Published in Agron J 99:747-754 (2007)
DOI: 10.2134/agronj2005.0346
© 2007 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Pasture Management
Empirical Analysis of Weaning and Pasture Rotation Frequency with Implications for Retained Ownership
Michael Poppa,*,
K. Coffeyb,
W. Coblentzc,
Z. Johnsonb,
D. Scarbroughd,
J. Humphrye,
T. Smithf,
D. Hubbellf and
J. Turnerg
a Dep. of Agricultural Economics and Agribusiness, 217 Agriculture Building, Univ. of Arkansas, Fayetteville, AR, 72701
b Dep. of Animal Sci., AFLS B106, Univ. of Arkansas, Fayetteville, AR, 72701
c USDA-ARS, U.S. Dairy Forage Research Center, Univ. of Wisconsin, Marshfield Agricultural Research Station, 8396 Yellowstone Dr., Marshfield, WI 54449
d 126 Jessie Dunn, Northwestern Oklahoma State Univ., Alva, OK 73717
e Humphry Environmental, Inc., Fayetteville, AR 72702
f Univ. of Arkansas Livestock and Forestry Branch Stn., 70 Experiment Station Dr., Batesville, AR 72501
g North Carolina State Univ. Mountain Research Stn., Waynesville, NC 28786
* Corresponding author (mpopp{at}uark.edu)
Received for publication December 19, 2005.
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ABSTRACT
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The economic impact of rotation frequency (twice weekly vs. twice monthly until time of weaning) and time of weaning (early April vs. 56 d later) was examined for fall-calving cows using a modified put and take grazing strategy implemented to maintain equal grazing pressure across production systems. Cow and/or calf death losses resulted in replacements with either bred cows or cow–calf pairs. While the analysis on heifer calves was limited to sale at time of weaning, steer calves were tracked through the feedlot stage to determine if the time of sale would alter production system recommendations. For the conditions presented in this study, cow–calf producers may be advised that (i) relative to late weaning, early weaned calves did not regain their weight disadvantage observed at time of weaning; (ii) more intensive pasture management (rotating twice weekly rather than twice monthly) was not worth the effort because partial return results for late-weaned steer and heifer calves did not differ statistically by rotation frequency, regardless of sale time; (iii) partial returns were highest for steer calves retained through the finishing stage at the feedlot (regardless of production system) compared with sale at the time of weaning or at the time of placement in the feedlot; (iv) the range of returns or financial risk exposure increased with length of calf ownership. However, use of long-term average prices excluded input price risk from the analysis and output price risk was only partially addressed.
Abbreviations: CDF, cumulative distribution function • hd, head
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INTRODUCTION
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COW–CALF PRODUCERS are often faced with the decision on when to wean (Myers et al., 1999a, 1999b) and/or at what time in the calf's life cycle to sell the herd's calves (Gill and Lusby, 2005; Marsh and Feuz, 2002; King-Brister, 2003). In the midsouthern USA, this decision can be somewhat complex, especially for producers using a fall-calving system. Calves can be weaned in early April to (i) allow for the weaning stress to occur during cooler temperatures; (ii) potentially sell calves at seasonally higher prices (King-Brister, 2003); and (iii) allow for additional grazing by other livestock or hay harvest. By the same token, weaning in late May or early June would delay weaning stress past the peak spring forage season which would allow for heavier weaning weights, albeit at seasonally lower prices. Further, if calves are retained through to the fall to be sold as yearlings to feedlots, how will early and late-weaned calves, pastured during the summer months, compare in terms of performance? Finally, if steer calves are retained through the finishing stage, what are the financial repercussions for the cow–calf producer, and second, will the cattle market send the same signal about what production system to use regardless of when the steer calves are sold?
A more basic question that may affect the above issues is how often to rotate pasture paddocks. Up to a point, a higher rotation frequency (holding stocking rate constant) is expected to allow for more optimal pasture utilization, thereby enhancing reproductive performance (Holechek et al., 1998), as well as beef production per acre (Walton et al., 1981; Bertelsen et al., 1993; Hoveland et al., 1997). However, individual animal performance may not be enhanced (Bertelsen et al., 1993; Hoveland et al., 1997; Barker et al., 1999; Lomas et al., 2000) or actually may be reduced (Volesky et al., 1990). Another benefit of more intensive forage management is improved forage persistence (Mathews et al., 1994; Hoveland et al., 1997). Lower rotation frequency, on the other hand, reduces investment in fencing and associated repair cost and is less management intensive.
The objectives of this 4-yr study were therefore to analyze (i) the impact of rotation frequency and weaning date of fall-born calves on economic performance per cow; (ii) identify the optimal sale time for steer calves (at time of early or late weaning, before placement in the feedlot in the fall, or at time of finish in the following spring); and (iii) determine whether production system recommendations change with the length of ownership of the steer calves.
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MATERIALS AND METHODS
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Experimental Description
Fall-calving 75% Angus x 25% Brangus cows were bred using a 100% Angus herd sire. These cows were stratified by weight and age and placed randomly on eleven pastures of varying size in April of 2000. While pasture size varied, the stocking rate of 
0.9 cows ha–1 (resulting in four to six cows per pasture) was held constant across production systems. Using a randomized complete block design, pastures were divided by main effects of (i) rotation frequency (twice weekly using eight equally sized paddocks per pasture or twice monthly with two equally sized paddocks); and (ii) time of weaning (early April vs. 56 d later). Three replicates for each production system were used each year with the exception of the 8E system, where only two replicates were available due to lack of pasture availability in the first 2 yr (the 12th pasture was added in year 3).
The pastures were located at the University of Arkansas Experiment Station near Batesville, AR (35°52' N, 91°45' W) on Clarksville (loamy-skeletal, siliceous, semiactive, mesic Typic Paleudults) and Gepp (very-fine, mixed, semiactive, mesic Typic Paleudalfs) very cherty silt-loam soils. These soils are characterized as being deep, somewhat excessively drained, having 8 to 40% slopes, and not adapted to tillage (Ferguson et al., 1982). Pastures consisted mainly of Neotyphodium coenophialum–infected tall fescue (Festuca arundinacea Schreb. L.; Coffey et al., 2005); they were fertilized and maintained according to recommendations of the University of Arkansas Cooperative Extension Service (Chapman, 2001). Pasture paddocks were only used for grazing, and excess forage during the spring peak growth period was managed by temporarily adding cull cows to pastures to control excess available forage. Depending on pasture treatment and size, this resulted in 43 to 49 d of grazing in 2000 and 14 to 22 d in 2001. The practice of adding cull cows during the spring period was discontinued for 2002 because (i) weather conditions were more droughty than expected, thereby reducing late-summer available forage below critical levels during 2000, and (ii) an armyworm (Pseudaletia unipuncta L.) infestation caused a shorter-than-expected grazing period in 2001.
Supplemental feeding during the winter months occurred in the form of tall fescue hay when available forage was limiting, and a corn–soybean meal supplement was fed during the 60-d breeding season. The corn–soybean meal supplement was formulated to maintain cows at their present body condition score (National Research Council, 1996), and was fed equally to each pasture group. Overall, the pasture management strategy across all treatments was to maintain consistent grazing pressure by adding or removing cull cows and/or adjusting for cow and calf death losses with cattle replacements (bred cows and/or cow–calf pairs as deemed similar to what a producer might do on a ranch).
All calves were weighed at both weaning dates. Heifer calves were either sold at time of weaning or retained for herd replacement. Once weaned, steer calves (castrated within 24 h of birth) were kept on separate pastures during the summer months without supplemental nutrition other than trace mineralized salt. They were weighed before shipment (beginning of October through mid-November) to a commercial feedlot in Kansas where they were offered a finishing ration in a common pen for 156, 187, and 203 d in 2001, 2002, and 2003, respectively.
Economic Analysis
A partial return analysis on a per-cow basis, accounting only for revenue and cost differences associated with weaning time, rotation frequency and time of calf sale was deemed appropriate for the following reasons: (i) differences in reproductive performance across production systems was negligible (Coffey et al., 2005) and could be accounted for by tracking cattle replacement costs as a result of breeding failure or death losses; (ii) the pastures were managed for consistent grazing pressure and thus the need to differentiate for production by unit of land was deemed unnecessary; (iii) calculation of actual profitability would not aid in differentiation across production systems; and (iv) accounting for death losses and calf sex differences requires fewer modifying assumptions on a per-cow rather than per-unit-of-land basis. Note that cost differences across systems included both operating and ownership charges.
Partial returns per cow are defined as calf and cull cow sales less cattle purchase, supplemental hay and feed, summer grazing, steer feedlot costs, cattle replacement, death loss, and prorated fencing and interest costs. These partial returns were further differentiated by sex of calf as the ratio of steer and heifer calves was inconsistent across production systems. The treatment with the highest partial returns would be preferred over its alternatives.
Calf and Cull Cow Sales
The 1996 to 2004 averages of monthly Arkansas and Kansas prices for calves, cull cows and replacement cows or cow–calf pairs were used depending on (i) weight of calf; (ii) sex of animal; (iii) pregnancy status and/or calf vs. no calf at side; and (iv) time and location of sale (Agricultural Marketing Service, 2005; Livestock Marketing Information Center, 2005). A 9-yr average monthly price was chosen to eliminate the effects of cyclically high or low cattle prices and because consistent price series for all prices were available for that period. All calf weight information was adjusted for 4% shrink to account for weight loss during transit and marketing. Since other marketing charges depend on trade terms and vary by location, they were not included in any of the treatment analyses. All cattle prices were adjusted for inflation using the seasonally unadjusted consumer price index to represent costs and returns in 2004 dollars (Bureau of Labor Statistics, 2005). Costs were representative for conditions in Arkansas in 2004.
Supplemental Hay and Rotational Fencing Charges
The amount of hay supplemented during winter months was recorded for each pasture to account for differences in feed costs that were expected as a result of differences in available stockpiled fescue (in turn a result of rotation frequency). Hay feeding costs were subsequently averaged by treatment and equally weighted across all years to remove the impact of unusually high or low feeding costs for any given year. The corn–soybean meal supplement was identical, regardless of treatment. Pastures with a higher rotation frequency required additional fencing and associated costs depend on the size of the cow herd, as well as the terrain of the pastures. Similar to King-Brister (2003), this analysis used (i) a capital recovery rate of 5%; (ii) a permanent five-strand barbed wire perimeter and two-strand electric cross-fence cost of $1.05 and $0.26 m–1, respectively; (iii) a useful life of 20 yr with zero salvage value; (iv) a 40% repair cost factor1; and (v) an adjustment to fencing costs by adding 20% to account for terrain-based fencing (curves, hills, etc.). On a per-cow basis, the difference in capital and repair costs for two vs. eight paddocks was approximately $1.50 cow–1. No other charges for the higher rotation frequency were assigned as they were deemed similar in terms of management & labor intensity as well as no observed effects on species composition (Coffey et al., 2005).
Adjustments for Time of Sale
Steer calves could be sold at (i) time of weaning in early April; (ii) 56 d later; (iii) as yearlings to the feedlot; or (iv) as finished cattle. To make partial returns per cow comparable across the aforementioned sale times, differences in summer grazing charges, capital returns foregone due to deferred sales, death losses, and feedlot charges of feed, insurance, and yardage were calculated. Table 1 presents a summary of feeding charges and opportunity cost adjustments necessary to calculate partial returns that conceptually would be achieved had all steer calves been sold by the time of slaughter. An early weaned steer would thus have investment returns from the proceeds of the sale that would be achieved from its time of sale until it would have been processed. Selling at the latest stage, by the same token, incurs a full charge of summer pasture, veterinary and incidental charges, death loss, feeding and operating interest charges, and no adjustment for foregone returns of capital.
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Table 1. Accounting for time of sale differences by adjusting for differences in feed and handling charges, foregone interest, and death losses on steer calves.
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Grazing Charges
Steer calves weaned in the spring were prepared for feedlot placement in the fall by grazing pasture during the summer months. All calves were commingled and grazed as a group in a rotational system utilizing predominantly bermudagrass [Cynodon dactylon (L.) Pers.] pastures. Costs associated with rotation frequency differences were therefore not maintained during this period and calves were also not supplemented to improve weight gain. The only summer grazing charges therefore included a pasture fee of $18 head–1 (hd) which represented mainly fertilizer, fuel, weed control, and operating interest (King-Brister, 2003). The fee was adjusted by length of stay to allow for differences in time of steer calf sale (i.e., for calves sold at weaning, late-weaned calves incurred part of the summer grazing fee whereas early weaned calves did not).
Estimation of Feedlot Charges
Kansas State University maintains an extensive database on average feedlot production costs as reported for thousands of head each month by commercial Kansas feedlots. Monthly data from 1996–2004 allowed estimation of long-run average cost of gain as follows:
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COG in $ lb–1 of weight added in the feedlot was the reported average, deflated feedlot cost of feed, veterinary charges, insurance, and yardage for steer calves finished in a particular month (Livestock Marketing Information Center, 2005); WGAIN in pounds hd–1 was the average weight added to steers during their stay in the feedlot; FCV represented feed conversion and was the ratio of average weight of feed hd–1 (dry matter basis) per WGAIN; CORN was the average, deflated price of corn in $ bu–1 during the previous 5 mo; and ALF was the deflated price of alfalfa hay in $ U.S. ton–1. Regression analysis, reported in Table 2, revealed that 98% of variation in COG was explained by the independent variables. Further, changes in the average cost of gain were driven mainly by fluctuations in the price of corn in the feed ration (Pearson correlation coefficient between COG and CORN was 0.94) rather than changes in FCV, WGAIN, or ALF.
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Table 2. Cost of Gain Regression Equation Results using 1996–2004 Feedlot Cost of Gain Data Reported for Commercial Kansas Feedlots.
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Since long-run average feedlot finishing costs, representative for Arkansas cattle typically shipped to Kansas, Oklahoma, or Texas feedlots, were not obtainable from this experiment, coefficients from Eq. [1] were used to approximate the cost of gain for individual steers on the basis of observed weight gain, holding all other values at the 1996 to 2004 averages (again adjusted for inflation).
Death Losses, Replacement Charges, and Cull-Cow Grazing Returns
Calf death losses occurred at or near time of fall calving and, in one instance, just before weaning. These losses were tracked by accounting for cattle replacement costs. There were no death losses during the summer grazing period. At the feedlot, four steers died in 2003. The value of these animals was approximated by averaging partial returns per cow at time of feedlot placement across all years and was deducted evenly from returns across all treatments.
Cattle replacement costs (sale, if any of the cull animal, less cost of replacement animal) as well as cull cow grazing returns (purchase cost less sale price in $ hd–1) were totaled across all years and treatments and an average replacement cost or grazing return was assigned to the treatments that required cattle replacement and/or had cull cows grazing rather than assigning the individual animal's actual replacement cost and/or grazing return. This was done to guard against the impact of unusually high or low costs of low performance of individual animals assigned to the different treatments while still capturing quantitative performance differences across treatments (e.g., a particular treatment could have relatively more cattle replacements but the cost of each replacement was the same across treatments).
Cattle Price Data
Weekly and monthly price and cost information were adjusted for inflation and averaged by month over the period of 1996 to 2004 as necessary. Simple average prices for different weight categories and animal types are reported in Tables 3 and 4. Use of long-run average prices was deemed appropriate to highlight effects of production system differences by eliminating effects of unusually high or low cattle prices as a result of cattle cycles, price trends, and random events. Output price risk was thus captured in the sense that the time of cattle sales was associated with its appropriate seasonally adjusted long-run average price but input price risk was not reflected.
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Table 3. 1996 through 2004 monthly Arkansas average prices for medium to large frame No. 1 feeder steers and heifers, cull cows, second- and third-stage pregnant cows, and cow–calf pair prices for months of transactions used.
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Risk Measurements
Annual partial return observations (in $ cow–1 for calves weaned or sold) were compared across systems by examining average partial returns as well as their empirical cumulative distribution functions (CDFs) constructed using Schlaifer's (1959) fractile method. This was done as visual examination of CDFs allows the reader their own unique interpretation of the riskiness of each of the production systems for heifer and/or steer production by time of sale by presenting minimum and maximum partial returns as well as the likelihood of attaining various levels of partial returns as compared to merely reporting the average and CV. Cumulative distribution functions with a narrower range of observations will be steeper than those with a wider range of observations and thus preferable to the risk-averse cattle producer. Further, the horizontal position of the CDF on the partial return scale allowed a comparison of return levels across the spectrum of return observations. Curves with observations furthest to the right would, at a given cumulative likelihood, experience the highest partial returns, and would therefore be deemed preferable to those that have observations to its left. Note, however, that a definitive statement about which production system a producer would choose is not possible using this analysis framework, as each individual producer may have different risk preferences.
Visual examination of the CDF analysis was complemented by testing for statistically significant differences across fixed effects of production systems (weaning date and rotation frequency) and time of sale (for steer calves only) using PROC MIXED in SAS (Littell et al., 1996). Year and pasture paddocks were treated as random effects and degrees of freedom were adjusted using the Satterthwaite option.
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RESULTS
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Rotation frequency, weaning date, and sale time are all significant either by themselves or as interactions at the 10% level of significance (Table 5). The overriding effect was weaning date and sale time for the steers and weaning date for the heifers. These results supported separate reporting of average performance statistics for the three fixed effects.
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Table 5. Probabilities of F values from Type III tests of fixed effects of weaning date, rotation frequency, and sale time as well as random effects of year and pasture replication on partial returns obtained from steer and heifer production obtained from SAS PROC MIXED analysis.
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Table 6 and Fig. 1 provide a comparison of partial returns for steers vs. heifers at time of weaning. On the revenue side, weaning weights were lower for the early weaning date treatments for both heifers and steers as expected. This disadvantage was partially offset by higher prices for lighter weight calves sold earlier in the season. Increasing the rotation frequency had minimal impact on weaning weights of steers and numerically decreased weaning weight of heifers (2E vs. 8E). On the cost side, supplemental hay costs and cow–calf replacement costs did not follow a priori expectations. The highest feed bill and cow–calf replacement charges were incurred by the 8E system. This was likely due to stockpiled fescue losses incurred as a result of excessive winter rainfall and ice that affected the 8E system the most. Removing the impact of these costs, however, had little impact on the ranking of the production systems, and as a result this effect was considered of little consequence for subsequent analyses.2 For both heifers and steers, the 8L system had highest average partial returns, and Fig. 1 revealed superior returns for most of the range of observations for both steers and heifers (CDF lies furthest to the right). Increasing the rotation frequency (8L) thus improved partial returns to the producer mainly by way of higher weaning weight but this was not statistically significant when compared with 2L (Coffey et al., 2005).
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Fig. 1. Comparison of empirical cumulative distribution functions of partial returns per cow at time of weaning for heifers (Panel A = Heifers) and steers (Panel B = Steers) born in 2000 through 2002. Production systems are defined by the number of paddocks and implies rotation frequency (2 is rotating twice monthly and 8 is rotating twice weekly) whereas the letter represents early (E) weaning in April vs. 56 d later (L). The number of observations is presented in parentheses for each production system. PR = partial returns.
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Fig. 2. Comparison of empirical cumulative distribution functions of partial returns per cow for steer calves born in 2000 through 2002 and sold at time of weaning (Panel A = Weaning) vs. time of feedlot placement (Panel B = Feedlot) and time of finish (Panel C = Finish). Production systems are defined by the number of paddocks and implies rotation frequency (2 is rotating twice monthly and 8 is rotating twice weekly) whereas the letter represents early (E) weaning in April vs. 56 d later (L). The number of observations is presented in parentheses for each production system. PR = partial returns.
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Table 7 and Fig. 2 exhibit the comparison of partial returns by steer production system for different times of sale (weaning vs. feedlot vs. finish). On the revenue side, the late weaning systems showed the best performance regardless of sale time, although the gap in weight and revenue was largely closed between 2E, 2L, and 8L by time of cattle slaughter. At the same time, comparison of least squares means revealed that while the 8L system proved superior across sale times, the 2L system had statistically similar returns. This suggests, again, that the higher rotation frequency is not economically justifiable given also the reported lack of differences in relative pasture performance for this study (Coffey et al., 2005). As mentioned previously, failure of more intensive rotational management to improve individual animal gains is not uncommon (Volesky et al., 1990; Bertelsen et al., 1993; Hoveland et al., 1997; Barker et al., 1999; Lomas et al., 2000).
On the cost side, small weight gains for the late-weaned calves over the hot part of the summer grazing period lead to high cost of gain for the period between weaning and time of placement. Early weaned calf weight gains proved superior to late-weaned calf weight gains over this period mainly because early weaned calf gains included gains from the 56-d feeding period at the start of the summer grazing period that is associated with cooler seasonal temperatures. All calves, regardless of production system, were not managed for high rates of gain during the summer period and therefore experienced attractive feedlot performance likely due to compensatory weight gain.
Three other results are interesting. One, the range of return observations increased with the length of time that ownership on the calves was retained (CDF plots became flatter when moving from Panel A to Panel C in Fig. 2). Two, the statistical ranking (bottom row of Table 7) of production systems for the two best performing systems (8L and 2L) did not change with the time of sale. Three, retaining ownership through the finishing phase in the feedlot resulted in the highest partial returns regardless of pasture rotation frequency and weaning date (P < 0.0149). These improvements in partial return per cow by retaining ownership through the finishing phase compared with sale at time of weaning ranged from 9.4% (8L) to 17.4% (2E) or from $44.66 (8L) to $72.47 (2E).
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CONCLUSIONS
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Cow–calf producers facing similar conditions as those described in this study may be advised that (i) early weaned calves did not regain the weight disadvantage observed at time of weaning, relative to late-weaned calves; (ii) more intensive pasture management (rotating twice weekly rather than twice monthly) was not worth the effort because partial return results for late-weaned steer and heifer calves did not differ statistically by rotation frequency regardless of sale time; (iii) partial returns were highest for calves retained through the finishing stage at the feedlot (regardless of production system) compared with sale at time of weaning or time of placement in the feedlot; (iv) the range of returns or financial risk exposure increased with length of calf ownership (excluding input price risk and only partially accounting for output price risk).
The study could be improved by increasing the number of years of observations to be able to determine trends in beef and/or pasture production associated with rotation frequency and weaning time as well as the incorporation of observed price risk. Also, the study utilized an average five-market weighted average price for cattle sales at time of finish. This was deemed appropriate since calves were sourced from similar genetic backgrounds and fed using the same feedlot ration during the same period of time in the feedlot each year. Results may have differed with more observations, which might have allowed capturing more individual performance statistics. For example, steers might be fed for different periods in the feedlot each year and thereby finish with potentially different quality grades.
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ACKNOWLEDGMENTS
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This project was funded in part by Grant No. 2001-35209-10079 from the USDA National Research Initiative Competetive Grants Agri-Systems Program. The authors also appreciate the support of the Division of Agriculture, University of Arkansas.
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NOTES
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1 The repair cost factor determines repair and maintenance cost as a percentage of original purchase price. 
2 Authors can be contacted for additional information.
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ABSTRACT
INTRODUCTION
for months of transactions used.