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1.
Achieving economically optimum livestock production on rangelands can conflict with conservation strategies that require lower stocking rate to maintain wildlife habitat. Combining the spatial and temporal interaction of fire and grazing (pyric–herbivory) is a conservation-based approach to management that increases rangeland biodiversity by creating heterogeneous vegetation structure and composition. However, livestock production under pyric–herbivory has not been reported. In both mixed-grass prairie and tallgrass prairie, we compared livestock production in pastures with traditional fire and grazing management (continuous grazing, with periodic fire on tallgrass prairie and without fire on mixed-grass prairie) and conservation-based management (pyric–herbivory applied through patch burning) at a moderate stocking rate. Stocker cattle weight gain, calf weight gain, and cow body condition score did not differ (P > 0.05) between traditional and conservation-based management at the tallgrass prairie site for the duration of the 8-yr study. At the mixed-grass prairie site, stocker cattle gain did not differ in the first 4 yr, but stocker cattle gained more (P ≤ 0.05) on conservation-based management and remained 27% greater for the duration of the 11-yr study. Moreover, variation among years in cattle performance was less on pastures under conservation management. Traditional management in mixed-grass prairie did not include fire, the process that likely was associated with increased stocker cattle performance under conservation management. We conclude that pyric–herbivory is a conservation-based rangeland management strategy that returns fire to the landscape without reduced stocking rate, deferment, or rest.  相似文献   

2.
Grazing management has focused largely on promoting vegetation homogeneity through uniform distribution of grazing to minimize area in a pasture that is either heavily disturbed or undisturbed. An alternative management model that couples grazing and fire (i.e., patch burning) to promote heterogeneity argues that grazing and fire interact through a series of positive and negative feedbacks to cause a shifting mosaic of vegetation composition and structure across the landscape. We compared patch burning with traditional homogeneity-based management in tallgrass prairie to determine the influence of the two treatments on the aboveground invertebrate community. Patch burning resulted in a temporal flush of invertebrate biomass in patches transitional between unburned and patches burned in the current year. Total invertebrate mass was about 50% greater in these transitional patches within patch-burned pastures as compared to pastures under traditional, homogeneity-based management. Moreover, the mosaic of patches in patch-burned pastures contained a wider range of invertebrate biomass and greater abundance of some invertebrate orders than did the traditionally managed pastures. Patch burning provides habitat that meets requirements for a broad range of invertebrate species, suggesting the potential for patch burning to benefit other native animal assemblages in the food chain.  相似文献   

3.
Through pyric herbivory (i.e., fire-induced grazing patterns), native grasslands were historically a spatially heterogeneous environment. It is hypothesized that the mosaic of habitats created by pyric herbivory supports a more diverse invertebrate community compared to modern range management. Patch-burn management, a pyric herbivory technique, is an application of prescribed fire and grazing whereby the timing and location of the burned and grazed patches is varied, creating a diversity of habitat conditions. Although disturbance in sandsage (Artemisia filifolium Torr.) prairie historically included fire and grazing, fire disturbance has been nearly eradicated from this ecosystem in western Oklahoma. We compared patch-burn management to traditional management (i.e., moderate grazing with no fire) in sandsage prairie to evaluate the impact of these two management regimes on aboveground invertebrates. We sampled invertebrates at 44 points in each of 3 mo (May, June, and July) with the use of Dietrick vacuum sampling. Diversity, total abundance, and abundance of seven invertebrate orders (Araneae, Diptera, Hemiptera, Homoptera, Hymenoptera, Lepidoptera, and Orthoptera) were similar between patch-burn and traditional pastures. When examined on a patch level, five invertebrate orders were also similar between their respective time since burn patch and the traditional patches. Araneae and Coleoptera abundance were higher in traditional patches, and Hemiptera abundance was higher in current-year burn patches. Our results suggest a heterogeneity-based management scheme based on pyric herbivory does not negatively impact the overall invertebrate community and may benefit a wider variety of invertebrates by providing areas of varying levels of disturbance. In comparison, homogeneous landscapes such as those created by traditional management may only benefit segments of the invertebrate community that have habitat associations with moderately disturbed or undisturbed areas. Therefore, a disturbance regime involving the interaction of fire and grazing may be valuable for maintaining biodiversity and productivity within sandsage prairie ecosystems.  相似文献   

4.
Knowledge of how tallgrass prairie vegetation responds to fire in the late growing season is relatively sparse and is based upon studies that are either spatially or temporally limited. To gain a more robust perspective of vegetation response to summer burning and to determine if repeated summer fire can drive vegetational changes in native tallgrass prairie, we evaluated species cover and richness over a 14-yr period on different topographic positions from ungrazed watersheds that were burned biennially in the growing season. We found that annual forbs were the primary beneficiaries of summer burning, but their fluctuations varied inconsistently among years. Concomitantly, species richness and diversity increased significantly with summer burning but remained stable through time with annual spring burning. After 14 yr, species richness was 28% higher in prairie that was burned in the summer than in prairie burned in the spring. Canopy cover of big bluestem (Andropogon gerardii Vitman) and Indiangrass (Sorghastrum nutans [L.] Nash) increased significantly over time with both summer and spring burning, whereas heath aster (Symphyotrichum ericoides [L.] Nesom), aromatic aster (Symphyotrichum oblongifolium [Nutt.] Nesom), and sedges (Carex spp.) increased in response to only summer burning. Kentucky bluegrass (Poa pratensis L.) cover declined in both spring-burned and summer-burned watersheds. Repeated burning in either spring or summer did not reduce the cover or frequency of any woody species. Most perennial species were neutral in their reaction to summer fire, but a few species responded with large and inconsistent temporal fluctuations that overwhelmed any clear patterns of change. Although summer burning did not preferentially encourage spring-flowering forbs or suppress dominance of the warm-season grasses, it is a potentially useful tool to increase community heterogeneity in ungrazed prairie.  相似文献   

5.
Restoration of grasslands dominated by tall fescue (Schedonorus phoenix [Scop.] Holub) to native tallgrass prairie usually requires burning, herbicides, or reseeding. We tested seasonal grazing by livestock in winter, combined with cessation of fertilization, as a restoration tool for modifying the competitive dynamics among herbaceous plants to restore tallgrass prairie communities in southeastern Kansas. In 2004–2005, we compared responses of grassland plants and birds across a chronosequence of pastures that were winter-grazed from 1 yr to 5 yr. We compared winter-grazed pastures to pastures grazed year-round and to local native prairie remnants as starting and endpoints for restoration, respectively. Abundance of native warm-season grasses increased from 2% to 3% mean relative frequency in pastures grazed year-round to 18% to 30% in winter-grazed pastures, and increased with duration of winter-grazing. Native warm-season grasses accounted for 1–6% of total live aboveground biomass in pastures grazed year-round, 1–34% in winter-grazed pastures, and 31–34% in native prairie remnants. Tall fescue abundance and biomass were similar among grazing treatments, with a trend for tall fescue to be less dominant in winter-grazed pastures. Tall fescue made up 9–40% of total aboveground biomass in year-round grazed pastures and 10–25% in winter-grazed pastures. Grassland birds showed variable responses to winter-grazing. Dickcissels (Spiza americana) and Henslow’s sparrows (Ammodramus henslowii) were more abundant in winter-grazed pastures, whereas eastern meadowlarks (Sturnella magna) and grasshopper sparrows (A. savannarum) had similar abundance in pastures grazed year-round and during winter. Winter-grazing of pastures dominated by tall fescue combined with suspension of nitrogen fertilization could be an effective restoration technique that allows use of prairie rangeland while improving habitat for sensitive grassland birds.  相似文献   

6.
Invasion of rangeland by exotic forage species threatens ecosystem structure and function and can cause catastrophic economic losses. Herbicide treatments often are the focus of management efforts to control invasions. Management with the fire-grazing interaction (or patch burning) might suppress an invasive forage species that has grazing persistence mechanisms developed apart from the fire-grazing interaction. We studied tallgrass prairies invaded by sericea lespedeza (Lespedeza cuneata [Dum.-Cours.] G. Don) to compare rate of invasion between traditional management and management with patch burning, to evaluate the effect of burn season on sericea lespedeza invasion within pastures managed with patch burning, and to correlate canopy cover of sericea lespedeza to canopy cover of other functional groups with and without herbicides. Sericea lespedeza canopy cover increased from 1999 to 2005 in both traditional- and patch-burn pastures, but sericea lespedeza increased from 5% to 16% canopy cover in traditionally managed pastures compared to 3% to 5% in the patch-burn pastures. Rate of increase in canopy cover of sericea lespedeza was less in patches burned in summer (0.41% · year-1) than in patches burned in spring (0.58% · year-1) within patch-burn pastures. Most plant functional groups, including forbs, were weak-negatively correlated with canopy cover of sericea lespedeza. Although herbicide application reduced mass of sericea lespedeza, other components of the vegetation changed little. Herbicide treatments temporarily reduced sericea lespedeza but did not predictably increase other plant functional groups. Patch burning reduced the rate of invasion by sericea lespedeza by maintaining young, palatable sericea plants in the burn patch, and could play a vital role in an integrated weed management strategy on rangelands.  相似文献   

7.
A 4-yr study was conducted to determine performance of stocker calves on tallgrass prairie under three grazing management strategies. Pastures were assigned to one of three grazing treatments. Grazing was initiated in June, and pastures were grazed only during the summer months for 57 to 104 d (79.5 ± 20.7 d). Two of the pastures were grazed season-long. Calves in one of the season-long treatments were fed a protein supplement during the second half of the grazing season; calves in the other season-long treatment were not supplemented (control group). The third pasture, an intensive early stocking (IES) treatment, was grazed at twice the stocking rate used in the season-long pastures for the first half of the grazing season (40 ± 11 d) and rested for the second half (39.5 ± 10 d). Individual stocker performance during the first half of the summer was similar among grazing treatments. Providing supplemental protein during the second half of the grazing season increased BW gain by 30 kg/ha during the last 40 d of the 80-d grazing season and increased BW gain by 12 kg/ha for the entire summer. Over the summer, IES stocker calves produced 24% more gain/ha than season-long stocked calves. Nonetheless, IES management was not more profitable than season-long grazing with or without protein supplementation. Under short-term ownership of calves in the IES system, fixed costs represented a large portion of the total cost.  相似文献   

8.
The objective of this study was to compare an introduced warm-season perennial grass (plains bluestem, Bothriochloa ischaemum) to native tallgrass prairie for cow-calf production. Three systems were used, two based on tallgrass prairie with two different forms of protein supplementation and one based on plains bluestem as the primary forage. The systems were as follows: 1) native tallgrass prairie with pelleted oilseed meal as the winter protein supplement (native-control); 2) native tallgrass prairie with limited access to wheat pasture as the winter protein supplement (native-wheat); and 3) plains bluestem with limited access to wheat pasture as the protein supplement (bluestem-wheat). Oilseed meal protein supplements were fed twice weekly. Cows grazing wheat pasture were allowed 6 h of grazing twice weekly. Ninety-nine cows per year were used over the 3-yr study. Cows were sired by either Charolais, Gelbvieh, Angus, or Hereford bulls out of commercial Angus-Hereford dams. Calves were sired by Simmental bulls. Calving and weaning rate increased over time but did not differ among systems or breed types. System did not influence the size or body condition score of cows or the performance of calves, but changes in the weight and condition scores of cows were greater on either native system than on the bluestem-wheat system. Cows from Charolais and Gelbvieh bulls were taller (P < 0.05), and heavier (P < 0.05), and weaned heavier (P < 0.05) calves than cows from Angus or Hereford bulls. The weight of cows on the bluestem-wheat system tended to decrease over time, whereas cows grazing on the native systems tended to gain weight over time. The native-control system was the most profitable system based on cow production. If excess hay produced from the bluestem-wheat system was sold as a cash crop, then this system was the most profitable. In general, we conclude that limit-grazing wheat pasture is a viable alternative to oilseed meal as protein supplement for wintering dry cows. Although the bluestem system had 2.5 times the carrying capacity of the native prairie systems, increased productivity was offset by increased production costs. All systems were equal on a cow basis for providing nutrients for the cow-calf production system.  相似文献   

9.
Summer droughts in North America's northern Great Plains are expected to increase in frequency and duration as precipitation shifts toward spring and fall. Two rangeland experimental stations in North Dakota experienced drought in 2017 relative to 25-year averages. The southwest location had a 170-mm deficit from the 360-mm normal rainfall and was grazed by cattle (Bos taurus L.) and sheep (Ovis aries L.); the south-central location had 109 mm below the 403-mm normal rainfall and was grazed by cattle. We evaluated patch-burn grazing as a drought resilient land management strategy in the northern Great Plains by comparing average daily gains, fecal density, available forage biomass, and forage crude protein content. At the southwest location, livestock performed better during the drought season compared with animals on the same pastures in the previous year, which had near-normal rainfall but no fire. At the central location, cows on patch-burned pastures performed better than cows on continuously-grazed, unburned pastures in the same year under drought conditions; all cows were nursing calves and calf gains did not vary between treatments. In both locations, the burned patches had higher fecal density and lower available forage biomass than patches not yet burned throughout the grazing season, indicating grazer attraction to burned areas. Despite drought, burned patches maintained grazer attraction and animal performance was maintained or even improved, which contrasts with the expected relationship between animal performance and precipitation. This study indicated that prescribed patch-burning might mitigate drought by buffering forage resources (crude protein content and availability) and maintaining animal performance (average daily gains).  相似文献   

10.
Prescribed burning of aboveground biomass in tallgrass prairie is common and may influence dynamics and magnitudes of carbon (C) movement between the surface and atmosphere. Carbon dioxide (CO2) fluxes were measured for 2 yr using conditional sampling systems on two adjacent watersheds in an ungrazed tallgrass prairie near Manhattan, Kansas. One watershed was burned annually (BA) and the other biennially (BB). Leaf and soil CO2 fluxes were measured in the source area. Net ecosystem exchange (NEE) of CO2 reached a maximum daily gain of 26.4 g CO2·m?2·d?1 (flux toward surface is positive) in July 1998 (year when both sites were burned and precipitation was above normal); gains were similar between sites in 1998. The maximum daily NEE loss of CO2 was ?21.8 g CO2·m?2·d?1 from BA in September 1997 (year when only BA was burned and precipitation was below normal). When data were integrated over the two years, both sites were net sources of atmospheric CO2; NEE was ?389 g C·m?2·2 yr?1 on BA and ?195 g C·m?2·2 yr?1 on BB. Burning increased canopy size and photosynthesis, but the greater photosynthesis was offset by corresponding increases in respiration (from canopy and soil). Carbon losses from fire represented 6–10% of annual CO2 emissions (bulk came from soil and canopy respiration). Data suggest that annual burning promotes C loss compared to less-frequently burned tallgrass prairie where prairie is not grazed by ungulates. Greater precipitation in 1998 caused large increases in biomass and a more positive growing season NEE, indicating that C sequestration appears more likely when precipitation is high. Because C inputs (photosynthesis) and losses (canopy and soil respiration) were large, small measurement or modeling errors could confound attempts to determine if the ecosystems are long-term CO2 sources or sinks.  相似文献   

11.
This research measured steer gains, aboveground biomass remaining at the end of the growing season, and economic returns of tallgrass prairie grazed under season-long stocking (SLS-C) and a grazing system that included a 2-yr rotation of SLS-rotated (SLS-R) and intensive early stocking (IES; 2× normal stocking rate) + late-season grazing at the normal stocking rate (IES + LSG-R). We hypothesized that even though the stocking rate on the IES + LSG-R pasture was above the recommended rate, the greater regrowth availability in the late season would result in steers gaining as well as or better than those stocked SLS at the normal rate. By rotating the IES + LSG treatment with SLS over 2 yr, we anticipated that the aboveground biomass productive capacity of the IES + LSG pasture would be restored in one growing season. Further, we hypothesized that the increased stocking rate with IES + LSG would increase net profit. Comparing traditional season-long stocking to the system, which was a combination of SLS and IES + LSG rotated sequentially over a 2-yr period, the system increased steer gains by 7 kg · hd?1 and by 30 kg · ha?1, had a consistent reduction of 429 kg · ha?1 biomass productivity, and increased net profit by $55.19 per steer and $34.28 per hectare.  相似文献   

12.
Awareness of herbivore diet composition is an essential element of rangeland stewardship. Objectives of our experiment were to characterize diet selection by yearling steers and mature ewes grazing native tallgrass prairie, changes in dietary preferences that occurred with advancing season, and overlap in selection patterns between ewes and steers. Eight contiguous native tallgrass pastures (31 ± 3.3 ha) were grazed by yearling beef steers (n = 279 per yr) from 15 April to 15 July for two grazing seasons. Mature ewes (n = 813 per yr) subsequently grazed four of the eight pastures (0.15 ha per ewe) from 1 August to 1 October each year. Beginning 1 May, five fresh fecal pats were collected along four permanent transects per pasture at 2-wk intervals until steers were removed on 15 July. Subsequently, fecal grab samples were collected from 25 designated ewes per pasture on 15 August and 15 September. Microhistological analyses were conducted on fecal samples to estimate dietary botanical composition, using 17 grass, forb, and browse species from the experimental site as reference standards. Botanical composition of pastures was estimated annually in October. Diet selection was evaluated using Kulcyznski’s Similarity Index. The proportions of total graminoids and total forbs in steer diets were not different (P = 0.37) among sampling periods. Steer diets were dominated by graminoids (≥ 88.4% of diets) throughout the experiment. Steers and ewes exhibited strong preference for Bouteloua gracilis, Buchloe dactyloides, Dalea purpurea, and Liatris punctata. Ewes also demonstrated strong preferences for Vernonia baldwinii and Ambrosia artemisiifolia. Steers avoided Lespedeza cuneata and Symphyotrichum ericoides, whereas ewes did not avoid any of the reference standards. Ewes selected approximately equal proportions of graminoids and forbs (58% and 42% of diets, respectively), and proportions did not differ (P = 0.67) between sampling periods. Diet selection by mature ewes and yearling steers overlapped by 65% under the conditions of our experiment.  相似文献   

13.
The nonergot alkaloid-producing endo-phyte, AR542, has been shown to improve the persistence and yield of tall fescue pastures without causing the animal disorders commonly associated with tall fescue toxicosis. A 3-yr grazing study was conducted to compare effects of AR542-infected tall fescue pastures with wild type endophyte-infected (E+) tall fescue pastures on cow-calf performance. Replicated 7.3-ha pastures of each treatment were grazed by cow-calf pairs (16 pairs per pasture replication) each year from March to weaning in September. The cows were exposed to breeding on their respective pasture treatments from April 1 through June 15. The treatment groups were compared for reproductive performance, ADG, BCS, calf growth rate, and weaning weight. Blood samples were also collected for serum prolactin (PRL) analysis. There were no significant differences in calving rate (P = 0.98) or calving interval (P = 0.62) between pasture treatments. Cows that grazed the AR542 pastures subsequently gave birth to calves that were heavier (P < 0.05) than calves from cows that had grazed the E+ pastures. Cows grazing the AR542 pastures had higher (P < 0.05) BCS at the end of the grazing period, and had higher ADG during the grazing period. Calves raised on the AR542 pasture had higher (P < 0.05) ADG and weaning weights than calves of the same sex raised on the E+ pastures. Serum PRL concentrations were decreased (P < 0.05) in both cows and calves on the E+ pastures compared with serum PRL concentrations in cows and calves grazing the AR542 pastures. The results indicate that grazing tall fescue pastures infected with the AR542 endophyte may give significant advantages in cow-calf growth rates and BCS over grazing E+ pastures. However, there did not seem to be any benefit in reproductive performance in this trial. There was a small, but significant increase in birth weight in cows grazing AR542 pasture.  相似文献   

14.
Factors influencing the distribution and abundance of black-tailed prairie dog (Cynomys ludovicianus) colonies are of interest to rangeland managers because of the significant influence prairie dogs can exert on both livestock and biodiversity. We examined the influence of 4 prescribed burns and one wildfire on the rate and direction of prairie dog colony expansion in shortgrass steppe of southeastern Colorado. Our study was conducted during 2 years with below-average precipitation, when prairie dog colonies were expanding throughout the study area. Under these dry conditions, the rate of black-tailed prairie dog colony expansion into burned grassland (X ¯ = 2.6 ha · 100-m perimeter-1 · y-1; range = 0.8–5.9 ha · 100-m perimeter-1 · y-1; N = 5 colonies) was marginally greater than the expansion rate into unburned grassland (X ¯ = 1.3 ha · 100-m perimeter-1 · y-1; range = 0.2–4.9 ha · 100-m perimeter-1 · y-1; N = 23 colonies; P = 0.066). For 3 colonies that were burned on only a portion of their perimeter, we documented consistently high rates of expansion into the adjacent burned grassland (38%–42% of available burned habitat colonized) but variable expansion rates into the adjacent unburned grassland (2%–39% of available unburned habitat colonized). While our results provide evidence that burning can increase colony expansion rate even under conditions of low vegetative structure, this effect was minor at the scale of the overall colony complex because some unburned colonies were also able to expand at high rates. This result highlights the need to evaluate effects of fire on colony expansion during above-average rainfall years, when expansion into unburned grassland may be considerably lower.  相似文献   

15.
This 9-yr study tested steer gains, residual aboveground biomass (AGB) in mid-July and early October, and economic returns and risk for tallgrass prairie grazed annually under season-long stocking (SLS) at 1.62 ha · steer−1 until early October or intensive early stocking (IES) at 0.81 ha · steer−1 until mid-July compared to a composite grazing system. The three-pasture, three-herd “IES+ System” is a 3-yr fixed sequence of SLS, IES, and IES (0.81 ha · steer−1) plus late-season grazing (LSG; 1.62 ha · steer−1) until early October (IES/LSG). All grazing treatments began in late April. Average gains per steer for SLS and SLS in the IES+ System did not differ, but were significantly less than gains for steers that grazed the entire season under IES/LSG. Gains per steer in mid-July under IES alone or in combination with LSG were similar to the same repeated grazing treatments, but were significantly less than those for steers grazed season-long. Gains per hectare under SLS did not differ, but were significantly less than those for IES treatments and the IES+ System. Gain per hectare in July was similar for IES repeated annually and IES/LSG, but there was greater gain per hectare for IES-treated pastures rotated within the system. Residual grass and total aboveground biomass (AGB) in mid-July did not vary among years and was generally greater on SLS than IES. In early October, grass AGB was similar for all treatments except IES/LSG, which had less residual AGB. When pasture rent was charged per head, the IES+ System increased the 20-yr mean return per hectare by $5.98 compared to repeated use of IES, and $8.52 compared to using only SLS. Measures of economic risk were generally intermediate for the IES+ system compared to IES, which consistently had the highest risk, and SLS.  相似文献   

16.
Patch burning (PB) uses frequent, spatially discrete fires throughout a pasture to create variation in the composition and structure of the plant community. The complex vegetation changes incurred from this type of burning regimen in addition to the focal grazing of cattle induced by PB should reduce tick populations by creating less favorable microhabitats. To determine if a reduction in tick populations occurred on PB pastures, three PB-treated pastures and three control pastures were used. PB pastures were divided into six subplots with one burned rotationally each spring and summer. Control pastures and each PB subplot had a burn interval of 3 yr. Pastures were dragged with 1-m2 flannel cloth panels to estimate tick abundance for 4 yr. (2006, 2007, 2009, and 2010). Infestation levels with ticks (i.e., tick burden) and weight for five calves and three cows per pasture were recorded once a month from April to October in 2009, 2010, and 2011. Differences in tick abundance between PB pastures and control pastures were not significant except in 2006 when fewer adult ticks were detected in PB pastures. A total of 13 609 ticks were observed on cattle. Animals on PB pastures had 4 028 (29.6%) ticks whereas 9 581 (70.4%) ticks were on cattle from control pastures. Tick burden was significantly reduced on animals in PB pastures compared to animals in control pastures in 4 out of 6 mo. Significant differences in average daily weight gain of calves in PB and control pastures were not detected. Although differences were not detected in questing tick abundance on pastures, significant reductions of tick burden on cattle in PB-treated pastures indicates that PB can be used to help control ticks in pastures.  相似文献   

17.
Fall-weaned crossbred steer calves (n = 300; 184 +/- 2.9 kg) received either no implant (Control) or were implanted with Synovex-C (SC = 10 mg estradiol benzoate + 100 mg progesterone), Synovex-S (SS = 20 mg estradiol benzoate + 200 mg progesterone), or Revalor-G (RG = 8 mg estradiol-17beta + 40 mg trenbolone acetate) to determine the effects of implants on weight gain during winter grazing on dormant tallgrass prairie, subsequent grazing and finishing performance, and carcass characteristics. Steers grazed two dormant tallgrass prairie pastures from October 16, 1996, until March 29, 1997 (164 d), and received 1.36 kg/d of a 25% CP supplement that supplied 100 mg of monensin/steer. Following winter grazing, all steers were implanted with Ralgro (36 mg zeranol) and grazed a common tallgrass prairie pasture until July 17 (110 d). After summer grazing, all steers were implanted with Revalor-S (24 mg estradiol-17beta + 120 mg trenbolone acetate), and winter implant treatment groups were equally allotted to four feedlot pens. Steers were harvested November 17, 1997, after a 123-d finishing period. Daily gains during the winter grazing phase averaged .28, .32, .32, or .35 kg/d, respectively, for Control, SC, SS, or RG steers and were greater (P < .01) for implanted steers than for Controls. Summer daily gains were similar (1.05 +/- .016 kg/d; P > or = .61) for all treatment groups. Feedlot daily gains were also similar (1.67 +/- .034 kg/d; P > or = .21), with implanted steers weighing 14 kg more than Control steers (P = .05) at harvest, despite similar management during summer grazing and feedlot phases. Control steers tended (P = .06) to have lower yield grades. There were no differences (P = .99) in marbling between implanted and nonimplanted steers. Steers implanted during the wintering phase had increased skeletal and overall (P < .01) carcass maturities compared with nonimplanted steers, which resulted in more "B" and "C" maturity carcasses. Because carcass maturity score affects quality grade, the increased maturities of implanted steers resulted in a $9.04 decrease in carcass value/100 kg (P < .01) compared with Controls. The results of this study indicate that growth-promoting implants are efficacious for cattle wintered on dormant native range despite low daily gains. This increased weight is maintained through the summer grazing and feedlot phases; however, the benefit of the increased weight may be offset by decreased carcass quality grade and value due to increased carcass maturity.  相似文献   

18.
Japanese brome (Bromus japonicus Thunb. ex Murr.) is an introduced, annual cool-season grass adapted to the central and northern Great Plains. Japanese brome has negatively impacted perennial grasses and decreased seasonal animal gains. Prescribed spring burning and defoliation have been effective in reducing brome density or cover, but little information directly compares the two common strategies. The objectives of this study were to 1) compare annual spring burning and grazing to reduce Japanese brome populations; and 2) evaluate trends of vegetative composition and biomass in burned, grazed, and unburned rangelands infested with Japanese brome. Paddocks with Japanese brome were assigned to one of four treatments: 1) annual prescribed spring burning, 2) spring grazing, 3) a combination of annual spring burning and grazing, and 4) an idle control. Treatments were applied annually from 2000 to 2004. Japanese brome density was greatest in the idle control in all years, even when low winter and spring precipitation limited Japanese brome recruitment. Late spring Japanese brome density was similar in all treatments with grazing or burning in four of the five seasons. Spring burning resulted in less than 65% litter cover the last 3 years, whereas the idle control and spring grazing had over 80% litter cover the last 4 years. Western wheatgrass (Pascopyrum smithii [Rydb.] A. Löve) decreased with spring grazing in burned and unburned paddocks. Buffalograss (Bouteloua dactyloides [Nutt] J. T. Columbus) composition decreased in the idle control treatment. Blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) and sideoats grama (Bouteloua curtipendula [Michx.] Torr.) composition varied by year. Even though annual burning and spring grazing were equally effective in limiting Japanese brome density and biomass compared to the idle control, Japanese brome was still present after 5 years, which indicates the difficulty of eradicating Japanese brome from ecosystems where it has become naturalized.  相似文献   

19.
Cow and calf performance was determined in a 2-yr, 2 x 2 factorial, grazing experiment using Coastal or Tifton 85 (T85) replicated Bermudagrass pastures (4 pastures each; each pasture 4.86 ha), without or with aeschynomene creep-grazing paddocks (n = 4, 0.202 ha each, planted in May of each year, 13.44 kg/ha). On June 10, 2004, and June 8, 2005, 96 winter-calving beef "tester" cows and their calves were grouped by cow breed (9 Angus and 3 Polled Hereford/group), initial cow BW (592.9 +/- 70.1 kg, 2-yr mean), age of dam, calf breed (Angus, Polled Hereford, or Angus x Polled Hereford), calf sex, initial calf age (117 +/- 20.1 d, 2-yr mean), and initial calf BW (161.3 +/- 30.4 kg) and were randomly assigned to pastures. Additional cow-calf pairs and open cows were added as the forage increased during the season. Forage mass was similar for all treatment pastures (P > 0.70; 2-yr mean, 6,939 vs. 6,628 kg/ha, Coastal vs. T85; 6,664 vs. 6,896 kg/ha, no creep grazing vs. creep grazing). Main effect interactions did not occur for performance variables (P > 0.10; 2-yr means), and year affected only the initial and final BW of the calves and cows. The 91-d tester calf ADG was greater for calves grazing T85 than Coastal (0.94 vs. 0.79 kg; P < 0.01), and for calves creep grazing aeschynomene compared with calves without creep grazing (0.90 vs. 0.82 kg; P < 0.03). Calf 205-d adjusted weaning weights were increased for calves grazing T85 compared with Coastal (252.9 vs. 240.3 kg; P < 0.01) and for calves with access to creep grazing (249.9 vs. 243.3 kg; P < 0.05). The IVDMD of esophageal masticate from pastures had a forage x creep grazing interaction (P < 0.05; Coastal, no creep grazing = 57.4%; Coastal, creep grazing = 52.1%; T85, no creep grazing = 59.1%; T85, creep grazing = 60.0%), and IVDMD was greater (P < 0.05) for T85 than for Coastal pastures. Cows were milked in August 2004, and in June and August 2005, with variable milk yields on treatments, but increased milk protein (P < 0.05) for cows grazing T85 compared with Coastal pastures in August each year, contributing to increased calf gains on T85 pastures. These results complement previous research with T85 and indicate increased forage quality and performance of cattle grazing T85 pastures. Calf gains on T85 pastures and for calves on creep-grazed aeschynomene paddocks were high enough to influence the efficiency of cow-calf operations.  相似文献   

20.
The majority of native prairie has been lost throughout North America. Much of the remaining prairie is used for livestock grazing, so conservation of prairie species depends on sustainable grazing practices. Our objective was to evaluate the benefits of twice-over rotational grazing, in comparison with continuous season-long grazing and ungrazed “idle” fields, in conserving prairie songbirds. Northern mixed-grass prairie in southwest Manitoba, Canada is near the northern range limits for many endangered grassland birds, and thus is an important area for evaluating the contribution of twice-over grazing in the conservation of songbirds, including species at risk. In 2008 and 2009, we compared the relative abundances and diversity of grassland birds on 22 twice-over rotation, 15 season-long, and 8 ungrazed sites, using multiple 100-m fixed-radius point-count plots per site. Analyses were conducted using generalized linear mixed models. Although one obligate grassland bird, Savannah sparrows (Passerculus sandwichensis), had significantly higher relative abundances on twice-over than season-long sites in 2009, season-long pastures had higher species richness and diversity of obligate grassland birds in both years. Season-long grazing may actually benefit grassland bird communities by creating spatially heterogeneous but temporally stable areas of high and low livestock use within the pasture, thus increasing diversity of microhabitats. We found little evidence that twice-over grazing contributed to the conservation of grassland songbirds in subhumid northern mixed-grass prairies.  相似文献   

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