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CASE STUDY: Productivity, quality characteristics, and beef cattle performance from cool-season annual forage mixtures
The Professional Animal Scientist 28 (2012):379–386
©2012 American Registry of Professional Animal Scientists
Ccharacteristics, S : Productivity, quality and beef cattle ASE
TUDY
performance from cool-season annual forage mixtures M. K. Mullenix,1,2 E. J. Bungenstab, PAS, J. C. Lin, B. E. Gamble, and R. B. Muntifering Department of Animal Sciences, Auburn University, Auburn, AL 36849-5415
ABSTRACT A grazing experiment was conducted to quantify productivity, quality characteristics, and beef cattle performance from mixtures of oat (Avena sativa L.) and ryegrass (Lolium multiflorum L.; O-RG), rye (Secale cereale L.) and ryegrass (R-RG), or oat and rye and ryegrass (O-R-RG) under continuous stocking. Six 1.42-ha paddocks were seeded with O-RG, R-RG, or O-R-RG mixtures (2 paddocks/treatment) in November 2008 and stocked initially with 3 yearling crossbred test steers (392 ± 31 kg initial BW) per paddock on January 8, 2009. Forage mass and nutritive quality were determined by clipping 0.25-m2 quadrats (8/paddock) before the beginning of grazing and every 2 wk during the experiment. Stocking densities were adjusted using put-and-take steers to maintain grasses in a vegetative state, and grazing was discontinued on May 28. Data were analyzed as a completely randomized design by the PROC GLM procedure of SAS. Steer ADG was greater (P < 0.10) for O-RG (1.39 kg/d) and O-R-RG (1.26 kg/d) than R-RG (1.13 kg/d). Number 1 Current address: University of Florida, 2197 McCarty Hall, PO Box 110500, Gainesville, FL 32611-0500. 2 Corresponding author: [email protected]
of steer-grazing-days was 547, 655, and 625 d for R-RG, O-RG, and O-R-RG, respectively, and mean forage allowance across all treatments was 1.06 kg DM/ kg steer BW over the 140-d grazing experiment. Results indicate that O-RG was superior to R-RG for supporting beef cattle performance under continuous stocking, and that inclusion of rye in a ternary mixture did not improve performance over that from O-RG. Key words: small grain, ryegrass, cool-season annual, nutritive quality, beef cattle
INTRODUCTION Opportunity exists in the Southeastern United States for beef production from pastures of ryegrass and small grains that differ in growth patterns and enable availability of high-quality forage to be distributed more uniformly throughout the winter grazing season. Although the use of smallgrain/ryegrass mixtures for winter grazing is not an especially novel practice, continuous grazing of these at a fixed stocking density is often characterized by underutilization of the small-grain component early in the season, resulting in shading out and underproduction of the ryegrass
component later in the season (Ball et al., 2007). By periodically adjusting grazing intensity in response to changes in forage DM production, there is an opportunity to maximize forage production by exploiting the intrinsic seasonal variation in herbage production among species. However, there is variation in forage quality within and among plant species (Adesogan et al., 2002), and it is therefore necessary to quantify productivity and quality characteristics of specific combinations of forages. Results from previous studies with small-grain/ryegrass mixtures have been inconsistent (Coffey et al., 2002; Beck et al., 2005). The objectives of the present study were to characterize productivity, quality characteristics, and beef cattle performance from small-grain/ryegrass mixtures using adjustable stocking densities in response to changing forage mass.
MATERIALS AND METHODS The study was conducted according to a research protocol that had been approved by the Institutional Animal Care and Use Committee of Auburn University. Six 1.42-ha paddocks (experimental unit; 2 paddocks per treatment) of mixtures of oat (Av-
380 ena sativa L.) and ryegrass (Lolium multiflorum L.; O-RG), rye (Secale cereale L.) and ryegrass (R-RG), or oat and rye and ryegrass (O-RRG) were planted at the Wiregrass Research and Extension Center in Headland, AL (31.35° N, 85.34° W). Pastures consisting of a Dothan fine sandy loam had previously been in a winter-annual grazing/summer rowcrop rotation, and were planted in annual peanut (Arachis hypogea L.) during the late spring until harvest in early fall. Pastures were tilled on November 4, and seed was drilled into prepared seedbeds on November 5, 2008. Seeding rates were 103 kg/ha of Wren’s Abruzzi rye (Hancock Seed Company, Dade City, FL) or Harrison oat (Arkansas County Seed, Roland, AR), and 11 kg/ha Marshall ryegrass (Wax Seed Company, Amory, MS) for binary mixtures, and 52 kg/ha of both rye and oat and 11 kg/ha ryegrass for the ternary mixture. Pastures initially received 45 kg N/ha, 67 kg P/ha, and 67 kg K/ha as NH4NO3, P2O5, and K2O, respectively, at planting according to soil test recommendations of the Auburn University Soil Testing Laboratory. Nitrogen fertilizer in the form of NH4NO3 and sulfur fertilizer in the form of (NH4)2SO4 were applied on December 19, 2008, and March 5, 2009, at rates of 67 kg N/ha total and 11 kg S/ha, respectively. Pastures were stocked initially with 3 yearling Angus × Simmental test steers (initial BW 392 ± 31 kg) per paddock. Steers were born in the fall of 2007 and were maintained on a bermudagrass (Cynodon dactylon) pasture after weaning until the beginning of the experiment. When forage availability became limiting during the late fall, steers were given ad libitum access to bermudagrass hay before the experiment. Steers were treated with moxidectin pouron (Pfizer Animal Health, New York, NY) dewormer at the beginning of the grazing experiment. All steers had ad libitum access to salt-mineral mix and water. Grazing was initiated on January 8, 2009, when forage mass had
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achieved approximately 2,000 kg DM/ ha. Calves were weighed at the end of successive intervals of 28, 28, 32, 29, and 23 d, and grazing was terminated on May 28, 2009, when forage quantity and quality could no longer support satisfactory animal performance. Forages were continuously grazed and managed throughout the study to maintain a target forage mass of 2,000 kg DM/ha, which is intermediate to values of 1,220 and 2,230 kg DM/ha that Hafley (1996) reported should result in maximum animal performance and forage DMI, respectively, by steers grazing ryegrass. Stocking densities were adjusted using the put-and-take method as described by Sollenberger and Burns (2001). Stocking density adjustments were made based on calculation of forage mass and animal utilization at the time of sampling. Net change in forage mass (less trampling, lodging, and consumption) was determined for each paddock every 2 wk as the difference in forage mass between the previous sampling date and the current sampling date. A daily DMI of 3% mean steer BW was used for forage utilization estimation between sampling dates. The difference in forage mass between sampling periods was then added to the amount presumptively consumed by cattle within a paddock to derive an estimate of forage DM accumulation during the most recent 2-wk period. Forage accumulation was then added to forage mass at the time of sampling to determine a projected amount of available forage mass during the next 2-wk period. Amount of projected forage mass over 2,000 kg DM/ha was regarded as that requiring management using put-and-take steers. Cattle were estimated to utilize 60% of the total amount of projected forage growth (Ball et al., 2007) over 2,000 kg DM/ha to account for waste and trampling. Stocking density adjustments were determined based on amount of predicted consumption by cattle within a paddock over a 2-wk period. Forage mass and nutritive quality were determined by clipping 0.25-
m2 quadrats (8/paddock) before the beginning of grazing and every 2 wk during the experiment. Forage within quadrats was clipped to an aboveground stubble height of approximately 2 cm. Fresh-cut forage was then placed into plastic, zip-closure bags and stored on ice for transportation to the Ruminant Nutrition Laboratory at Auburn University. Samples from each paddock were placed in a paper bag, oven-dried at 60°C for 72 h, air-equilibrated, and weighed. Dry matter availability was calculated for each paddock based on dry-weight data multiplied by the area of the paddock. Dried, air-equilibrated forage samples were ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass a 1-mm screen. Forage concentrations of CP and DM were determined according to procedures of AOAC (1995), and concentrations of NDF, ADF, and ADL were determined sequentially according to procedures of Van Soest et al. (1991). Samples were prepared for total nonstructural carbohydrate (TNC) analysis according to a modification of the Weinmann (1947) procedure for fructosan accumulators. Samples (0.20 to 0.25 g) were boiled in 50 mL of 0.05 N H2SO4 for 1 h and placed in a shallow ice bath, after which 1.0 N NaOH was added to adjust the pH of the sample to 4.5. One mL of diluted amyloglucosidase (Aspergillus niger, Lot No. A 9913, Sigma-Aldrich Inc., St. Louis, MO) solution was added to samples, which were then covered and incubated at 60°C for 1 h. Samples were filtered and brought to volume in a 250-mL volumetric flask with 2 mL of 0.1 N NaOH and deionized H2O. Ten milliliters of Sheffer-Somogyi reagent (AOAC, 1995) were combined with a 10-mL aliquot of sample in a 25 × 200 mm capped test tube and boiled for 15 min. Tubes were then cooled in an ice bath, and 2 mL of potassium iodide-potassium oxalate solution was added to each sample. Next, 10 mL of 1.0 N H2SO4 and 1 mL of gelatinized starch solution were added to each tube before titration.
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Table 1. Monthly mean air temperatures (°C) and precipitation (mm) for January to May 2009, and 30-yr averages for Headland, AL (AWIS Weather Services Inc., Auburn, AL) Month January February March April May
Avg. high, °C
Avg. low, °C
Mean, °C
30-yr avg., °C
Precipitation, mm
30-yr avg., mm
18 18 22 25 29
6 5 11 12 19
12 12 17 19 24
9 11 15 19 23
50 53 182 146 233
160 132 157 97 107
Samples were titrated with 0.02 N sodium thiosulfate until the solution turned light blue. Concentration of TNC in samples was calculated as the amount of reducing sugar in the sample, multiplied by the dilution factor × 100, divided by the sample weight. Forage IVDMD was determined according to the Van Soest et al. (1991) modification of the Tilley and Terry (1963) procedure using the DaisyII incubator system (Ankom Technology Corporation, Fairport, NY). Ruminal fluid was collected from a fistulated, dry Holstein cow at the Auburn University College of Veterinary Medicine. The cow was fed a corn silagebased diet containing cottonseed meal and Megalac supplement (Church and Dwight Co., Princeton, NJ), and had ad libitum access to bermudagrass pasture and alfalfa (Medicago sativa) hay. Fluid was stored in prewarmed thermos containers and transported to the Ruminant Nutrition Laboratory where it was then prepared for the batch-culture IVDMD procedure. Data were analyzed using the PROC GLM procedure (SAS Inst. Inc., Cary, NC) for a completely randomized design. Data were analyzed by individual weigh period because of unequal number of days in each period. The PDIFF option of LSMEANS in SAS (SAS Inst. Inc.) was used for mean separation of treatments when protected by F-test at α = 0.10.
RESULTS AND DISCUSSION Temperature and Precipitation Except for April, monthly mean air temperatures were slightly greater
than 30-yr averages for Headland, AL (Table 1). For January and February, monthly total precipitation (Table 1) was 69 and 60% less, respectively, than the 30-yr average. Precipitation was 16, 50, and 118% greater than the 30-yr average in March, April, and May, respectively. Average precipitation during January and February was considerably below 30-yr averages; however, beginning in March, rainfall was considerably greater than the 30yr average.
Forage Mass From January 8 to February 5, R-RG had 494 and 437 kg DM/ha greater forage mass (Table 2) than O-RG (P = 0.04) and O-R-RG (P = 0.02), respectively. Rye is more cold-tolerant than the other common small-grain species, and it is often available and ready for grazing earlier in the growing season (Ball et al., 2007). Bruckner and Raymer (1990) reported that differences in seasonal distribution of small-grain forages was most evident in January and February when rye produced greater forage yields than triticale, oat, or wheat. Subfreezing nighttime temperatures in mid-January likely retarded oat production in the present study. Between January 12 and January 23, early-morning low temperatures were below 0°C on all but 2 d, including 5 d below −3°C for which the lowest temperature was below −6°C, and some frost damage was evident as tip burn in pastures containing oat during that period. However, yield distribution favored the production of oat from February 5 to March 5,
during which time R-RG had less forage mass than O-RG (P = 0.04) and O-R-RG (P = 0.01). Further, mixed pastures containing rye had less (P < 0.01) herbage mass than O-RG from March 5 to April 6, and forage mass with mixtures containing rye steadily decreased throughout the remainder of the experiment. Differences in forage mass among treatments were most evident from April 6 to May 5, in which O-RG had 129 and 157% greater herbage mass than O-R-RG (P = 0.0001) and R-RG (P = 0.0001), respectively. Forage mass was greatest during this period, most likely because of oat reaching maximum productivity and maturity in conjunction with peaking productivity of ryegrass. Redfearn et al. (2005) noted that the greatest forage production of ryegrass occurred from March onward, although yield was variety dependent. Spring productivity of ryegrass was illustrated over a 2-yr trial at 4 locations in Oklahoma (Redfearn et al., 2002) in which 40% of the total forage production of different ryegrass cultivars occurred early in the growing season (December through February), and 60% occurred as late-season growth (March through May). Forage mass in O-RG pastures continued to exceed 2,000 kg DM/ha until the final period, even under management using put-and-take steers. From May 5 to May 28, herbage mass decreased markedly for all forage mixtures, although O-RG available DM was still 78 and 134% greater, respectively, than that in the O-R-RG (P = 0.001) and R-RG (P = 0.0001) mixed-pasture systems.
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Table 2. Forage mass (kg DM/ha) in mixed small-grain/ryegrass pastures Treatment1 Period
O-RG
R-RG
Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28
2,110 2,611a 2,185c 3,260e 1,787e a
2,604 2,145b 1,488d 1,270f 767f b
O-R-RG
SE
2,167 2,741a 1,671d 1,426f 1,005f
153 160 129 134 160
a
Within a row, means without common superscripts differ (P < 0.05). Within a row, means without common superscripts differ (P < 0.01). e,f Within a row, means without common superscripts differ (P < 0.0001). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass. a,b c,d
Although each pasture was initially stocked with 3 test steers (equivalent to 2.1 steers/ha), rapid and sustained increases in forage growth warranted use of put-and-take steers to varying degrees to maintain forage DM availability at the target value of 2,000 kg/ha. Figure 1 illustrates the implementation of stocking density adjustments that were needed to maintain a forage mass of 2,000 kg/ ha. Stocking densities were not different among treatments except from April 6 to May 5 when O-RG was stocked with more than twice as many steers as R-RG and O-R-RG. Mean forage allowance across all treatments was 1.06 kg DM/kg steer BW over the 140-d grazing experiment. Minson (1990) noted a break point at which DMI decreased with decreasing forage allowance between 30 and 50 g DM/ kg BW. Results from McCollum et al. (1992) indicate that peak DMI occurred on wheat pastures at 300 g DM/kg BW. Using these values, even at the lowest forage mass in the present study, the mean forage allowance across this experiment was clearly sufficient to support an adequate level of intake.
Cell Wall Constituents No differences were observed among treatments in forage NDF concentration (Table 3) from January 8 to Feb-
ruary 5 (P > 0.10), April 6 to May 5 (P > 0.10), and May 5 to May 28 (P > 0.10). However, O-RG forage had less NDF than O-R-RG (P = 0.07) and R-RG (P = 0.001) treatments, respectively, and O-R-RG contained less NDF (P = 0.02) than R-RG from February 5 to March 5. Mean NDF was also less for O-RG forage than O-R-RG (P = 0.004) and R-RG (P = 0.008) treatments from March 5 to April 6, which may be partially attributed to earlier maturation of rye compared with oat and ryegrass. Across the entire grazing season, NDF concentrations ranged from 37 to 69% for all treatments. These results are consistent with those of Redfearn et al. (2002), who reported that concentration of NDF in ryegrass increased from 39 to 58% across the growing season. Moreover, Juskiw et al. (2000) observed NDF concentration of >50% for barley, oat, and triticale in the dough stage of development before harvest. Forage concentration of ADF (Table 3) decreased between January 8 and March 5, with mixtures containing oat having less ADF than R-RG. The observed decrease in ADF contrasts with the pattern of increasing NDF observed during the same time period. From February 5 to March 5, O-RG contained less ADF than O-R-RG (P = 0.02) and R-RG (P = 0.001), and O-R-RG contained less (P = 0.10)
ADF than R-RG. From March 5 to April 6, O-RG forage had 3.3 and 2.3 percentage units lower ADF concentration than O-R-RG (P = 0.02) and R-RG (P = 0.09) treatments, respectively. Mean ADF increased within each forage treatment throughout the remainder of the experiment, which is expected with advancing plant maturity. Juskiw et al. (2000) reported 32% ADF for oat in the dough stage of development, and similar values for other small grains. Although no differences were observed among treatments from May 5 to May 28, mean ADF was slightly greater for all treatments than those reported by Juskiw et al. (2000). During the first 28 d of the experiment, mean ADL (Table 3) was greater for R-RG than O-RG (P = 0.02) and O-R-RG (P = 0.03) treatments. Lignin concentration increased in all treatments with increasing plant maturity; however, no differences were observed among treatments throughout the remainder of the trial. Mean ADL for forage species in the present study was relatively low, but comparable with values reported by Muir and Bow (2009) for cool-season annual forages grown under nutrientrich conditions. During the first year of Muir and Bow (2009), ADL was <3% for barley, oat, triticale, rye, and ryegrass from September to April in Stephenville, TX.
Crude Protein Concentration of CP (Table 4) was greatest for all treatments (≥21%) during the first 28 d of the trial, which is expected for cool-season annual forages in a vegetative stage of maturity. An increase in CP was observed between February 5 to April 6, which may be attributed in part to application of NH4NO3 and (NH4)2SO4 fertilizer at the beginning of March. Mean CP was less for O-RG than O-R-RG (P = 0.06) and R-RG (P = 0.03) from February 5 to March 5. From March 5 to April 6, CP was less for O-R-RG than the O-RG (P = 0.05) and R-RG (P = 0.007) treatments, but was not different (P
Beef production from cool-season annual forages
383
for concentration of CP in ryegrass from December to May (26 to 12%) in Oklahoma. Ball et al. (2007) reported a decline in concentration of CP in rye of 28, 24 and 13% at the vegetative, flower/boot, and fruit/head stages of maturity, respectively.
Total Nonstructural Carbohydrates
Figure 1. Stocking densities for oat and ryegrass (O-RG), oat and rye and ryegrass (O-R-RG), and rye and ryegrass (R-RG) pastures.
> 0.10) between O-RG and R-RG. No differences were observed among treatments in concentration of CP in any other periods throughout the
grazing experiment. Mean CP decreased from roughly 22 to 12% across the entire grazing season. Redfearn et al. (2002) observed a similar pattern
Table 3. Forage concentration (%, DM basis) of cell-wall constituents in mixed small-grain/ryegrass pastures Treatment1 Item NDF, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 ADF, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 ADL, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28
O-RG 37.9 42.7a 49.8a 52.4 68.8 28.7 22.1a 27.6d 27.9 38.5 0.39f 0.53 1.09 1.05 3.20
R-RG 38.7 49.8b 54.5b 53.8 65.3 28.5 27.8b 29.9e 28.1 39.6 0.61g 1.27 1.65 1.87 2.49
O-R-RG 36.6 45.8c 55.2b 51.4 64.7 28.6 25.6c 30.9e 27.1 35.5 0.39f 0.91 1.29 0.94 2.34
SE 1.2 1.0 1.0 2.2 2.7 3.1 0.9 0.9 1.1 3.2 0.06 0.26 0.26 0.35 0.42
Within a row, means without common superscripts differ (P < 0.01). Within a row, means without common superscripts differ (P < 0.05). f,g Within a row, means without common superscripts differ (P < 0.10). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass.
a–c d,e
Concentration of TNC (Table 4) in O-RG was greater than O-R-RG (P = 0.004) and R-RG (P < 0.001) forages, and O-R-RG was greater (P = 0.07) than R-RG from February 5 to March 5. Chatterton et al. (2006) noted that sugar concentration was generally greatest when oat forage plants were young (tiller and joint growth stages) and concentration of fiber was relatively low; glucose, fructose, and sucrose averaged 15% DM in hay in the boot stage, and declined to 1 to 2% of DM with increasing plant maturity. Van Soest (1994) reported that cool-season grasses typically contain 3 to 6% DM of soluble sugars, 0 to 2% DM of starch, and 3 to 10% DM of fructans, which additively is comparable with the total concentration of TNC observed in the present study for pastures containing oat. Percentage of TNC in all treatments decreased from March 5 to April 6, with R-RG containing less TNC than both O-RG (P < 0.001) and O-R-RG (P = 0.02), and O-RG containing greater (P = 0.001) TNC concentration than O-R-RG from March 5 to April 6. No differences among treatments were observed in percentage of TNC from to February 5 to March 5, April 6 to May 5, and May 5 to May 28.
In Vitro Dry Matter Digestibility Percentage IVDMD (Table 4) was not different between O-RG and OR-RG (P > 0.10), but was greater for O-RG (P = 0.08) and O-R-RG (P = 0.03) than R-RG during January 8 to February 5. Digestibility of O-RG was greater than O-R-RG (P = 0.02) and R-RG (P = 0.001) treatments, and digestibility of O-R-RG and R-RG were
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Mullenix et al.
Table 4. Forage concentration (%, DM basis) of CP and total nonstructural carbohydrates (TNC), and forage IVDMD in mixed smallgrain/ryegrass pastures Treatment1 Item CP, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 TNC, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 IVDMD, % Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28
O-RG
R-RG
O-R-RG
21.5 12.1a 18.6c 12.6 12.9
22.0 15.6b 19.5c 14.3 13.6
22.3 15.0b 16.9d 13.9 12.2
18.0 24.9e 12.0h 17.8 8.1
15.8 13.6f 7.4i 15.3 6.3
17.3 17.5g 9.0j 17.5 8.0
95.5a 91.3e 88.3e 82.4 68.1
92.7b 88.3f 83.1f 78.5 65.1
95.0a 89.3f 78.8g 79.6 71.1
SE 2.3 1.0 0.5 0.6 1.5 3.3 1.4 0.4 1.6 0.9 0.6 0.6 1.7 1.9 2.6
Within a row, means without common superscripts differ (P < 0.10). Within a row, means without common superscripts differ (P < 0.05). e–g Within a row, means without common superscripts differ (P < 0.01). h–j Within a row, means without common superscripts differ (P < 0.0001). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass. a,b
c,d
not different (P > 0.10) from February 5 to March 5. Values observed for IVDMD of mixed small grain/ryegrass pasture from January 8 to February 5 of the present study were greater than those observed in other studies with cool-season annual pastures. Moyer and Coffey (2000) reported average IVDMD was 74.5% for rye cultivars, 69.8% for wheat cultivars, and 72.1% for barley in an evaluation of forage quality of small grains grown in monoculture. Redfearn et al. (2002) observed a decrease in IVDMD of annual ryegrass from 84 to 70% with increasing plant maturity. The relatively high values observed for digestibility during the first 2 mo of the present study may be attributed to the extremely low concentrations of cell wall constituents, notably lignin, observed during the beginning of the grazing trial. Forages in the young, vegetative stage are high quality, and
if not extensively lignified, structural components of the cell wall are more readily available for digestion. Mixed forages of O-RG had greater digestibility than R-RG (P = 0.04) and O-R-RG (P = 0.001), and R-RG had greater (P = 0.10) digestibility than O-R-RG from March 5 to April 6. No differences were observed among forage treatments for digestibility in all other periods during the experiment. Forage IVDMD decreased across the grazing trial for all treatments with increasing plant maturity.
Average Daily Gain and Grazing Days Test-steer ADG from April 6 to May 5 (Table 5) was less for R-RG than the O-RG (P = 0.008) and O-R-RG (P = 0.02) treatments. Average daily gain over the 140-d grazing period was greater for O-RG
than R-RG (P = 0.03), but was not different from that of O-R-RG (P > 0.10). No differences (P > 0.10) were observed in ADG among treatments from January 8 to February 5, February 5 to March 5, March 5 to April 6, or May 5 to May 28. Observations for cattle ADG were in general agreement with other studies with cool-season forage systems (Ball et al., 2007; Beck et al., 2005, 2007). When small-grain/ryegrass mixtures were interseeded into bermudagrass sod, Beck et al. (2007) reported ADG from O-RG was intermediate to that of other mixed-forage systems and not different among treatments during yr 1 of a 2-yr grazing trial. In yr 2, no significant differences were observed among treatments in spring ADG of mixed forages, and ADG for cattle grazing O-RG pasture was 1.33 kg/d, similar to the O-RG gain in the present study. Cattle ADG from O-R-RG was slightly greater than that (0.98 kg/d) observed by Myer et al. (2008) in a grazing trial in Florida. Although R-RG pasture produced the least ADG in the present study, these values agree with those reported by Cleere et al. (2004) in which steers grazing a combination of R-RG gained between 1.01 and 1.28 kg/d from December to May across 2 stocking rates and grazing systems in Overton, TX. No differences were observed among treatments for steer-grazing-days over the 140-d grazing trial (Table 5). From April 6 to May 5, steergrazing-days were greater for O-RG than R-RG (P = 0.02) and O-R-RG (P = 0.03) treatments. No differences among treatments were observed in the other periods. Number of steergrazing-days was greatest for O-RG from April 6 to May 5 due to increased forage DM availability and capacity to support increased stocking rate as indicated by increased use of forage management using put-andtake steers. Across the entire grazing season, forage treatments containing oats had ≥625 steer-grazing-days, equivalent to 440 grazing-d/ha. Comparable results were observed by Myer et al. (2008), observing 421 and
Beef production from cool-season annual forages
Table 5. Performance of steers grazing mixed small-grain/ryegrass pastures Treatment1 Item
O-RG
R-RG
O-R-RG
Initial BW, kg Final BW, kg ADG, kg Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 Jan 8 to May 28 Grazing days, d Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 Jan 8 to May 28
351 536
362 523 1.48 1.87 1.31 0.68b 0.26 1.13d 122 98 118 101b 80 547
355 532
1.60 2.03 1.37 1.30a 0.07 1.38c 84 154 128 170a 126 655
1.63 1.90 1.06 1.17a 0.39 1.26c 101 133 175 109b 69 625
SE 4.56 13.0 0.08 0.16 0.11 0.14 0.14 0.05 24 16 22 12 33 48
Within a row, means without common superscripts differ (P < 0.05). Within a row, means without common superscripts differ (P < 0.10). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass. a,b c,d
403 grazing-d/ha for O-R-RG and O-RG, respectively, in a grazing trial in Florida. Beck et al. (2007) reported slightly greater values of 595 (yr 1) and 697 grazing-d/ha (yr 2) for O-RG overseeded into bermudagrass sod in Arkansas.
evaluation of other small-grain forage and legumes grown in mixtures with ryegrass to enhance knowledge that can be used to develop management tools for producers, consultants, and extension educators.
IMPLICATIONS
LITERATURE CITED
Results from this study illustrate the potential value of small-grain/ ryegrass mixtures for beef cattle production systems in the Southeastern United States. Under the growing conditions in the present study, mixtures containing oat were more productive and showed less rapid changes in forage quality across the grazing season than R-RG. Although pastures containing oats provided superior animal performance in this study, oats are cold-sensitive and may be winterkilled in some parts of the Southeast; mixtures containing oats may be best suited for milder winter climates such as in the Gulf Coast region. Future research opportunities exist for
Adesogan, A. T., L. E. Sollenberger, Y. C. Newman, and J. M. B. Vendramini. 2002. Factors affecting forage quality. Univ. of Florida/IFAS Ext. Publ. SS-AGR-93. AOAC. 1995. Official Methods of Analysis. 16th ed. Assoc. Off. Anal. Chem., Washington, DC. Ball, D., C. S. Hoveland, and G. D. Lacefield. 2007. Southern Forages. 4th ed. Int. Plant Inst., Norcross, GA. Beck, P. A., D. S. Hubbell, K. B. Watkins, S. A. Gunter, and L. B. Daniels. 2005. Performance of stocker cattle grazing cool-season annual grass mixtures in northern Arkansas. Prof. Anim. Sci. 21:465–473. Beck, P. A., C. B. Stewart, J. M. Phillips, K. B. Watkins, and S. A. Gunter. 2007. Effects of species of cool-season annual grass interseeded into bermudagrass on the performance of growing calves. J. Anim. Sci. 85:536–544.
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Bruckner, P. L., and P. L. Raymer. 1990. Factors influencing species and cultivar choice of small grains for winter forage. J. Prod. Agric. 3:349–355. Chatterton, N. J., K. A. Watts, K. B. Jensen, P. A. Harrison, and W. H. Horton. 2006. Nonstructural carbohydrates in oat forage. J. Nutr. 136:2111S–2113S. Cleere, J. J., F. M. Rouquette Jr., and G. M. Clary. 2004. Impact of stocking rate and stocking strategy on gain per animal and gain per hectare of steers grazing rotational or continuous stocked rye-ryegrass pasture. J. Anim. Sci. 87(Suppl. 1):292. (Abstr.) Coffey, K. P., W. K. Coblentz, T. G. Montgomery, J. D. Shockey, K. J. Bryant, P. B. Francis, C. F. Rosenkrans Jr., and S. A. Gunter. 2002. Growth performance of stocker calves backgrounded on sod-seeded winter annuals or hay and grain. J. Anim. Sci. 80:926–932. Hafley, J. L. 1996. Comparison of Marshall and Surrey ryegrass for continuous and rotational grazing. J. Anim. Sci. 74:2269–2275. Juskiw, P. E., J. H. Helm, and D. F. Salmon. 2000. Forage yield and quality for monocrops and mixtures of small grain cereals. Crop Sci. 40:138–147. McCollum, F. T., M. D. Cravey, S. A. Gunter, J. M. Mieres, P. B. Beck, R. San Julian, and G. W. Horn. 1992. Forage availability affects wheat forage intake by stocker cattle. Oklahoma Agric. Exp. Stn. Publ. MP-136:312. Oklahoma Agric. Exp. Stn., Stillwater. Minson, D. J. 1990. Forage in Ruminant Nutrition. Academic Press, San Diego, CA. Moyer, J. L., and K. P. Coffey. 2000. Forage quality and production of small grains interseeded into bermudagrass sod or grown in monoculture. Agron. J. 92:748–753. Muir, J. P., and J. R. Bow. 2009. Herbage, phosphorous, and nitrogen yields of winterseason forages on high-phosphorous soil. Agron. J. 101:764–768. Myer, R. O., A. R. Blount, J. N. Carter, C. L. Mackowiak, and D. L. Wright. 2008. Influence of pasture planting method and forage blend on annual cool-season pasture forage availability for grazing by growing beef cattle. Prof. Anim. Sci. 24:239–246. Redfearn, D. D., B. C. Venuto, M. W. Alison, and J. D. Ward. 2002. Cultivar and environment effects on annual ryegrass forage yield, yield distribution, and nutritive value. Crop Sci. 42:2049–2054. Redfearn, D. D., B. C. Venuto, W. D. Pitman, D. C. Blouin, and M. W. Alison. 2005. Multilocation annual ryegrass performance over a twelve-year period. Crop Sci. 45:2388–2393. Sollenberger, L. E., and J. C. Burns. 2001. The conduct of grazing trials: Rationale,
386 treatment selection, and basic measurements. Proc 56th Southern Pasture Forage Crop Improvement Conf., Springdale, AR. April 21–22, 2001. D. Lang, ed. Accessed Apr. 26, 2010. http://spfcic.okstate.edu/proceedings/2001/utilization/sollenberger_burns.htm. Tilley, J. M. A., and R. A. Terry. 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassl. Soc. 18:104–111. Van Soest, P. J. 1994. Nutritional Ecology of the Ruminant. 2nd ed. Cornell University Press, Ithaca, NY.
Mullenix et al. Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583–3597. Weinmann, H. 1947. Determination of total available carbohydrates in plants. Plant Physiol. 22:279–290.
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Ccharacteristics, S : Productivity, quality and beef cattle ASE
TUDY
performance from cool-season annual forage mixtures M. K. Mullenix,1,2 E. J. Bungenstab, PAS, J. C. Lin, B. E. Gamble, and R. B. Muntifering Department of Animal Sciences, Auburn University, Auburn, AL 36849-5415
ABSTRACT A grazing experiment was conducted to quantify productivity, quality characteristics, and beef cattle performance from mixtures of oat (Avena sativa L.) and ryegrass (Lolium multiflorum L.; O-RG), rye (Secale cereale L.) and ryegrass (R-RG), or oat and rye and ryegrass (O-R-RG) under continuous stocking. Six 1.42-ha paddocks were seeded with O-RG, R-RG, or O-R-RG mixtures (2 paddocks/treatment) in November 2008 and stocked initially with 3 yearling crossbred test steers (392 ± 31 kg initial BW) per paddock on January 8, 2009. Forage mass and nutritive quality were determined by clipping 0.25-m2 quadrats (8/paddock) before the beginning of grazing and every 2 wk during the experiment. Stocking densities were adjusted using put-and-take steers to maintain grasses in a vegetative state, and grazing was discontinued on May 28. Data were analyzed as a completely randomized design by the PROC GLM procedure of SAS. Steer ADG was greater (P < 0.10) for O-RG (1.39 kg/d) and O-R-RG (1.26 kg/d) than R-RG (1.13 kg/d). Number 1 Current address: University of Florida, 2197 McCarty Hall, PO Box 110500, Gainesville, FL 32611-0500. 2 Corresponding author: [email protected]
of steer-grazing-days was 547, 655, and 625 d for R-RG, O-RG, and O-R-RG, respectively, and mean forage allowance across all treatments was 1.06 kg DM/ kg steer BW over the 140-d grazing experiment. Results indicate that O-RG was superior to R-RG for supporting beef cattle performance under continuous stocking, and that inclusion of rye in a ternary mixture did not improve performance over that from O-RG. Key words: small grain, ryegrass, cool-season annual, nutritive quality, beef cattle
INTRODUCTION Opportunity exists in the Southeastern United States for beef production from pastures of ryegrass and small grains that differ in growth patterns and enable availability of high-quality forage to be distributed more uniformly throughout the winter grazing season. Although the use of smallgrain/ryegrass mixtures for winter grazing is not an especially novel practice, continuous grazing of these at a fixed stocking density is often characterized by underutilization of the small-grain component early in the season, resulting in shading out and underproduction of the ryegrass
component later in the season (Ball et al., 2007). By periodically adjusting grazing intensity in response to changes in forage DM production, there is an opportunity to maximize forage production by exploiting the intrinsic seasonal variation in herbage production among species. However, there is variation in forage quality within and among plant species (Adesogan et al., 2002), and it is therefore necessary to quantify productivity and quality characteristics of specific combinations of forages. Results from previous studies with small-grain/ryegrass mixtures have been inconsistent (Coffey et al., 2002; Beck et al., 2005). The objectives of the present study were to characterize productivity, quality characteristics, and beef cattle performance from small-grain/ryegrass mixtures using adjustable stocking densities in response to changing forage mass.
MATERIALS AND METHODS The study was conducted according to a research protocol that had been approved by the Institutional Animal Care and Use Committee of Auburn University. Six 1.42-ha paddocks (experimental unit; 2 paddocks per treatment) of mixtures of oat (Av-
380 ena sativa L.) and ryegrass (Lolium multiflorum L.; O-RG), rye (Secale cereale L.) and ryegrass (R-RG), or oat and rye and ryegrass (O-RRG) were planted at the Wiregrass Research and Extension Center in Headland, AL (31.35° N, 85.34° W). Pastures consisting of a Dothan fine sandy loam had previously been in a winter-annual grazing/summer rowcrop rotation, and were planted in annual peanut (Arachis hypogea L.) during the late spring until harvest in early fall. Pastures were tilled on November 4, and seed was drilled into prepared seedbeds on November 5, 2008. Seeding rates were 103 kg/ha of Wren’s Abruzzi rye (Hancock Seed Company, Dade City, FL) or Harrison oat (Arkansas County Seed, Roland, AR), and 11 kg/ha Marshall ryegrass (Wax Seed Company, Amory, MS) for binary mixtures, and 52 kg/ha of both rye and oat and 11 kg/ha ryegrass for the ternary mixture. Pastures initially received 45 kg N/ha, 67 kg P/ha, and 67 kg K/ha as NH4NO3, P2O5, and K2O, respectively, at planting according to soil test recommendations of the Auburn University Soil Testing Laboratory. Nitrogen fertilizer in the form of NH4NO3 and sulfur fertilizer in the form of (NH4)2SO4 were applied on December 19, 2008, and March 5, 2009, at rates of 67 kg N/ha total and 11 kg S/ha, respectively. Pastures were stocked initially with 3 yearling Angus × Simmental test steers (initial BW 392 ± 31 kg) per paddock. Steers were born in the fall of 2007 and were maintained on a bermudagrass (Cynodon dactylon) pasture after weaning until the beginning of the experiment. When forage availability became limiting during the late fall, steers were given ad libitum access to bermudagrass hay before the experiment. Steers were treated with moxidectin pouron (Pfizer Animal Health, New York, NY) dewormer at the beginning of the grazing experiment. All steers had ad libitum access to salt-mineral mix and water. Grazing was initiated on January 8, 2009, when forage mass had
Mullenix et al.
achieved approximately 2,000 kg DM/ ha. Calves were weighed at the end of successive intervals of 28, 28, 32, 29, and 23 d, and grazing was terminated on May 28, 2009, when forage quantity and quality could no longer support satisfactory animal performance. Forages were continuously grazed and managed throughout the study to maintain a target forage mass of 2,000 kg DM/ha, which is intermediate to values of 1,220 and 2,230 kg DM/ha that Hafley (1996) reported should result in maximum animal performance and forage DMI, respectively, by steers grazing ryegrass. Stocking densities were adjusted using the put-and-take method as described by Sollenberger and Burns (2001). Stocking density adjustments were made based on calculation of forage mass and animal utilization at the time of sampling. Net change in forage mass (less trampling, lodging, and consumption) was determined for each paddock every 2 wk as the difference in forage mass between the previous sampling date and the current sampling date. A daily DMI of 3% mean steer BW was used for forage utilization estimation between sampling dates. The difference in forage mass between sampling periods was then added to the amount presumptively consumed by cattle within a paddock to derive an estimate of forage DM accumulation during the most recent 2-wk period. Forage accumulation was then added to forage mass at the time of sampling to determine a projected amount of available forage mass during the next 2-wk period. Amount of projected forage mass over 2,000 kg DM/ha was regarded as that requiring management using put-and-take steers. Cattle were estimated to utilize 60% of the total amount of projected forage growth (Ball et al., 2007) over 2,000 kg DM/ha to account for waste and trampling. Stocking density adjustments were determined based on amount of predicted consumption by cattle within a paddock over a 2-wk period. Forage mass and nutritive quality were determined by clipping 0.25-
m2 quadrats (8/paddock) before the beginning of grazing and every 2 wk during the experiment. Forage within quadrats was clipped to an aboveground stubble height of approximately 2 cm. Fresh-cut forage was then placed into plastic, zip-closure bags and stored on ice for transportation to the Ruminant Nutrition Laboratory at Auburn University. Samples from each paddock were placed in a paper bag, oven-dried at 60°C for 72 h, air-equilibrated, and weighed. Dry matter availability was calculated for each paddock based on dry-weight data multiplied by the area of the paddock. Dried, air-equilibrated forage samples were ground in a Wiley mill (Thomas Scientific, Swedesboro, NJ) to pass a 1-mm screen. Forage concentrations of CP and DM were determined according to procedures of AOAC (1995), and concentrations of NDF, ADF, and ADL were determined sequentially according to procedures of Van Soest et al. (1991). Samples were prepared for total nonstructural carbohydrate (TNC) analysis according to a modification of the Weinmann (1947) procedure for fructosan accumulators. Samples (0.20 to 0.25 g) were boiled in 50 mL of 0.05 N H2SO4 for 1 h and placed in a shallow ice bath, after which 1.0 N NaOH was added to adjust the pH of the sample to 4.5. One mL of diluted amyloglucosidase (Aspergillus niger, Lot No. A 9913, Sigma-Aldrich Inc., St. Louis, MO) solution was added to samples, which were then covered and incubated at 60°C for 1 h. Samples were filtered and brought to volume in a 250-mL volumetric flask with 2 mL of 0.1 N NaOH and deionized H2O. Ten milliliters of Sheffer-Somogyi reagent (AOAC, 1995) were combined with a 10-mL aliquot of sample in a 25 × 200 mm capped test tube and boiled for 15 min. Tubes were then cooled in an ice bath, and 2 mL of potassium iodide-potassium oxalate solution was added to each sample. Next, 10 mL of 1.0 N H2SO4 and 1 mL of gelatinized starch solution were added to each tube before titration.
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Table 1. Monthly mean air temperatures (°C) and precipitation (mm) for January to May 2009, and 30-yr averages for Headland, AL (AWIS Weather Services Inc., Auburn, AL) Month January February March April May
Avg. high, °C
Avg. low, °C
Mean, °C
30-yr avg., °C
Precipitation, mm
30-yr avg., mm
18 18 22 25 29
6 5 11 12 19
12 12 17 19 24
9 11 15 19 23
50 53 182 146 233
160 132 157 97 107
Samples were titrated with 0.02 N sodium thiosulfate until the solution turned light blue. Concentration of TNC in samples was calculated as the amount of reducing sugar in the sample, multiplied by the dilution factor × 100, divided by the sample weight. Forage IVDMD was determined according to the Van Soest et al. (1991) modification of the Tilley and Terry (1963) procedure using the DaisyII incubator system (Ankom Technology Corporation, Fairport, NY). Ruminal fluid was collected from a fistulated, dry Holstein cow at the Auburn University College of Veterinary Medicine. The cow was fed a corn silagebased diet containing cottonseed meal and Megalac supplement (Church and Dwight Co., Princeton, NJ), and had ad libitum access to bermudagrass pasture and alfalfa (Medicago sativa) hay. Fluid was stored in prewarmed thermos containers and transported to the Ruminant Nutrition Laboratory where it was then prepared for the batch-culture IVDMD procedure. Data were analyzed using the PROC GLM procedure (SAS Inst. Inc., Cary, NC) for a completely randomized design. Data were analyzed by individual weigh period because of unequal number of days in each period. The PDIFF option of LSMEANS in SAS (SAS Inst. Inc.) was used for mean separation of treatments when protected by F-test at α = 0.10.
RESULTS AND DISCUSSION Temperature and Precipitation Except for April, monthly mean air temperatures were slightly greater
than 30-yr averages for Headland, AL (Table 1). For January and February, monthly total precipitation (Table 1) was 69 and 60% less, respectively, than the 30-yr average. Precipitation was 16, 50, and 118% greater than the 30-yr average in March, April, and May, respectively. Average precipitation during January and February was considerably below 30-yr averages; however, beginning in March, rainfall was considerably greater than the 30yr average.
Forage Mass From January 8 to February 5, R-RG had 494 and 437 kg DM/ha greater forage mass (Table 2) than O-RG (P = 0.04) and O-R-RG (P = 0.02), respectively. Rye is more cold-tolerant than the other common small-grain species, and it is often available and ready for grazing earlier in the growing season (Ball et al., 2007). Bruckner and Raymer (1990) reported that differences in seasonal distribution of small-grain forages was most evident in January and February when rye produced greater forage yields than triticale, oat, or wheat. Subfreezing nighttime temperatures in mid-January likely retarded oat production in the present study. Between January 12 and January 23, early-morning low temperatures were below 0°C on all but 2 d, including 5 d below −3°C for which the lowest temperature was below −6°C, and some frost damage was evident as tip burn in pastures containing oat during that period. However, yield distribution favored the production of oat from February 5 to March 5,
during which time R-RG had less forage mass than O-RG (P = 0.04) and O-R-RG (P = 0.01). Further, mixed pastures containing rye had less (P < 0.01) herbage mass than O-RG from March 5 to April 6, and forage mass with mixtures containing rye steadily decreased throughout the remainder of the experiment. Differences in forage mass among treatments were most evident from April 6 to May 5, in which O-RG had 129 and 157% greater herbage mass than O-R-RG (P = 0.0001) and R-RG (P = 0.0001), respectively. Forage mass was greatest during this period, most likely because of oat reaching maximum productivity and maturity in conjunction with peaking productivity of ryegrass. Redfearn et al. (2005) noted that the greatest forage production of ryegrass occurred from March onward, although yield was variety dependent. Spring productivity of ryegrass was illustrated over a 2-yr trial at 4 locations in Oklahoma (Redfearn et al., 2002) in which 40% of the total forage production of different ryegrass cultivars occurred early in the growing season (December through February), and 60% occurred as late-season growth (March through May). Forage mass in O-RG pastures continued to exceed 2,000 kg DM/ha until the final period, even under management using put-and-take steers. From May 5 to May 28, herbage mass decreased markedly for all forage mixtures, although O-RG available DM was still 78 and 134% greater, respectively, than that in the O-R-RG (P = 0.001) and R-RG (P = 0.0001) mixed-pasture systems.
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Table 2. Forage mass (kg DM/ha) in mixed small-grain/ryegrass pastures Treatment1 Period
O-RG
R-RG
Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28
2,110 2,611a 2,185c 3,260e 1,787e a
2,604 2,145b 1,488d 1,270f 767f b
O-R-RG
SE
2,167 2,741a 1,671d 1,426f 1,005f
153 160 129 134 160
a
Within a row, means without common superscripts differ (P < 0.05). Within a row, means without common superscripts differ (P < 0.01). e,f Within a row, means without common superscripts differ (P < 0.0001). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass. a,b c,d
Although each pasture was initially stocked with 3 test steers (equivalent to 2.1 steers/ha), rapid and sustained increases in forage growth warranted use of put-and-take steers to varying degrees to maintain forage DM availability at the target value of 2,000 kg/ha. Figure 1 illustrates the implementation of stocking density adjustments that were needed to maintain a forage mass of 2,000 kg/ ha. Stocking densities were not different among treatments except from April 6 to May 5 when O-RG was stocked with more than twice as many steers as R-RG and O-R-RG. Mean forage allowance across all treatments was 1.06 kg DM/kg steer BW over the 140-d grazing experiment. Minson (1990) noted a break point at which DMI decreased with decreasing forage allowance between 30 and 50 g DM/ kg BW. Results from McCollum et al. (1992) indicate that peak DMI occurred on wheat pastures at 300 g DM/kg BW. Using these values, even at the lowest forage mass in the present study, the mean forage allowance across this experiment was clearly sufficient to support an adequate level of intake.
Cell Wall Constituents No differences were observed among treatments in forage NDF concentration (Table 3) from January 8 to Feb-
ruary 5 (P > 0.10), April 6 to May 5 (P > 0.10), and May 5 to May 28 (P > 0.10). However, O-RG forage had less NDF than O-R-RG (P = 0.07) and R-RG (P = 0.001) treatments, respectively, and O-R-RG contained less NDF (P = 0.02) than R-RG from February 5 to March 5. Mean NDF was also less for O-RG forage than O-R-RG (P = 0.004) and R-RG (P = 0.008) treatments from March 5 to April 6, which may be partially attributed to earlier maturation of rye compared with oat and ryegrass. Across the entire grazing season, NDF concentrations ranged from 37 to 69% for all treatments. These results are consistent with those of Redfearn et al. (2002), who reported that concentration of NDF in ryegrass increased from 39 to 58% across the growing season. Moreover, Juskiw et al. (2000) observed NDF concentration of >50% for barley, oat, and triticale in the dough stage of development before harvest. Forage concentration of ADF (Table 3) decreased between January 8 and March 5, with mixtures containing oat having less ADF than R-RG. The observed decrease in ADF contrasts with the pattern of increasing NDF observed during the same time period. From February 5 to March 5, O-RG contained less ADF than O-R-RG (P = 0.02) and R-RG (P = 0.001), and O-R-RG contained less (P = 0.10)
ADF than R-RG. From March 5 to April 6, O-RG forage had 3.3 and 2.3 percentage units lower ADF concentration than O-R-RG (P = 0.02) and R-RG (P = 0.09) treatments, respectively. Mean ADF increased within each forage treatment throughout the remainder of the experiment, which is expected with advancing plant maturity. Juskiw et al. (2000) reported 32% ADF for oat in the dough stage of development, and similar values for other small grains. Although no differences were observed among treatments from May 5 to May 28, mean ADF was slightly greater for all treatments than those reported by Juskiw et al. (2000). During the first 28 d of the experiment, mean ADL (Table 3) was greater for R-RG than O-RG (P = 0.02) and O-R-RG (P = 0.03) treatments. Lignin concentration increased in all treatments with increasing plant maturity; however, no differences were observed among treatments throughout the remainder of the trial. Mean ADL for forage species in the present study was relatively low, but comparable with values reported by Muir and Bow (2009) for cool-season annual forages grown under nutrientrich conditions. During the first year of Muir and Bow (2009), ADL was <3% for barley, oat, triticale, rye, and ryegrass from September to April in Stephenville, TX.
Crude Protein Concentration of CP (Table 4) was greatest for all treatments (≥21%) during the first 28 d of the trial, which is expected for cool-season annual forages in a vegetative stage of maturity. An increase in CP was observed between February 5 to April 6, which may be attributed in part to application of NH4NO3 and (NH4)2SO4 fertilizer at the beginning of March. Mean CP was less for O-RG than O-R-RG (P = 0.06) and R-RG (P = 0.03) from February 5 to March 5. From March 5 to April 6, CP was less for O-R-RG than the O-RG (P = 0.05) and R-RG (P = 0.007) treatments, but was not different (P
Beef production from cool-season annual forages
383
for concentration of CP in ryegrass from December to May (26 to 12%) in Oklahoma. Ball et al. (2007) reported a decline in concentration of CP in rye of 28, 24 and 13% at the vegetative, flower/boot, and fruit/head stages of maturity, respectively.
Total Nonstructural Carbohydrates
Figure 1. Stocking densities for oat and ryegrass (O-RG), oat and rye and ryegrass (O-R-RG), and rye and ryegrass (R-RG) pastures.
> 0.10) between O-RG and R-RG. No differences were observed among treatments in concentration of CP in any other periods throughout the
grazing experiment. Mean CP decreased from roughly 22 to 12% across the entire grazing season. Redfearn et al. (2002) observed a similar pattern
Table 3. Forage concentration (%, DM basis) of cell-wall constituents in mixed small-grain/ryegrass pastures Treatment1 Item NDF, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 ADF, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 ADL, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28
O-RG 37.9 42.7a 49.8a 52.4 68.8 28.7 22.1a 27.6d 27.9 38.5 0.39f 0.53 1.09 1.05 3.20
R-RG 38.7 49.8b 54.5b 53.8 65.3 28.5 27.8b 29.9e 28.1 39.6 0.61g 1.27 1.65 1.87 2.49
O-R-RG 36.6 45.8c 55.2b 51.4 64.7 28.6 25.6c 30.9e 27.1 35.5 0.39f 0.91 1.29 0.94 2.34
SE 1.2 1.0 1.0 2.2 2.7 3.1 0.9 0.9 1.1 3.2 0.06 0.26 0.26 0.35 0.42
Within a row, means without common superscripts differ (P < 0.01). Within a row, means without common superscripts differ (P < 0.05). f,g Within a row, means without common superscripts differ (P < 0.10). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass.
a–c d,e
Concentration of TNC (Table 4) in O-RG was greater than O-R-RG (P = 0.004) and R-RG (P < 0.001) forages, and O-R-RG was greater (P = 0.07) than R-RG from February 5 to March 5. Chatterton et al. (2006) noted that sugar concentration was generally greatest when oat forage plants were young (tiller and joint growth stages) and concentration of fiber was relatively low; glucose, fructose, and sucrose averaged 15% DM in hay in the boot stage, and declined to 1 to 2% of DM with increasing plant maturity. Van Soest (1994) reported that cool-season grasses typically contain 3 to 6% DM of soluble sugars, 0 to 2% DM of starch, and 3 to 10% DM of fructans, which additively is comparable with the total concentration of TNC observed in the present study for pastures containing oat. Percentage of TNC in all treatments decreased from March 5 to April 6, with R-RG containing less TNC than both O-RG (P < 0.001) and O-R-RG (P = 0.02), and O-RG containing greater (P = 0.001) TNC concentration than O-R-RG from March 5 to April 6. No differences among treatments were observed in percentage of TNC from to February 5 to March 5, April 6 to May 5, and May 5 to May 28.
In Vitro Dry Matter Digestibility Percentage IVDMD (Table 4) was not different between O-RG and OR-RG (P > 0.10), but was greater for O-RG (P = 0.08) and O-R-RG (P = 0.03) than R-RG during January 8 to February 5. Digestibility of O-RG was greater than O-R-RG (P = 0.02) and R-RG (P = 0.001) treatments, and digestibility of O-R-RG and R-RG were
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Mullenix et al.
Table 4. Forage concentration (%, DM basis) of CP and total nonstructural carbohydrates (TNC), and forage IVDMD in mixed smallgrain/ryegrass pastures Treatment1 Item CP, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 TNC, % of DM Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 IVDMD, % Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28
O-RG
R-RG
O-R-RG
21.5 12.1a 18.6c 12.6 12.9
22.0 15.6b 19.5c 14.3 13.6
22.3 15.0b 16.9d 13.9 12.2
18.0 24.9e 12.0h 17.8 8.1
15.8 13.6f 7.4i 15.3 6.3
17.3 17.5g 9.0j 17.5 8.0
95.5a 91.3e 88.3e 82.4 68.1
92.7b 88.3f 83.1f 78.5 65.1
95.0a 89.3f 78.8g 79.6 71.1
SE 2.3 1.0 0.5 0.6 1.5 3.3 1.4 0.4 1.6 0.9 0.6 0.6 1.7 1.9 2.6
Within a row, means without common superscripts differ (P < 0.10). Within a row, means without common superscripts differ (P < 0.05). e–g Within a row, means without common superscripts differ (P < 0.01). h–j Within a row, means without common superscripts differ (P < 0.0001). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass. a,b
c,d
not different (P > 0.10) from February 5 to March 5. Values observed for IVDMD of mixed small grain/ryegrass pasture from January 8 to February 5 of the present study were greater than those observed in other studies with cool-season annual pastures. Moyer and Coffey (2000) reported average IVDMD was 74.5% for rye cultivars, 69.8% for wheat cultivars, and 72.1% for barley in an evaluation of forage quality of small grains grown in monoculture. Redfearn et al. (2002) observed a decrease in IVDMD of annual ryegrass from 84 to 70% with increasing plant maturity. The relatively high values observed for digestibility during the first 2 mo of the present study may be attributed to the extremely low concentrations of cell wall constituents, notably lignin, observed during the beginning of the grazing trial. Forages in the young, vegetative stage are high quality, and
if not extensively lignified, structural components of the cell wall are more readily available for digestion. Mixed forages of O-RG had greater digestibility than R-RG (P = 0.04) and O-R-RG (P = 0.001), and R-RG had greater (P = 0.10) digestibility than O-R-RG from March 5 to April 6. No differences were observed among forage treatments for digestibility in all other periods during the experiment. Forage IVDMD decreased across the grazing trial for all treatments with increasing plant maturity.
Average Daily Gain and Grazing Days Test-steer ADG from April 6 to May 5 (Table 5) was less for R-RG than the O-RG (P = 0.008) and O-R-RG (P = 0.02) treatments. Average daily gain over the 140-d grazing period was greater for O-RG
than R-RG (P = 0.03), but was not different from that of O-R-RG (P > 0.10). No differences (P > 0.10) were observed in ADG among treatments from January 8 to February 5, February 5 to March 5, March 5 to April 6, or May 5 to May 28. Observations for cattle ADG were in general agreement with other studies with cool-season forage systems (Ball et al., 2007; Beck et al., 2005, 2007). When small-grain/ryegrass mixtures were interseeded into bermudagrass sod, Beck et al. (2007) reported ADG from O-RG was intermediate to that of other mixed-forage systems and not different among treatments during yr 1 of a 2-yr grazing trial. In yr 2, no significant differences were observed among treatments in spring ADG of mixed forages, and ADG for cattle grazing O-RG pasture was 1.33 kg/d, similar to the O-RG gain in the present study. Cattle ADG from O-R-RG was slightly greater than that (0.98 kg/d) observed by Myer et al. (2008) in a grazing trial in Florida. Although R-RG pasture produced the least ADG in the present study, these values agree with those reported by Cleere et al. (2004) in which steers grazing a combination of R-RG gained between 1.01 and 1.28 kg/d from December to May across 2 stocking rates and grazing systems in Overton, TX. No differences were observed among treatments for steer-grazing-days over the 140-d grazing trial (Table 5). From April 6 to May 5, steergrazing-days were greater for O-RG than R-RG (P = 0.02) and O-R-RG (P = 0.03) treatments. No differences among treatments were observed in the other periods. Number of steergrazing-days was greatest for O-RG from April 6 to May 5 due to increased forage DM availability and capacity to support increased stocking rate as indicated by increased use of forage management using put-andtake steers. Across the entire grazing season, forage treatments containing oats had ≥625 steer-grazing-days, equivalent to 440 grazing-d/ha. Comparable results were observed by Myer et al. (2008), observing 421 and
Beef production from cool-season annual forages
Table 5. Performance of steers grazing mixed small-grain/ryegrass pastures Treatment1 Item
O-RG
R-RG
O-R-RG
Initial BW, kg Final BW, kg ADG, kg Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 Jan 8 to May 28 Grazing days, d Jan 8 to Feb 5 Feb 5 to Mar 5 Mar 5 to Apr 6 Apr 6 to May 5 May 5 to May 28 Jan 8 to May 28
351 536
362 523 1.48 1.87 1.31 0.68b 0.26 1.13d 122 98 118 101b 80 547
355 532
1.60 2.03 1.37 1.30a 0.07 1.38c 84 154 128 170a 126 655
1.63 1.90 1.06 1.17a 0.39 1.26c 101 133 175 109b 69 625
SE 4.56 13.0 0.08 0.16 0.11 0.14 0.14 0.05 24 16 22 12 33 48
Within a row, means without common superscripts differ (P < 0.05). Within a row, means without common superscripts differ (P < 0.10). 1 O-RG = oat and ryegrass; R-RG = rye and ryegrass; O-R-RG = oat and rye and ryegrass. a,b c,d
403 grazing-d/ha for O-R-RG and O-RG, respectively, in a grazing trial in Florida. Beck et al. (2007) reported slightly greater values of 595 (yr 1) and 697 grazing-d/ha (yr 2) for O-RG overseeded into bermudagrass sod in Arkansas.
evaluation of other small-grain forage and legumes grown in mixtures with ryegrass to enhance knowledge that can be used to develop management tools for producers, consultants, and extension educators.
IMPLICATIONS
LITERATURE CITED
Results from this study illustrate the potential value of small-grain/ ryegrass mixtures for beef cattle production systems in the Southeastern United States. Under the growing conditions in the present study, mixtures containing oat were more productive and showed less rapid changes in forage quality across the grazing season than R-RG. Although pastures containing oats provided superior animal performance in this study, oats are cold-sensitive and may be winterkilled in some parts of the Southeast; mixtures containing oats may be best suited for milder winter climates such as in the Gulf Coast region. Future research opportunities exist for
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