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© 2009 Plant Management Network.
Accepted for publication 20 January 2009. Published 18 March 2009.

Stockpiled Prairiegrass Provides High-Quality Fall Grazing for Lambs

Kimberly A. Cassida, James P. S. Neel, and David P. Belesky, USDA-ARS, Appalachian Farming Systems Research Center, Beaver WV 25813

Corresponding author: Kimberly A. Cassida. kim.cassida@ars.usda.gov

Cassida, K. A., Neel, J. P. S., and Belesky, D. P.. 2009. Stockpiled prairiegrass provides high-quality fall grazing for lambs. Online. Forage and Grazinglands doi:10.1094/FG-2009-0318-01-RS.

Abstract

New varieties of prairiegrass (Bromus catharticus Vahl. = B. willdenowii Kunth.) exhibit improved persistence over ‘Grasslands Matua’ under USA growing conditions, but animal performance data are lacking. We evaluated performance of lambs grazing stockpiled ‘Dixon’ prairiegrass on West Virginia hill pasture in autumn. In 2006 and 2007, a three-year-old stand of Dixon was cut for hay in late July, fertilized with 56 kg/ha of N, and stockpiled for eight weeks. Three pasture replicates of stockpiled forage were grazed by ewe lambs under a put-and-take grazing system for a total of 24 days (25 September to 19 October) with budgeted grazing intensities of 50% (GI50) or 75% (GI75) removal of forage mass. At the end of the grazing period, lambs were heavier (42.3 vs. 41.2 kg), and had greater average daily gain (ADG) (264 vs. 216 g/day) on the GI50 vs. GI75 treatment, respectively, but gain per ha was greater on the GI75 treatment (193 vs. 253 kg/ha). Fall grazing intensity did not affect forage mass, botanical composition, tiller density, or nutritive value of stands harvested for hay in the following May. Good forage mass production and excellent lamb gains on stockpiled prairiegrass indicate this grass deserves serious consideration for fall-finishing of lambs.

Value of Prairiegrass for Grazing Sheep

Prairiegrass attracted renewed attention for grazing in the USA with the introduction of ‘Grasslands Matua’ in the 1980s. Prairiegrass is a high yielding, high quality, palatable forage, but unfortunately Matua proved highly susceptible to winter-kill and powdery mildew (Blumeria graminis) under growing conditions in the USA (15). Plant breeders developed varieties of prairiegrass with better mildew (‘Dixon’) (16) and cold (‘Lakota’) (15) tolerance for growing conditions in the USA. In Appalachia, these new varieties produced total annual forage mass of 5300 to 7050 kg/ha (1,2).

Productivity of most Appalachian cool-season pastures is typically declining in autumn when spring lambs being pasture finished for ethnic holiday markets have their greatest demand for high quality forage. There is often a need for relatively short-term pasture that will produce gain to fill the gap between decline of summer pastures and the holiday markets. The fall productivity of prairiegrass in Appalachia (1,2) suggests it could meet this need, but there are no published reports of sheep performance while grazing prairiegrass at any time of year in the USA. Fall harvest management factors such as defoliation intensity and timing affect prairiegrass productivity in subsequent years (5,6,7), but these have not been studied in the cultivars that were developed for the USA. Therefore, we conducted a grazing trial in order to evaluate: (i) potential of fall-stockpiled Dixon prairiegrass for producing short-term gain on pasture-finished lambs; and (ii) effect of fall grazing intensity and timing on persistence of prairiegrass over winter.

Prairiegrass Management

Dixon prairiegrass was established in 2004 on a Gilpin silt loam (fine-loamy, mixed, mesic Typic Hapludults) in Raleigh County, WV (37°45’N, 80°58’W, 875 m above sea level). Prairiegrass was cut for hay in mid-May and late July each year, and was stockpiled for approximately 8 week after the July harvest to prepare for autumn grazing in 2006 and 2007. Stands were fertilized with 56 kg/ha each of N, P₂O₅, and K₂O in April, and an additional 56 kg/ha of N was applied after each hay cutting. Powdery mildew was almost always present in isolated patches within the prairiegrass stand. A widespread outbreak of mildew during the hot, dry summer of 2007 prompted application of additional N (168 kg/ha) in late June to assist grass in outgrowing the mildew (W. Rumball, personal communication).

Grazing Management and Measurements

Experimental design was a randomized complete block with three pasture replications. Size of pastures was 0.20 ha in 2006 and 0.27 ha in 2007. Pasture size was increased in 2007 in an effort to achieve a longer duration of grazing. Paddock size was always 0.07 ha (three paddocks per pasture in 2006 and four in 2007). In 2007, prairiegrass was lost from all parts of the field, grazed and ungrazed, that were shaded by adjacent woods. This affected a large proportion of Replication 3, which was therefore moved to a previously unused section of the field. Each paddock was grazed only once per year. Pre-grazing dry forage mass in each paddock was calculated from dry weights in five randomly placed 0.19-m² quadrats clipped to ground level and reported as means across paddocks within pastures. Subsamples ground through a 2-mm cyclone mill screen were analyzed for neutral and acid detergent fiber (NDF, ADF) in a Fiber Analyzer (Ankom Technology, Fairport, NY) and for in vitro true digestibility (IVTD) in a Daisy Digester (Ankom Technology, Fairport, NY). Subsamples ground through a 0.5-mm screen were analyzed for crude protein (CP) using an elemental analyzer (Flash EA, 1112 Series, Thermo Electron Corp., Rodano, Milan, Italy), and for total nonstructural carbohydrates (TNC) using an autoanalyzer (Alpkem Corp., Clackamas, OR).

Spring-born Polypay × Suffolk ewe lambs (average start weight 34.5 and 37.3 kg in 2006 and 2007, respectively) grazed each pasture using the put-and-take method for a total duration of 24 days in 2006 (25 September to 19 October) and 25 days in 2007 (24 September to 19 October). Animal weights on and off study were taken early morning with water being withheld overnight. Prior to this trial, lambs were grazing mixed pasture containing primarily orchardgrass (Dactylis glomerata). Before placement on treatment paddocks, lambs were sorted by body weight, randomly assigned to pasture treatment, and then to pasture replication within treatment. Within treatment replicate, six lambs were randomly assigned as "tester" animals. Testers remained on pastures throughout the grazing period and were weighed at the start and end of the trial. Testers were moved to new paddocks at approximately 8-day intervals in 2006 and 6-day intervals in 2007. Each time animals were moved to new paddocks within the grazing sequence, stocking density was adjusted based on pre-graze forage mass estimates, using additional grazer animals to ensure an equal time frame for forage removal across all pastures. Stocking densities for the two grazing intensity treatments were set to utilize 50% (GI50 "take half, leave half") and 75% (GI75) of the pre-grazing forage mass, using an estimated daily dry matter intake of 1.18 kg/head/day (11,12). Animals in both treatments were moved to new paddocks when visual estimation of 75% removal was observed on the GI75 treatment. Water and trace mineralized salt were continuously available in each paddock. Animal grazing days per hectare were calculated as the stocking density multiplied by the number of grazing days.

The effect of grazing treatments on winter survival of prairiegrass was measured by recording tiller densities from three 0.19-m² quadrats per paddock, and botanical composition, forage mass, and nutritive value in samples collected from five 0.19-m² quadrats per paddock in mid-May of the spring following each grazing period.

Data were analyzed using PROC MIXED (SAS Release 9.1, SAS Institute Inc., Cary, NC). Initial weight of lambs was used as a covariate for individual animal data. Pasture replication and year were considered to be random, and other treatment effects were fixed. Forage data collected from paddocks were treated as subplots within pastures in order to evaluate whether date of grazing influenced prairiegrass persistence. All results are significant at P < 0.05 unless otherwise stated.

Lamb Performance

Stocking rates for the entire grazing period averaged 30 and 47 lambs/ha for the GI50 and GI75 treatments, respectively. Individual lambs on GI50 grazing intensity had 22% greater ADG than lambs on the more densely stocked GI75 treatment, gained more weight, and were 1.1 kg heavier at the end of the grazing period (Table 1). Total animal grazing days were 55% greater for GI75. Total lamb gain per ha was 31% greater for GI75 than for GI50. Grazing period during both years was shorter than anticipated, but was within reported time durations for lamb performance data in both pasture and finishing studies (8,10,14). It is unclear why this result occurred, with possible contributing factors of greater intake by animals than predicted or inaccuracy in estimating forage mass.

Table 1. Performance of ewe lambs strip-grazed on stockpiled Dixon prairiegrass at grazing intensities set to utilize 50% (GI50) and 75% (GI75) of forage mass in autumn 2006 and 2007.

*,**,*** Significantly different at P < 0.05, 0.01, and 0.001, respectively.

 ^x ADG = average daily gain.

Lamb performance was excellent on both grazing treatments and was similar to that reported for lambs grazing prairiegrass in New Zealand (3). Our ADG were greater than those previously reported for lambs fall-grazed on an orchardgrass (Dactylis glomerata L.)-white clover (Trifolium repens L.) pasture at the same location and were comparable to those of grain-fed lambs (17). Lambs grazed prairiegrass readily even when offered grass in full head that was taller than the lambs, and consumed almost all of the leaves and seed heads as well as much of the stem.

Our results are typical of variable stocking rate trials where ADG generally decreases and gain per ha increases within sustainable ranges of stocking rate (13). Choice of stocking rate depends on whether a producer is targeting maximum gain per ha, production of animals with a specific end weight, or budgeting available forage to last for a specific time interval.

Prairiegrass Yield and Forage Quality

Forage mass did not differ between grazing intensity treatments (Table 2). Microenvironment variability across the field was reflected in greater forage mass in the second paddock of each pasture compared to the others (3.98 vs. 3.42 Mg/ha, respectively). Forage mass averaged 4.88 and 4.12 Mg/ha during the grazing periods in 2006 and 2007. Good forage production occurred in 2007 despite drought conditions during the stockpiling/grazing period (cumulative precipitation from 1 August to 19 October was 312 mm in 2006 and 108 mm in 2007). Stockpiled forage mass was similar to that reported for tall fescue in Tennessee (4) and greater than Matua, tall fescue, and perennial ryegrass in Pennsylvania (6).

Table 2. Mean forage mass and nutritive composition of stockpiled Dixon prairiegrass grazed by lambs at grazing intensities set to utilize 50% (GI50) and 75% (GI75) of forage mass in autumn 2006 and 2007.

 ^x CP = crude protein, NDF = neutral detergent fiber, ADF = acid detergent fiber, TNC = total nonstructural carbohydrates, IVTD = in vitro true digestibility.

Nutritive quality of stockpiled prairiegrass was adequate to meet requirements for finishing lambs (11), and did not differ between grazing intensity treatments for CP, NDF, ADF, IVTD, or TNC (Table 2). Concentrations of CP, NDF, ADF, and IVTD did not change over time during the grazing period (data not shown, P > 0.05). However, pregrazing samples harvested on 24 September from the first paddock entered had lower TNC concentrations than samples from paddocks entered on 2, 9, or 15 October (7.9 vs. 9.4, 9.9, 10.4, respectively, P < 0.05). Week to week variability of fall prairiegrass nutritive quality was also reported by Hall et al. (5). In general, our forage nutritive quality was slightly less than that reported for stockpiled Matua harvested on comparable dates in Pennsylvania (5) and slightly greater than stockpiled tall fescue harvested in Tennessee (4).

At the May harvest, forage mass averaged 5.31 Mg/ha and was not affected by grazing intensity treatments imposed the previous fall (Table 3). This contrasts with a maximum spring forage mass of 1.98 Mg/ha for Matua in Pennsylvania, where spring forage mass was reduced by greater defoliation intensity (i.e., shorter stubble height) the previous fall (7). Grazing intensity did not affect botanical composition of stands, prairiegrass tiller density, or forage nutritive value in our study (Table 3). A large number of seedlings observed between drill rows during spring tiller counting suggested that self-reseeding contributed significantly to stand persistence, in agreement with Jung et al. (7), who reported that opening the plant canopy via fall harvest improved the reseeding capability of Matua by reducing shading.

Table 3. Spring forage mass, tiller density, and nutritive composition of Dixon prairiegrass grazed by lambs in autumn 2006 and 2007 at grazing intensities set to utilize 50% (GI50) and 75% (GI75) of forage mass.

 * Significantly different at P < 0.05.

 ^x T = grazing intensity treatment, D = harvest date, CP = crude protein, NDF = neutral detergent fiber, ADF = acid detergent fiber, TNC = total nonstructural carbohydrates, IVTD = in vitro true digestibility.

Date of fall grazing did not affect spring forage mass, botanical composition of stands, prairiegrass tiller density, CP, NDF, ADF, or IVTD (Table 3), but TNC of spring-harvested forage was reduced in paddocks that were grazed earlier in the fall (September 12.0% vs. October 14.1%, P < 0.01). In Pennsylvania, Matua failed to persist longer than two years under any fall grazing management including a comparable single grazing in September (6). Spring forage mass of Matua decreased as fall harvest date advanced from September to December (7) in Pennsylvania, but fall harvest date had no effect on spring nutritive quality (5). While our data should be interpreted cautiously because the study was not designed to examine a wide range of defoliation treatments, it does indicate that grazing stockpiled Dixon once at moderate to high intensity in early fall (late September-October) resulted in acceptable stand productivity and persistence.

Summary

Stockpiled Dixon prairiegrass produced forage mass of excellent nutritive value and supported excellent lamb gains when grazed in early fall in West Virginia. Individual lamb performance was greatest at grazing intensities targeted to 50% forage utilization while gain per ha was greatest at 75%. Grazing stockpiled prairiegrass through mid-October with stocking rates up to 47 lambs/ha resulted in acceptable stand productivity and persistence in the following spring. This grass deserves further research attention and serious consideration for inclusion in small ruminant production systems.

Literature Cited

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