Forage Intake and Performance by Beef Heifers Grazing Cool-Season Pasture Supplemented with De-Oiled Rice Bran or Corn

The Professional Animal Scientist 20 (2004):394–400

Forage Intake and Performance by Beef Heifers Grazing Cool-Season Pasture Supplemented with De-Oiled Rice Bran or Corn M. S. GADBERRY*, PAS, P. A. BECK†, PAS, and S. A. GUNTER†,1, PAS *University of Arkansas, Cooperative Extension Service, Little Rock 72203 and †University of Arkansas, Southwest Research and Extension Center, Hope 71801

Abstract The effects of de-oiled rice bran (DORB) and/or corn supplementation on forage intake and performance by replacement beef heifers grazing winter-annual pasture was evaluated in two trials. In Trial 1, 60 crossbred heifers (189 ± 3.8 kg) were randomly assigned to one of six 5.1-ha pastures. Treatments included one of the following: 1) DORB, 2) 1:1 (wt:wt) DORB plus corn (DORB + C), or 3) corn; all were fed at 1% BW (DM basis). Heifer BW and ADG did not differ (P=0.30) among treatments on any date. In addition, breeding date (calving date − 283 d) was not affected by treatment (P=0.64). In Trial 2, 12 crossbred heifers (234 ± 5.7 kg) were used to determine the effects of the supplements on forage intake and digestibility. The treatments were the same as Trial 1 plus a fourth non-supplemented control. Predicted forage OM intake was greatest for heifers on the control treatment (6.0 kg/d) and the corn treatment (5.6 kg/d) and was least (P<0.05) for heifers on the DORB + C (4.0 kg/d) and DORB (3.9

1

To whom correspondence should be addressed: [email protected]

kg/d) treatments. Forage OM digestibility was less (P<0.05) for heifers fed the corn treatment compared with those fed the control, DORB + C, and DORB treatments (68.0, 77.1, 73.1, and 75.6%, respectively). Total digestible OM intake was greatest (P<0.05) for heifers fed the corn treatment (5.7 kg/d) and least for heifers fed the DORB treatment (3.9 kg/d). Supplement effects on forage OM intake and digestibility did not fully explain the similarities in performance. Based on these results, the effect of supplementing forages with DORB warrants further investigation. (Key Words: Beef Cattle, Heifers, De-Oiled Rice Bran, Corn, Supplementation.)

Introduction Grazing annual cool-season pasture is an alternative to hay-based winter-feeding programs for stocker cattle or replacement heifers. However, in a grazing-based system, land resources dictate trade-offs between carrying capacity and animal performance. During periods when forage availability is limited because of plant growth, supplementing grazing cattle may be-

come necessary to achieve targeted rates of gain. Co-product feeds such as wheat middlings, soybean hulls, and corn gluten feed are commonly utilized alternatives to grain. One beneficial effect of many co-product feedstuffs, as compared with corn, is less starch content and greater digestible fiber content, which compliment foragebased programs (Poore et al., 2002). However, despite the differences in sources of energy, starch vs fiber, similarities in animal performance and effects on stocking rate have been observed (Horn et al., 1995). De-oiled rice bran (DORB) is a readily available co-product of the rice milling industry in the South Central US. However, there is limited research on the performance of beef cattle supplemented with rice milling co-products (Forster et al., 1994). The objectives of these studies were to evaluate the effects of DORB or cracked corn supplements on the performance of growing heifers grazing cool-season annual grasses and the effects of these supplements on forage intake and digestibility.

Materials and Methods Trial 1. The purpose of this study was to evaluate the perfor-

Cool-Season Pasture Supplementation

mance of growing replacement heifers grazing cool-season annual grass and supplemented with DORB or corn. Sixty crossbred heifers (189 ± 3.8 kg) were randomly assigned to one of six, 5.1-ha pastures located at the University of Arkansas, Southwest Research & Extension Center. Pastures consisted of Southern States 535 wheat (Triticum aestivum L.) and Marshall annual ryegrass (Lolium multiflorum Lam.) no-till drilled into a warmseason grass sod of bermudagrass (Cynodon dactylon [L.] Pers.) and dallisgrass (Paspalum dilatatum Poir.). Wheat and annual ryegrass (100.8 and 22.4 kg/ha) were planted into Ora fine sandy loam soil (Hoelscher and Laurent, 1979) beginning October 22, 2001. A 17-17-17 (N, P, and K percentages, respectively) blended fertilizer was applied December 13 at a rate of 336 kg/ha. In addition, 168 kg/ha of ammonium nitrate were applied February 21. Grazing was initiated on December 11 and terminated on April 22. Each of the six pastures was randomly assigned to one of three supplement treatments. Supplements were as follows 1) DORB, 2) 1:1 (wt:wt, as-fed basis) DORB plus corn (DORB + C), or 3) corn. Supplements were fed at 1% BW (DM basis), and the blended feed used in the DORB + C supplement was achieved by feeding the commodities sequentially. Heifers were fed in groups, adjusting feeding rate to accommodate feeding 6 d/wk. Heifers were weighed monthly, and supplemental feeding was adjusted accordingly. Heifers were also provided complete mineral mix; 15% Ca, 7% P, 5% Mg, 1% S, 14% NaCl, 1000 ppm Mn, 2355 ppm Fe, 1250 ppm Cu, 3000 ppm Zn, 26 ppm Se, 20 ppm Co, 25 ppm I, 661,500 IU vitamin A, 66,150 IU vitamin D, and 221 IU vitamin E (Sunbelt Custom Minerals; Sulphur Springs, TX), which contained 1764 g lasalocid/metric ton and was topdressed on the supplemental feed

daily. Hay was offered for ad libitum consumption. Forage availability was estimated monthly by rising plate meter (Michell and Large, 1983) beginning in January. Twenty height measures were taken from each pasture. The rising plate meter was calibrated by clipping the forage within a 4.72- × 4.72-cm square at three locations in each pasture, representing a low, moderate, and high meter reading. To determine whether potential quality differences in pasture treatments existed as a result of the differences in live vs dead plant material, in January and February, each point measured by the rising plate was also visually appraised for percent of living vs dead plant material. At the conclusion of the grazing period, the heifers were comingled and were exposed to three bulls throughout a 60-d breeding season. Pregnancy results, via rectal palpation, and calving records were used to evaluate the effects of supplemental feeding on pregnancy rates and conception date. Trial 2. Twelve crossbred heifers (234 ± 5.7 kg) were used to determine the effects of supplement type on forage intake and digestibility. Heifers were randomly assigned to one four treatments: 1) no supplement (control), 2) DORB, 3) DORB + C, or 4) corn. All were fed at 1% BW (DM basis). Heifers were the experimental unit and were separated each morning and supplemented individually; then, heifers were comingled while grazing. The 3.2-ha pasture was managed as described in Trial 1. On d 7 of the 14-d study, heifers were dosed with Yb. The Yb dose consisted of 2.5 g ytterbium chloride weighed into gelatin capsules (Torpac威, lock ring, #10; Pharmacopeia, Princeton, NJ). Fecal samples were collected 4, 8, 12, 16, 20, 24, 30, 36, 48, 54, 60, and 72 h after dosing to estimate rate of passage and fecal output (Krysl et al., 1985). After collection, feces were

395

dried in a forced-air oven at 60°C. On d 14, a ruminally fistulated steer, adapted to grazing with the heifers, was evacuated of ruminal contents and allowed to graze for 30 min. After grazing, the fresh forage sample was collected and immediately frozen. In addition, on d 14, forage availability was determined as described in Trial 1. The masticate sample was lyophilized, and it, along with the supplement and fecal subsamples, was ground (2-mm screen), dried at 105°C for DM determination, and ashed at 500°C (AOAC, 1990). Masticate and supplement samples were analyzed for N as described by the AOAC (1990) and for NDF and ADF according to Goering and Van Soest (1970) (Table 1) at a commercial laboratory (Dairy One, Ithaca, NY). Ytterbium was extracted from fecal samples (Hart and Polan, 1984), and concentration was determined on a SPECTRO CIROS ICP (Agricultural Diagnostics Laboratory, Fayetteville, AR). Indigestible ADF was determined sequentially for supplement, forage (masticate), and pooled (within animal) fecal samples following 96-h in situ incubation (Vanzant et al., 2002) in ANKOM威 filter bags (ANKOM Technology, Macedon, NY). Total tract digestibilities for forage and fecal samples were determined by partitioning fecal output into the percentage derived from supplement and forage based on indigestible ADF content. Statistical Analysis. Forage availability prediction equations for rising plate data were generated by the REG procedure of SAS (SAS Inst., Inc., Cary, NC). Treatment effects on predicted available forage during the grazing study were analyzed as a repeated measure using the MIXED procedure (SAS Inst., Inc.). Percent live vs dead plant material and the number of round bales fed was analyzed by ANOVA. Heifer growth performance was analyzed using the MIXED procedure. Pasture was the random experimen-

396

Gadberry et al.

TABLE 1. Nutrient composition of forage masticate and supplements for Trials 1 and 2. Item

Masticatea

De-oiled rice bran

Cracked corn

(% of DM) CP ADF NDF IADF Ash

24.4 29.0 63.1 5.3 9.9

17.6 11.5 24.1 9.1 13.5

8.5 3.1 10.3 1.0 1.9

a

Masticate sample was collected from the rumen of a steer evacuated of ruminal contents before grazing in Trial 2 only.

tal unit, and the model included the main effect of treatment and random effect of pasture within treatment. Calving rate was analyzed by the FREQ procedure (SAS Inst., Inc.), and effect of treatment on breeding, Julian date (calving date − 283 d), was analyzed by the MIXED procedure. Individual heifer was the random experimental unit in Trial 2. Rate of passage was determined using the NLIN procedure (SAS Inst., Inc.) with an age-dependent, one-compartment model (Ellis et al., 1979). Analysis of variance was conducted for treatment effects on digestion kinetics, estimated fecal output, and predicted OM intake and digestion by the GLM procedure (SAS Inst., Inc.).

and bermudagrass mix pasture beginning in the spring with either corn (0.6% BW) or DORB (0.8 and 1.1% BW). In their study, calves supplemented with corn over an 84-d period had a significantly greater rate of gain (0.13 kg/d) as compared with calves supplemented with DORB, but rate of gain did not differ between the two levels of DORB. A significant treatment × time interaction occurred for pasture DM availability (Figure 1.) predicted

Trial 1. Despite a greater level of OM supplementation with corn and DORB + C treatments as compared with DORB, heifer weights did not differ (P=0.20) among treatments throughout the study (Table 2). Similarly, ADG did not differ (P>0.20) between treatments with means of 0.95, 0.82, and 0.73 kg/d for heifers on the DORB, DORB + C, and corn treatments, respectively. Forster et al. (1994) supplemented calves grazing an endophyte-infected tall fescue, clover,

from the calibrated rising plate meter (R2 = 0.95). Heifers receiving the corn supplement had less (P≤0.05) available pasture forage than the DORB or DORB + C supplemented heifers in January, February, and March. Forage availability did not differ (P>0.20) between the DORB and DORB + C supplemented pastures in January or February; however, in March and April, the DORB+ C supplemented pastures had more (P≤0.05) available forage than the DORB-supplemented pastures. Percent live vs

TABLE 2. Effects of de-oiled rice bran and corn supplementation on performance of heifers grazing winter-annual pasture (Trial 1). Treatmenta,b Item

Results and Discussion

Figure 1. Forage availability for heifers grazing winter-annual pastures in Trial 1 that were supplemented with corn, de-oiled rice bran and corn (1:1, wt/wt; DORB + C), or DORB at 1% BW (DM basis).

Corn

DORB + C

BW December 11 January 10 February 13 March 27 April 22 ADG December to January January to February February to March March to April Overall

DORB

SE

200.6 226.9 261.2 290.7 321.4

5.9 6.4 8.7 11.3 12.2

(kg) 204.6 220.5 244.7 271.8 298.5 0.53 0.71 0.65 1.07 0.73

199.1 219.3 251.8 276.6 303.7 0.67 0.95 0.59 1.08 0.82

0.87 1.01 0.70 1.23 0.95

0.07 0.16 0.06 0.13 0.08

a Treatments consisted of corn, de-oiled rice bran and corn (DORB + C), and DORB fed at 1% BW (DM basis). b Least squares means within rows did not differ (P<0.10).

Cool-Season Pasture Supplementation

dead plant material (data not shown) did not differ among treatment pastures (P=0.69). The lesser forage availability for heifers grazing the corn pastures might have resulted in similar animal performance, despite greater levels of OM contained within the corn treatment as compared with the OM content of the DORB treatment (Table 1). Based on NRC (1996) models, if initial pasture mass exceeds 1150 kg/ha or if forage availability is ≥4 × DMI, forage availability is not expected to limit intake. Pasture mass in January exceeded 1150 kg/ha. Heifers on the corn treatment had a mean daily forage DM allowance of 2659 g/kg shrunk BW (SBW) from January through April ([1000 g/kg × 5.1 ha × 1413 kg/ha] ÷ [271 kg SBW × 10 calves]). Therefore, based on forage availability, the performance of heifers grazing pastures on the corn treatment would not have been limited because of standing herbage mass. Supporting this conclusion, the number of round hay bales offered did not differ between groups (P= 0.39) and averaged 10.2 ± 0.31 bales. In the case of limited pasture intake for the corn treatment, hay consumption and hay fed would theoretically be greater. Alternatively, differences in forage mass could also have been attributed to differences in treatment effects, where DORB would have resulted in a greater substitution ratio than corn. Calving rate differed by treatment (P<0.01). For the DORB, DORB + C, and corn treatments, percentages of heifers that calved were 95, 50, and 80%, respectively. The lesser calving percentages for heifers on the DORB + C treatment compared with the calving rate of heifers on DORB or corn treatments alone would suggest that the supplement was not directly responsible for the low calving rate. The reason for the low calving percentage for heifers on the DORB + C supplement is unknown and may

be an artifact of having a small sample size (20 head per treatment) in which 1 heifer represents 5% of the sample. The breeding date for heifers that calved was not affected by supplemental feed (P=0.64) and averaged d 131 (May 11) ± 4.4 d. Trial 2. Passage rate and mean retention time in the gastrointestinal tract did not differ (P>0.15) between treatments (Table 3). Time from marker dose to first appearance in the feces was 30% faster (P<0.05) for heifers on the corn treatment than for heifers on the DORB, DORB + C, and control treatments. Fecal OM output was not different (P>0.05) between heifers on the DORB and corn treatments, but was significantly greater (P<0.05) than the fecal output from heifers on the control and DORB + C treatments. Predicted forage OM intake was similar for heifers on the control (6.0 kg/d) and corn (5.6 kg/d) treatments and was greater (P<0.05) than the forage OM intake for heifers on the DORB + C and DORB treatments. Corn supplementation did not change forage OM intake as compared with the control treatment. As a result, heifers on the corn treatment had the greatest (P<0.05) total OM intake (7.6 kg/d) compared with the other three groups. Based on these observations, the greater OM intake of heifers on the corn treatment explained the lesser forage DM availability observed in Trial 1. Total OM intake did not differ (P>0.50) among heifers on the control, DORB + C, and DORB treatments. Organic matter digestibilities of the three supplements differed (P<0.001) and were 94.3, 74.7, and 51.9%, for the corn, DORB + C, and DORB supplements, respectively. Forage OM digestibility was less (P<0.05) for the corn treatment as compared with the control, DORB + C, and DORB treatments: 68.0, 77.1, 73.1, and 75.6%, respectively. The DORB + C treatment suppressed total tract forage OM digestibility by four percentage units

397

(73.1 and 77.1% for DORB + C and control, respectively). The total tract OM digestibility of the forage for the DORB treatment (75.6%) did not differ (P>0.10) from the control or DORB + C treatments. Total tract OM digestibility for the total diet did not differ (P>0.10) between the control (77.1%) and corn (75.0%) treatments, and total tract OM digestibility did not differ (P=0.26) between the corn and DORB + C (73.6%) treatments. The total tract OM digestibility of the DORB treatment (68.2%) was the least of all treatments (P<0.05). Total digestible OM intake was greatest (P<0.05) for heifers on the corn supplement (5.7 kg/d) and least (P<0.05) for heifers on the DORB supplement (3.9 kg/d). The digestible OM intake of the control (4.7 kg/d) and DORB + C (4.4 kg/d) treatments did not differ (P>0.10). Because OM intake was greater with the corn supplement compared with the DORB supplement, suppression of forage fiber digestibility and increased OM intake with starch supplementation for the corn treatment could have resulted in the similarities in performance observed during the performance study. Ruminal disappearance rate and effective degradability of N has been shown to be high with coolseason forages (Vogel, 1988; Coblentz et al., 2001). Lake et al. (1974) suggested that an improvement in performance of calves grazing irrigated ryegrass pasture and supplemented with energy from corn was the result of more efficient N utilization. However, starch supplementation has been implicated to suppress forage intake and digestibility (Chase and Hibberd, 1987; Olson et al., 1999). Studies have indicated that when there is sufficient ruminally degraded protein, the negative associative effect of starch supplementation on forage intake should not be apparent (Bodine et al., 2001). The similarity in forage intake between heifers on

398

Gadberry et al.

TABLE 3. Effect of de-oiled rice bran and corn supplementation on digestion parameters and predicted intake of heifers grazing winter-annual pasture (Trial 2). Treatmenta Item Digestion kineticsb K0, µg Tau, h K1, %/h GMRT, h FOc, g/h OM intaked, kg/d Supplement Forage Total % of BW OM digestibility, % Supplement Forage Total CP intake, kg/d Digestible OM intake, kg/d

Control

Corn

DORB + C

DORB

SE 1136.6 0.4 0.4 1.0 5.0

19,602.5e 7.3e 6.2 26.7 58.0e

14,228.2f 4.9f 6.4 23.8 79.2f

17,095.5ef 6.7e 6.6 24.7 66.3e

15,035.2f 7.1e 7.3 23.6 76.0f

6.0e 6.0e 2.7e

2.0 5.6e 7.6f 3.4f

2.0 4.0f 6.0e 2.5e

1.8 3.9f 5.7e 2.4e

0.08 0.31 0.34 0.18

94.3h 68.0g 75.0ef 1.53e 5.7e

74.7i 73.1f 73.6f 1.25f 4.4f

51.9j 75.6ef 68.2g 1.26f 3.9g

1.2 1.0 0.8 0.08 0.23

e

77.1 77.1e 1.48ef 4.7f

a Treatments consisted of non-supplemented controls and supplements of corn, de-oiled rice bran and corn (DORB + C), and DORB fed at 1% BW (DM basis). b Digestion parameters: K0 = initial concentration of marker in the compartment, tau = time from dose to first appearance of marker in the feces, K1 = particulate rate of passage, and GMRT = mean resident time in the gastrointestinal tract. c Fecal output (FO) estimated from dose/K0. d Predicted from FO and indigestible ADF of masticate, supplements, and fecal samples. e,f,g Least squares means within rows with uncommon superscripts differ (P<0.05). h,i,j Least squares means within rows with uncommon superscripts differ (P<0.01).

the control and corn supplements might have been due, in part, to the high CP (24% DM) concentration of the grazed forage (Table 1). However, Klevesahl et al. (2003) found that increasing ruminally degraded protein improved total tract NDF digestibility; however, the negative effect of starch supplementation on forage OM intake was never completely alleviated. Elizalde et al. (1999) noted that the effects of corn supplementation on forage intake and digestion generally focus on low quality forages. When evaluating the effects of corn supplementation on fresh-cut alfalfa, they found a 0.69 substitution ratio (units of change in forage OM intake per unit of increase in supplement OM intake) for alfalfa with corn, but estimated for-

age total tract digestibility was unaffected by corn supplementation. Cravey et al. (1992) found a similar substitution ratio, 0.88 and 0.84, for calves grazing wheat pasture and supplemented with either a high starch (corn) or high fiber (soybean hulls) supplement, respectively. Despite the high substitution ratio observed in these studies, corn supplementation did not influence predicted forage intake as compared with the control treatment in the present study, but it did reduce forage total tract OM digestibility. Based on the results of Trial 2, greater total OM intake and digestibility with the corn supplement heifers on the corn supplement, in Trial 1, would be expected to out-perform heifers on the DORB supplement.

There was a tendency for CP intake to be affected by treatment (P=0.07). Total CP intake was greatest for heifers on the corn supplement (1.53 kg/d) and least for heifers on the DORB + C (1.25 kg/d) and DORB (1.26 kg/d) treatments. Crude protein intake for the control group (1.48 kg/d) did not differ (P>0.10) from any supplement group. Despite corn being less in CP (Table 1) than DORB, heifers fed the corn supplement had a greater total CP intake as a result of greater forage intake. Supplementing high protein forages with feedstuffs, such as DORB, which contain less starch and more protein as compared with corn, wheat, and sorghum, may lead to concerns with excessive ammonia production in the rumen. Excess

Cool-Season Pasture Supplementation

ammonia may lead to reductions in feed intake (Conrad et. al., 1977; Choung et. al., 1990) to alleviate potential effects of ammonia toxicity. The effects of ammonia on intake were shown to be related to greater ruminal pH, allowing more ammonia to be absorbed from the rumen as opposed to a lesser ruminal pH, which traps ammonia within the rumen (Kertz et al., 1982, 1983). In the study of Forster et al. (1994), peak ruminal ammonia nitrogen concentrations were greater with defatted rice bran and wheat middlings than with nonsupplemented and corn-supplemented mature beef cows fed equal portions of alfalfa, orchardgrass, and bermudagrass hay. Neither ruminal pH nor total OM intake differed among control, corn, and defatted rice bran treatments; however, cows were limit fed hay in that study. The high CP of the DORB supplement, along with lesser OM intake and OM digestibility in the present study, might have allowed a greater ruminal ammonia concentration that could more readily diffuse across the rumen wall, therefore, leading to a reduction in forage intake as compared with the controls. However, this would not explain the reduction in forage OM intake of heifers on the DORB + C supplement. Studies by Goetsch et al. (1993) suggested that high ruminally degraded protein supplements (soybean meal) do not have a detrimental effect on intake when fed with moderate- to high-protein forages. Similarly, Nicholson et al. (1992) observed no effect of ruminally degraded protein supplements on intake despite increased blood ammonia levels with urea supplementation; blood ammonia was not affected by soybean meal supplementation. Therefore, the observed reduction in forage OM intake in the present study is likely only a substitution effect. High blood urea and/or ammonia N has been indicated to cause a

reduction in conceptions rates (Visek, 1982). There was no difference in calving rate between heifers on the DORB and corn supplements. The similarity in calving rate was interpreted as 1) an offset in forage intake during the study that was sufficient to prevent excessive blood urea and/or ammonia N to interfere with reproduction or 2) no residual effect from supplementation into the breeding season (supplementation ceased before the breeding season).

Implications Calves grazing high quality pasture and supplemented at 1% BW (DM basis) with DORB may perform similarly to calves supplemented with corn. Similarities in performance between corn and DORB supplementation in the present study may be the result of the effects of high starch supplementation on forage intake; however, predicted forage intake of heifers supplemented with corn in the intake study did not differ from controls despite a reduction in forage digestibility with corn supplementation. Based on these results, the effects of supplementing forages with DORB warrants further investigation.

Acknowledgments Appreciation is expressed to Patrick Capps for assisting with sample collection and analysis and to Riceland Foods, Inc. (Stuttgart, AR) for donation of the DORB.

Literature Cited AOAC. 1990. Official Methods of Analysis. (15th Ed.). Assoc. Offic. Anal. Chem., Arlington, VA. Bodine, T. N., H. T. Purvis, and D. L. Lalman. 2001. Effects of supplement type on

399

animal performance, forage intake, digestion, and ruminal measurements of growing beef cattle. J. Anim. Sci. 79:1041. Chase, C. C., Jr., and C. A. Hibberd. 1987. Utilization of low-quality native grass hay by beef cows fed increasing quantities of corn grain. J. Anim. Sci. 65:557. Choung, J. J., D. G. Chamberlain, P. C. Thomas, and I. Bradbury. 1990. The effects of intraruminal infusions of urea on the voluntary intake and milk production of cows receiving grass silage diets. J. Dairy Res. 57:455. Coblentz, W. K., K. P. Coffey, J. E. Turner, D. A. Scarborough, J. S. Weyers, K. F. Harrison, Z. B. Johnson, L. B. Daniels, C. F. Rosenkrans, Jr., and D. W. Kellogg. 2001. Ruminal nitrogen disappearance from sodseeded cereal grain forages in Northern Arkansas. Anim. Feed Sci. Technol. 89:17. Conrad, H. R., C. A. Bailey, and J. Mayer. 1977. Changing meal patterns and suppression of feed intake with increasing amounts of dietary non-protein nitrogen in ruminants. J. Dairy Sci. 60:1725. Cravey, M. D., G. W. Horn, F. T. McCollum, and P. A. Beck. 1992. Effect of highstarch versus high-fiber energy supplements on forage intake of steers grazing wheat pasture. J. Anim. Sci. 70 (Suppl. 1):89(Abs.). Ellis, W. C., J. H. Matis, and C. Lascano. 1979. Quantitating ruminal turnover. Fed. Proc. 38:2702. Forster, L. A., Jr., A. L. Goetsch, D. L. Galloway, Sr., W. Sun, A. R. Patil, and Z. B. Johnson. 1994. Digestion characteristics, feed intake and live weight gain by cattle consuming forage supplemented with defatted rice bran or other feedstuffs. Anim. Feed Sci. Technol. 47:259. Elizalde, J. C., N. R. Merchen, and D. B. Faulkner. 1999. Supplemental cracked corn for steers fed fresh alfalfa: I. Effects on digestion of organic matter, fiber, and starch. J. Anim. Sci. 77:457. Goering, H. K., and P. J. Van Soest. 1970. Forage fiber analysis (apparatus, reagents, procedures, and some applications). Agric. Handbook No. 379. ARS-USDA, Washington, DC. Goetsch, A. L., D. L. Galloway, Sr., L. A. Forster, Jr., G. E. Murphy, E. W. Grant, W. Sun, A. Patil, and C. P. West. 1993. Effects of various supplements on voluntary intake and performance by growing cattle consuming forage moderate to high in crude protein. Arch. Anim. Nutr. 44:163. Hart, S. P., and C. E. Polan. 1984. Simultaneous extraction and determination of ytterbium and cobalt ethylenediaminetetraacetate complex in feces. J. Dairy Sci. 67:888. Hoelscher, J. E., and G. D. Laurent. 1979. Soil Survey of Hempstead County, Arkansas. US Dep. Agric., Soil Conservation Serv.

400

Horn, G. W., M. D. Cravey, F. T. McCollum, C. A. Strasia, E. G. Krenzer, Jr., and P. L. Claypool. 1995. Influence of high-starch vs high-fiber energy supplements on performance of stocker cattle grazing wheat pasture and subsequent feedlot performance. J. Anim. Sci. 73:45. Kertz, A. F., M. K. Koepke, L. E. Davidson, N. L. Betz, J. R. Norris, L. V. Skoch, B. R. Cords, and D. T. Hopkins. 1982. Factors influencing intake of high urea-containing rations by lactating dairy cows. J. Dairy Sci. 65:587. Kertz, A. F., L. E. Davidson, B. R. Cords, and H. C. Puch. 1983. Ruminal infusion of ammonium chloride in lactating cows to determine effect of pH on ammonia trapping. J. Dairy Sci. 66:2597. Klevesahl, E. A., R. C. Cochran, E. C. Titgemeyer, T. A. Wickersham, C. G. Farmer, J. I. Arroquy, and D. E. Johnson. 2003. Effect of a wide range in the ratio of supplemental rumen degradable protein to starch on utilization of low-quality, grass hay by beef steers. Anim. Feed Sci. Technol. 105:5.

Gadberry et al.

Krysl, L. J., F. T. McCollum, and M. L. Galyean. 1985. Estimation of fecal output and particulate passage rate with a pulse dose of ytterbium-labeled forage. J. Range Mgmt. 38:180.

tration of supplemental degradable intake protein and starch on utilization of lowquality warm-season grass hay by beef steers. J. Anim. Sci. 77:1016.

Lake, R. P., R. L. Hildebrand, D. C. Clanton, and L. E. Jones. 1974. Limited energy supplementation of yearling steers grazing irrigated pasture and subsequent feedlot performance. J. Anim. Sci. 39:827.

Poore, M. H., J. T. Johns, and W. R. Burris. 2002. Soybean hulls, wheat middlings, and corn gluten feed as supplements for cattle on forage-based diets. Vet. Clin. Food Anim. 18:213.

Michell, P., and R. V. Large. 1983. The estimation of herbage mass of perennial ryegrass swards: A comparative evaluation of a rising-plate meter and a single probe capacitance meter calibrated at and above ground level. Grass Forage Sci. 38:295. NRC. 1996. Nutrient Requirements of Beef Cattle. (7th Ed.). National Academy Press, Washington, DC. Nicholson, J. W. G., E. Charmley, and R. S. Bush. 1992. The effect of supplemental protein source on ammonia levels in rumen fluid and blood and intake of alfalfa silage by beef cattle. Can. J. Anim. Sci. 72:853. Olson, K. C., R. C. Cochran, T. J. Jones, E. S. Vanzant, E. C. Titgemeyer, and D. E. Johnson. 1999. Effects of ruminal adminis-

Vanzant, E. S., K. B. Combs, D. W. Bohnert, D. L. Harmon, and B. T. Larson. 2002. Methods for measuring indigestible ADF as a digestion marker for fescue based diets. Beef Res. Rep. PR-463. Kentucky Agric. Exp. Stn., Univ. Kentucky, Lexington. Visek, W. J. 1982. Ammonia: Its effects on biological systems, metabolic hormones, and reproduction. J. Dairy Sci. 67:481. Vogel, G. J. 1988. Kinetics of ruminal nitrogen digestion of wheat forage and high protein feedstuffs and the effects of supplemental protein on the performance of growing cattle on wheat pasture. Ph.D. Diss., Oklahoma State University, Stillwater.