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Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism^1,2

W. T. Choat^*, C. R. Krehbiel^*,3, G. C. Duff^,4, R. E. Kirksey, L. M. Lauriault, J. D. Rivera, B. M. Capitan, D. A. Walker, G. B. Donart and C. L. Goad^¶

^* Departments of Animal Science and and Statistics, Oklahoma State University, Stillwater 74078; and Clayton Livestock Research Center, Clayton, NM 88415; and Agricultural Science Center, Tucumcari, NM 88401; and and ^¶ Department of Animal and Range Sciences, New Mexico State University, Las Cruces, NM 88003

	Abstract

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A winter grazing/feedlot performance experiment repeated over 2 yr (Exp. 1) and a metabolism experiment (Exp. 2) were conducted to evaluate effects of grazing dormant native range or irrigated winter wheat pasture on subsequent intake, feedlot performance, carcass characteristics, total-tract digestion of nutrients, and ruminal digesta kinetics in beef cattle. In Exp. 1, 30 (yr 1) or 67 (yr 2) English crossbred steers that had previously grazed native range (n = 38) or winter wheat (n = 59) for approximately 180 d were allotted randomly within previous treatment to feedlot pens (yr 1 native range = three pens [seven steers/pen], winter wheat = two pens [eight steers/pen]; yr 2 native range = three pens [eight steers/pen], winter wheat = four pens [10 or 11 steers/pen]). As expected, winter wheat steers had greater (P < 0.01) ADG while grazing than did native range steers. In contrast, feedlot ADG and gain efficiency were greater (P < 0.02) for native range steers than for winter wheat steers. Hot carcass weight, longissimus muscle area, and marbling score were greater (P < 0.01) for winter wheat steers than for native range steers. In contrast, 12th-rib fat depth (P < 0.64) and yield grade (P < 0.77) did not differ among treatments. In Exp. 2, eight ruminally cannulated steers that had previously grazed winter wheat (n = 4; initial BW = 407 ± 12 kg) or native range (n = 4; initial BW = 293 ± 23 kg) were used to determine intake, digesta kinetics, and total-tract digestion while being adapted to a 90% concentrate diet. The adaptation and diets used in Exp. 2 were consistent with those used in Exp. 1 and consisted of 70, 75, 80, and 85% concentrate diets, each fed for 5 d. As was similar for intact steers, restricted growth of cannulated native range steers during the winter grazing phase resulted in greater (P < 0.001) DMI (% of BW) and ADG (P < 0.04) compared with winter wheat steers. In addition, ruminal fill (P < 0.01) and total-tract OM digestibility (P < 0.02) were greater for native range than for winter wheat steers across the adaptation period. Greater digestibility by native range steers early in the finishing period might account for some of the compensatory gain response. Although greater performance was achieved by native range steers in the feedlot, grazing winter wheat before finishing resulted in fewer days on feed, increased hot carcass weight, and improved carcass merit.

Key Words: Carcass Quality • Cattle • Digestibility • Range Pastures • Winter Wheat

	Introduction

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Nutrient restriction during some portion of the growth phase is a tool commonly used by beef cattle producers to improve performance at a later date when input costs are usually greater (Drouillard and Kuhl, 1999). The effects of nutrient restriction on subsequent performance, carcass characteristics, and body composition have been well documented with some variation in results due to differences in the duration and severity of the restriction, as well as differences in the genetic potential of the cattle (Carstens et al., 1991; Sainz et al., 1995; Phillips et al., 2001). However, little information is available for nutrient-restricted cattle grazing forage ad libitum or the subsequent effects that nutrient restriction has on ruminal metabolism during adaptation to a high-grain diet. We hypothesized that cattle grazing dormant native range during winter would exhibit compensatory growth in the feedlot compared with cattle grazing winter wheat, and that increased intake (% of BW) and similar nutrient digestibility by native range steers during adaptation to a high-grain diet would be part of the mechanism. Therefore, our objectives were 1) to determine the effects of previous grazing of either dormant native range (NR) or winter wheat (WW) pasture on subsequent feedlot performance and carcass characteristics by beef steers and 2) to determine the effects of previous grazing of dormant NR or WW pasture on intake, apparent total-tract digestibility, digesta kinetics, and ruminal metabolite profiles, while cattle were being adapted to a high-concentrate diet.

	Experimental Procedures

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All procedures were in accordance with New Mexico State University Animal Care and Use Guidelines.

Performance Experiment
A performance experiment was replicated in two consecutive years to determine the effect of winter grazing on subsequent feedlot performance and carcass characteristics. At weaning (yr 1 = November 19, 1997; yr 2 = November 6, 1998), English crossbred steers were allotted to graze either NR (yr 1 initial BW = 222 ± 26 kg, n = 14; yr 2 initial BW = 236 ± 21 kg, n = 24) or irrigated WW pasture (yr 1 initial BW = 227 ± 22 kg, n = 16; yr 2 initial BW = 230 ± 23 kg, n = 43). During both years, cattle grazed irrigated WW (Triticum aestivum) at the Clayton Livestock Research Center, Clayton, NM, whereas cattle grazed NR at the Tucumcari Agricultural Science Center, Tucumcari, NM, during yr 1, and at the Clayton Livestock Research Center and Tucumcari Agricultural Science Center during yr 2. At Tucumcari, the dominant grass species included blue grama (Bouteloua gracilis), sideoats grama (B. curtipeudula), and sand dropseed (Sporobous cryptandrus). Subdominant grasses were yellow bluestem (Bothrichloa ischaemum), threeawns (Aristida spp.), lovegrass (Eragrostis spp.), vine mesquite (Panicum obtusum), and silver bluestem (B. saccharoides; Kloppenburg et al., 1995). Grasses at Clayton were dominated by blue grama, buffalograss (Buchloe dactyloides), and tobosa grass (Hilaria mutica). Other grasses included bottlebrush squirreltail (Sitanion hystrix), sand dropseed, sideoats grama, silver bluestem, vine mesquite, western wheatgrass (Agropyron smithii), and threeawns (Funk et al., 1987). Steers grazing NR were supplemented with 38% CP cubes at a rate of 0.91 kg•steer^-1•d^-1. All steers were allowed to graze for 170 d in yr 1 and 185 d in yr 2.

At the conclusion of the winter grazing period (yr 1 = May 8, 1998; yr 2 = May 10, 1999), steers were moved to the feedlot at the Clayton Livestock Research Center for finishing. Steers from Tucumcari were transported approximately 180 km. Upon arrival at the feedlot, steers were sorted by previous grazing treatment and randomly allotted to pens (yr 1 NR = two pens [seven steers/pen], WW = two pens [eight steers/pen]; yr 2 NR = three pens [eight steers/pen], WW = four pens [10 or 11 steers/pen]). Pens (12.2 m x 35.0 m) were uncovered and soil-surfaced, and provided 11 m of bunk space, with one automatic fence-line water trough per pen. All steers received a single Synovex-S implant (Fort Dodge Animal Health, Overland Park, KS) and a single i.m. injection of Ultrabac 7 (Pfizer Animal Health, Lee’s Summit, MO) before placement in the feedlot. Steers were adapted to a 90% concentrate diet using four adaptation diets each fed for 5 d (Table 1). Due to feed delivery problems with sorghum hay, alfalfa hay was included as a roughage source. Initial intake was set at 2.0% of BW (as-fed basis) and feed offered was increased by 0.45 kg•steer^-1•d^-1 when a slick bunk was evident at the morning feed call. Bunks were monitored periodically throughout the day and the quantity of feed to offer was made at 0730 before the once daily feeding. Steers were weighed on d 14 and 28, and at 28-d intervals thereafter; all weights reported and used in calculations were given a 4% pencil shrink. All steers were fed to a similar body composition end point based on subjective evaluation. Due to differences in placement weight, WW steers were fed for 105 and 70 d, and NR steers were fed for 137 and 122 d in yr 1 and 2, respectively. Final live weights were taken the morning before slaughter.

Metabolism Experiment
Ruminally cannulated steers (n = 8; mean initial BW = 228 ± 15 kg) were used in a completely random design to evaluate the effect of previous grazing on intake, apparent total-tract digestion, ruminal fermentation, and digesta kinetics during adaptation and subsequent feeding of a high-concentrate diet. Cannulated steers grazed NR (n = 4) or irrigated WW (n = 4) pastures from November 6 through May 22, 1999. During grazing, chromic oxide (15 g•steer^-1•d^-1) was dosed via gelatin capsules (two capsules•steer^-1•d^-1, beginning April 18 and ending April 30, 1999) through the ruminal cannula of each steer as an indigestible marker of digesta flow. Fecal grab samples were collected on the mornings of April 26, 27, 28, 29, and 30. On April 26, steers were pulse-dosed with 200 mL of CoEDTA at approximately 0700. Ruminal fluid samples were collected at 0, 3, 6, 9, 12, and 24 h after dosing. Immediately after collection, 200 mL of ruminal fluid was strained through four layers of cheesecloth and pH was measured. A 10-mL aliquot was acidified with 0.5 mL of 6 N HCl and frozen for later ammonia N analysis (Huntington, 1982). Another 30 mL of ruminal fluid was frozen for VFA and Co analysis. On April 28, steers were gathered and all ruminal contents were removed, thoroughly mixed and subsampled for DM determination. Steers were allowed to graze their respective pastures for 30 to 40 min, after which time a masticate sample was removed from the rumen and the previously removed ruminal contents were replaced.

On May 23, 1999, steers were removed from their respective pastures and moved to the Clayton Livestock Research Center where they were allotted randomly to 2.4-m x 6.1-m individual outdoor pens (uncovered). The dietary adaptation used for this experiment was the same as that used for Exp. 1, except that intake was set at 1.5% of initial BW (DM basis). Feed was increased 0.45 kg•steer^-1 •d^-1 when a slick bunk was evident at the morning feed call (approximately 0730). Dry matter intake was recorded on a daily basis; all refusals were weighed, and DM content was determined and subtracted from total intake of each 5-d adaptation period. Chromic oxide (15 g/d) was dosed via gelatin capsules (two per steer) as an indigestible marker of digesta flow throughout the entire 30-d experiment.

Sampling.
A sufficient quantity of total mixed ration for each adaptation period was mixed at one time and stored in a bulk bag. Feed was sampled from the bag on a daily basis and composited by diet concentrate level for subsequent proximate analysis. Due to natural drying of the diet over time, three diet DM analyses were conducted during each 5-d adaptation period and the average taken. On d 7 through 10 (75% concentrate), 17 through 20 (85% concentrate), and 27 through 30 (final diet), fecal grab samples were collected at approximately 0730 and frozen (-20°C). At approximately 0730 on d 5 (Co-EDTA only), 15, and 25 (corresponding to 70% concentrate, 80% concentrate, and final diets, respectively), Co-EDTA (200 mL) and steam-flaked corn (1 kg/steer) labeled with ytterbium acetate were pulse-dosed intraruminally. Ytterbium-labeled corn and Co-EDTA have been shown to be reliable external markers for corn and fluid (Sindt et al., 1993) and were prepared as outlined by Teeter et al. (1984) and Uden et al. (1980), respectively. Ruminal fluid and particulate matter were collected at 0, 3, 6, 9, 12, 18, and 24 h after dosing. Immediately after collection, 200 mL of ruminal fluid was strained through four layers of cheesecloth and pH was measured using a combination electrode. A 10-mL aliquot of ruminal fluid was acidified with 0.5 mL of 6 N HCl and frozen (-20°C) for later ammonia-N analysis (Huntington, 1982). Another 30 mL of ruminal fluid was frozen for VFA and Co analysis. On d 16 and 26 before the morning feeding (80% concentrate and final diet, respectively), steers were weighed; total ruminal contents were removed, weighed, and mixed thoroughly, after which a subsample was obtained, and DM analyses were completed for determination of total ruminal DM and fluid contents.

Laboratory Analyses.
Samples of ruminal contents, feed, orts, and feces were dried in a forced-air oven at 55°C for DM determination. Dried ruminal contents were ground to pass through a 2-mm screen and analyzed for Yb concentration as outlined by Karimi et al. (1987). Nitrogen content of feed, refusals, and feces was determined by the combustion method (Leco NS2000, St. Joseph, MI; AOAC, 1996). Acid detergent fiber concentrations of feed, refusals, and feces were determined by the methods of Van Soest et al. (1991). Acid detergent-insoluble nitrogen (ADIN) content of masticate and fecal samples from fistulated steers grazing WW and NR were determined by performing N analysis (combustion method) on the remains of the sample following ADF analysis. Feed, refusals, and feces were analyzed for starch in accordance with procedures outlined by MacRae and Armstrong (1968). Chromium concentrations of feces were quantified using an inductively coupled plasma spectrophotometer (ICP Spectro Analytical Instruments, Fitchburg, MA). Concentrations of Co in ruminal fluid and concentrations of Yb in ruminal particulate samples were also determined by ICP analysis. The wavelengths used to measure optical emission of Cr, Co, and Yb were 267.7, 228.6, and 265.4 nm respectively. Ruminal ammonia N and VFA concentrations were determined using procedures outlined by Broderick and Kang (1980) and Goetsch and Galyean (1983), respectively.

Calculations and Statistical Analyses.
For grazing and all adaptation periods, fecal DM output was calculated as Cr consumed (g/d)/Cr concentration in feces (g/g of DM). Forage DM intake was calculated as fecal DM output x (100/% indigestibility of DM; Merchen, 1988) using ADIN as an internal marker. Dilution rates of Co and passage rate of Yb were calculated by regressing the natural log of marker concentration on time after dosing. Retention time and time for 50% turnover were calculated as 1/dilution rate and 0.693/dilution rate, respectively. Ruminal volume was calculated by dividing dose by ruminal concentration extrapolated to 0 h, and ruminal outflow rate was calculated as ruminal volume divided by the dilution rate.

All statistical analyses were performed using the Mixed procedure of SAS (SAS Inst. Inc., Cary, NC). Animal grazing performance was analyzed separately with pasture (Exp. 1; n = 2/yr) or animal (Exp. 2) as the experimental unit. The statistical model included fixed effects of treatment and year with year as a block term to account for error. Feedlot performance and carcass response variables were analyzed as a randomized complete block design. Pen was the experimental unit. Pen within treatment was used as the error term and the model included treatment and year.

Digestibility and digesta kinetics data during the adaptation from Exp. 2 were analyzed as a completely random design with repeated measures over adaptation periods; the model included fixed effects of treatment, period, and treatment x period (Littell et al., 1998). Data were repeated over period, and the proper covariance structure was determined. Ruminal pH, NH₃-N, and VFA data (adaptation only) were repeated over period and time (i.e., 0, 3, 6, . . ., 24 h). The model included fixed effects of treatment, period, treatment x period, time, treatment x time, period x time, and treatment x period x time. Results are discussed as significant if P 0.05 and as tendencies if P > 0.05 and P 0.10. Least squares means were used to separate means at the highest-level interaction that was significant (P < 0.05).

	Results

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Performance Experiment
Grazing Phase.
Forage allowance for steers grazing NR vs. WW was 3,100 vs. 763 and 918 vs. 814 kg of DM/steer in yr 1 and 2, respectively, at the initiation of grazing. Initial BW did not differ (P < 0.90) among treatments; however, as expected, steers grazing WW had greater (P < 0.01) ADG (1.03 vs. 0.29 ± 0.02 kg/d) and final BW (412 vs. 280 ± 4.6 kg) than steers grazing NR.

Feedlot Phase.
Initial and final feedlot BW were greater (P < 0.001) for WW steers compared with NR steers (Table 2). In contrast, overall feedlot ADG was 7.4% greater (P < 0.02) for NR than WW steers. Interim ADG followed patterns similar to overall ADG, although NR steers did not seem to begin to compensate until after d 14. From d 0 to 14 (P < 0.01) and d 15 to 28 (P < 0.03), DMI was greater for WW than NR steers; however, across the entire feeding period (d 0 to end), DMI was not different (P < 0.43) among treatments. Dry matter intake expressed as a percentage of mean finishing BW was 16.8% greater (P < 0.001) for NR compared with WW steers. Interim (P < 0.06) and overall (P < 0.001) gain efficiencies were greater for NR steers compared with steers previously grazing WW.

Grazing Digestibility and Ruminal Kinetics.
Digestibility, ruminal kinetics, and fermentation data for cannulated steers during grazing is shown in Table 4. Estimated intake and fecal output of OM, ADF, and N were greater (P < 0.04) for steers grazing WW compared with steers grazing NR; however, no differences (P < 0.23) in total-tract digestibility of OM, ADF, or N were observed. Dry matter and fluid fill were twofold greater (P < 0.003) in NR than WW steers, whereas fluid dilution rate was 2.24-fold greater (P < 0.001) in WW than NR steers. Ruminal pH (P < 0.15) and total VFA concentration in the rumen (P < 0.98) did not differ among treatments; however, molar proportion of acetate was lower (P < 0.001) and propionate (P < 0.001) and butyrate (P < 0.001) greater in steers that grazed WW. Acetate:propionate was 70% greater (P < 0.001) in steers that grazed NR compared with steers that grazed WW. Concentrations of ruminal NH₃-N in steers grazing NR or WW did not differ (P < 0.34).

Ruminal Kinetics During Adaptation.
Ruminal DM fill was similar among treatments when the 80% concentrate adaptation diet was fed, but was greater for NR steers than WW steers when the 90% concentrate diet was fed (treatment x adaptation period interaction, P < 0.006; Table 6). During the adaptation period, NR steers had greater (P = 0.01) fluid fill (g/kg of BW) than WW steers. Fluid dilution rate, ruminal volume and outflow rate increased (P < 0.001) as adaptation diets increased from 70 to 90% concentrate, whereas retention time and time for 50% ruminal turnover decreased (P < 0.001). Particulate passage rate was greater when the 90 vs. the 80% concentrate diet was fed to NR steers, whereas particulate passage rate was greater when the 80 vs. the 90% concentrate diet was fed to WW steers (treatment x adaptation period interaction, P < 0.03).

View larger version (23K): [in this window] [in a new window]   Figure 1. Ruminal pH of steers that previously grazed dormant native range or winter wheat pasture and subsequently adapted to a high-concentrate diet, with adaptation diets containing 70, 80, and 90% concentrate (Exp. 2). The treatment x adaptation period x time interaction was not significant (P = 0.07); however, a time x adaptation period interaction was observed (P < 0.01). Standard error of the least squares means = 0.13 (n = 4).

View larger version (22K): [in this window] [in a new window]   Figure 2. Ruminal NH3-N concentrations of steers that previously grazed dormant native range or winter wheat pasture and subsequently being adapted to a high-concentrate diet, with adaptation diets containing 70, 80, and 90% concentrate (Exp. 2). A treatment x adaptation period x time interaction (P < 0.01) occurred. Standard error of the least squares means = 1.47 (n = 4).

	Discussion

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Nutrient intake restriction during some portion of the growth process in ruminants has resulted in lower ME requirements (Ledger and Sayers, 1977) and increased rate and efficiency of gain during a subsequent nonrestrictive period (Fox et al., 1972; Phillips et al., 1991). A potential benefit of this compensatory growth is that the time of restriction or lower performance can coincide with times when input costs are low (grazing of dormant NR) and allow the expression of compensatory growth to occur when input costs are high (feedlot; Drouillard and Kuhl, 1999), which is consistent with the present Exp. 1. Across both years of Exp.1, feedlot ADG and gain efficiency were 7.4 and 11% greater for NR than WW steers, respectively. Similar to our results, Phillips et al. (1991; 2001) reported increased gains and improved feed efficiency during finishing for cattle previously grazing dormant native grass compared with steers that had grazed winter wheat. In contrast, Hersom et al. (2003a) reported that steers that had previously grazed dormant native range or winter wheat pasture at two rates of gain had similar performance in the feedlot. Discrepancies among experiments are difficult to explain, but differences might be due to the number of days steers were grazed, degree of restriction during winter grazing, winter ADG for both restricted and nonrestricted steers, initial body composition, genetic potential for growth, among others (Klopfenstein et al., 1999). For steers grazing dormant native range, winter grazing (132 d) ADG averaged 0.16 kg/d in the experiments of Hersom et al. (2003a), whereas ADG during winter grazing (180 d) was 0.29 kg/d for NR steers in the present Exp. 1, suggesting a greater degree of restriction occurred for steers in the former experiments (Hersom et al., 2003a). Whether cattle can be restricted to a degree that compromises compensatory growth remains to be determined.

The percent compensation of NR steers in Exp. 1 was 60%, which is similar to responses reviewed by Klopfenstein et al. (1999). This resulted in final live weights that were 30 kg greater for WW than NR steers across both years of Exp. 1, which compares favorably with the 23-kg difference reported by Phillips et al. (2001). Although studies concerning compensatory growth by grazing steers are limited, the results of the present experiment can be compared to others in which restriction was inflicted either by limit-feeding a total mixed ration (Carstens et al., 1991) or by limiting supplementation of grazing cattle (Lewis et al., 1990). In both experiments, compensatory growth was similar to the present Exp. 1. The lower final live weights by NR steers might have resulted from too few days on feed or more likely that restricted steers were unable to completely compensate for lost performance as supported by the calculated percentage compensation (Klopfenstein et al., 1999). Twelfth-rib fat depth was similar among treatments in the present experiment.

Across both years, hot carcass weight was 26 kg greater for WW compared with NR steers. Dressing and carcass fat percentage typically increase with increasing final live weight (Owens et al., 1995), which is consistent with the present experiment. At similar levels of 12th-rib fat, WW steers had greater percentages of KPH and marbling scores than NR steers. The greater marbling scores observed in WW steers compared with NR steers (Exp. 1) might be attributed to increased nutrient intake earlier in the growth curve of these steers. Smith and Crouse (1984) reported that glucose incorporation into fatty acids was significantly greater in intramuscular adipose tissue than in subcutaneous adipose tissue. In our Exp. 2, greater (39.3%) molar proportions of propionate were observed in steers grazing WW pasture compared with NR. Greater absorption of this gluconeogenic precursor earlier in the growth period might have resulted in increased intramuscular fat deposition. In support, steers harvested after grazing winter wheat had fourfold greater marbling than steers that had grazed dormant native range (Hersom et al., 2003a).

Metabolism.
Although a plethora of data exists demonstrating the phenomena of compensatory growth, much less information is available that describes the associated physiological mechanisms. The growing and adaptation performance of the fistulated steers in Exp. 2 were similar with results of Exp. 1. Across the adaptation period, ADG and gain efficiency were 39.4 and 54.5% greater, respectively, for NR compared with WW steers. Greater intakes (% of BW) by NR steers might be attributable to the greater ruminal DM fill during grazing and the greater ruminal fluid fill during grazing and the adaptation period relative to BW. Hersom et al. (2003b) reported that steers grazing dormant native range had approximately 12% greater reticulorumen mass (proportion of BW) than steers grazing winter wheat at a high (1.20 kg/d) rate of gain. In their experiment, DMI (percentage of mean BW) during a subsequent finishing period was 11.4% greater for native range than winter wheat steers, similar to the present results. Whether increased intake in our experiments was a result of increased gut size or metabolic activity cannot be determined. However, Sainz et al. (1995) reported that increased feed DMI accounted for 60 to 104% of the increased growth rate during finishing of previously restricted steers.

Lack of response in total-tract digestibility of OM, ADF, and N among steers grazing WW vs. NR was unexpected. However, no difference in total-tract digestibility might have been related with the dates (April 26 through 30) on which samples were collected, as quality of warm-season NR grasses was most likely increasing relative to WW. Our results did show increased digestibility of nutrients by NR compared with WW steers during the 30-d adaptation period. In contrast, Hersom et al. (2003c) reported no difference in diet digestibility during adaptation to a high-grain diet by cattle that had previously gained 0.75 vs. 1.25 kg/d on wheat pasture. In addition, lower diet DM digestibility has been reported in realimented cattle that had been previously energy restricted for 92 d (Hayden et al., 1993). Differences among experiments most likely result in part from differences in diets used for restriction. To our knowledge, these are the first data to report digestibility across the adaptation period in steers that had previously grazed forages of different quality.

The pattern of ruminal pH, VFA, and NH₃-N concentrations across the high-grain adaptation period were generally similar among NR and WW steers. Similar to our previous research (Choat, 2001), molar proportions of acetate and acetate:propionate decreased and molar proportion of propionate increased as dietary concentrate increased; however, this response did not differ among NR and WW steers in the present study (Exp. 2). Therefore, differences in total VFA concentration and molar proportions of VFA most likely contributed to differences in grazing, but not finishing performance.

	Implications

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Steers that graze dormant native range before placement on a high-grain finishing diet have greater daily gains than steers that previously grazed winter wheat. Greater ruminal dry matter and fluid fill late in the grazing period and increased nutrient intake (percentage of body weight) and digestibility early in the finishing period may account for some of the compensatory gain response by native range steers. However, when fed to a similar 12th-rib fat, cattle that grazed wheat pasture before finishing required fewer days on feed, and had increased final live weight, increased carcass weight, and improved carcass merit compared with cattle grazed on dormant native range.

	Footnotes

 
¹ Approved for publication by the Director of the Oklahoma Agric. Exp. Stn. This research was supported by the Oklahoma (project H-2438) and New Mexico Agric. Exp. Stn.

² The authors acknowledge L. Blan, K. Malcolm-Callis, and M. Wiseman from the Clayton Livestock Research Center, Clayton, NM; T. Bodine, C. Lunsford, D. Perry, C. Stout, and J. Summers from the Ruminant Nutrition Laboratory, Stillwater, OK; and T. Montgomery and students from West Texas A&M University, Canyon, for their important contributions to these experiments.

⁴ Present Address: Univ. of Arizona, Dept. of Anim. Sci., 217 Shantz Bldg., Tucson, 85721.

³ Correspondence: 208 Anim. Sci. Bldg. (phone: 405-744-8857; fax: 405-744-7390; E-mail: kclinto{at}okstate.edu).

Received for publication April 10, 2003. Accepted for publication July 31, 2003.

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