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Setting stocking rate of steers grazing wheat pasture based on forage allowance1
The Professional Animal Scientist 31 (2015):434–442; http://dx.doi.org/10.15232/pas.2015-01410 ©2015 American Registry of Professional Animal Scientists
Sgrazing etting stocking rate of steers wheat pasture based on forage allowance1
P. Beck,*2 PAS, S. Gadberry,† PAS, D. Hubbell,‡ and T. Hess‡ *Division of Agriculture, Southwest Research and Extension Center, University of Arkansas, 362 Hwy 174 N, Hope 71801; †Division of Agriculture, Cooperative Extension Service, University of Arkansas, 2301 S. University Ave. Rm. 308F, Little Rock 72204; and ‡Division of Agriculture, Livestock and Forestry Research Center, University of Arkansas, 70 Experiment Station Dr., Batesville 72701
ABSTRACT Performance of heavy BW (HVY, n = 16 steers per experiment in 4 pastures, BW ± SD = 285 ± 18.1 kg) and light BW (LT, n = 12 steers in 3 pastures in Exp. 1 and n = 16 steers in 4 pastures in Exp. 2, BW ± SD = 193 ± 18.8 kg) steers stocked to wheat pasture at 2.5 steer/ha was compared with LT BW steers stocked on wheat pastures at equivalent forage allowance to HVY steers (LTFA, n = 20 in 3 pastures in Exp. 1 and n = 23 in 4 pastures in Exp. 2, BW ± SD = 190 ± 13.7 kg). Grazing periods were 177 d (Exp. 1) and 133 d (Exp. 2). Fall ADG of LT was greater (P < 0.01) than LTFA and tended (P = 0.07) to be greater than HVY, whereas HVY and LTFA did not differ (P = 0.38). During the spring, ADG of HVY and LT were greater than (P < 0.01) those of LTFA. Grazing days per hectare was greater (P < 0.01) for LTFA than HVY and LT, yet BW gain per hectare did not differ (P = 0.21). Profit per This project was conducted with funding from the University of Arkansas Agricultural Experiment Station, Hatch Project No. AR002265, and gifts from Elanco Animal Health Stocker District (Guthrie, OK). 2 Corresponding author: [email protected] 1
hectare did not differ (P = 0.73) among treatments, averaging $781 ± 350/ha. Even though changes in animal production were observed, the lack of difference in profitability per hectare suggests that additional light BW calves can be stocked during the fall with little effect on total enterprise profitability. Key words: growing calf, forage allowance, stocking rate, wheat pasture
INTRODUCTION Cool-season annual grasses provide high-quality forage during the fall and winter, a time of year that high-quality growing forage is scarce (Beck et al., 2005; Bowman et al., 2008; Morgan et al., 2012). The nutrient-dense nature of cool-season annual forages indicates that reductions in animal performance are likely due to restrictions in forage availability (Redmon et al., 1995; Gregorini et al., 2011). Forage production of cool-season annual grasses follows a biphasic growth curve in which forage production is much greater in the spring than during the fall and winter, and common stocking rates (SR) are correspondingly greater (4.9 to 7.4 calves/ha) in the spring than in the fall (1.9 to
3.7 calves/ha; Bowman et al., 2008; Morgan et al., 2012). Stocking rate is a fundamental management variable with a distinct relationship to animal performance (Bransby et al., 1988). If SR can be matched with available forage, then opportunities to achieve the desired level of performance are more certain, if expected forage quality is available. Setting SR based on forage allowance (FA; defined as the kilograms of available forage DM per kilogram of calf BW) allows us to objectively set SR for desired performance. Beck et al. (2013) compiled the forage and animal performance data from 8 yr of experiments on wheat (Triticum aestivum L.) pasture (reported in Bowman et al., 2008; Morgan et al., 2012) and determined that an initial FA of 5 kg of forage DM/kg of calf BW maximized ADG at 1.24 kg/d. Although the forage-allowance analysis in Beck et al. (2013) provides important management information, BW of all calves used in this analysis were within a narrow range. Dry matter intake by grazing calves is, to a large extent, determined not by BW but by metabolic BW (NRC, 1996), which is used in determination of animal unit equivalency (Meyer et al., 2012). This research was designed
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to determine the relationship between SR, FA and performance of growing steers of varying BW on wheat pasture over multiple years.
MATERIALS AND METHODS All procedures in the following experiments were approved by the University of Arkansas Institutional Animal Care and Use Committee (Protocol #12053). Two experiments compared heavy (HVY) and light (LT) BW growing steers placed on wheat pasture during the fall at equivalent SR of 2.5 steer/ ha and LT BW steers stocked on wheat pastures at equivalent FA to HVY steers (LTFA) at the University of Arkansas Livestock and Forestry Branch Station near Batesville, Arkansas (35°50′N, 91°48′W; elevation 150 m).
Treatments and Grazing Management This research was conducted in 2 experiments over 2 consecutive years. A summary of treatments, SR, FA, and grazing dates is presented in Table 1. In the HVY treatment, steers (n = 16 per experiment, BW ± SD = 282 ± 15.8 kg and 287 ± 20.3 kg in Exp. 1 and 2, respectively) were placed on 1.6-ha wheat pastures (n = 4 in each experiment) during the fall grazing season at a SR of 2.5 steers/ ha with FA of 3.3 ± 0.70 kg of forage DM/kg of steer BW in Exp. 1 and 2.4 ± 0.25 kg of forage DM/kg of steer BW in Exp. 2. In the LT treatment, steers (n = 12 in Exp. 1 and 16 in Exp. 2, BW ± SD = 189 ± 14.8 kg and 196 ± 21.8 kg in Exp. 1 and 2, respectively) were placed on 1.6-ha wheat pastures (n = 3 in Exp. 1 and 4 in Exp. 2) during the fall grazing season at a SR of 2.5 steers/ha with FA of 5.3 ± 0.34 kg of forage DM/kg of steer BW in Exp. 1 and 3.7 ± 1.01 kg of forage DM/kg of steer BW in Exp. 2. In the LTFA treatment, steers (n = 20 in Exp. 1 and 23 in Exp. 2, BW ± SD = 191 ± 13.7 kg and 197 ± 21.1 kg in Exp. 1 and 2, respectively) were placed on 1.6-ha wheat pas-
tures (n = 3 in Exp. 1 and 4 in Exp. 2) during the fall grazing season at a SR that would provide steers with equivalent FA to HVY (FA of 3.2 ± 0.24 kg of forage DM/kg of initial steer BW in Exp. 1 and 2.3 ± 0.24 kg of forage DM/kg of initial steer BW in Exp. 2). Because the SR of LTFA was based on FA, the SR ranged from 3.75 to 4.38 steers/ha in Exp. 1 and 1.88 to 5.00 steers/ha in Exp. 2. Grazing was initiated for all treatments on November 7, 2012, and December 18, 2013, in Exp. 1 and 2,
respectively. In Exp. 1, steers in HVY treatment were removed from pastures on February 15, 2013, and replaced with a new set of spring-purchased steers (n = 9 per pasture, BW ± SD = 282 ± 18.4 kg) for the spring grazeout period on March 1, 2013, whereas steers in LT and LTFA remained on pastures through the spring graze-out period (with the exception of an 11-d period with limited forage availability from March 29 to April 9 for LTFA). Additional spring-purchased steers (BW ± SD = 283 ± 12.6 kg) were
Table 1. Summary of treatments, stocking rates, initial forage availability, and grazing dates for Exp. 1 and 2 Treatment1 Item Exp. 1 Fall grazing season Grazing initiation Grazing termination Stocking rate, steer/ha Initial forage mass2 Forage allowance3 Spring grazing season Grazing initiation Grazing termination Stocking rate,4 steer/ha Added steers/pasture5 Exp. 2 Fall grazing season Grazing initiation Grazing termination Stocking rate, steer/ha Initial forage mass2 Forage allowance3 Spring grazing season Grazing initiation Grazing termination Stocking rate,4 steer/ha Added steers5
HVY
LT
Feb 15, 2013 2.5 2,032 ± 172 3.3 ± 0.70
Nov 7, 2012 — 2.5 2,230 ± 198 5.3 ± 0.34
— 3.75 to 4.38 2,208 ± 198 3.2 ± 0.24
Mar 1, 2013
LTFA
5.63 9
Feb 15, 2013 Apr 26 to May 9 5.63 5
Feb 15, 2013 5.63 2 to 3
2.5 1,513 ± 208 2.4 ± 0.25
Dec 18, 2013 Feb 4, 2014 2.5 1,606 ± 208 3.7 ± 1.01
1.88 to 5.00 1,423 ± 208 2.3 ± 0.24
5.63 9
Mar 13, 2014 May 1, 2014 5.63 5
5.63 2 to 6
Treatments: HVY = heavy BW steers (285 ± 18.1 kg) stocked at 2.5 steers/ha; LT = light BW steers (193 ± 18.8 kg) stocked at 2.5 steers/ha; and LTFA = light BW steers (190 ± 13.7 kg) stocked at stocking rates to provide equivalent average initial forage allowance to HVY. 2 Kilograms of forage DM per hectare. 3 Kilograms of forage DM per 100 kg of steer BW. 4 Steers were added to pastures to increase stocking rate to 5.63 steers/ha (n = 9 total steers/pasture). 5 Steers in HVY treatment were removed from pastures on February 4, 2014, and replaced with a new set of steers (n = 9 per pasture) for the spring graze-out period on March 13, 2014, while steers in LT and LTFA were put back on original pastures through the spring graze-out period with additional spring-purchased steers added to LT and LTFA to increase stocking rate to 5.63 steers/ha. 1
436 added to LT and LTFA on March 1, 2013, to increase spring graze-out SR to 5.63 steers/ha (n = 9 total steers per pasture). Steers were removed from pastures to end the spring graze-out as required by either limited forage availability (<1,000 kg/ha) or limiting forage quality (below 11% CP and 60% TDN, NRC, 1996) between April 26 and May 9, 2013. In Exp. 2, ice and snow cover of wheat pastures made it necessary to remove all cattle from pastures on February 4, 2014. Steers in HVY were replaced with a new set of spring-purchased steers (n = 9 per pasture, BW ± SD = 247 ± 36.0 kg) as described for Exp. 1 on March 13, 2014. Steers in LT and LTFA treatments were held in drylot pens and fed bermudagrass hay (10% CP and 56% TDN) and 1 kg of corn gluten feed–based supplement daily until their return to wheat pasture for the spring graze-out period on March 13, 2014. Additional spring-purchased steers (BW ± SD = 248 ± 30.6 kg) were added to LT and LTFA on March 13, 2013, to increase spring graze-out SR to 5.63 steers/ ha (n = 9 total steers per pasture). Steers were removed from pastures to end the spring graze-out on May 1, 2014, when forage DM availability became limiting (<1,000 kg/ha).
Animal Management Steers were medium and large frame, muscling score number 1, and Continental or English crossbred. Calves were purchased in September for fall grazing and January for spring graze-out at local sale barns by a cooperating owner, received at the research site, and preconditioned for a minimum of 42 d before initiation of the experiments. Receiving protocols were as described by Poe et al. (2013). Calves were housed in 0.4-ha pens and provided a 22% CP corn gluten feed–based supplement at 1% BW (DM basis) and free-choice access to bermudagrass hay (10% CP and 56% TDN) for the entire 42-d receiving period with an estimated daily cost of $0.97/calf. During Exp.
Beck et al.
2, while LT and LTFA steers were removed from pastures because of ice and snow cover, daily supplement and hay cost was estimated to be $0.97/ calf. Calves gained 0.65 kg/d during the 42-d receiving period, had 51% overall morbidity, 1.6% death loss, and $14.16/calf bovine respiratory disease treatment cost. Total receiving costs were estimated to be $74.50/ calf. Before turnout on pasture, calves were stratified to grazing treatment based on BW and breed characteristics and implanted with 29 mg of tylosin tartrate, 40 mg of trenbolone acetate, and 8 mg of estradiol (Component TE-G with Tylan, Elanco Animal Health, Greenfield, IN). While steers were on pasture, a customblended mineral mixture (Sunbelt Custom Minerals Inc., Sulfur Springs, TX) was offered ad libitum in covered mineral feeders located in each pasture. The mineral mixtures contained 14% Ca and 7% P from CaCO3 and Ca2PO4, 5% Mg from MgO, and 14% NaCl as well as vitamins (661,500 IU/kg vitamin A, 221 IU/kg vitamin E, and 66,150 IU/ kg vitamin D) and trace minerals (1,000 mg/kg Mn from MnSO4, 2,355 mg/kg Fe from FeSO4, 1,250 mg/kg Cu from CuSO4, 3,000 mg/kg Zn from ZnSO4, 20 mg/ kg Co from CoCO3, and 25 mg/kg I from ethylenediamine dihydroiodide) designed to meet NRC (1996) requirements. Free-choice mineral intake was assumed to be 114 g/d based on the product label with a cost of $0.98/ kg of mineral. Steer BW was based on a single weight recorded following 16-h removal from feed and water at the beginning and end of each grazing period and at 28-d intervals during the grazing periods.
Pasture Establishment The study site consisted of Peridge silt loam soil, a deep well-drained upland soil with moderate native fertility. Wheat (Exp. 1 cultivar Oakes and Magnolia, AgriPro, Sengenta Cereals, Berthoud, CO; Exp. 2 cultivar Roane, University of Arkan-
sas Pinetree Research Station, Colt, AR) was established the first week of September each year by planting wheat at 100 kg/ha to a depth of 2.5 cm in dedicated wheat fields using no-till techniques as described by Bowman et al. (2008) and Morgan et al. (2012). The pastures used in this study have been in continuous notill for 8 yr. Briefly, no-till pastures were sprayed with 48.7% glyphosate (Roundup Original Max, Monsanto Co., St. Louis, MO) 3 times (on removal of calves following graze-out the previous spring, midsummer, and before planting) as a chemical fallow, and wheat was planted directly into the residue of the previous crop, with >85% ground cover from residue. Pastures were fertilized with 56 kg of N/ ha as ammonium nitrate in both the fall and spring. Cost of establishment and management of wheat pasture was estimated at $355/ha (Anders et al., 2007). During the fall, pastures were continuously stocked beginning when forage height was visually estimated to have reached approximately 20 cm in early November of Exp. 1 and in December of Exp. 2. In Exp. 1, HVY steers from fall and winter grazing were removed from pastures and replaced with another set of steers when forage growth accelerated necessitating the increase in SR for the graze-out period. Fall steers from LT and LTFA remained on pastures, with additional calves added to increase grazing pressure for the spring grazeout period. At the end of winter grazing in Exp. 2, all cattle were removed when forage mass reached <1,000 kg of DM/ha, a level that limits OM intake by calves (Redmon et al., 1995). At the end of the spring grazeout period, all cattle were removed from pasture when residual forage mass (Redmon et al., 1995) or forage maturity reduced nutritive quality (CP or digestibility, NRC, 1996) to limit animal performance. Steers in all pastures were allowed free access to drinking-water sourced from a well in automatic-fill freeze-proof containers (Mirafount 3390, MIRACO Livestock Water Systems, Grinnell, IA).
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Pasture Sampling Forage mass in each pasture was estimated monthly during the grazing season using a calibrated disk meter with 20 sampling points per pasture (Michell and Large, 1983). Calibration samples were collected by clipping all
forage within a single 0.1-m2 frame in each pasture at each sampling to 2.5cm stubble height with hand shears. Clipped calibration samples were dried to a constant weight under forced air at 50°C. Dry weights of these clippings were used to relate forage mass (kg of DM/ha) to plate
height within each treatment using linear regression for forage mass prediction. Forage mass prediction equations for the rising plate data were generated using the regression procedure of SAS (SAS Institute Inc., Cary, NC) using the clipping data for each collection period. The regression of rising plate reading on clipped DM mass resulted in equations that explained ≥97% of the variation (P < 0.01) in forage mass (kg/ha). At the time of rising plate meter readings, forage samples were collected to be representative of diets consumed by grazing calves from all pastures by clipping forage to mimic forage selected. Samples were dried to constant weight at 50°C in a forced-air oven, ground to pass a 2-mm screen (Thomas A. Wiley Laboratory Mill, Model 4, Thomas Scientific, Swedesboro, NJ) for nutrient analysis using near-infrared reflectance spectroscopy (Feed & Forage Analyzer model 6500, FOSS North America, Eden Prairie, MN). The CP calibration equation had a SE of calibration of 0.92, a SE of cross validation of 0.93, and R2 of 0.96. The NDF calibration equation had a SE of calibration of 2.63, a SE of cross validation of 2.73, and R2 of 0.95. The ADF calibration equation had a SE of calibration of 1.66, a SE of cross validation of 1.70, and R2 of 0.93. Total digestible nutrient content of forages was calculated using the equation developed in Arkansas (Davis et al., 2002) for cool-season annual forages.
Economic Analysis
Figure 1. Forage nutritive quality (mean ± SD) during the fall and spring grazing seasons in Exp. 1.
Enterprise budgeting techniques were used to compute expected values for revenue, costs, and net returns for each grazing treatment. Production costs included both pasture establishment (herbicide, planting, labor, and fertilizer) and animal management costs (total receiving costs, hay and supplement when LT and LTFA were removed from pastures, labor, and mineral). Price and profitability scenarios were constructed using 5-yr average Arkansas prices from 2009 to 2014 of medium-framed, number
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Statistical Analysis Data were analyzed as a randomized complete block design using the mixed-models procedure of SAS and pasture within each experiment was the experimental unit, individual calf was the sampling unit, experiment was considered the random block and was used in the random statement, and the fixed effect in the model was treatment. Least squares means were separated using the predicted differences option in SAS. Statistical significance was declared when P ≤ 0.05, and tendencies were considered to be 0.05 < P ≤ 0.10.
RESULTS AND DISCUSSION Forage Nutritive Quality
Figure 2. Forage nutritive quality (mean ± SD) during the fall and spring grazing seasons in Exp. 2.
1 steers. Purchase prices were based on reported Arkansas auction market prices in October for fall of Exp. 1, in November for fall of Exp. 2, and January for spring of Exp. 1 and 2. Sales prices were based on reported Arkansas auction market prices in February for fall-graze HVY steers and May for all other steers. Steer prices were
adjusted from the closest BW range reported by applying a $0.09/kg price slide. Values of BW gain were determined by subtracting the initial cost per steer from the sales price per steer and dividing by the amount of BW gain. Net return was calculated by subtracting total steer and production costs from calculated proceeds.
Mean (±SD) forage CP, NDF, ADF, and TDN (% DM basis) for Exp. 1 and 2 are presented in Figures 1 and 2, respectively. As discussed in Beck et al. (2013), wheat pasture herbage was extremely high in CP, containing in excess of 25% CP (DM basis) at all points during the experiment except for at the end of graze-out in both experiments (Figures 1 and 2). Wheat forage was also low in fiber, containing from ≤50% NDF and 25% ADF (DM basis) at all times. Calculated TDN content of the wheat forage was thus in excess of 70% DM basis during both experiments of the study, which is equivalent to NEm and NEg of 1.63 and 1.04 Mcal/kg, respectively (NRC, 1996). The CP content was in excess of requirements, and estimated energy content of the forages was adequate for a 250-kg growing steer to gain at least 1.13 kg/d (NRC, 1996) during the grazing periods of both experiments.
Forage Mass and Forage Allowance Forage mass (Table 2) from November through January did not differ among treatments (P ≥ 0.38), averaging 2,156 ± 198.1, 2,263 ± 760.2, and 2,507 ± 138.1 kg of DM/ha for November, December, and January, respectively. Whereas in February,
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forage mass of LT was 21% greater (P = 0.03) than HVY and 37% greater (P < 0.01) than LTFA. During the spring graze-out period, forage mass of HVY and LT during March was 58 and 65% greater (P < 0.01) than LTFA, respectively, but did not differ (P ≥ 0.64) on the April or May sampling date. As expected, FA (Table 2) during the fall grazing period from November to February was greater (P < 0.01) for LT than HVY and LTFA, which did not differ (P ≥ 0.23). At the start of the spring graze-out period in March, FA of HVY and LT were 59% greater (P ≤ 0.01) than LTFA, but FA did not differ (P ≥ 0.57) among treatments during April or May. Until the start of graze-out in March, forage mass in this experiment did not reach the critical values identified by Redmon et al. (1995), which was the forage level above which forage digestibility (1,339 kg/ ha), forage OM intake (1,243 kg/ha), and estimated ADG (1,264 kg/ha)
was found to plateau, indicating that the available forage mass would not be expected to limit forage intake or animal performance during fall and winter grazing. Gregorini et al. (2011) found that as herbage mass decreased, grazing steers altered grazing patterns by increasing eating steps per minute, eating distance, bite rate, and area grazed while decreasing intake per feeding station, bite depth, and bites per feeding station to sustain diet quality and minimize effects on herbage intake in the short term. But as reported by Redmon et al. (1995), sustained DMI cannot be maintained because forage mass becomes limiting. As FA declines, Redmon et al. (1995) found that forage intake and forage digestibility decline, which leads to decreases in animal performance (Redmon et al., 1995; Pinchak et al., 1996). Beck et al. (2013) reported that during the fall, wheat pasture ADG is maximized at 1.24 kg/d with FA of 3.5 kg of forage DM/ kg of steer BW, whereas McCartor
and Rouquette (1977) reported that gains of steers grazing pearl millet was maximized at a FA of 3.3 kg of forage DM/kg of steer BW, which indicates this plateau in animal performance may be universal across forage species.
Animal Performance and Economics The effect of fall SR and BW on performance of steers grazing wheat pasture across both experimental years is presented in Table 3. As per the design of the experiment, initial BW of steers in HVY (285 ± 4.3 kg/ steer) was greater (P < 0.01) than LT (193 ± 4.3 kg/steer) and LTFA (194 ± 4.3 kg/steer). Total BW gain during the fall was greater (P = 0.01) for LT (90 ± 4.3 kg) than LTFA (81 ± 4.3 kg). Steers in HVY (86 ± 4.3 kg) tended (P = 0.10) to have greater fall total BW gain than LTFA but did not differ (P = 0.31) from LT. Fall ADG of LT (1.22 ± 0.05 kg/d) was
Table 2. Effect of fall stocking rate and BW on forage mass (kg of DM/ha) and forage allowance (kg of forage DM/100 kg of BW) during the fall and spring grazing seasons Treatment1 Item Forage mass, kg of DM/ha November December January February March April May Forage allowance, kg of DM/100 kg of BW November December January February March April May
HVY
2,032 2,138 2,372 1,677a 1,676b 1,132 1,186 2.8a 3.2a 3.1a 2.0a 1.2b 0.7 0.7
LT
2,208 2,298 2,645 2,033b 1,747b 917 973 4.4b 5.2b 4.9b 3.2b 1.2b 0.6 0.6
LTFA
2,229 2,353 2,506 1,483a 1,058a 1,011 1,055 2.7a 3.3a 2.8a 1.6a 0.7a 0.6 0.6
SEM
198.1 760.2 138.1 978.9 414.1 304.9 263.1 0.57 0.42 0.29 0.24 0.18 0.13 0.12
P-value
0.71 0.55 0.38 0.01 0.01 0.64 0.67 <0.01 <0.01 <0.01 <0.01 0.04 0.57 0.60
Least squares means within rows with differing superscripts differ (P ≤ 0.05). Treatments: HVY = heavy BW steers (285 ± 18.1 kg) were stocked at 2.5 steers/ha with average initial forage allowance of 3.3 and 2.4 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively; LT = light BW steers (193 ± 18.8 kg) were stocked at 2.5 steers/ ha with average initial forage allowance of 5.3 and 3.7 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively; and LTFA = light BW steers (190 ± 13.7 kg) stocked at stocking rates to provide equivalent average initial forage allowance to HVY (3.2 and 2.3 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively).
a,b 1
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Table 3. Effect of fall stocking rate and BW on performance of steers grazing wheat pasture during the fall and spring grazing seasons Treatment1 Item Fall grazing season Gain, kg/steer ADG, kg/d Grazing days/ha BW gain/ha, kg Spring grazing season2 Gain, kg/steer ADG, kg/d Grazing days/ha BW gain/ha, kg Economic analysis Cost of gain, $/kg Fall purchase Spring purchase Value of gain, $/kg Fall purchase Spring purchase Profit, $/steer Fall purchase Spring purchase
HVY
LT
LTFA
86ab 1.13ab 175a 204a
90b 1.22b 185a 225a
81a 1.09a 284b 310b
65a 1.18b 308 362
65a 1.18b 308 358
56b 0.98a 309 308
1.87c 1.90a 1.93a 3.55 57.87a 109.66
1.29a 1.95a 2.43b 3.38 195.07c 96.84
1.53b 2.40b 2.59b 3.59 168.09b 92.44
SEM
4.3 0.05 80.4 95.8 2.5 0.12 40.3 23.0 0.55 0.17 0.29 0.17 22.90 11.40
P-value
0.03 0.02 0.03 <0.01 <0.01 <0.01 0.52 0.20 <0.01 0.03 <0.01 0.33 <0.01 0.28
Least squares means within rows with differing superscripts differ (P ≤ 0.05). Treatments: HVY = heavy BW steers (285 ± 18.1 kg) were stocked at 2.5 steers/ha with average initial forage allowance of 3.3 and 2.4 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively; LT = light BW steers (193 ± 18.8 kg) were stocked at 2.5 steers/ha with average initial forage allowance of 5.3 and 3.7 kg of forage DM/ kg of steer BW in Exp. 1 and 2, respectively; and LTFA = light BW steers (190 ± 13.7 kg) stocked at stocking rates to provide equivalent average initial forage allowance to HVY (3.2 and 2.3 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively). 2 Steers in HVY treatment were removed from pasture at the end of the fall grazing season and were replaced with 5.6 steers/ha for the spring grazing season. Steers in LT and LTFA treatments remained on pasture (Exp. 1) or were returned to pastures (Exp. 2) for the spring grazing season with additional steers added to bring stocking rate up to 5.63 steer/ha. a–c 1
greater (P < 0.01) than LTFA (1.09 ± 0.05 kg/d) and tended (P = 0.07) to be greater than HVY (1.13 ± 0.05 kg/d), whereas HVY and LTFA did not differ (P = 0.38). Grazing days per hectare during the fall grazing period was increased (P < 0.01) with LTFA by 38 and 52% compared with LT and HVY, respectively, which did not differ (P = 0.68). Performance of steers during the fall averaged in excess of 1.14 kg/d, which is in agreement with other research conducted at this laboratory in previous years (Beck et al., 2013; Beck et al., 2014). The decrease in BW gain and ADG in LTFA in comparison
with LT is in agreement with Morgan et al. (2012), who found linear decreases in BW gain and ADG with increasing SR of calves grazing wheat pasture. Horn et al. (1995) reported that ADG of steers grazing wheat pasture at SR of 1.24 or 1.51 steer/ ha did not differ (0.91 and 0.94 kg/d) but ADG decreased to 0.8 kg/d at SR of 1.79 steer/ha. Even though steers in HVY and LT were managed using the same SR, the tendency for improved performance in LT indicates that increasing FA can result in increased animal performance as shown in the analysis reported in Beck et al. (2013). Beck
et al. (2013) reported in a nonlinear analysis of 8 yr of wheat pasture grazing experiments containing 117 records that maximum ADG of 1.24 kg/d was expected at an average FA of 3.5 kg of forage DM/kg of steer BW, which is very similar to the ADG of LT steers in the current experiment (1.22 kg/d). An analysis of the forage mass and BW during the experiment reported by Horn et al. (1995) showed that average FA of the 1.24 and 1.51 steer/ha SR (which did not differ in ADG) were 5.0 and 3.7 kg of forage/kg of steer BW, respectively, yet the average FA of the 1.79 steer/ha SR (which had lesser ADG than lower SR treatments) was 2.46 kg of forage/kg of steer BW, supporting the analysis reported by Beck et al. (2013). Fieser et al. (2006) reported that peak fall and winter ADG of steers stocked to wheat pastures based on initial FA was achieved at 7.0 kg of forage DM/kg of steer BW, which is only slightly greater than the plateau of 5.0 kg of initial forage/kg of steer BW identified by Beck et al. (2013). Setting SR of steers of varying BW based on FA (HVY vs. LTFA) resulted in the numerical reduction in ADG and tendency for reduced BW gain per steer. This may indicate that using FA based on BW alone may lead to overstocking of pastures when smaller calves are used and perhaps SR should be based on FA on a metabolic BW basis. By design, during the spring grazeout period the initial BW of the steers added to pastures did not differ (P = 0.52) among treatments, averaging 261 ± 20.4 kg/steer. Possibly related to greater forage mass and FA (Table 2), during the spring, ADG and total BW gain were increased (P < 0.01) by 20 and 16%, respectively, in HVY and LT compared with LTFA (Table 3). Grazing days per hectare in the spring were not affected (P = 0.52) by treatment, because SR and calendar grazing days were managed similarly among treatments during the graze-out period. Spring BW gain per hectare, although not differing statistically (P = 0.20), was numerically 50 and 54 kg/ha less for LTFA
Forage allowance for grazing steers
Figure 3. Steer BW on removal from wheat pastures stocked with heavy BW steers (HVY) in the fall and replaced with newly purchased steers for spring graze-out, and from pastures stocked with light BW steers during the fall at similar stocking rate (LT) or similar forage allowance (LTFA) to HVY. Additional steers were placed on pastures for spring graze-out. a–cColumns with differing letters differ (P < 0.01).
than HVY or LT, respectively, during the spring graze-out period. Sales BW of fall-purchased HVY (374 ± 33.4 kg/steer) steers, removed from pastures at the end of the fall– winter grazing period in February (Figure 3), were 24 kg heavier (P < 0.01) than sales BW of fall-purchased LT steers (350 ± 33.4 kg/steer) when removed from pastures in May, and fall-purchased LT steers were 24 kg heavier (P < 0.01) than fall-purchased LTFA (326 ± 33.4 kg/steer) upon removal from pasture in May. Bodyweight of steers placed on pasture for spring graze-out did not differ (P = 0.40) among treatments, averaging 325 ± 20.2 kg/steer (Figure 3). Morgan et al. (2012) reported that steer BW, ADG, and BW gain per steer were unaffected by SR in the previous fall. Similar to the management of HVY, in the experiment reported by Morgan et al. (2012), all steers placed on pasture for the fall and winter grazing period were removed, and pastures were not restocked with a new set of calves until pasture regrowth was sufficient, delaying the start of grazing in pastures with the highest SR in 3 yr of the 4-yr study. In the current study, LTFA affected forage development and regrowth during the early
spring graze-out period and reduced forage mass in March, leading to the observed reductions in ADG and BW gain per hectare. Overall grazing days per hectare was 23% greater (P < 0.01) for LTFA than HVY and LT, yet total BW gain per hectare did not differ (P = 0.21) among treatments, although BW gain per hectare (Figure 4) of LTFA was numerically 21 kg greater than HVY and 14 kg greater than LT. Previous research with wheat pasture (Horn et al., 1995; Fieser et al., 2006; Morgan et al., 2012) reported that increasing fall SR increased total grazing days per hectare and total BW gain per hectare, which is in agreement with the numerical increases observed with LTFA in the current experiment. The results of the partial budgeting economic analysis on a per-steer basis are presented in Table 3. Cost of gain per kilogram for steers purchased in the fall was less (P < 0.01) for LT than LTFA, which in turn was less (P < 0.01) than HVY. The reason for lesser cost of gain during the fall for LT than LTFA and HVY is likely because total costs were distributed across more units of BW gain in LT than LTFA and HVY. For calves purchased for the spring graze-out period, cost per kilogram of gain was
441 not different (P = 0.74) for HVY and LT but was greater (P ≤ 0.04) for LTFA than other treatments, which is due to the reduced BW gain of LTFA calves during graze-out. Values of BW gain for cattle purchased in the fall were greater (P < 0.01) for LT ($2.43 ± 0.29/kg) and LTFA ($2.59 ± 0.29/kg) than HVY ($1.93 ± 0.29/ kg) and tended to be greater (P = 0.10) for LTFA than LT, whereas value of BW gain of cattle purchased for spring graze-out did not differ (P = 0.33). Profitability per steer for fall-purchased steers was greater (P < 0.01) for LT ($195.07 ± 22.9/steer) than LTFA ($168.09 ± 22.9/steer), which in turn was greater (P < 0.01) than HVY ($57.87 ± 22.9/steer); the changes in relative profitability among treatments for calves purchased in the fall was due to the changes in BW gain placed on the steers for each of the grazing systems. Profitability per steer for spring-purchased steers did not differ due to treatment, averaging $99.64 ± 11.4/steer. In an economic analysis by Beck et al. (2005), cattle purchased for fall grazing generated average profits ranging from $85 to $116/steer, whereas cattle purchased for spring graze-out were not profitable, which is in disagreement with the current economic analysis and reflects changes in annual cattle price cycle between these analyses. Profitability per steer in the current experiment is similar to that reported for the 5-yr average value of gain by Beck et al. (2014). Profit per hectare did not differ (P = 0.73) among treatments, averaging $781 ± 350/ha. The absence of treatment effects on profitability per hectare even though grazing days per hectare were increased with LTFA treatment is a reflection of BW gain per hectare (Figure 4), which also did not differ (P = 0.21). There was a reduction in performance of LTFA calves during the spring graze-out, which led to increased cost of gain for spring-purchased calves in LTFA treatment (Table 3). Seemingly small reductions in performance can have a large effect on profitability as is observed in the current experiment with
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Beck et al. ficiencies of Arkansas forages for beef cattle. Prof. Anim. Sci. 18:127–134. Fieser, B. G., G. W. Horn, and E. G. Krenzer Jr. 2006. Effects of planting date and forage allowance on steer growth performance and grain yield in a dual-purpose winter wheat system. Prof. Anim. Sci. 22:424–431. Gregorini, P., S. A. Gunter, M. T. Bowman, J. D. Caldwell, C. A. Masino, W. K. Coblentz, and P. A. Beck. 2011. Effect of herbage depletion on short-term foraging dynamics and diet quality of steers grazing wheat pasture. J. Anim. Sci. 89:3824–3830.
Figure 4. Total grazing days per hectare (SE = 120.2), BW gain per hectare (kg/ ha, SE = 105.7), and profit per hectare ($/ha, SE = 158.9) for wheat pastures stocked with heavy BW steers (HVY) in the fall and replaced with newly purchased steers for spring graze-out, or for pastures stocked with light BW steers during the fall at similar stocking rate (LT) or similar forage allowance (LTFA) to HVY. Additional steers were placed on pastures for spring graze-out. a,bColumns with differing letters differ (P < 0.01).
LTFA treatment, yet because greater grazing days per hectare resulted in similar BW gain per hectare, there was no difference in total profit per hectare. Profitability per hectare in the current experiment using recent economic conditions is approximately 3-times larger than profitability of an economic analysis by Beck et al. (2005), which is an indication of the improved economic circumstances of the stocker industry.
IMPLICATIONS Increased FA (kg of forage DM/ kg of steer BW) of LT treatment results in increased BW gain per steer compared with LTFA and HVY calves during the fall, yet increasing SR in LTFA resulted in increased BW gain per hectare compared with LT and HVY during the fall. Increased fall SR in LTFA resulted in reduced spring FA, and steer performance during spring graze-out declined compared with LT and HVY. The lack of difference in profitability per hectare suggests that additional light-BW calves can be stocked during the fall with little effect on total enterprise profitability.
LITERATURE CITED Anders, M., P. Beck, S. Gadberry, and B. Watkins. 2007. Impact of Conservation Tillage Practices on Winter Wheat Production for Grazing Stocker Cattle. Fact Sheet FSA3116. Univ. Arkansas Coop. Ext. Serv., Little Rock. Beck, P., M. Anders, B. Watkins, S. Gunter, D. Hubbell, and S. Gadberry. 2013. Invited: Improving the production, environmental, and economic efficiency of the stocker cattle industry in the Southeastern United States. J. Anim. Sci. 91:2456–2466. Beck, P. A., S. A. Gunter, D. S. Hubbell III, L. B. Daniels, and K. B. Watkins. 2005. Performance of stocker cattle grazing cool-season annual grass mixtures in northern Arkansas. Prof. Anim. Sci. 21:465–473. Beck, P. A., T. Hess, D. Hubbell, G. D. Hufstedler, B. Fieser, and J. Caldwell. 2014. Additive effects of growth promoting technologies on performance of grazing steers and economics of the wheat pasture enterprise. J. Anim. Sci. 92:1219–1227. Bowman, M. T., P. A. Beck, K. B. Watkins, M. M. Anders, M. S. Gadberry, K. S. Lusby, S. A. Gunter, and D. S. Hubbell. 2008. Tillage systems for production of small grain pasture. Agron. J. 100:1289–1295. Bransby, D. I., B. E. Conrad, H. M. Dicks, and J. W. Drane. 1988. Justification for grazing intensity experiments: Analysis and interpreting grazing data. J. Range Manage. 41:274–279. Davis, G. V., M. S. Gadberry, and T. R. Troxel. 2002. Composition and nutrient de-
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. 73:45–54. McCartor, M. M., and F. M. Rouquette Jr. 1977. Grazing pressures and animal performance from pearl millet. Agron. J. 69:983– 987. Meyer, T. L., L. A. Stalker, J. D. Volesky, D. C. Adams, R. N. Funston, T. J. Klopfenstein, and W. H. Schacht. 2012. Technical Note: Estimating beef-cattle forage demand: Evaluating the animal unit concept. Prof. Anim. Sci. 28:664–669. Michell, P., and R. V. Large. 1983. The estimation of herbage mass of perennial ryegrass swards: A comparative evaluation of a risingplate meter and a single probe capacitance meter calibrated at or above ground level. Grass Forage Sci. 38:295–300. Morgan, M. S., P. A. Beck, T. Hess, D. S. Hubbell, and S. Gadberry. 2012. Effects of establishment method and fall stocking rate of wheat pasture on forage mass, forage chemical composition, and performance of growing steers. J. Anim. Sci. 90:3286–3293. NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. Natl. Acad. Press, Washington, DC. Pinchak, W. E., W. D. Worrall, S. P. Caldwell, L. J. Hunt, N. J. Worrall, and M. Conoly. 1996. Interrelationships of forage and steer growth dynamics on wheat pasture. J. Range Manage. 49:126–130. Poe, K., P. Beck, J. T. Richeson, M. S. Gadberry, T. W. Hess, and D. S. Hubbell III. 2013. Effects of respiratory vaccination timing and growth-promoting implant on health, performance, and immunity of high-risk, newly received stocker cattle. Prof. Anim. Sci. 29:413–419. Redmon, L. A., F. T. McCollum III, G. W. Horn, M. D. Cravey, S. A. Gunter, P. A. Beck, J. M. Mieres, and R. San Julian. 1995. Forage intake by beef steers grazing winter wheat with varied herbage allowances. J. Range Manage. 48:198–201.
Sgrazing etting stocking rate of steers wheat pasture based on forage allowance1
P. Beck,*2 PAS, S. Gadberry,† PAS, D. Hubbell,‡ and T. Hess‡ *Division of Agriculture, Southwest Research and Extension Center, University of Arkansas, 362 Hwy 174 N, Hope 71801; †Division of Agriculture, Cooperative Extension Service, University of Arkansas, 2301 S. University Ave. Rm. 308F, Little Rock 72204; and ‡Division of Agriculture, Livestock and Forestry Research Center, University of Arkansas, 70 Experiment Station Dr., Batesville 72701
ABSTRACT Performance of heavy BW (HVY, n = 16 steers per experiment in 4 pastures, BW ± SD = 285 ± 18.1 kg) and light BW (LT, n = 12 steers in 3 pastures in Exp. 1 and n = 16 steers in 4 pastures in Exp. 2, BW ± SD = 193 ± 18.8 kg) steers stocked to wheat pasture at 2.5 steer/ha was compared with LT BW steers stocked on wheat pastures at equivalent forage allowance to HVY steers (LTFA, n = 20 in 3 pastures in Exp. 1 and n = 23 in 4 pastures in Exp. 2, BW ± SD = 190 ± 13.7 kg). Grazing periods were 177 d (Exp. 1) and 133 d (Exp. 2). Fall ADG of LT was greater (P < 0.01) than LTFA and tended (P = 0.07) to be greater than HVY, whereas HVY and LTFA did not differ (P = 0.38). During the spring, ADG of HVY and LT were greater than (P < 0.01) those of LTFA. Grazing days per hectare was greater (P < 0.01) for LTFA than HVY and LT, yet BW gain per hectare did not differ (P = 0.21). Profit per This project was conducted with funding from the University of Arkansas Agricultural Experiment Station, Hatch Project No. AR002265, and gifts from Elanco Animal Health Stocker District (Guthrie, OK). 2 Corresponding author: [email protected] 1
hectare did not differ (P = 0.73) among treatments, averaging $781 ± 350/ha. Even though changes in animal production were observed, the lack of difference in profitability per hectare suggests that additional light BW calves can be stocked during the fall with little effect on total enterprise profitability. Key words: growing calf, forage allowance, stocking rate, wheat pasture
INTRODUCTION Cool-season annual grasses provide high-quality forage during the fall and winter, a time of year that high-quality growing forage is scarce (Beck et al., 2005; Bowman et al., 2008; Morgan et al., 2012). The nutrient-dense nature of cool-season annual forages indicates that reductions in animal performance are likely due to restrictions in forage availability (Redmon et al., 1995; Gregorini et al., 2011). Forage production of cool-season annual grasses follows a biphasic growth curve in which forage production is much greater in the spring than during the fall and winter, and common stocking rates (SR) are correspondingly greater (4.9 to 7.4 calves/ha) in the spring than in the fall (1.9 to
3.7 calves/ha; Bowman et al., 2008; Morgan et al., 2012). Stocking rate is a fundamental management variable with a distinct relationship to animal performance (Bransby et al., 1988). If SR can be matched with available forage, then opportunities to achieve the desired level of performance are more certain, if expected forage quality is available. Setting SR based on forage allowance (FA; defined as the kilograms of available forage DM per kilogram of calf BW) allows us to objectively set SR for desired performance. Beck et al. (2013) compiled the forage and animal performance data from 8 yr of experiments on wheat (Triticum aestivum L.) pasture (reported in Bowman et al., 2008; Morgan et al., 2012) and determined that an initial FA of 5 kg of forage DM/kg of calf BW maximized ADG at 1.24 kg/d. Although the forage-allowance analysis in Beck et al. (2013) provides important management information, BW of all calves used in this analysis were within a narrow range. Dry matter intake by grazing calves is, to a large extent, determined not by BW but by metabolic BW (NRC, 1996), which is used in determination of animal unit equivalency (Meyer et al., 2012). This research was designed
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to determine the relationship between SR, FA and performance of growing steers of varying BW on wheat pasture over multiple years.
MATERIALS AND METHODS All procedures in the following experiments were approved by the University of Arkansas Institutional Animal Care and Use Committee (Protocol #12053). Two experiments compared heavy (HVY) and light (LT) BW growing steers placed on wheat pasture during the fall at equivalent SR of 2.5 steer/ ha and LT BW steers stocked on wheat pastures at equivalent FA to HVY steers (LTFA) at the University of Arkansas Livestock and Forestry Branch Station near Batesville, Arkansas (35°50′N, 91°48′W; elevation 150 m).
Treatments and Grazing Management This research was conducted in 2 experiments over 2 consecutive years. A summary of treatments, SR, FA, and grazing dates is presented in Table 1. In the HVY treatment, steers (n = 16 per experiment, BW ± SD = 282 ± 15.8 kg and 287 ± 20.3 kg in Exp. 1 and 2, respectively) were placed on 1.6-ha wheat pastures (n = 4 in each experiment) during the fall grazing season at a SR of 2.5 steers/ ha with FA of 3.3 ± 0.70 kg of forage DM/kg of steer BW in Exp. 1 and 2.4 ± 0.25 kg of forage DM/kg of steer BW in Exp. 2. In the LT treatment, steers (n = 12 in Exp. 1 and 16 in Exp. 2, BW ± SD = 189 ± 14.8 kg and 196 ± 21.8 kg in Exp. 1 and 2, respectively) were placed on 1.6-ha wheat pastures (n = 3 in Exp. 1 and 4 in Exp. 2) during the fall grazing season at a SR of 2.5 steers/ha with FA of 5.3 ± 0.34 kg of forage DM/kg of steer BW in Exp. 1 and 3.7 ± 1.01 kg of forage DM/kg of steer BW in Exp. 2. In the LTFA treatment, steers (n = 20 in Exp. 1 and 23 in Exp. 2, BW ± SD = 191 ± 13.7 kg and 197 ± 21.1 kg in Exp. 1 and 2, respectively) were placed on 1.6-ha wheat pas-
tures (n = 3 in Exp. 1 and 4 in Exp. 2) during the fall grazing season at a SR that would provide steers with equivalent FA to HVY (FA of 3.2 ± 0.24 kg of forage DM/kg of initial steer BW in Exp. 1 and 2.3 ± 0.24 kg of forage DM/kg of initial steer BW in Exp. 2). Because the SR of LTFA was based on FA, the SR ranged from 3.75 to 4.38 steers/ha in Exp. 1 and 1.88 to 5.00 steers/ha in Exp. 2. Grazing was initiated for all treatments on November 7, 2012, and December 18, 2013, in Exp. 1 and 2,
respectively. In Exp. 1, steers in HVY treatment were removed from pastures on February 15, 2013, and replaced with a new set of spring-purchased steers (n = 9 per pasture, BW ± SD = 282 ± 18.4 kg) for the spring grazeout period on March 1, 2013, whereas steers in LT and LTFA remained on pastures through the spring graze-out period (with the exception of an 11-d period with limited forage availability from March 29 to April 9 for LTFA). Additional spring-purchased steers (BW ± SD = 283 ± 12.6 kg) were
Table 1. Summary of treatments, stocking rates, initial forage availability, and grazing dates for Exp. 1 and 2 Treatment1 Item Exp. 1 Fall grazing season Grazing initiation Grazing termination Stocking rate, steer/ha Initial forage mass2 Forage allowance3 Spring grazing season Grazing initiation Grazing termination Stocking rate,4 steer/ha Added steers/pasture5 Exp. 2 Fall grazing season Grazing initiation Grazing termination Stocking rate, steer/ha Initial forage mass2 Forage allowance3 Spring grazing season Grazing initiation Grazing termination Stocking rate,4 steer/ha Added steers5
HVY
LT
Feb 15, 2013 2.5 2,032 ± 172 3.3 ± 0.70
Nov 7, 2012 — 2.5 2,230 ± 198 5.3 ± 0.34
— 3.75 to 4.38 2,208 ± 198 3.2 ± 0.24
Mar 1, 2013
LTFA
5.63 9
Feb 15, 2013 Apr 26 to May 9 5.63 5
Feb 15, 2013 5.63 2 to 3
2.5 1,513 ± 208 2.4 ± 0.25
Dec 18, 2013 Feb 4, 2014 2.5 1,606 ± 208 3.7 ± 1.01
1.88 to 5.00 1,423 ± 208 2.3 ± 0.24
5.63 9
Mar 13, 2014 May 1, 2014 5.63 5
5.63 2 to 6
Treatments: HVY = heavy BW steers (285 ± 18.1 kg) stocked at 2.5 steers/ha; LT = light BW steers (193 ± 18.8 kg) stocked at 2.5 steers/ha; and LTFA = light BW steers (190 ± 13.7 kg) stocked at stocking rates to provide equivalent average initial forage allowance to HVY. 2 Kilograms of forage DM per hectare. 3 Kilograms of forage DM per 100 kg of steer BW. 4 Steers were added to pastures to increase stocking rate to 5.63 steers/ha (n = 9 total steers/pasture). 5 Steers in HVY treatment were removed from pastures on February 4, 2014, and replaced with a new set of steers (n = 9 per pasture) for the spring graze-out period on March 13, 2014, while steers in LT and LTFA were put back on original pastures through the spring graze-out period with additional spring-purchased steers added to LT and LTFA to increase stocking rate to 5.63 steers/ha. 1
436 added to LT and LTFA on March 1, 2013, to increase spring graze-out SR to 5.63 steers/ha (n = 9 total steers per pasture). Steers were removed from pastures to end the spring graze-out as required by either limited forage availability (<1,000 kg/ha) or limiting forage quality (below 11% CP and 60% TDN, NRC, 1996) between April 26 and May 9, 2013. In Exp. 2, ice and snow cover of wheat pastures made it necessary to remove all cattle from pastures on February 4, 2014. Steers in HVY were replaced with a new set of spring-purchased steers (n = 9 per pasture, BW ± SD = 247 ± 36.0 kg) as described for Exp. 1 on March 13, 2014. Steers in LT and LTFA treatments were held in drylot pens and fed bermudagrass hay (10% CP and 56% TDN) and 1 kg of corn gluten feed–based supplement daily until their return to wheat pasture for the spring graze-out period on March 13, 2014. Additional spring-purchased steers (BW ± SD = 248 ± 30.6 kg) were added to LT and LTFA on March 13, 2013, to increase spring graze-out SR to 5.63 steers/ ha (n = 9 total steers per pasture). Steers were removed from pastures to end the spring graze-out on May 1, 2014, when forage DM availability became limiting (<1,000 kg/ha).
Animal Management Steers were medium and large frame, muscling score number 1, and Continental or English crossbred. Calves were purchased in September for fall grazing and January for spring graze-out at local sale barns by a cooperating owner, received at the research site, and preconditioned for a minimum of 42 d before initiation of the experiments. Receiving protocols were as described by Poe et al. (2013). Calves were housed in 0.4-ha pens and provided a 22% CP corn gluten feed–based supplement at 1% BW (DM basis) and free-choice access to bermudagrass hay (10% CP and 56% TDN) for the entire 42-d receiving period with an estimated daily cost of $0.97/calf. During Exp.
Beck et al.
2, while LT and LTFA steers were removed from pastures because of ice and snow cover, daily supplement and hay cost was estimated to be $0.97/ calf. Calves gained 0.65 kg/d during the 42-d receiving period, had 51% overall morbidity, 1.6% death loss, and $14.16/calf bovine respiratory disease treatment cost. Total receiving costs were estimated to be $74.50/ calf. Before turnout on pasture, calves were stratified to grazing treatment based on BW and breed characteristics and implanted with 29 mg of tylosin tartrate, 40 mg of trenbolone acetate, and 8 mg of estradiol (Component TE-G with Tylan, Elanco Animal Health, Greenfield, IN). While steers were on pasture, a customblended mineral mixture (Sunbelt Custom Minerals Inc., Sulfur Springs, TX) was offered ad libitum in covered mineral feeders located in each pasture. The mineral mixtures contained 14% Ca and 7% P from CaCO3 and Ca2PO4, 5% Mg from MgO, and 14% NaCl as well as vitamins (661,500 IU/kg vitamin A, 221 IU/kg vitamin E, and 66,150 IU/ kg vitamin D) and trace minerals (1,000 mg/kg Mn from MnSO4, 2,355 mg/kg Fe from FeSO4, 1,250 mg/kg Cu from CuSO4, 3,000 mg/kg Zn from ZnSO4, 20 mg/ kg Co from CoCO3, and 25 mg/kg I from ethylenediamine dihydroiodide) designed to meet NRC (1996) requirements. Free-choice mineral intake was assumed to be 114 g/d based on the product label with a cost of $0.98/ kg of mineral. Steer BW was based on a single weight recorded following 16-h removal from feed and water at the beginning and end of each grazing period and at 28-d intervals during the grazing periods.
Pasture Establishment The study site consisted of Peridge silt loam soil, a deep well-drained upland soil with moderate native fertility. Wheat (Exp. 1 cultivar Oakes and Magnolia, AgriPro, Sengenta Cereals, Berthoud, CO; Exp. 2 cultivar Roane, University of Arkan-
sas Pinetree Research Station, Colt, AR) was established the first week of September each year by planting wheat at 100 kg/ha to a depth of 2.5 cm in dedicated wheat fields using no-till techniques as described by Bowman et al. (2008) and Morgan et al. (2012). The pastures used in this study have been in continuous notill for 8 yr. Briefly, no-till pastures were sprayed with 48.7% glyphosate (Roundup Original Max, Monsanto Co., St. Louis, MO) 3 times (on removal of calves following graze-out the previous spring, midsummer, and before planting) as a chemical fallow, and wheat was planted directly into the residue of the previous crop, with >85% ground cover from residue. Pastures were fertilized with 56 kg of N/ ha as ammonium nitrate in both the fall and spring. Cost of establishment and management of wheat pasture was estimated at $355/ha (Anders et al., 2007). During the fall, pastures were continuously stocked beginning when forage height was visually estimated to have reached approximately 20 cm in early November of Exp. 1 and in December of Exp. 2. In Exp. 1, HVY steers from fall and winter grazing were removed from pastures and replaced with another set of steers when forage growth accelerated necessitating the increase in SR for the graze-out period. Fall steers from LT and LTFA remained on pastures, with additional calves added to increase grazing pressure for the spring grazeout period. At the end of winter grazing in Exp. 2, all cattle were removed when forage mass reached <1,000 kg of DM/ha, a level that limits OM intake by calves (Redmon et al., 1995). At the end of the spring grazeout period, all cattle were removed from pasture when residual forage mass (Redmon et al., 1995) or forage maturity reduced nutritive quality (CP or digestibility, NRC, 1996) to limit animal performance. Steers in all pastures were allowed free access to drinking-water sourced from a well in automatic-fill freeze-proof containers (Mirafount 3390, MIRACO Livestock Water Systems, Grinnell, IA).
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Pasture Sampling Forage mass in each pasture was estimated monthly during the grazing season using a calibrated disk meter with 20 sampling points per pasture (Michell and Large, 1983). Calibration samples were collected by clipping all
forage within a single 0.1-m2 frame in each pasture at each sampling to 2.5cm stubble height with hand shears. Clipped calibration samples were dried to a constant weight under forced air at 50°C. Dry weights of these clippings were used to relate forage mass (kg of DM/ha) to plate
height within each treatment using linear regression for forage mass prediction. Forage mass prediction equations for the rising plate data were generated using the regression procedure of SAS (SAS Institute Inc., Cary, NC) using the clipping data for each collection period. The regression of rising plate reading on clipped DM mass resulted in equations that explained ≥97% of the variation (P < 0.01) in forage mass (kg/ha). At the time of rising plate meter readings, forage samples were collected to be representative of diets consumed by grazing calves from all pastures by clipping forage to mimic forage selected. Samples were dried to constant weight at 50°C in a forced-air oven, ground to pass a 2-mm screen (Thomas A. Wiley Laboratory Mill, Model 4, Thomas Scientific, Swedesboro, NJ) for nutrient analysis using near-infrared reflectance spectroscopy (Feed & Forage Analyzer model 6500, FOSS North America, Eden Prairie, MN). The CP calibration equation had a SE of calibration of 0.92, a SE of cross validation of 0.93, and R2 of 0.96. The NDF calibration equation had a SE of calibration of 2.63, a SE of cross validation of 2.73, and R2 of 0.95. The ADF calibration equation had a SE of calibration of 1.66, a SE of cross validation of 1.70, and R2 of 0.93. Total digestible nutrient content of forages was calculated using the equation developed in Arkansas (Davis et al., 2002) for cool-season annual forages.
Economic Analysis
Figure 1. Forage nutritive quality (mean ± SD) during the fall and spring grazing seasons in Exp. 1.
Enterprise budgeting techniques were used to compute expected values for revenue, costs, and net returns for each grazing treatment. Production costs included both pasture establishment (herbicide, planting, labor, and fertilizer) and animal management costs (total receiving costs, hay and supplement when LT and LTFA were removed from pastures, labor, and mineral). Price and profitability scenarios were constructed using 5-yr average Arkansas prices from 2009 to 2014 of medium-framed, number
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Statistical Analysis Data were analyzed as a randomized complete block design using the mixed-models procedure of SAS and pasture within each experiment was the experimental unit, individual calf was the sampling unit, experiment was considered the random block and was used in the random statement, and the fixed effect in the model was treatment. Least squares means were separated using the predicted differences option in SAS. Statistical significance was declared when P ≤ 0.05, and tendencies were considered to be 0.05 < P ≤ 0.10.
RESULTS AND DISCUSSION Forage Nutritive Quality
Figure 2. Forage nutritive quality (mean ± SD) during the fall and spring grazing seasons in Exp. 2.
1 steers. Purchase prices were based on reported Arkansas auction market prices in October for fall of Exp. 1, in November for fall of Exp. 2, and January for spring of Exp. 1 and 2. Sales prices were based on reported Arkansas auction market prices in February for fall-graze HVY steers and May for all other steers. Steer prices were
adjusted from the closest BW range reported by applying a $0.09/kg price slide. Values of BW gain were determined by subtracting the initial cost per steer from the sales price per steer and dividing by the amount of BW gain. Net return was calculated by subtracting total steer and production costs from calculated proceeds.
Mean (±SD) forage CP, NDF, ADF, and TDN (% DM basis) for Exp. 1 and 2 are presented in Figures 1 and 2, respectively. As discussed in Beck et al. (2013), wheat pasture herbage was extremely high in CP, containing in excess of 25% CP (DM basis) at all points during the experiment except for at the end of graze-out in both experiments (Figures 1 and 2). Wheat forage was also low in fiber, containing from ≤50% NDF and 25% ADF (DM basis) at all times. Calculated TDN content of the wheat forage was thus in excess of 70% DM basis during both experiments of the study, which is equivalent to NEm and NEg of 1.63 and 1.04 Mcal/kg, respectively (NRC, 1996). The CP content was in excess of requirements, and estimated energy content of the forages was adequate for a 250-kg growing steer to gain at least 1.13 kg/d (NRC, 1996) during the grazing periods of both experiments.
Forage Mass and Forage Allowance Forage mass (Table 2) from November through January did not differ among treatments (P ≥ 0.38), averaging 2,156 ± 198.1, 2,263 ± 760.2, and 2,507 ± 138.1 kg of DM/ha for November, December, and January, respectively. Whereas in February,
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forage mass of LT was 21% greater (P = 0.03) than HVY and 37% greater (P < 0.01) than LTFA. During the spring graze-out period, forage mass of HVY and LT during March was 58 and 65% greater (P < 0.01) than LTFA, respectively, but did not differ (P ≥ 0.64) on the April or May sampling date. As expected, FA (Table 2) during the fall grazing period from November to February was greater (P < 0.01) for LT than HVY and LTFA, which did not differ (P ≥ 0.23). At the start of the spring graze-out period in March, FA of HVY and LT were 59% greater (P ≤ 0.01) than LTFA, but FA did not differ (P ≥ 0.57) among treatments during April or May. Until the start of graze-out in March, forage mass in this experiment did not reach the critical values identified by Redmon et al. (1995), which was the forage level above which forage digestibility (1,339 kg/ ha), forage OM intake (1,243 kg/ha), and estimated ADG (1,264 kg/ha)
was found to plateau, indicating that the available forage mass would not be expected to limit forage intake or animal performance during fall and winter grazing. Gregorini et al. (2011) found that as herbage mass decreased, grazing steers altered grazing patterns by increasing eating steps per minute, eating distance, bite rate, and area grazed while decreasing intake per feeding station, bite depth, and bites per feeding station to sustain diet quality and minimize effects on herbage intake in the short term. But as reported by Redmon et al. (1995), sustained DMI cannot be maintained because forage mass becomes limiting. As FA declines, Redmon et al. (1995) found that forage intake and forage digestibility decline, which leads to decreases in animal performance (Redmon et al., 1995; Pinchak et al., 1996). Beck et al. (2013) reported that during the fall, wheat pasture ADG is maximized at 1.24 kg/d with FA of 3.5 kg of forage DM/ kg of steer BW, whereas McCartor
and Rouquette (1977) reported that gains of steers grazing pearl millet was maximized at a FA of 3.3 kg of forage DM/kg of steer BW, which indicates this plateau in animal performance may be universal across forage species.
Animal Performance and Economics The effect of fall SR and BW on performance of steers grazing wheat pasture across both experimental years is presented in Table 3. As per the design of the experiment, initial BW of steers in HVY (285 ± 4.3 kg/ steer) was greater (P < 0.01) than LT (193 ± 4.3 kg/steer) and LTFA (194 ± 4.3 kg/steer). Total BW gain during the fall was greater (P = 0.01) for LT (90 ± 4.3 kg) than LTFA (81 ± 4.3 kg). Steers in HVY (86 ± 4.3 kg) tended (P = 0.10) to have greater fall total BW gain than LTFA but did not differ (P = 0.31) from LT. Fall ADG of LT (1.22 ± 0.05 kg/d) was
Table 2. Effect of fall stocking rate and BW on forage mass (kg of DM/ha) and forage allowance (kg of forage DM/100 kg of BW) during the fall and spring grazing seasons Treatment1 Item Forage mass, kg of DM/ha November December January February March April May Forage allowance, kg of DM/100 kg of BW November December January February March April May
HVY
2,032 2,138 2,372 1,677a 1,676b 1,132 1,186 2.8a 3.2a 3.1a 2.0a 1.2b 0.7 0.7
LT
2,208 2,298 2,645 2,033b 1,747b 917 973 4.4b 5.2b 4.9b 3.2b 1.2b 0.6 0.6
LTFA
2,229 2,353 2,506 1,483a 1,058a 1,011 1,055 2.7a 3.3a 2.8a 1.6a 0.7a 0.6 0.6
SEM
198.1 760.2 138.1 978.9 414.1 304.9 263.1 0.57 0.42 0.29 0.24 0.18 0.13 0.12
P-value
0.71 0.55 0.38 0.01 0.01 0.64 0.67 <0.01 <0.01 <0.01 <0.01 0.04 0.57 0.60
Least squares means within rows with differing superscripts differ (P ≤ 0.05). Treatments: HVY = heavy BW steers (285 ± 18.1 kg) were stocked at 2.5 steers/ha with average initial forage allowance of 3.3 and 2.4 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively; LT = light BW steers (193 ± 18.8 kg) were stocked at 2.5 steers/ ha with average initial forage allowance of 5.3 and 3.7 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively; and LTFA = light BW steers (190 ± 13.7 kg) stocked at stocking rates to provide equivalent average initial forage allowance to HVY (3.2 and 2.3 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively).
a,b 1
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Table 3. Effect of fall stocking rate and BW on performance of steers grazing wheat pasture during the fall and spring grazing seasons Treatment1 Item Fall grazing season Gain, kg/steer ADG, kg/d Grazing days/ha BW gain/ha, kg Spring grazing season2 Gain, kg/steer ADG, kg/d Grazing days/ha BW gain/ha, kg Economic analysis Cost of gain, $/kg Fall purchase Spring purchase Value of gain, $/kg Fall purchase Spring purchase Profit, $/steer Fall purchase Spring purchase
HVY
LT
LTFA
86ab 1.13ab 175a 204a
90b 1.22b 185a 225a
81a 1.09a 284b 310b
65a 1.18b 308 362
65a 1.18b 308 358
56b 0.98a 309 308
1.87c 1.90a 1.93a 3.55 57.87a 109.66
1.29a 1.95a 2.43b 3.38 195.07c 96.84
1.53b 2.40b 2.59b 3.59 168.09b 92.44
SEM
4.3 0.05 80.4 95.8 2.5 0.12 40.3 23.0 0.55 0.17 0.29 0.17 22.90 11.40
P-value
0.03 0.02 0.03 <0.01 <0.01 <0.01 0.52 0.20 <0.01 0.03 <0.01 0.33 <0.01 0.28
Least squares means within rows with differing superscripts differ (P ≤ 0.05). Treatments: HVY = heavy BW steers (285 ± 18.1 kg) were stocked at 2.5 steers/ha with average initial forage allowance of 3.3 and 2.4 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively; LT = light BW steers (193 ± 18.8 kg) were stocked at 2.5 steers/ha with average initial forage allowance of 5.3 and 3.7 kg of forage DM/ kg of steer BW in Exp. 1 and 2, respectively; and LTFA = light BW steers (190 ± 13.7 kg) stocked at stocking rates to provide equivalent average initial forage allowance to HVY (3.2 and 2.3 kg of forage DM/kg of steer BW in Exp. 1 and 2, respectively). 2 Steers in HVY treatment were removed from pasture at the end of the fall grazing season and were replaced with 5.6 steers/ha for the spring grazing season. Steers in LT and LTFA treatments remained on pasture (Exp. 1) or were returned to pastures (Exp. 2) for the spring grazing season with additional steers added to bring stocking rate up to 5.63 steer/ha. a–c 1
greater (P < 0.01) than LTFA (1.09 ± 0.05 kg/d) and tended (P = 0.07) to be greater than HVY (1.13 ± 0.05 kg/d), whereas HVY and LTFA did not differ (P = 0.38). Grazing days per hectare during the fall grazing period was increased (P < 0.01) with LTFA by 38 and 52% compared with LT and HVY, respectively, which did not differ (P = 0.68). Performance of steers during the fall averaged in excess of 1.14 kg/d, which is in agreement with other research conducted at this laboratory in previous years (Beck et al., 2013; Beck et al., 2014). The decrease in BW gain and ADG in LTFA in comparison
with LT is in agreement with Morgan et al. (2012), who found linear decreases in BW gain and ADG with increasing SR of calves grazing wheat pasture. Horn et al. (1995) reported that ADG of steers grazing wheat pasture at SR of 1.24 or 1.51 steer/ ha did not differ (0.91 and 0.94 kg/d) but ADG decreased to 0.8 kg/d at SR of 1.79 steer/ha. Even though steers in HVY and LT were managed using the same SR, the tendency for improved performance in LT indicates that increasing FA can result in increased animal performance as shown in the analysis reported in Beck et al. (2013). Beck
et al. (2013) reported in a nonlinear analysis of 8 yr of wheat pasture grazing experiments containing 117 records that maximum ADG of 1.24 kg/d was expected at an average FA of 3.5 kg of forage DM/kg of steer BW, which is very similar to the ADG of LT steers in the current experiment (1.22 kg/d). An analysis of the forage mass and BW during the experiment reported by Horn et al. (1995) showed that average FA of the 1.24 and 1.51 steer/ha SR (which did not differ in ADG) were 5.0 and 3.7 kg of forage/kg of steer BW, respectively, yet the average FA of the 1.79 steer/ha SR (which had lesser ADG than lower SR treatments) was 2.46 kg of forage/kg of steer BW, supporting the analysis reported by Beck et al. (2013). Fieser et al. (2006) reported that peak fall and winter ADG of steers stocked to wheat pastures based on initial FA was achieved at 7.0 kg of forage DM/kg of steer BW, which is only slightly greater than the plateau of 5.0 kg of initial forage/kg of steer BW identified by Beck et al. (2013). Setting SR of steers of varying BW based on FA (HVY vs. LTFA) resulted in the numerical reduction in ADG and tendency for reduced BW gain per steer. This may indicate that using FA based on BW alone may lead to overstocking of pastures when smaller calves are used and perhaps SR should be based on FA on a metabolic BW basis. By design, during the spring grazeout period the initial BW of the steers added to pastures did not differ (P = 0.52) among treatments, averaging 261 ± 20.4 kg/steer. Possibly related to greater forage mass and FA (Table 2), during the spring, ADG and total BW gain were increased (P < 0.01) by 20 and 16%, respectively, in HVY and LT compared with LTFA (Table 3). Grazing days per hectare in the spring were not affected (P = 0.52) by treatment, because SR and calendar grazing days were managed similarly among treatments during the graze-out period. Spring BW gain per hectare, although not differing statistically (P = 0.20), was numerically 50 and 54 kg/ha less for LTFA
Forage allowance for grazing steers
Figure 3. Steer BW on removal from wheat pastures stocked with heavy BW steers (HVY) in the fall and replaced with newly purchased steers for spring graze-out, and from pastures stocked with light BW steers during the fall at similar stocking rate (LT) or similar forage allowance (LTFA) to HVY. Additional steers were placed on pastures for spring graze-out. a–cColumns with differing letters differ (P < 0.01).
than HVY or LT, respectively, during the spring graze-out period. Sales BW of fall-purchased HVY (374 ± 33.4 kg/steer) steers, removed from pastures at the end of the fall– winter grazing period in February (Figure 3), were 24 kg heavier (P < 0.01) than sales BW of fall-purchased LT steers (350 ± 33.4 kg/steer) when removed from pastures in May, and fall-purchased LT steers were 24 kg heavier (P < 0.01) than fall-purchased LTFA (326 ± 33.4 kg/steer) upon removal from pasture in May. Bodyweight of steers placed on pasture for spring graze-out did not differ (P = 0.40) among treatments, averaging 325 ± 20.2 kg/steer (Figure 3). Morgan et al. (2012) reported that steer BW, ADG, and BW gain per steer were unaffected by SR in the previous fall. Similar to the management of HVY, in the experiment reported by Morgan et al. (2012), all steers placed on pasture for the fall and winter grazing period were removed, and pastures were not restocked with a new set of calves until pasture regrowth was sufficient, delaying the start of grazing in pastures with the highest SR in 3 yr of the 4-yr study. In the current study, LTFA affected forage development and regrowth during the early
spring graze-out period and reduced forage mass in March, leading to the observed reductions in ADG and BW gain per hectare. Overall grazing days per hectare was 23% greater (P < 0.01) for LTFA than HVY and LT, yet total BW gain per hectare did not differ (P = 0.21) among treatments, although BW gain per hectare (Figure 4) of LTFA was numerically 21 kg greater than HVY and 14 kg greater than LT. Previous research with wheat pasture (Horn et al., 1995; Fieser et al., 2006; Morgan et al., 2012) reported that increasing fall SR increased total grazing days per hectare and total BW gain per hectare, which is in agreement with the numerical increases observed with LTFA in the current experiment. The results of the partial budgeting economic analysis on a per-steer basis are presented in Table 3. Cost of gain per kilogram for steers purchased in the fall was less (P < 0.01) for LT than LTFA, which in turn was less (P < 0.01) than HVY. The reason for lesser cost of gain during the fall for LT than LTFA and HVY is likely because total costs were distributed across more units of BW gain in LT than LTFA and HVY. For calves purchased for the spring graze-out period, cost per kilogram of gain was
441 not different (P = 0.74) for HVY and LT but was greater (P ≤ 0.04) for LTFA than other treatments, which is due to the reduced BW gain of LTFA calves during graze-out. Values of BW gain for cattle purchased in the fall were greater (P < 0.01) for LT ($2.43 ± 0.29/kg) and LTFA ($2.59 ± 0.29/kg) than HVY ($1.93 ± 0.29/ kg) and tended to be greater (P = 0.10) for LTFA than LT, whereas value of BW gain of cattle purchased for spring graze-out did not differ (P = 0.33). Profitability per steer for fall-purchased steers was greater (P < 0.01) for LT ($195.07 ± 22.9/steer) than LTFA ($168.09 ± 22.9/steer), which in turn was greater (P < 0.01) than HVY ($57.87 ± 22.9/steer); the changes in relative profitability among treatments for calves purchased in the fall was due to the changes in BW gain placed on the steers for each of the grazing systems. Profitability per steer for spring-purchased steers did not differ due to treatment, averaging $99.64 ± 11.4/steer. In an economic analysis by Beck et al. (2005), cattle purchased for fall grazing generated average profits ranging from $85 to $116/steer, whereas cattle purchased for spring graze-out were not profitable, which is in disagreement with the current economic analysis and reflects changes in annual cattle price cycle between these analyses. Profitability per steer in the current experiment is similar to that reported for the 5-yr average value of gain by Beck et al. (2014). Profit per hectare did not differ (P = 0.73) among treatments, averaging $781 ± 350/ha. The absence of treatment effects on profitability per hectare even though grazing days per hectare were increased with LTFA treatment is a reflection of BW gain per hectare (Figure 4), which also did not differ (P = 0.21). There was a reduction in performance of LTFA calves during the spring graze-out, which led to increased cost of gain for spring-purchased calves in LTFA treatment (Table 3). Seemingly small reductions in performance can have a large effect on profitability as is observed in the current experiment with
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Beck et al. ficiencies of Arkansas forages for beef cattle. Prof. Anim. Sci. 18:127–134. Fieser, B. G., G. W. Horn, and E. G. Krenzer Jr. 2006. Effects of planting date and forage allowance on steer growth performance and grain yield in a dual-purpose winter wheat system. Prof. Anim. Sci. 22:424–431. Gregorini, P., S. A. Gunter, M. T. Bowman, J. D. Caldwell, C. A. Masino, W. K. Coblentz, and P. A. Beck. 2011. Effect of herbage depletion on short-term foraging dynamics and diet quality of steers grazing wheat pasture. J. Anim. Sci. 89:3824–3830.
Figure 4. Total grazing days per hectare (SE = 120.2), BW gain per hectare (kg/ ha, SE = 105.7), and profit per hectare ($/ha, SE = 158.9) for wheat pastures stocked with heavy BW steers (HVY) in the fall and replaced with newly purchased steers for spring graze-out, or for pastures stocked with light BW steers during the fall at similar stocking rate (LT) or similar forage allowance (LTFA) to HVY. Additional steers were placed on pastures for spring graze-out. a,bColumns with differing letters differ (P < 0.01).
LTFA treatment, yet because greater grazing days per hectare resulted in similar BW gain per hectare, there was no difference in total profit per hectare. Profitability per hectare in the current experiment using recent economic conditions is approximately 3-times larger than profitability of an economic analysis by Beck et al. (2005), which is an indication of the improved economic circumstances of the stocker industry.
IMPLICATIONS Increased FA (kg of forage DM/ kg of steer BW) of LT treatment results in increased BW gain per steer compared with LTFA and HVY calves during the fall, yet increasing SR in LTFA resulted in increased BW gain per hectare compared with LT and HVY during the fall. Increased fall SR in LTFA resulted in reduced spring FA, and steer performance during spring graze-out declined compared with LT and HVY. The lack of difference in profitability per hectare suggests that additional light-BW calves can be stocked during the fall with little effect on total enterprise profitability.
LITERATURE CITED Anders, M., P. Beck, S. Gadberry, and B. Watkins. 2007. Impact of Conservation Tillage Practices on Winter Wheat Production for Grazing Stocker Cattle. Fact Sheet FSA3116. Univ. Arkansas Coop. Ext. Serv., Little Rock. Beck, P., M. Anders, B. Watkins, S. Gunter, D. Hubbell, and S. Gadberry. 2013. Invited: Improving the production, environmental, and economic efficiency of the stocker cattle industry in the Southeastern United States. J. Anim. Sci. 91:2456–2466. Beck, P. A., S. A. Gunter, D. S. Hubbell III, L. B. Daniels, and K. B. Watkins. 2005. Performance of stocker cattle grazing cool-season annual grass mixtures in northern Arkansas. Prof. Anim. Sci. 21:465–473. Beck, P. A., T. Hess, D. Hubbell, G. D. Hufstedler, B. Fieser, and J. Caldwell. 2014. Additive effects of growth promoting technologies on performance of grazing steers and economics of the wheat pasture enterprise. J. Anim. Sci. 92:1219–1227. Bowman, M. T., P. A. Beck, K. B. Watkins, M. M. Anders, M. S. Gadberry, K. S. Lusby, S. A. Gunter, and D. S. Hubbell. 2008. Tillage systems for production of small grain pasture. Agron. J. 100:1289–1295. Bransby, D. I., B. E. Conrad, H. M. Dicks, and J. W. Drane. 1988. Justification for grazing intensity experiments: Analysis and interpreting grazing data. J. Range Manage. 41:274–279. Davis, G. V., M. S. Gadberry, and T. R. Troxel. 2002. Composition and nutrient de-
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. 73:45–54. McCartor, M. M., and F. M. Rouquette Jr. 1977. Grazing pressures and animal performance from pearl millet. Agron. J. 69:983– 987. Meyer, T. L., L. A. Stalker, J. D. Volesky, D. C. Adams, R. N. Funston, T. J. Klopfenstein, and W. H. Schacht. 2012. Technical Note: Estimating beef-cattle forage demand: Evaluating the animal unit concept. Prof. Anim. Sci. 28:664–669. Michell, P., and R. V. Large. 1983. The estimation of herbage mass of perennial ryegrass swards: A comparative evaluation of a risingplate meter and a single probe capacitance meter calibrated at or above ground level. Grass Forage Sci. 38:295–300. Morgan, M. S., P. A. Beck, T. Hess, D. S. Hubbell, and S. Gadberry. 2012. Effects of establishment method and fall stocking rate of wheat pasture on forage mass, forage chemical composition, and performance of growing steers. J. Anim. Sci. 90:3286–3293. NRC. 1996. Nutrient Requirements of Beef Cattle. 7th ed. Natl. Acad. Press, Washington, DC. Pinchak, W. E., W. D. Worrall, S. P. Caldwell, L. J. Hunt, N. J. Worrall, and M. Conoly. 1996. Interrelationships of forage and steer growth dynamics on wheat pasture. J. Range Manage. 49:126–130. Poe, K., P. Beck, J. T. Richeson, M. S. Gadberry, T. W. Hess, and D. S. Hubbell III. 2013. Effects of respiratory vaccination timing and growth-promoting implant on health, performance, and immunity of high-risk, newly received stocker cattle. Prof. Anim. Sci. 29:413–419. Redmon, L. A., F. T. McCollum III, G. W. Horn, M. D. Cravey, S. A. Gunter, P. A. Beck, J. M. Mieres, and R. San Julian. 1995. Forage intake by beef steers grazing winter wheat with varied herbage allowances. J. Range Manage. 48:198–201.