL

90.4 4.8 50.4 12.1 8.4

90.7 4.7 50.3 11.9 8.8

90.5 4.8 50.4 12.2 8.4

89.6 4.2 51.4 11.8 8.6

89.9 4.4 51.4 12.2 8.3

89.9 4.5 51.4 12.8 8.4

1Corn: whole (W), ground through a 3-ram screen (G). 2Prairie hay: coarselychopped (long, L), ground through a 3.8-cm screen (medium, M), ground through a 4-ram screen (short, S). 3Trace mineralizedsalt contained minimum levels of 95% NaC1, 0.25% Mn, 0.2% Fe, 0.03% S, 0.033% Cu, 0.0025% Co, 0.007% I and 0.005% Zn. arrangement of treatments. Diets (Table I) were fed at a rate of 70 g of dry matter ( DM ) kg-o.75 of body weight. Corn was fed whole ( W ) or after grinding through a 3-mm screen in a hammermill (G). Prairie hay was chopped in a hammermill without a screen ( long, L ) , or ground through a 3.8-cm (medium length, M) or a 4-ram screen ( short, S). Chopping hay increased ease of handling and mixing, though long hay was similar to long-stemmed hay. Corn, supplement and prairie hay diet components were weighed individually, and hand-mixed thoroughly before each feeding. Animals were fed equal quantities of diet at 07.00 and 19.00 h daily. Meals were consumed in under 30 min. Feeds were sampled throughout the experiment, and composite samples were formed within period on an air-dry basis.

Sampling Periods lasted 14 days, with the first 10 days used for adaptation to the new diets and the last 4 days for sampling of digesta. On Day 10 at 19.00 h, 125 g (air-dry) of corn, labeled with ytterbium (Yb) ( Goetsch and Galyean, 1983 ) was mixed with the meal and fed. Corn in the whole form was labeled with Yb,

154 and a portion was ground through a 3-mm screen to be fed with ground-corn diets. At 2, 6 and 10 h after the 07.00 h feeding on Days 11 and 12, duodenal (200 ml) and fecal samples were obtained, and composites were constructed on a wet basis. Remaining feces and composite samples were dried in a forcedair oven at 55 ° C for 48 h, and air equilibrated for 24 h. Fecal grab samples were also obtained on Day 11 at 05.00 and 21.00 h, Day 13 at 07.00 and 19.00 h and Day 14 at 07.00, 19.00 and 06.30 h and were dried at 55 ° C. Individual fecal samples and composite feed, duodenal and fecal samples were ground through a 2-mm screen. At 07.00 h on Day 13, before the morning feeding, cobalt ethylenediaminetetraacetic acid (CoEDTA) in 100 ml deionized water (Uden et al., 1980; 544 mg Co) was dosed intraruminally. Ruminal fluid samples were taken 2, 6 and 10 h after Co dosing. The buffering capacity (Haaland et al., 1982) was measured for the 2 h samples from pH 7.0 to 3.0. The pH was also measured at each sampling time. Ruminal fluid (350 ml) taken at each sampling time was mixed with a saline-formalin solution for isolation of bacterial cells by differential centrifugation (Merchen and Satter, 1983 ). Pellets of isolated bacterial cells ( IBC ) were dried for 24 h at 55 ° C and crushed for mixing. The remaining ruminal fluid was acidified with 20% (v/v) H2S04 and frozen.

Laboratory analyses and calculations Composite samples of feed and duodenal and fecal digesta were analyzed for DM, ash, nitrogen (N; A.O.A.C., 1984), starch (MacRae and Armstrong, 1968), acid detergent fiber (ADF; Goering and Van Soest, 1970) and chromium ( Hill and Anderson, 1958). Duodenal digesta was assayed for nucleic-acid-N (NAN; Zinn and Owens, 1982) and ammonia-N (NHa-N; A.O.A.C., 1984). Isolated bacterial samples were analyzed for DM, N and NA-N. Digestion in the rumen and total digestive tract was determined from chromium intake and concentration in duodenal and fecal samples. Post-ruminal digestibility was estimated by difference. The N content and ratio of NA-N:N in IBC, and an assumption that microbial DM is 20% ash (Smith, 1975), were used to calculate true ruminal organic matter (OM) and N disappearances. Individual fecal samples were analyzed for DM and combusted. Ash was solubilized in acid (Ellis et al., 1982), and Yb content was determined by atomic absorption spectrophotometry. Passage rate of Yb was determined by regressing the natural logarithm of Yb content against time post-dosing. Samples before and at the time of peak marker concentration were omitted from analysis. Ruminal fluid was centrifuged at 10 000 × g for 10 min for analysis of NH~N (Broderick and Kang, 1980) and Co by atomic absorption spectrophotometry. Ruminal dilution rate of Co within a feeding cycle was determined by regression of Co concentration against sampling time. Ruminal fluid volume was estimated by dividing Co dose by the extrapolated Co concentration at zero time.

155

Statistical analysis Data were analyzed considering heifer, period and treatment in the statistical model. T r e a t m e n t was subdivided into effects of forms of corn and prairie hay and the interaction between these factors. When the interaction was not significant ( P < 0.05), the main effects of corn and hay forms were examined. Simple correlations were also calculated across all observations. RESULTS AND DISCUSSION

Ruminal conditions Ruminal pH was higher for heifers fed whole than ground corn at 2 ( P < 0.05) and 6 h ( P < 0.08) after feeding, but at 10 h post-feeding pH was similar (Table II). Roughage type did not affect pH in the rumen, duodenum or rectum ( P > 0.05 ). Duodenal pH was higher ( P < 0.05 ) for ground ( 2.60 ) than whole ( 2.51 ) corn and was not affected by hay form ( P > 0.10 ), while fecal pH tended to be lowest ( P < 0.14) for ground corn. Ruminal fluid ammonia-N concentration (mg d1-1) was similar for all diets; the range was 7.1-10.7 at 2 h, 3.0-7.3 at 6 h and 4.1-7.0 at 10 h after feeding. Buffering capacity was higher ( P < 0 . 0 5 ) for whole than for ground corn between pH 7 and 5.5 at 2 h after feeding (Table II), possibly indicating a greater flow of buffers in saliva (Haaland et al., 1982), primarily bicarbonate (Turner and Hodgetts, 1955), with whole corn. Slower entry of whole than ground corn into ruminal fermentation, with an accompanying low rate of vol-atile fatty acid production in early hours post-feeding, may have been involved. No differences were observed below pH 5.5 ( P > 0.05 ). In general, ground corn with medium length hay resulted in a lower buffering capacity than did short hay, whereas the buffering capacity between pH 7.0 and 5.0 was intermediate for ground corn with long hay. The buffering capacity ranking of roughage forms with whole corn changed with varying pH range. Hay form had little influence on buffering capacity 2 h after feeding, when buffering is most critical for animals fed high grain diets. With these conditions, greater protection from ruminal acidosis could not be achieved by increasing particle length of dietary roughage. Nucleic-acid-N content of IBC was not different ( P > 0 . 0 5 ) among diets ( Table II), but as a percentage of bacterial N ( not in tabular form ) NA-N was slightly higher than the 15-20% reported by Ellis and Pfander (1965). Nitrogen content of IBC was lower than the 8.16% reported by Smith (1975), and an interaction between corn and hay form was detected (P < 0.05 ), with N in IBC being higher for WM than WS and GM diets, and higher for the WL than WS diet ( P < 0 . 0 5 ) .

0.44 a 0. 57" 9.67 0.98 1.29 1.07 0.63 0.41

5.95 ab

1.38

0.41 ~ 0.47 b 0.60 0.90 1.22 1.03 0.66 0.38

5.84

6.05 6.17 6.37

GM

6-60 ~bc

1.47

0.43 ~ 0-54 ~h 0.65 0.93 1.20 1.10 0.59 0.31

5.90

6.20 6.39 6,80

GL

5.89 a

1.51

0.47 ~b 0.62 c 0,70 1.04 1.24 1.04 0.59 0.39

5.97

6.47 6.47 6.63

WS

7.67 c

1.85

0,468 0.59 ~ 0.69 0.96 1.21 1,08 0.75 0.32

6.11

6.33 6.42 6.53

WM

7,17 ¢

1.62

0.44

0.52 h 0.58 ~ 0.71 0.97 1.25 1.09 0.59

5.98

6.43 6.57 6,65

WL

0.425

0.189

0.018 0.027 0.030 0.043 0,063 0.056 0.054 0.055

0.129

0.105 0.139 0,136

SE 3

1.45

0.43 a 0,52 ~ 0,64 ~ 0.94 1.24 1.07 0.62 0.37

5.86

6.14 ~ 6.28 6.61

G

1.66

0.48 b 0.60 b 0.70 b 0.99 1.23 1.07 0.64 0.38

6.02

6.41 b 6.48 6.60

W

Corn form ~

1.51

0.45 0.60 0.68 1.01 1.27 1.05 0.61 0.40

5.91

6.33 6.38 6.66

S

1.61

0.44 0.53 0.65 0.93 1.22 1.05 0.70 0.35

5.98

6.19 6.29 6.45

M

Hay form ~

'Corn: whole ( W ) , ground t h r o u g h a 3-ram screen ( G ) . 2Prairie hay: coarsely chopped (long, L ) , ground t h r o u g h a 3.8-cm screen (medium, M ) , ground t h r o u g h a 4-ram screen (short, S ) . :*SE = standard error of the t r e a t m e n t m e a n based on 6 observations per t r e a t m e n t . 4Milliequivalents of hydrogen ions per 40 ml r u m e n fluid required for t h e p H change. ~An interaction existed between corn a n d h a y form ( P < 0.05). °'b'CMeans in a row within diet, corn- or hay-form groupings with different superscripts differ ( P < 0.05).

6.86abc

7.0-6.5 6.5-6.0 6.0-5.5 5.5-5.0 5.0-4.5 4.5-4,0 4.0-3.5 3.5-3.0

Buffering capacity

5.84

Nitrogen (% of dry m a t t e r ) ~

Mean

Fecal p H

6.18 6.28 6.69

1.50

2 6 10

Ruminal p H

GS

Diet ~,2

Nucleic acid-nitrogen ( % of dry m a t t e r )

Time after feeding ( h )

Item

1.54

0.47 0,56 0.68 0.95 1.23 1.09 0.59 0.37

5.94

6.31 6.48 6.72

L

Effects of corn a n d hay form on r u m i n a l a n d fecal pH, buffering capacity a t 2 h after feeding a n d isolated bacterial-cell composition in beef heifers fed high-concentrate diets

T A B L E II

~55

F.

157 TABLE III Effects of corn and hay form on ruminal-fluid dilution rate and volume and particulate passage rate in beef heifers fed high-concentrate diets Item

Diet 1'2

GS

SE 3

GM

GL

WS

WM

WL

Ruminal fluid dilution rate (% h -a) 10.8 9.0 10.0 11.0 1 0 . 1 1 0 . 4 Ruminal fluid volume (liters)4 44.9 46.7 62.5 46.5 46.3 40.9 Ruminal fluid outflow rate (litersh 1) 4.95 4.36 5.60 4.89 4.76 4.0I Particulate passage rate (% h 1) 3.5 3.7 4.0 2.9 3.4 3.5

Corn form 1

Hay form 2

G

S

1 . 2 9 9.9

W

1 0 . 5 10.9

M

L

9.6

10.2

4.95 0.534 4.97

4.55

4.92 4.56

4.81

0.30

3.3

3.2

3.8

3.7

3.5

'Corn: whole (W), ground through a 3-ram screen (G). 2Prairie hay: coarsely chopped ( long, L), ground through a 3.8-cm screen (medium, M), ground through a 4-ram screen (short, S). 3SE = standard error of the treatment mean based on six observations per treatment. tAn interaction existed between corn and hay form ( P < 0.06).

Passage rate Ruminal fluid dilution rate was higher t h a n expected with an 85% concentrate diet (Table III), but similar to values observed with a concentrate diet containing 6% pelleted alfalfa and 14% cottonseed hulls ( Goetsch and Owens, 1985 ). Fluid dilution rate was not affected by dietary particle forms, although an interaction between corn and hay form was detected for ruminal fluid volume ( P < 0.05; Table III). Long hay tended to elevate ruminal fluid volume with ground corn, but to depress volume with whole corn ( corn- and hay-form interaction, P < 0.05). This may have been due to more fiber accumulating in the rumen, as indicated by the trend towards inverse changes in ruminal ADF digestion and hay size (Table IV ). Ruminal fluid volume and ADF disappearance were correlated for the ground-corn diets only ( r = - 0.50; P < 0.04 ). Particulate passage rate was faster ( P < 0.07 ) for corn in the ground t h a n in the whole form (Table III). Longer retention of whole corn in the rumen may be attributable to the settling of intact grain in the ventral sac. In addition, the position in the rumen of masticated whole corn particles may lead t h e m to remain there longer t h a n corn ingested in the ground form, because differences in rate of hydration, specific gravity and properties lead to the adherence of fermentation gases. Passage rate of Yb-labeled corn tended to decrease with more extensive roughage processing with both corn forms. Perhaps the ruminal space occupied by roughage shortly after feeding rose as roughage size increased, thereby reducing space in the rumen available for concentrate, or

Organic matter Passage ( g d a y - 1 ) Intake Entering duodenum 4 Exiting rectum Digestion Apparent ruminal 4'5 True ruminal 4'5 Post-ruminal 4'S Post-ruminal 4'6 Total tract S Starch Passage ( g d a y - 1) Intake Entering duodenum Exiting rectum Digestion Ruminal S Post-ruminal S Post-ruminal ~ Post-ruminal v Total tract S

Item

67.5 27.5 82.5 a 71.1 95.0"

2548 876 128

54.6 63.0 26.7 56.4 81.3

5056 2356 939

GS

Diet 1'2

62.6 31.5 80.7 a 66.7 94.0 a

2548 997 151

53.6 62.3 26.1 53.3 79.7

5068 2406 1026

GM

62.8 30.8 78.3 ~ 67.3 93.6 ~b

2548 991 155

45.5 53.8 35.3 61.7 80.8

5056 2800 949

GL

52.7 34.9 68.9" 59.4 87.6 b

2591 1232 322

40.9 52.3 37.1 59.8 77.9

5039 2941 1109

WS

61.3 28.3 67.4 ~ 68.4 89.6 ab

2591 1053 270

42.3 49.9 36.2 59.0 78.5

5045 3007 1087

WM

Effects of corn and hay form on digestion in beef heifers fed high-concentrate diets

TABLE IV

68.4 19.3 43.4 b 78.4 87.7 b

2591 850 309

59.6 66.6 21.2 45.1 80.8

5042 2081 945

WL

5.53 5.04 6.89 5.73 1.55

143.8 38.7

4.98 4.69 4.51 3.98 1.35

257.3 72.5

SE 3

64.3 29.9 80.5 ~ 68.3 94.2 a

2548 955 145

80.6

972

5060

G

60.8 27.5 59.9 b 68.8 88.3 b

2591 1047 300

79.1

1047

5042

W

Corn form I

60.1 31.2 72.7 65.2 91.3

2570 1054 225

79.6

1024

5047

S

61.9 29.9 74.0 67.6 91.8

2570 1025 210

79.1

1057

5057

M

Hay form 2

65.6 25.1 60.8 72.8 90.7

2570 923 232

80.8

947

5049

L

Oo

249 46.4

8.5

10.8

168 61.7

46.6 23.6 64.2 70.2

45.7 25.0 67.0 70.7

467

85.9 27.0 54.1 4.8 30.5

95.1 34.4 54.8 5.9 30.2

447

101.1

103.2

268 40.6

448

13.0

34.1 36.3 71.3 70.4

108.7 34.0 67.6 7.1 30.1

103.4

294 29.8

450

17.0

32.3 35.5 70.5 67.7

109.9 37.4 64.7 7.7 31.3

99.7

198 53.2

435

16.3

24.1 44.1 71.7 68.2

119.9 34.0 79.4 6.4 31.8

102.9

155 63.5

441

9.7

55.0 18.4 62.4 73.5

84.4 29.1 49.4 5.9 28.1

108.4

46.0 10.23

2.80

8.96 7.71 2.63 2.20

9.13 5.05 8.44 0.88 1.68

228

454

10.8

216

442

14.3

69.8

6.7 30.4

5.9 30.3

70.4

33.5

103.6

31.8

102.5

231

449

13.9

69.2

6.8 30.8

35.9

101.4

224

451

12.4

69.2

5.6 31.1

30.5

102.0

ICorn: whole (W), ground through a 3-ram screen (G). 2Prairie hay: coarsely chopped (long, L), ground through a 3.8-cm screen (medium, M), ground through a 4-ram screen (short, S ). 3SE = standard error of the treatment mean based on six observations per treatment. 4An interaction existed between corn and hay form (P < 0.05 ). SPercentage of intake. SPercentage of available substrate. 7Percentage of total digestion. a,bMeans in a row, within diet, corn or hay form groupings with different superscripts differ ( P < 0.05).

Nitrogen Passage (g d a y - 1) Intake Entering duodenum Total 4 Microbial Feed 4 Ammonia Exiting rectum Disappearance Ruminal 4's Post-ruminal 4'5 Post-ruminal 4,8 Total tract s Microbial efficiency (g microbial nitrogen per kg organic matter fermented) Acid detergent fiber Intake (g d a y - l) Entering duodenum (gday-~) Ruminal digestion 4's 211

445

11.4

71.9

6.5 29.1

31.5

105.9

~D

160

perhaps increasing rumen motility, saliva flow and mastication with increasing roughage size were responsible.

Digestion An interaction between corn and roughage forms was detected for apparent and true digestion of OM in the rumen (Table IV, P < 0.05 ). Ruminal digestion tended to be greater for ground than for whole corn fed with short and medium hays. Turgeon et al. (1983) fed beef steers 90% concentrate diets with whole or cracked corn in ad libitum amounts, and noted that mminal digestion of cracked corn was lower than that of corn fed whole. In this trial, however, digestion of OM in the rumen with long hay tended to be lowest with ground corn, while with whole corn it tended to be highest. An interaction ( P < 0.05) between corn and hay form in post-ruminal disappearance of available OM was present, most likely as a result of an interaction in ruminal OM disappearance in the opposite direction. Starch digestion in the rumen tended to be depressed with long hay (Table IV). Ruminal starch disappearance with whole corn tended to increase with increasing particle size of roughage, as noted for OM. With ground corn, digestion in the rumen tended to be greater for short than for long or medium forms of hay. Particulate passage rate was negatively related to ruminal starch digestion with ground ( r = -0.45; P < 0.06) but not with whole corn diets. Totaltract starch digestion was lower ( P < 0.05) for whole than for ground corn in agreement with most reports (NRC, 1984). Post-ruminal starch digestion as a percentage of starch intake ranged from 18 to 33%, tending to be lowest for the WL diet. Post-ruminal digestion of available starch was higher ( P < 0.05) for corn fed after grinding, tended to decrease slightly as particle size of roughage increased, and was lowest ( P < 0.05 ) for the WL diet. Intestinal digestion of high-concentrate diets is thought to be limited primarily by the size and surface area of particles leaving the rumen (Kim and Owens, 1985), though fiber in the intestine may have an effect as well (Dunaif and Schneeman, 1981 ). The lower post-ruminal digestion of starch with ground corn with 2 of the roughage forms may have been due to larger particles of grain passing from the rumen with whole than ground corn. However, a correlation of - 0.36 (P < 0.03) between post-ruminal digestion of available starch and ruminal ADF digestion suggests that intestinal entry of larger fiber particles was associated with lower starch disappearance, possibly by increasing the rate of grain-particle passage. With ground-corn diets, ruminal disappearance of ingested N was higher, and post-ruminal disappearance was lower, for long than for short and medium hays (P < 0.05 ), while opposing trends were noted with whole corn ( corn- and hay-form interaction, P < 0.05; Table IV). The rate of ruminal N disappearance of soybean meal in situ increases with increasing pH ( Loerch et al., 1983), but the extent of N disappearance did not correlate with ruminal pH in this

161 study. About 60% of N consumed was from corn, and N-solubility of corn protein increases as pH declines, in contrast to the change in solubility of N in SBM as pH is varied ( Isaacs and Owens, 1972 ). Hence, the escape of corn and SBM protein from ruminal degradation may vary inversely to each other as pH changes. Treatment differences in ruminal, post-ruminal and total N disappearance resemble those of OM. High ruminal disappearance of N for the WL diet may be partially responsible for low post-ruminal disappearance of available N. Flow of MN to the duodenum was similar for all treatments, but interactions between corn and hay forms were noted for passage of total and fed N to the duodenum (Table IV). Microbial efficiency tended to be greater for whole than for ground corn, in agreement with Aguirre et al. (1984), and tended to decrease with increasing length of hay. An interaction in ruminal ADF digestion between corn and hay forms was detected (P<0.05; Table IV). Digestion of ADF in the rumen tended to be greater for ground than for whole corn with short hay, despite the trend for higher ruminal pH with whole corn at 2 and 6 h post-feeding. As might be expected if grinding of hay decreased ruminal retention of hay, ruminal ADF digestion tended to decrease as length of hay in ground-corn diets increased, but an opposite response was shown with whole corn. Hence, ADF was probably affected more by ruminal residence time than by pH. The tendency for greater ruminal ADF digestion of whole than of ground corn with 2 of the hay forms was probably responsible for the similarity of total-tract OM digestion for both forms of corn, despite a total-tract starch digestion that was greater for ground than for whole corn. DISCUSSION Feeding ground grain may create a more segmented type of ruminal fermentation than feeding whole or less processed grain, by increasing starch disappearance early after feeding which in turn delays the onset of fiber digestion. Preferential use of more readily available carbohydrate by fiber-digesting bacteria, greater proliferation of starch-digesting bacteria at the expense of fiberdigesting bacteria, or a direct postponement of the initiation of fiber digestion because of low pH may be involved ( Hoover, 1986). For maximal fiber digestion during a substantial starch fermentation, which occurs with diets high in processed grain, the particle size of roughage must be small, necessitating little mastication and maximizing the opportunity for attachment of fiber-degrading bacteria. With whole corn, the extent of ruminal fiber digestion may depend on the susceptibility of hay particles to rumen washout, and on the capacity of dietary roughage to stimulate rumination. Increasing the length of dietary roughage particles apparently increased ruminal washout of potentially-digestible corn to an extent that lowered rumen

162 digestion with ground but not with whole corn. Because size or surface area of whole corn particles in the rumen limits both the initiation and the rate of fermentation, mastication largely determines the extent of ruminal digestion (Galyean et al., 1981). Feeding hay in the long form with whole corn may therefore have lengthened eating time or re-mastication, leading to more disintegration of corn particles and greater susceptibility to rumen microbial fermentation and so increasing the extent of digestion. The range of size of cereal grain particles that can pass from the rumen is wide, owing to their nature after hydration and to the relatively large opening of the reticuloomasal orifice (Kim and Owens, 1985 ). A much larger change in the extent of digestion than in the ruminal passage rate of rare-earth-labeled corn could therefore have taken place. Higher levels of dietary roughage or ad libitum feeding might accentuate the effects of roughage form on particulate passage rate. Perhaps a level of roughage adequate to establish layering of digesta in the rumen is necessary to produce a marked effect on the rate of ruminal outflow of corn fed in the whole form. The physical form of grain could affect the roughage requirement for stratification because of differences in the rate of hydration and in specific gravity before, during and after hydration. These should affect the rate of descent of corn particles and the concurrent disturbance of floating particles high in fiber, as the particles of corn pass to the ventral rumen after being moved to the dorsal area by rumen-wall contractions. Differences in ruminal raft formation could not be quantified in this trial, since cannulae were small to prevent digesta loss during sampling. However, it is likely that the physical form of hay affects ruminal behavior of grain particles, even without the formation of a distinct high-fiber layer through changes in mastication. The changes observed in the site of digestion when the dietary ingredients were varied were assumed to be caused by differences in the physical characteristics of digesta particles, which affected the relative tendency towards ruminal digestion or towards exit. Grinding corn appears useful to maximize totaltract digestion of starch. If the ideal site of starch digestion is in the small intestine, it may be best to feed long roughage with ground corn, but ground roughage could be desirable in whole-corn diets because of an apparent cumulative lowering of post-ruminal digestion of starch as corn and hay particle sizes increased. Differences in intake level and in environmental conditions between this trial and field conditions may preclude unquestioning extrapolation of these data to production situations. Nonetheless, performance, and probably feed efficiency, of cattle fed ground-corn diets should be higher with long than with short and medium hays because of differences in the site of digestion. There may also be greater protection from ruminal acidosis when long hay is used. An additional response to differences in site of digestion should be that whole corn with short and medium hays would give a better performance than with long hay, although susceptibility to ruminal acidosis would probably not differ greatly. Overall, performance might be highest for ground corn with long hay,

163 l o w e s t f o r w h o l e c o r n w i t h l o n g h a y a n d i n t e r m e d i a t e f o r o t h e r diets, o w i n g t o similar total-tract OM digestion and a corresponding ranking of efficiency of d i g e s t i o n . F u t u r e r e s e a r c h s h o u l d e x a m i n e s u c h f a c t o r s as t h e s o u r c e a n d levels o f b o t h r o u g h a g e a n d g r a i n a n d t h e level o f f e e d i n t a k e .

REFERENCES Aguirre, E.O., Goetsch, A.L. and Owens, F.N., 1984. Corn grain processing and site of digestion by heifers. Oklahoma Agricultural Experiment Station, Miscellaneous Publication No. 116, pp. 190-193. Association of Official Analytical Chemists, 1984. Official Methods of Analysis, 14th edn., A.O.A.C., Washington, DC, pp. 152-157. Broderick, G.A. and Kang, J.H., 1980. Automated simultaneous determination of ammonia and total amino acids in ruminal fluid and in vitro media. J. Dairy Sci., 63: 64-75. Dunaif, G. and Schneeman, B.O., 1981. The effect of dietary fiber on human pancreatic enzyme activity in vitro. Am. J. Clin. Nutr., 34: 1034-1035. Ellis, W.C. and Pfander, W.C., 1965. Rumen microbial polynucleotide synthesis and its possible role in ruminant nitrogen utilization. Nature (London), 205: 974-975. Ellis, W.C., Lascano, C., Teeter, R. and Owens, F.N., 1982. Solute and particulate flow markers. In: F.N. Owens (Editor), Proceedings: Protein Requirements for Cattle: Symposium. Oklahoma Agricultural Experiment Station, Miscellaneous Publication No. 109, pp. 37-56. Galyean, M.L., Wagner, D.G. and Owens, F.N., 1979. Corn particle size and site and extent of digestion by steers. J. Anim. Sci., 49: 204-210. Galyean, M.L., Wagner, D.G. and Owens, F.N., 1981. Dry matter and starch disappearance of corn and sorghum as influenced by particle size and processing. J. Dairy Sci., 64: 1804-1812. Goering, H.K. and Van Soest, P.J., 1970. Forage Fiber Analyses. Apparatus, Reagents, Procedures and Some Applications, A.R.S., U.S.D.A. Agricultural Handbook No. 379, Washington, DC, pp. 1-20. Goetsch, A.L. and Galyean, M.L., 1983. Ruthenium phenanthroline, dysprosium and ytterbium as particulate markers in beef steers fed an all-alfalfa hay diet. Nutr. Rep. Int., 27: 171-178. Goetsch, A.L. and Owens, F.N., 1985. Effects of sampling site on passage rate estimates in heifers fed alfalfa hay or a high concentrate diet. J. Dairy Sci., 68: 914-922. Haaland, G.L., Tyrell, H.F., Moe, P.W. and Wheeler, W.E., 1982. Effect of crude protein level and limestone buffer in diets fed at two levels of intake on rumen pH, ammonia-nitrogen, buffering capacity and volatile fatty acid concentration of cattle. J. Anim. Sci., 55: 943-950. Hill, F.N. and Anderson, D.L., 1958. Comparison of metabolizable energy determinations with growing chicks. J. Nutr., 64: 587-603. Hoover, W.H., 1986. Chemical factors involved in ruminal fiber digestion. J. Dairy Sci., 69: 2755. Isaacs, J. and Owens, F.N., 1972. Protein soluble in rumen fluid. J. Anim. Sci., 35:267 (abstract). Kim, Y.K. and Owens, F.N., 1985. Starch digestion by feedlot cattle: Influence of roughage and intake level and particle size. Oklahoma Agricultural Experiment Station, Miscellaneous Publication No. 109, pp. 298-302. Ledoux, D.R., Williams, J.E., Stroud, T.E., Garner, G.B. and Paterson, J.A., 1985. Influence of forage level on passage rate, digestibility and performance of cattle. J. Anim. Sci., 61: 1559-1565. Loerch, S.C., Berger, L.L., Gianola, D. and Fahey, G.C., 1983. Effects of dietary protein source and energy level on in situ nitrogen disappearance of various protein sources. J. Anim. Sci., 56: 201-216. MacRae, J.C. and Armstrong, D.G., 1968. Enzyme method for determination of alpha-linked glucose polymers in biological materials. J. Sci. Food Agric., 19: 578-581.

164 Merchen, N.R. and Satter, L.D., 1983. Digestion of nitrogen by lambs fed alfalfa conserved as baled hay or as low moisture silage. J. Anim. Sci., 56: 943-951. National Research Council, 1984. Nutrient Requirements of Beef Cattle, 6th edn., National Academy Press, Washington, DC. National Research Council, 1985. Ruminant Nitrogen Usage, National Academy Press, Washington, DC, pp. 37-45. Owens, F.N. and Goetsch, A.L., 1986. Digesta passage rate and microbial protein synthesis. In: L.P. Milligan, W.L. Grovum and A. Dobson (Editors), Control of Digestion and Metabolism in Ruminants. Prentice Hall, Englewood Cliffs, NJ, pp. 196-223. Smith, R.H., 1975. Nitrogen metabolism in the rumen and the composition and nutritive value of nitrogen compounds entering the duodenum. In: I.W. McDonald and A.C .I. Warner (Editors), Digestion and Metabolism in the Ruminant. University of New England Printing Unit, Armidale, New South Wales, pp. 399-415. Turgeon, O.A., Brink, D.R. and Britton, R.A., 1983. Corn particle size mixtures, roughage level and starch utilization in finishing steer diets. J. Anim. Sci., 57: 739-749. Turner, A.W. and Hodgetts, V.E., 1955. Buffer systems in the rumen of sheep. II. Buffering properties in relationship to composition. Aust. J. Agric. Res., 6: 124-144. Uden, P., Colucci, P.E. and Van Soest, P.J., 1980. Investigation of chromium, cerium and cobalt as markers in digesta rate of passage studies. J. Sci. Food Agric., 31: 625-632. Vance, R.D., Preston, R.L., Klosterman, E.W. and Cahill, V.R., 1972. Utilization of whole shelled and crimped corn and varying properties of corn silage by growing-finishing steers. J. Anim. Sci., 35: 598-605. Zinn, R.A. and Owens, F.N., 1982. A rapid procedure for microbial protein estimation. In" F.N. Owens (Editor), Protein Requirements of Cattle: Symposium. Oklahoma Agricultural Experiment Station, Miscellaneous Publication No. 109, pp. 26-30.